Dissertations / Theses on the topic 'Iron Metallurgy'

Iran, a country rich in mineral resources, has a long history of metal working. Copper objects first appeared in the 7th millennium BC and in the following millennia, copper became the material of choice for the production of many objects. Artefacts of iron began to appear in the mid 2nd millennium BC and by the mid 1st, iron had replaced bronze for most uses, but the reasons for this change remain unclear. This thesis seeks to examine the transition from bronze to iron metallurgy from a new angle. By looking at changes in copper-based metallurgy between the Bronze Age and the Iron Age, it attempts to better understand the context in which iron metallurgy developed. To that end, the results of previously published chemical analyses of over 5000 copper-based objects from Iran and neighbouring regions and the lead isotope analyses of about 380 objects were assembled in a database. The tin, arsenic, nickel, antimony and silver concentrations in particular are studied. The data is divided into 16 metal groups based on the absence or presence of the latter four elements. The study of the main groups allows us to describe interesting new patterns of metal movement and recycling. It appears that before the end of the Bronze Age, a number of copper sources and/or trade routes from both east and west declined, leading to a reliance on more local sources for copper and tin in the Iron Age. The practice of recycling from the 3rd millennium BC onward is also evidenced. Overall, it seems that iron appeared within a thriving bronze industry, with a good access to metal resources and a developed understanding of the possibilities offered by copper (alloying, recycling, mixing…). Was it then the more ‘permanent’ nature of iron that attracted the ancient metal-workers and led to its advent?

In this work, the metal and slag phase mixing in three steps of a ladle refining operation of steel melts and for an oxygen balance during cooling of cast iron melts have been studied at two Swedish steel plants and at two Swedish cast iron foundries, respectively. In order to predict the oxygen activity in the steel bulk in equilibrium with the top slag as well as in metal droplets in the top slag in equilibrium with the top slag, three slag models were used. In addition, the assumptions of a sulphur-oxygen equilibrium between steel and slag and the dilute solution model for the liquid steel phase were utilized in the calculations. Measured oxygen activities in steel bulk, which varied between 3.5-6 ppm, were compared to predicted oxygen activities. The differences between the predicted and measured oxygen activities were found to be significant (0-500%) and the reasons for the differences are discussed in the thesis. Slag samples have been evaluated to determine the distribution of the metal droplets. The results show that the relatively largest numbers of metal droplets are present in the slag samples taken before vacuum degassing. Also, the projected interfacial area between steel bulk and top slag has been compared to the interfacial area between the metal droplets and slag. The results show that the droplet-slag interfacial area is 3 to 14 times larger than the flat projected interfacial area between the steel and top slag. Furthermore, the effect of the reactions between top slag and steel and the slag viscosity on the metal droplet formation is discussed. The results show significant differences between the steel bulk and steel droplet compositions and the reasons for the differences are discussed in the thesis. The oxygen activity in different cast irons was studied. Plant trials were performed at three occasions for lamellar, compacted and nodular iron melts. The results show that at temperatures close to the liquidus temperature the oxygen activities were 0.03-0.1 ppm for LGI, around 0.02 ppm for CGI, and 0.001ppm for SGI. In addition, it was found that as the oxygen activities increased with time after an Mg treatment, the ability to form a compact graphite or a nodular graphite in Mg-treated iron melts was decreased. Also, extrapolated oxygen activity differences up to 0.07 ppm were found for different hypoeutectic iron compositions for lamellar graphite iron at the liquidus temperature. Overall, the observed differences in the dissolved oxygen levels were believed to influence how graphite particles are incorporated into the austenite matrix and how the graphite morphology will be in the cast product.

QC 20160518

During the Middle Ages, Sweden was a coveted exporter of high-quality iron in Europe. Bloomery furnaces could have produced osmund iron. However, most osmund iron was produced in blast furnaces. The iron was then treated in the finery process and cut into pieces. Previous studies establish osmund iron’s definition regarding properties, microstructure and trace elements. They were often slag-rich and varied greatly in carbon content, proportion of inclusions, corrosion and microstructure. The report examined osmund iron as related to medieval iron production, exports and quality. This was done by comparing the microstructures and slag inclusions in Swedish and Estonian pieces of medieval iron, through analyses by SEM-EDS and under an optical microscope. The Estonian samples had more slag inclusions. The samples with corroded inclusions/slag were rejected. The varying microstructure can be linked to the cooling rate and the actual production in the blast furnace, bloomery furnace and finery process. It gave materials with poor properties. A large proportion of the samples had one side with a higher carbon content while the other had lower carbon content. The iron with lower carbon content could be connected to come from the bloomery furnace and the higher to the blast furnace. The samples containing higher levels of silica, magnesium and calcium could be connected to the blast furnace. In summary, the Swedish samples were of better quality than the Estonian ones and all pieces were considered to come from the blast furnace.
Under medeltiden var Sverige en eftertraktad exportör av högkvalitativt järn i Europa. Osmundjärn kunde produceras i en blästerugn, men det mesta osmundjärnet framställdes i masugnen. Därefter färskades järnet och höggs upp i delar. Tidigare analyser definierar osmundjärns utseende, egenskaper, mikrostruktur och spårämnen. De var ofta slaggrika och varierade mycket i kolhalt, andel inneslutningar, mikrostruktur och mängd korrosion. I den här studien analyserades osmundjärn relaterat till medeltida järnframställning, export och kvalité. Det gjordes genom att jämföra mikrostrukturer och slagginneslutningar i svenska och estniska prover av medeltida järn, genom analyser i SEM-EDS och i ljusmikroskop. De estniska proverna hade mer slagginneslutningar. Proverna med korroderade inneslutningar/slagg uteslöts ur analysen. Den varierande mikrostrukturen kan kopplas till kylningshastigheten och själva produktionen i masugnen, blästerugnen och färskningsprocessen. Det gav material med dåliga egenskaper. En stor andel prover hade en sida med högre kolhalt och den andra delen hade lägre kolhalt. Järnet med lägre kolhalt kan kopplas till att komma från blästerugnen och det med högre kolhalt till masugnen. De proverna som innehöll högre halter kiseldioxid, magnesium och kalcium kan kopplas till masugnen. De svenska proverna hade sammanfattningsvis bättre kvalité än de estniska och alla bitar ansågs komma från masugnen.

The practise of slag foaming has become increasingly important within the scrap-based steelmaking, conducted in the electric arc furnace, due to its many advantages. In addition to increasing the efficiency in the furnace, the foaming protects the furnace equipment from wear and reduces noise pollution. The purpose of this project was to investigate the slag foaming generated through chemical reactions that occur at the addition of carbonaceous iron to the slag, as well as to evaluate the experimental method used. A slag composition of 25 wt% FeO, 40 wt% CaO and 35 wt% SiO2 was chosen. The experiments were conducted using an induction furnace, in a magnesium oxide crucible, placed in a graphite crucible. Iron particles with varying carbon content were added to the magnesium oxide crucible and the subsequent foaming was filmed and observed from above. The method enabled a division of foaming into four stages, which were studied and evaluated separately. The results indicate that the incubation time, referring to the time that passes from the addition of carbonaceous iron particles to the slag until the reactions occur, is dependent of size. A correlation can also be seen between carbon content and foaming time, where increased carbon content results in lengthier foaming.
Utövandet av slaggskumning har blivit allt viktigare inom den skrotbaserade ståltillverkningen som utförs i ljusbågsugen, på grund av dess många fördelar. Förutom att öka effektiviteten i ugnen så skyddar den skummande slaggen även ugnsutrustningen mot slitage och reducerar buller. Syftet med detta projekt var att undersöka slaggskumning genererad genom de kemiska reaktioner som inträffar vid tillsats av kolhaltigt järn till slaggen, samt att utvärdera den experimentella metoden som användes. En slaggsammansättning av 25 vikt% FeO, 40 vikt% CaO och 35 vikt% SiO2 valdes. Experiment genomfördes med hjälp av en induktionsugn, i en magnesiumoxiddegel, placerad i en grafitdegel. Järnpartiklar med varierande kolhalt tillsattes i magnesiumoxiddegeln och den efterföljande skumningen filmades och observerades från ovan. Metoden möjliggjorde en uppdelning av skumning i fyra stadier, vilka studerades och utvärderades separat. Resultaten visar på att inkubationstiden, alltså tiden som passerar från att järnpartiklar tillsätts till slaggen, till dess att reaktioner sker, har ett storleksberoende. Ett samband kan även ses mellan kolhalt och skumningstid, där en ökad skumningstid ges av en högre kolhalt.

In this thesis, the effects of iron(II) on arsenic(V) removal from acidic sulphate solutions in lime neutralization systems were investigated. The role of Fe(II) was analyzed via different types of experiments. Firstly, 2-stage continuous coprecipitation (CCPTN) circuit experiments were run, involving variable Fe(II)/Fe(III) fractions whilst maintaining an Fe(tot)/As(V) molar ratio of 4, and the resultant products were subjected to stability testing. It was found that CCPTN results were reproducible; that increasing the Fe(II) content resulted in somewhat lower initial arsenic(V) removal, but still better results than those obtained from equimolar Fe(III)-As(V) solutions in the absence of ferrous pointing to the latter's beneficial effect on arsenic(V) precipitation and retention. Coprecipitates aged at constant pH 8, drifting pH and at various temperatures reached pseudoequilibrium after several months. Notably, long term stability testing of the coprecipitates showed that up to an Fe(II)/Fe(III) ratio of 1 at 20 °C, As(V) release was maintained below 1 mg/L after 463 days with "drifting pH" stabilized at 5 increasing only to 1.9 mg/L upon pH adjustment to 8. Secondly, the behaviour of Fe(II) was studied in batch reactor set-ups as part of hydrolysis and oxidation experiments with and without As(V). It was shown in the absence of As(V), Fe(II) precipitated out of solution completely between pH 7.5 and 8.5. Subsequent oxidation of the ferrous hydroxide slurry was found to proceed via a series of transformations starting from ferrous hydroxide to green rust, to magnetite and finally goethite. The oxidation kinetics were governed by oxygen mass transfer. In the presence of As(V) both Fe(II) and As(V) precipitated from solution starting at pH 3 with the latter ultimately dropping below 1 mg/L between pH 6.5 to 9 via the proposed precipitation of a ferrous arsenate compound (symplesite). Subsequent oxidation of the Fe(II)-As(V) slurry at constant pH 8 led to destabilization of the ferrous arsenate phase and concomitant partial release of As(V). The bulk control of As(V) in the latter case switched from ferrous arsenate to ferric arsenate or arsenate adsorption on freshly formed iron(III) hydroxide.
Cette thèse à pour objet d'étudier les effets des ions ferreux (Fe(II)) sur la stabilisation, par neutralisation à base de chaux, de l'arsenic (As(V)) contenu dans des solutions acides sulfatées. Le rôle des ions ferreux a été analysé à l'aide de différents types d'expériences. Premièrement, des essais de co-précipitation en circuit continu (CCPTN) comprenant deux étapes ont été réalisés pour différentes fractions de Fe(II)/Fe(III), tout en conservant un rapport molaire Fe(tot.)/As(V) égal à 4; les produits obtenus ont par la suite été soumis à des tests de stabilité à long terme. Les résultats de ces tests ont montré de façon reproductible qu'une augmentation de la teneur en ions ferreux réduisait l'effet de stabilisation de l'As(V) initialement présent; ces résultats étaient cependant meilleurs que dans le cas de tests de stabilisation de l'As(V) présent dans des solutions équimolaires de Fe(III)-As(V), en l'absence d'ions ferreux, validant l'effet positif des ces derniers sur la précipitation et la rétention de l'As(V). Après plusieurs mois de vieillissement dans des conditions variées de pH constant (ajusté à pH 8), de pH non-ajusté et de températures, les produits de co-précipitation ont fini par atteindre un état de pseudo-équilibre. Notamment, les tests de stabilité à long terme ont montré que pour une fraction molaire Fe(II)/Fe(III) allant jusqu'à 1 et une température de 20 °C, la libération d'As(V) en solution après 463 jours était maintenue en-dessous de 1 mg/L, respectivement 1.9 mg/L, dans le cas d'une solution au pH non-ajusté (se stabilisant à pH 5), respectivement d'une solution au pH constamment ajusté à pH 8. Deuxièmement, le comportement des ions ferreux a été étudié à l'aide d'un réacteur discontinu, dans le cadre de tests d'hydrolyse et d'oxydation, en présence ou non d'As(V). Les résultats de cette partie de l'étude ont montré qu'en l'absence d'As(V), les ions ferreux précipitent intégralement entre pH 7.5 et 8.5. Par la suite, l'oxydation de la suspension d'hydroxyde de fer (II) procède selon une série de transformations allant de la rouille verte, à la magnétite et finalement à la goethite. Les résultats ont également montré que la cinétique d'oxydation était gouvernée par le transfert de masse d'oxygène. En présence d'As(V), la précipitation du Fe(II) et de l'As(V) à été observée à partir de pH 3, sous la forme suggérée d'un composé d'arséniate de fer (II) (symplésite), la concentration finale d'As(V) non-précipité atteignant moins d'1 mg/L entre pH 6.5 et 9. Par la suite, l'oxydation de la suspension de Fe(II)-As(V) à pH 8 constant a entrainé la déstabilisation de la phase d'arséniate de fer et la remise en solution partielle d'As(V). En effet, dans ce cas particulier, le control de l'As(V) à entrainé la conversion de la majorité de la phase d'arséniate de fer (II) en arséniate de fer (III) ou possiblement son adsorption à la surface d'hydroxyde de fer (III) fraichement oxydé.

Valmet AB has ha foundry located I Karlstad, Sweden. The foundry has specialized in large components in ductile and gray iron. This report is a part of an evaluation of a new alloy that Valmet has produced. The alloy is called S550 where 550 is the expected tensile strength in a cast on sample. S550 is a ferritic ductile alloy with 4,15-4,25% silicone. In this experiment the alloy is casted in very large sections to better match the intended final product. The purpose of the report is to promote a better understanding of how silicon works in large castings. Ultimate tensile strength, yield strength and elongation will be measured. The microstructure will be mapped and described. This as a step to ensure that the material is ready to use to produce castings in large dimensions. In the experiment, the microstructure is examined from 3 charges. Mechanical properties are collected from the 3 charges by widened specimens from 3 details of 2785 kg/piece and 4 drilled samples from 4 details about 600 kg/piece. The samples are processed to test bars according to standard SS-EN1563: 2012. Thereafter the rods are dragged in a tensile testing machine to collect data. The microstructure is mapped through light optic microscopy. The samples where machined according to SS-EN1563:2012. Tensile testing machine was used to record the mechanical values. Microstructure was mapped using a light-optic microscope. The material achieved a tensile strength of 544 MPa on average which is below the expected value. The yield strength was 436 MPa in average. The material shows low dispersion, mainly in fracture limit and yield limit. The elongation in average 12.8% varied in the different geometries but with lower variations within the same geometry. The alloy got better mechanical values on Detail B that had a shorter cooling time. In Detail A, micro porosity and slag were found which adversely affected their mechanical properties. The ground mass is considered as ferritic. The graphite nodes had a size of 82μm and a nodule density of 75 nodules / mm2. Most nodules had graphite form VI, small amount of graphite V and III have been found. No degenerated graphite forms as chunky or exploded graphite has been found.

Flotation of sphalerite with xanthate in the presence of iron ions has been studied as a function of pH. Sphalerite floated readily at pH 8-11 in the presence of ferrous ions, but not in the presence of ferric ions. The Fe$ sp{2+}$ ion concentration, pH and oxygen concentration were shown to be factors in controlling flotation. Electrokinetic measurements indicated that the surface charge increased in the presence of Fe$ sp{2+}$ ions and oxygen, and decreased upon adding xanthate and in the presence of Fe$ sp{2+}$ ions with the absence of oxygen.
As a prelude to surface analysis to try to identify the species responsible for the sphalerite flotation, bulk precipitates formed from iron salt and xanthate solutions under various conditions were obtained and analysed. Analysis techniques included ultraviolet spectroscopy, infrared spectroscopy, x-ray diffraction and Mossbauer spectroscopy.
It was tentatively concluded that the bulk precipitates contained three ferric components: two hydroxy xanthates, Fe(OH)$ sb2$X and Fe(OH)X$ sb2$ and an iron oxide, FeO$ sb{ rm x}.$
Iron xanthate precipitates prepared over the pH range 6-12 showed a flotation response and electrokinetic behaviour similar to those of Fe$ sp{2+}$/xanthate-treated sphalerite.
An ex situ X-ray photoelectron spectroscopic (XPS), ex situ infrared (DRIFTS) and in situ infrared (ATR) investigation of the interaction of sphalerite with ferrous, ferric and xanthate ions at pH 10 was undertaken. The formation of the hydrophobic surface species was found to involve initial adsorption of Fe$ sp{2+},$ followed by oxidation to Fe$ sp{3+}$ and subsequent reaction with xanthate. There was no significant incorporation of Fe$ sp{3+}.$
A three-step reaction mechanism is proposed to account for Fe$ sp{2+}$ ion activation of sphalerite: (i) adsorption of Fe(OH)$ sp+,$ (ii) oxidation to Fe(OH)$ sp{2+}$ on the surface, (iii) reaction with xanthate to form Fe(OH)$ sb2$X or Fe(OH)X$ sb2.$

The texture of electrodeposits has attracted increasing interest, as it is recognized that it is a possible to benefit from the texture and to improve the various properties of electrodeposits or electrolytic coatings. For example, the corrosion resistance of materials is affected by texture. If appropriate textures are introduced in electrodeposited coatings, their corrosion resistance would be enhanced and the coatings will therefore have a longer service time. Texture development during electrodeposition is still poorly understood, and this makes it difficult to control the texture formation during the electrodeposition processes. In order to better understand the texture formation during electrodeposition, extensive theoretical and experimental investigation are undertaken in this thesis.
A computer model was proposed to describe texture development. In this model, the microstructure of deposit was represented using a two dimensional triangle lattice. The deposit growth was modelled as previously empty lattice sites are being occupied based on fundamental physical rules. The author proposed that the main driving force for the development of microstructure and texture is the minimization of the system's free energy. This results in texture development, and the minimization of the free energy includes deposit's surface energy and occasionally the magnetic energy. Based on this hypothesis, the texture formation during iron electrodeposition and its variation with the deposition condition were simulated. It was demonstrated that the crystallographic anisotropy of deposit's surface energy plays an important role in the formation of the deposit's fibre texture. The study also indicated that the surface-energy anisotropy could be modified by hydrogen co-deposition and the deposit's texture can be modified by varying the current density, temperature, or pH value of the bath. In addition, the study illustrated that the magnetization energy also plays an important role in texture development during electrodeposition of magnetic materials. When external magnetic fields of sufficient strength are applied during the deposition of magnetic materials, the magnetic fields align grains in such a way that the deposits' fibre textures may transform to non-fibre textures.
In order to further justify the minimum-energy texturing mechanism proposed in the model, and to obtain a clear physical picture of the texture formation during electrodeposition, the process of texture development was analyzed using classical thermodynamics. Various experiments were conducted to verify the computer simulation. A positive correlation between the results of the simulation and the experiments were found.

The rejection of iron sulphides (pyrite and pyrrhotite) using nitrogen was evaluated on three Canadian complex sulphide ores. Laboratory scale work (at McGill and on-site) was conducted and, in addition, continuous minicell testwork was conducted on-site.
The promotion of pyrite flotation using nitrogen was confirmed. It was evaluated at Brunswick Mining ahead of zinc flotation (using the minicells), and at Kidd Creek Mines in a laboratory scale investigation of reverse flotation. This latter also showed enhanced chalcopyrite flotation with nitrogen.
The explanation of pyrite flotation using nitrogen was based on weakening of galvanic coupling with other sulphides.
Nitrogen proved more effective than air in depression of pyrrhotite in processing a pentlandite/chalcopyrite ore. Under some conditions, chalcopyrite was also depressed by nitrogen (apparently when the pulp potential was less than O V vs. S.H.E.).
The depressant action of nitrogen on pyrrhotite was interpreted as a reduction in the density of surface OH$ sp-$ sites necessary for electrostatic interaction with xanthate ion in the Hodgson/Agar model of pyrrhotite floatability.

The thesis paper here focuses on the effects of the austempering temperature (TA) and the austempering time (tA) on the unalloyed fully ferrite Compacted Graphite Iron (CGI), to obtain improve in mechanical properties and the study of the microstructure. The unalloyed CGI samples were austenitised at 850oC for 60 and 90 min and were then heat treated at 275, 325 and 375oC with different holding times at 30,60,90, and 120 mins. Mechanical properties like the tensile strength, yield strength, young’s modulus, Brinell and Vickers harness were conducted to perform the analysis on the samples. LOM was used for the study of the microstructure and SEM was used for the study of fractography of the fractured tensile bar.

In the present study, magnetite pellets with the additives olivine, calcite and quartzite were isothermally reduced in a tubular furnace to study the interaction between iron oxides and the additives. Exaggerated amounts of additives were used in order to enable analyses of phases that do not otherwise occur in sufficient amounts for X-ray diffraction and EDS-analyses. The reduction was set to yield either magnetite or wüstite in the temperature range 500-1300ºC. For olivine, reduction tests were also performed to allow metallization in the range 1000-1300ºC. The mineralogical phases which had formed were studied after oxidation as well as after reduction. The results showed that it was possible to identify, by X-ray diffraction, the main phases formed by the additives in all samples, after oxidation as well as reduction.In the olivine sample, the forsteritic olivine particles react partly during the oxidation pre-treatment to form magnesioferrite and vitreous silica along the particle corona. This breakdown of the olivine particles during oxidation liberates magnesium from the particles, which do not react until temperatures of above 1150°C in reducing atmosphere. When the hematite in the sample is reduced, and when temperature is high enough to allow solid-state diffusion at ~800ºC, the magnesium of the magnesioferrite redistributes so that the magnesium concentration approaches the same level throughout the structure. For magnetite, this does not occur below 800°C. At 1000°C, this magnesium reacts further with the silica in the glassy slag phase, which crystallizes into fayalitic olivine. At this temperature the magnesium diffuses over distances more than 600µm from the olivine particles. From this point the binding media to resist the swelling tensions in the pellet is mainly solid fayalite. The metallization front concentrates the MgO in the remaining wustite which can lead to MgO levels of up to 10% locally. The melting point of the fayalite is raised from 1145ºC to a melting range of 1238-1264ºC due to the MgO-increase, as estimated based on the phase diagram tuned to the pellets tested. Much of the olivine which remained unaltered in the oxidation process will be encapsulated by iron before the magnesium begin to dissolve in reducing conditions, and therefore play no role in the reduction before final melting of the particles occur.The quartzite particles are not affected by the oxidation pre-treatment. The binding strength of quartzite pellets therefore comes from the sintering of quartzite particles to neighboring hematite as well as the glassy slag resulting from the acid gangue and the bentonite. Substantial reaction of the quartzite particles during reduction did not occur before 1000ºC even though the process has occurred to a very low extent already at 900ºC. Also the glassy slag crystallizes into fayalite in the presence of quartzite. From this point fayalite represents the binding media in the pellet. Pure fayalite melts already at 1177ºC and can at this temperature dissolve up to 76wt% FeO. This leads to early softening, which is one of the main concerns for the softening/melting properties of the pellet. In the pellets with calcite, CaO reacts with Fe2O3 during induration to form a low-melting calcium ferrite slag in the pellet that melts to react with silica in the pellets. If more calcium is added than what is required to react with the silica, calciumferrites becomes part of the binding mass together with the dicalciumsilicate. The calciumferrites forming in pellets with larger additions of calcite are weak to resist the tensions arising due to the low-temperature reduction of hematite and are associated with low temperature disintegration. As the reduction proceeds to wustite, the calcium from the ferrite dissolves in the wustite so that porous calciumwustite forms. The dicalciumsilicate remain stable during the entire reduction until reaction and melting of the phase begin at 1283ºC.
Godkänd; 2013; 20130411 (parsem); Tillkännagivande disputation 2013-05-20 Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Pär Semberg Ämne: Processmetallurgi/Process Metallurgy Avhandling: Interactions Between Iron Oxides and the Additives Olivine, Quartzite and Calcite in Magnetite Pellets Opponent: Professor Abdel-Hady Abdel-Hady El-Geassy, CMRDI, Cairo, Egypt Ordförande: Professor Bo Björkman, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Måndag den 10 juni 2013, kl 10.00 Plats: F531, Luleå tekniska universitet

A technique for accurately monitoring fatigue crack growth at near threshold growth rates has been established. The characteristics of near threshold fatigue crack growth of a number of iron-silicon alloys has been quantitatively and qualitatively investigated. Relationships have been established relating the stress intensity factor, AK, and the fatigue crack growth rate da/dN. At fatigue crack growth rates approaching threshold the material has shown some microstructural sensitivity and this has been related to the stress intensity factor and the yield stress. A relationship has been shown to exist between the value of the threshold stress intensity factor and the inverse root of the grain size, d~2, for each of the alloys investigated. A model for near threshold fatigue crack growth has been proposed and includes the contributions made by grain size and crack tip plasticity. This work has also shown that fatigue crack closure plays an important role in the micromechanisms of fatigue crack growth near the threshold at low R ratio s. A number of mechanisms have been identified: crack closure due tothe presence of oxidation products on fracture surfaces in tests conducted in air, and closure due to the presence of fatigue fretting, facet contact and a contribution of mixed mode opening.

The formation of iron-bearing intermetallics in the 413 type of aluminum alloys was investigated comprehensively. Both synthetic and commercial 413 alloys were studied with iron concentrations in the range of 0.4-1.2 wt. % and manganese up to 0.5 wt.%. The effects of cooling rate during solidification and of melt chemistry on the morphology of iron intermetallic phases were determined. Image analysis was used to quantify the intermetallic size, volume fraction, and number, as a function of both melt chemistry and cooling rate. The total volume fraction of intermetallic compounds in these alloys was related to cooling rate by an exponential equation.
The kinetics of both dissolution of intermetallics on melting, and of re-formation on cooling of the liquid were investigated by means of quenching experiments. Quantitative evaluation of intermetallic size and number revealed that the change in volume fraction of intermetallics in the liquid state is controlled by nucleation.
The effect of settling time and the rate of gravity segregation of intermetallic compounds in a stagnant liquid metal were investigated. It was found that, in the absence of convection, settling obeys Stokes' law with the terminal velocity reached at very short times and very close to the melt surface.
Strontium was used to modify or eliminate the iron-intermetallics. (Abstract shortened by UMI.)

Industrial experience has revealed that when used to treat multi-component metal chloride waste liquors, existing fluidized bed acid regeneration facilities are not as efficient as when employed for the pyrohydrolysis of conventional iron chloride solutions (i.e. waste pickle liquor). As a result, experimental studies and thermochemical modelling were performed to characterize the transformation of a saturated Al-Fe-Mg-Cl solution at 105°C, after it is injected into a reactor at 850°C. Efforts were geared toward defining the sequence of reactions that take place as the liquor gradually transforms into oxides.C, after it is injected into a reactor at 850°C. Efforts were geared toward defining the sequence of reactions that take place as the liquor gradually transforms into oxides.C, after it is injected into a reactor at 850°C. Efforts were geared toward defining the sequence of reactions that take place as the liquor gradually transforms into oxides.C, after it is injected into a reactor at 850°C. Efforts were geared toward defining the sequence of reactions that take place as the liquor gradually transforms into oxides.
Upon completing a comprehensive literature review, testwork was initially performed with a simplified experimental set-up to study the physical behaviour of the chloride solution as it is exposed to a static bed of oxides at 850°C, and ultimately identify the various phases of the transformation process. Subsequently, controlled evaporative crystallization experiments were conducted under pseudo-equilibrium conditions to define the McClx·yH 2O precipitation path that takes place during the H2O evaporation phase and to determine whether the chlorides precipitate independently or as complex compounds. Further experiments were performed in a fully instrumented tube furnace to elaborate on the nature of the reactions (dehydration and/or pyrohydrolysis) that take place after all of the water in the starting solution has evaporated (i.e. T=300°C+).
In an effort to assist with the interpretation of the experimental results, thermochemical modelling was performed to predict the equilibrium phase assemblages that could occur during the transformation of the saturated Al-Fe-Mg-Cl solution, at reaction temperatures of 200°C+.
The research study at hand has shown that when the saturated Al-Fe-Mg-Cl solution at 105°C is exposed to fluidized bed pyrohydrolyzer operating conditions at 850°C, the following sequence of events take place: (1) rapid solvent H2O evaporation (i.e. vigorous boiling) and onset of solid metal chloride precipitation. (2) slurry densification due to a gradual increase in crystal content (i.e. AlCl·6H2O, FeCl2 ·xH2O, and MgCl2·xH2O, where x = 2 or 4). (3) hydrated crystal drying and onset of pyrohydrolysis (i.e. thermal decomposition of McClx·yH2O). The same holds true for the high temperature hydrolysis of typical waste pickle liquors (i.e. primarily FeCl2 solution).
The crystallization studies revealed that when the Al-Fe-Mg-Cl solution is allowed to gradually evaporate at 105°C,.AlCl3·6H 2O precipitates when 15% of the solvent water evolves from the liquor, followed by FeCl2·xH2O and MgCl2·xH 2O (where x = 2 or 4) at 26 and 41% evaporation, respectively. Ferric chloride remains in solution even after 54% of the water has been driven from the liquor. The latter result suggests that higher ferric concentrations in the reactor feed are more than likely to favour an increase in the quantity of liquor entrainment by the fluidizing gases and therefore lead to lower process efficiencies. Dedicated pyrohydrolysis experiments, with a simulated reactor atmosphere (gaseous, not dynamic), have shown that excluding kinetic effects, the transformation of the Al-Fe-Mg-Cl solution occurs primarily over the 300 to 600°C temperature range.
Thermochemical modelling revealed that with the exception of AlCl 3·6H2O hydrolysis, the majority of the reactions taking place as the saturated Al-Fe-Mg-Cl liquor is introduced into and eventually reaches 850°C are governed by either reaction kinetics or diffusion. Furthermore, the resulting phase assemblage at any given temperature was predicted to vary significantly with oxygen potential. A liquid chloride phase (including molten salt), other than the feed liquor, was not predicted to form at any temperature (i.e. 200°C or above) under the range of oxidizing or reducing conditions considered.
The findings of this research were quite useful in identifying the means for improving the performance of a commercial fluidized bed pyrohydrolyzer for a spent chloride liquor containing the said species.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (v. 2, p. 375-377).
The Early Iron Age (750-450 BCE) marks a time in the European Alpine Region in which cultural ideologies surrounding bronze objects and bronze production were changing. Iron was becoming the preferred material from which to make many utilitarian objects such as weapons and agricultural tools; this change can be clearly seen in the different treatments of bronze object deposits from the Late Bronze Age to the Early Iron Age. The Early Iron Age hillfort settlement of Sticna in what is now southeastern Slovenia was one of the first incipient commercial centers to take advantage of the new importance placed on iron, conducting trade with Italy, Greece, the Balkans, and northern Europe. This metallurgical study of bronze funerary objects from Sticna identifies construction techniques, use patterns, and bronze metallurgical technologies from the ancient region of Lower Carniola. This information is then used to explore the cultural importance of bronze at Early Iron Age Sticna and to compare the bronze work of Lower Carniola with that of other regions in central Europe and Italy from this time of great change in Iron Age Europe.
S.M.

The crystallization behaviour of iron intermetallics during solidification and the dissolution behaviour of iron intermetallics during heat treatment and their subsequent effect on mechanical properties have been studied.
Addition of iron decreases DAS and affects eutectic silicon particle size as nucleation and growth of silicon crystals takes place on the $ beta$-AlFeSi platelets, thus minimizing isothermal dendrite arm coarsening at the eutectic temperature. Increase of iron also increases the size and volume percent of the iron bearing intermetallics.
In the absence of manganese, the iron intermetallics crystallize in the $ beta$-phase, at all cooling rates ranging from 0.1 to 20$ sp circ$C/s when cast from a normal casting temperature of 750$ sp circ$C. In the presence of manganese, the iron intermetallic crystallizes in $ alpha$-phase at low cooling rates and in both the $ alpha$- and $ beta$-phases at high cooling rates. This reverse crystallization behaviour is explained based on the segregation effect displayed by the phase diagram.
When the melt is superheated to a high temperature (about 200 to 300 degrees above the liquidus temperature), the iron intermetallic crystallizes in the $ alpha$-phase at high cooling rates. This behaviour is attributed to the fact that $ gamma$-alumina which forms at low melt temperatures ($ le$750$ sp circ$C) acts as a nucleus for crystallization of $ beta$-phase. When the melt is superheated to a high temperature ($ ge$850$ sp circ$C), the $ gamma$-alumina transforms to $ alpha$-alumina. The $ alpha$-alumina is found to be a poor nucleus for the $ beta$-phase crystallization, and as a result the $ alpha$-phase forms. The importance of nucleation and growth undercooling for the crystallization of iron intermetallics is highlighted.
Investigation of the dissolution behaviour of the iron intermetallics on non-equilibrium heat treatment indicates that the $ beta$-phase platelets dissolve slowly through concurrent fragmentation and then dissolution at the plate tips. Addition of manganese hinders the dissolution of iron intermetallics. The amount of liquid phase formed during non-equilibrium heat treatment increases dramatically once a critical temperature is exceeded. This critical temperature is estimated to be 520 and 515$ sp circ$C for samples initially solidified at 10 and 15$ sp circ$C/s respectively.
The 0.15% Fe alloy exhibits the highest tensile strength and percent elongation compared to 1.0% Fe and 1.0% Fe + 0.5% Mn alloys under as-cast and equilibrium heat treated conditions. However, under non-equilibrium heat treatment conditions, ie., 30 degrees above the T4 equilibrium solution temperature, the strength properties of 1.0% Fe alloy exceed, or at least equal, that of the equilibrium heat treated 0.15% Fe alloy.
An attempt is made to correlate the iron intermetallics present in the microstructure and mechanical properties with the associated fracture mode in this alloy.

Iron content in aluminum-silicon casting alloys, which contribute to the formation of Al$ sb5$FeSi intermetallic, can be very detrimental to the physical properties of the final cast part.
Thermal analysis could provide a cost effective and reliable method to quantify the iron content of the alloy melt before the casting process is performed. The formation of the Al$ sb5$FeSi intermetallic can be resolvable on the cooling curves for aluminum-silicon alloys if the iron content is equal to or greater than 0.6%wt when the cooling rate is 0.10$ sp circ$C/sec. As the iron content gradually increases, the formation temperature of Al$ sb5$FeSi increases and this results in an increase in the duration of the Al$ sb5$FeSi thermal anomaly. A time based parameter associated with the Al$ sb5$FeSi thermal anomaly is also used to quantify the Fe content. Time parameters can be very accurate if the melt volume and heat extraction for the solidifying thermal analysis sample are strictly controlled.
Results of Fe quantification via apparent time parameter of the Al$ sb5$FeSi crystallization for 356,319 and 413 alloys using thermal analysis has been completed for this thesis. (Abstract shortened by UMI.)

Rare-Earth elements by virtue of its typical magnetic, electronic and chemical properties are gaining importance in power, electronics, telecommunications and sustainable green technology related industries. The Magnets from RE-alloys are more powerful than conventional magnets which have more longevity and high temperature workability. The dis-equilibrium in the Rare-Earth element supply and demand has increased the importance of recycling and extraction of REE's from used permanent Magnets. However, lack of the thermodynamic data on RE alloys has made it difficult to design an effective extraction and recycling process. In this regard, Computational Thermodynamic calculations can serve as a cost effective and less time consuming tool to design a waste magnet recycling process. The most common RE permanent magnet is Nd magnet (Nd2Fe14B). Various elements such as Dy, Tb, Pr, Cu, Co, Ni, etc. are also added to increase its magnetic and mechanical properties. In order to perform reliable thermodynamic calculations for the RE recycling process, accurate thermodynamic database for RE and related alloys are required. The thermodynamic database can be developed using the so-called CALPHAD method. The database development based on the CALPHAD method is essentially the critical evaluation and optimization of all available thermodynamic and phase diagram data. As a results, one set of self-consistent thermodynamic functions for all phases in the given system can be obtained, which can reproduce all reliable thermodynamic and phase diagram data. The database containing the optimized Gibbs energy functions can be used to calculate complex chemical reactions for any high temperature processes. Typically a Gibbs energy minimization routine, such as in FactSage software, can be used to obtain the accurate thermodynamic equilibrium in multicomponent systems. As part of a large thermodynamic database development for permanent magnet recycling and Mg alloy design, all thermodynamic and phase diagram data in the literature for the fourteen Fe-RE binary systems: Fe-La, Fe-Ce, Fe-Pr, Fe-Nd, Fe-Sm, Fe-Gd, Fe-Tb, Fe-Dy, Fe-Ho, Fe-Er, Fe-Tm, Fe-Lu, Fe-Sc and Fe-Y are critically evaluated and optimized to obtain thermodynamic model parameters. The model parameters can be used to calculate phase diagrams and Gibbs energies of all phases as functions of temperature and composition. This database can be incorporated with the present thermodynamic database in FactSage software to perform complex chemical reactions and phase diagram calculations for RE magnet recycling process.
Les terres rares, en vertu de leurs propriétés magnétiques, électroniques et chimiques uniques, gagnent en importance dans les industries électroniques, des centrales, des télécommunications et des technologies vertes. Les aimants de terres rares possèdent des propriétés très supérieures par rapport aux aimants traditionnels. Ils disposent d'une puissance et d'une longévité plus élevées, et d'une meilleure usinabilité à haute température. Le déséquilibre entre la demande et l'approvisionnement en terres rares a accru l'importance du recyclage et de l'extraction des terres rares à partir des aimants permanents usagés. Cependant, le manque de données thermodynamiques sur les systèmes de terre rare a rendu difficile la conception de procédés efficaces de recyclage et d'extraction. À cet égard, les calculs thermodynamiques peuvent servir d'outil rentable en termes de temps et d'argent afin de concevoir un procédé de recyclage des aimants permanents usagés. L'aimant permanent de terre rare le plus commun est l'aimant au néodyme (Nd2Fe14B). Divers éléments tels que Dy, Tb, Pr, Cu, Co, Ni, etc. sont également ajoutés pour améliorer ses propriétés magnétiques et mécaniques.Afin d'effectuer des calculs thermodynamiques fiables pour le procédé de recyclage des terres rares, des bases de données thermodynamiques précises pour les terres rares et leurs alliages sont requises. Les bases de données thermodynamiques peuvent être développées en utilisant la méthode dite CALPHAD. Le développement de bases de données basé sur la méthode CALPHAD consiste essentiellement en l'évaluation critique et en l'optimisation de toutes les données thermodynamiques et de diagramme de phase disponibles. En conséquence, un ensemble de fonctions thermodynamiques cohérentes pouvant reproduire tous les données thermodynamiques et de diagramme de phase fiables est obtenu pour toutes les phases dans un système donné. La base de données contenant les fonctions optimisées d'énergie libre de Gibbs peut être utilisée pour calculer des réactions chimiques complexes pour n'importe quels procédés à haute température. Typiquement, une routine de minimisation de l'énergie libre de Gibbs, telle que présente dans le logiciel FactSage, peut être utilisée pour obtenir l'équilibre thermodynamique précis dans un système comprenant de multiples composants.Dans le cadre du développement d'une base de données thermodynamiques pour le recyclage des aimants permanents et la conception d'alliages de magnésium, toutes les données thermodynamiques et de diagramme de phase dans la littérature pour les quatorze systèmes binaires Fe-terre rare incluant Fe-La, Fe-Ce, Fe-Pr, Fe-Nd, Fe-Sm, Fe-Gd, Fe-Tb, Fe-Dy, Fe-Ho, Fe-Er, Fe-Tm, Fe-Lu, Fe-Sc et Fe-Y sont évaluées de manière critique et optimisées pour obtenir les paramètres du modèle thermodynamique. Les paramètres du modèle peuvent ensuite être utilisés pour calculer les diagrammes de phases et les énergies libres de Gibbs de toutes les phases en fonction de la température et de la composition. Cette base de données peut être incorporée à la base de données thermodynamiques présente dans le logiciel FactSage afin de calculer des réactions chimiques complexes et des diagrammes de phase pour le procédé de recyclage des aimants de terres rares.

The manufacture of an air-melted, Durville cast, nickel-iron based superalloy, XD1102, for the automotive industry has been studied. In particular the formation of the air-gap and the heat transfer between the casting and the mould interface has been measured for an aluminum alloy, LM25 and the XD1102 alloy cast into the same size mould. The experimental results were used to verify ProCAST 3D model simulations providing confidence that the software could be used for practical applications where destructive measuring techniques is not viable. A second aspect of this thesis was to identify, trace the origin of, illustrate the root cause analysis, and the mitigation of a feature which has been observed on numerous valve heads. Lastly the investigation into whether the substantial thermo-mechanical work received by an ingot after casting minimised the benefits of a carefully poured cast via the Durville method has been discussed.

Iron- and steel production is a material- and energy intensive industrial activity. The production of one tonne of steel commonly results in some 400 kilograms of residual materials such as metallurgical slags, dusts, sludge and scales generated in the processes. Much work is continuously devoted to finding possible ways of using residual materials and minimising landfilled volumes. As these materials often contain considerable amounts of valuable elements such as iron, coal, manganese and calcium, it may be profitable to use them to replace virgin raw materials or to sell them as products that may be useful in other industries and/or processes.    The thesis is based on case studies that exemplify how the use of process integration, through system analysis, can assist in assessing effects and opportunities for different concepts for increased material efficiency in Nordic ore-based steelmaking systems. The process integration approach taken for this research work was the simulation of a specific iron- and steel production system and the use of an optimisation tool for the evaluation of an extended system including the symbiosis between four steel plants.   Three different cases were studied including: system effects of increased magnesium oxide content in the lime raw material, investigation of the prospects for vanadium enrichment and slag reduction concept and a study of the logistics perspective for a joint residual material upgrading and recycling venture between four steel plants. The analysed cases present possibilities to improve the material efficiency by: •      Enhanced recovery of residual materials; •      Upgrading of residual materials to products; •      Specific elements recovery; •      Decreased use of virgin raw material; •      Improved quality of residual materials; •      Decreased amounts of materials placed in long-term storage or landfills.   From the results of the cases studied, the best scenarios and potential gains by enhanced material efficiency is presented. In the case of system effects of increased magnesium oxide content in the lime raw material, the issue was mainly to obtain maximum usage of metallurgical slags without compromising the quality of the main product. The calculated possibility of increased slag recirculation enabled further a decreased consumption of iron ore pellet and limestone. Regarding the investigation of the vanadium enrichment and slag reduction concept, the best scenario markedly increased the internal slag recirculation in order to enrich the vanadium content in the slag for ferrovanadium production. By the vanadium enrichment and recovery concept, considerable amounts of vanadium would be made useful instead of ending up in long-term storage. The study of a shared Nordic concept for residual materials upgrading and use demonstrated the potential for upgrading the materials to a direct reduced iron product for recovery in blast furnace. The concept showed high potential for significantly reducing the amount of material being long-term stored or deposited to landfill and thus a potential step towards achieving the zero-waste philosophy target.   None of the concepts for enhanced material efficiency studied in this thesis work has been implemented; however, they are still of relevance for the Nordic steel industry.

During the Early Middle Ages, the iron production in Sweden depended on the bloomery furnace, which up to that point was well established as the only way to produce iron. Around the Late Middle Ages, the blast furnace was introduced in Sweden. This made it possible to melt the iron, allowing it to obtain a higher carbon composition and thereby form new iron-carbon phases. This study examines the microstructure and hardness of several tools and objects originating from archaeological excavations of Medieval Sigtuna and Lapphyttan. The aim is to examine the differences in quality and material properties of iron produced by respectively blast furnaces and bloomery furnaces. Both methods required post-processing of the produced iron, i.e. decarburization for blast furnaces and carburization for bloomeries. These processes were also studied, to better understand why and how the material properties and qualities of the items may differ. The results show that some of the studied items must have been produced from blast furnace iron, due to their material composition and structure. These items showed overall better material quality and contained less slag. This was concluded because of the increased carbon concentration that allowed harder and more durable structures such as pearlite to form. The study also involved an investigation of medieval scissors, also known as shears, made from carburized bloomery furnace iron. Here, one specific aim was to find out if the different sections of the shears had different properties, and if so, if these properties correlated with the functions of the different parts of the shears. Our microstructure analysis showed that the blade indeed was the hardest part due to intentional carburization and forming of martensite. The blade is connected to a softer ferritic handle, which in turn is connected to a ductile bow, also ferritic but with a larger grain size.
Den svenska järnproduktionen var under medeltiden beroende av blästerugnen som då var väl etablerad i hela landet. Under denna period introducerades även masugnen i Sverige, vilket gjorde det möjligt att smälta järn. Den nya tekniken gjorde det möjligt att uppnå en ökad kolhalt och därmed bilda nya järn/kol-faser. Den här studien undersöker mikrostrukturer och sammansättningar i medeltida järnföremål från arkeologiska utgrävningar i Sigtuna och Lapphyttan. Syftet är att undersöka vilka egenskaper och materialkvaliteter som gick att uppnå i järn som tillverkats med masugn respektive blästerugn. Båda tillverkningsmetoderna kräver efterbearbetningar som förbättrar järnets egenskaper. Även dessa efterbearbetningsmetoder studeras, för att kunna dra slutsatser angående hur det slutligt producerade järnets egenskaper och materialkvalitet skiljer sig mellan de två produktionsmetoderna. Analyserna visade att järn som tillverkats i masugn innehöll mindre slagg och generellt var av bättre kvalitet. Detta järn innehöll även mer kol vilket tillät perlit att bildas. Därmed blev järnet betydlig hårdare. Slutsatsen är att dessa järnföremål hade övergripande bättre mekaniska egenskaper och materialkvalitet än de järnföremål som tillverkats med järn från en blästerugn. I studien undersöks även medeltida fårsaxar, tillverkade av järn från en blästerugn som sedan genomgått uppkolning. Syftet är att utifrån mikrostrukturen i materialet ta reda på om de olika sektionerna i en fårsax har olika egenskaper, och om dessa egenskaper i så fall är anpassade till den aktuella sektionens användning.Analysen visade att bladet var hårdast på grund av avsiktlig uppkolning och martensitbildning. Därefter följde ett mjukare handtag med en ferritisk struktur. Den böjda delen av saxen var den mest duktila och fjädrande, eftersom den uppvisade en rent ferritisk struktur med större kornstorlekar än i handtaget.

Aspects of early Greek extractive iron metallurgy are investigated here, for the first time, with particular emphasis on Macedonia, Greece's most metals-rich province. The subject is approached experimentally by considering equally the ores, slag and artefacts of iron in Macedonia, through the analytical examination of archaeological slag and artefacts, the experimental smelting of Macedonian ores and subsequent analytical investigation of the slag and blooms produced. The mineral resources geology of Macedonia is presented. The historical background to mining and metal working in Macedonia from the Early Iron Age (tenth century BC) to the turn of the present century is documented. The literature on the introduction of iron into Greece, and the East Mediterranean more generally, is critically reviewed, and in the light of results obtained, especially from Thasos, it is argued that the origins of iron making in Macedonia, if not elsewhere in Greece, should be sought locally during the Late Bronze Age. Despite the absence of excavated furnace remains, it has been possible, through analytical examination of metallurgical waste, to trace the operation of the bloomery in Macedonia continuously for nearly thirty centuries. That a considerable variety of iron ores were exploited was elucidated by the analysis of slag inclusions in a large number of iron artefacts from Vergina and from sites on Thasos and the East Macedonian Mainland, spanning chronologically the Early Iron Age to the Byzantine period. The titanium-rich magnetite sands on Thasos and at Vrontou on the Mainland were shown to have been worked from the Hellenistic/Roman to the turn of this century. A second century BC nickel-rich bloom found at the Hellenistic site at Petres in West Macedonia testified, for the first time, to the smelting of nickel-rich iron laterites in Greece, while the manganese-rich iron deposits in Palaia Kavala district were worked for their precious metals content, probably during Ottoman times and perhaps as early as the Classical period. It is suggested that the Skapte Hyle of the classical texts may be located in the Palaia Kavala district. A fresh appraisal of the depiction of furnaces on Black and Red Figure Attic vases of the sixth and fifth centuries BC suggests that the bloomery process may have developed at that time to a level not previously suspected. The classical texts, the function of the cauldron on the furnace top and experimental meltings carried out in the process of this work all point to the production of wrought iron/steel through the decarburisation of high carbon iron in a fining hearth. It is argued that the furnaces depicted on the vases are themselves fining hearths, the cauldron sealing the furnace top in order for the air blast to be directed over the molten mass.

Phase transformation studies have been carried out on VS2241A, Fe-9.14Ni -0.002C alloy. This alloy was chosen because it was expected that the speed of austenite decomposition would be slow enough to allow continuous cooling transformation and isothermal transformation experiments to be carried out on the same alloy. Upon furnace cooling, massive ferrite was the predominate phase formed. TEM inspection observed low angle sub-boundaries inside ferrite grains. Pre-polished surface examination showed the presence of Widmanstatten ferrite as evident by tent-shaped surface relief. Martensite-austenite (M-A) constituent was also observed under TEM inspection indicating that partition of carbon had occurred during transformation. Quantitative analysis of the dilatation curve showed continuous cooling consisted of two portions. One between 575 +/- 5°C and 558 +/- 3°C corresponding to the formation of grain boundary nucleated massive ferrite while the portion between 558°C to 500°C was thought to correspond to Widmastatten ferrite formation. The observation of an experimental T[0] temperature of 623 +/- 5°C and a theorectical T[0] temperature of 614 +/- 5°C implied that transformation took place below T[0] in the two phase field. Microanalysis using a FEG-STEM system with a windowless LINK X-ray detector was carried out at Liverpool University. This showed that the Ni content across a ferrite grain was constant at 8.8 +/- 0.2wt%Ni and 12.98 +/- 0.43wt%Ni was detected on a grain boundary confirming that the massive transformation was composition invariant, but local partitioning occurred in the interface during transformation. Thermal arrest experiments observed bainitic ferrite and lath martensite transformed at temperatures ~ 486°C and ~ 384°C respectively. Incomplete transformation was observed for all the isothermally transformed structures in the Fe-9Ni alloy below T[0]. It was suggested that this phenomenon would apply to all transformations occurring in the two phase field below the T[0] temperature. Separate but overlapping C-curves in a TTT diagram for Fe-9Ni were proposed to account for the coexistence of massive ferrite and Widmanstatten ferrite at the same temperature. The lath formation of Widmastatten ferrite was interpreted as a product of partial coherent interfaces propagated by means of a ledge mechanism, thermally activated by the trans-interphase diffusion of solute atoms. A thermal arrest at 707 +/- 5°C was observed on air cooling an Fe- 3.5Ni alloy,VS2239A. This corresponded to equi-axed ferrite transformation in the single phase region. In an iced brine quenched Fe-4Cu alloy, massive ferrite and Widmastatten ferrite were observed. A 6° misorientation was calculated between two adjacent ferrite grains seperated by a ragged grain boundary. Charpy impact testing of Fe-9Ni alloy, VS2241A gave a DBTT of -140°C and -100°C for massive ferrite and bainitic ferrite respectively. Massive ferrite showed a higher upper shelf energy on the transition curve.

This present study is concerned with developing a new alloy system which is capable of forming a metallic glass on rapid solidification of the melt, rather than modifying a known glass forming composition, and assessing its glass forming ability. Iron (Fe) was chosen as the solvent element because it is significantly cheaper than the base elements found in some other metallic glasses and does not require the addition of large quantities of expensive alloying elements to enable vitrification. A ternary system using carbon (C) and boron (B) was studied initially as these metalloids are known to aid glass formation in other systems. Manganese and molybdenum were selected as secondary alloying additions in order to determine if they would have an effect on the Fe-C-B alloy with the best glass forming ability. A combination of optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffractometry and secondary ion mass spectroscopy was used to investigate the microstructure of as-cast and rapidly solidified alloys. Differential scanning calorimetry (DSC) was used to investigate the thermal behaviour of the alloys. The ability of the iron-based alloys to form a glass on rapid solidification from the melt could not be predicted by observation of the as-cast microstructure or through computational methods. It was found that vitrification of the ternary system was only possible for compositions which were close to a eutectic point and that stabilisation of the supercooled liquid was caused by competition for nucleation between austenite and metastable phases, rather than between primary equilibrium solidification products. Of the ternary compositions where an amorphous phase was produced it was concluded that Fe₈₀.₉C₅B₁₄.₁ had the best glass forming ability (GFA). It was determined that the addition of manganese and/or molybdenum to the base composition generally had the effect of improving the GFA through the increased complexity of the system making it more difficult for recrystallisation to occur. Of the multi-component alloys it was concluded that Fe₆₀.₉Mn₁₀Mo₁₀C₅B₁₄.₁ had the best GFA as it had the highest values for each of the parameters used to describe GFA. It is believed that this is due to competition between the austenite and alpha stabilisers (manganese and molybdenum respectively) causing enhanced stability of the supercooled liquid.

The hydrolysis of iron(III) from sulphate bearing aqueous solutions was investigated to significantly improve the neutralization of acidic mineral effluents. Both theoretical and experimental studies were undertaken. A literature review and a thermodynamic analysis of the Fe(III)-SO$ sb4$-H$ sb2$O system were performed.
The thermodynamic analysis determined that Fe(III)-sulphato complexes dominate in the acidic pH range (pH $<$ 4) while at neutral to mild alkaline pH range Fe(OH)$ sb3 sp circ sb{ rm (aq)}$ is the dominant species. It was found that a relationship exists between the precipitation pH and the sulphate content of the precipitate (17% at pH 3, 7-9% at pH 6 and 1-2% at pH 9) and it was attributed in part to the existence of the precursor Fe(III)-sulphato complexes and in part to SO$ sb4 sp{2-}$ adsorption on the Fe(III) oxyhydroxide solid phase.
Several variables were examined for their influence on the properties of the iron(III) hydrolysis products, such as: pH, neutralization rate, temperature, agitation rate, sulphate concentration and ionic strength. Tests were performed in a batch reactor and NaOH was selected as the most effective neutralizing reagent. Treatment sludges were characterized physically (e.g., solids content, settling rate, etc.), chemically and morphologically, while the treated effluent was examined for residual iron(III) content. These tests proved only partially successful as the precipitates produced were highly amorphous with low solids content (${<8 %}$) and poor settling (${<3}$ m/hr). However, exceptionally good precipitates were produced when the hydrolysis tests were performed under supersaturation control. This work led to the development of a novel approach to neutralization of effluents involving sludge recycling and staged neutralization in order to maintain a low and controlled supersaturation level. Via this novel method partially crystallized precipitates of excellent properties were produced at 50$ sp circ$C after eight recycles. (Abstract shortened by UMI.)

This thesis presents the results of an investigation on the impact of continuous circuit and solution parameters on coprecipitation of arsenic with ferric iron from acidic sulphate solution. The techniques employed were selected, or developed, to emulate industrial practice. The concept behind the work was to better understand the link between the process of precipitation and the stability of arsenic in the resultant coprecipitates. This was performed by examining the role of circuit design and co-ions on both arsenic removal during coprecipitation and arsenic retention during ageing. The parameters/factors investigated included continuous versus batch operation, number of stages (pH profile), recycling and Ca2+, Ni2+ and Al3+ as co-ions. Arsenic removal was found to be greatly improved by continuous rather than batch coprecipitation. In addition, the presence of calcium (introduced as slaked lime) was found to be instrumental in the removal and retention of arsenic. Arsenic retention during ageing (up to 300 days) at various temperatures (3, 22, 40 and 70°C) was observed to reach an "equilibrium" that was strongly affected by the continuous circuit design, as well as the co-ions present during coprecipitation. Evidence is presented of the partitioning of arsenic within the coprecipitates in two principal phases, namely ferric arsenate (FeAsO4•xH2O) and arsenic adsorbed ferrihydrite. Continuous circuit design parameters, such as staging, that resulted in enhanced stability appear to yield coprecipitates with higher ferric arsenate content. Analysis of the kinetic and "equilibrium" arsenic retention data yielded activation energy (~ 60 kJ/mol) and enthalpy (~ -38.5 kJ/mol) values that suggest a reaction controlled exothermic dissolution mechanism.
Ce mémoire de maîtrise présente les résultats d'une étude portée sur la co-précipitation de l'arsenic et des ions ferriques en solution aqueuse sulfatée. L'utilisation d'un procédé continu et les paramètres de la solution ont été considérés comme cibles d'étude. Les techniques employées ont été sélectionnées ou développées afin de simuler les méthodes opératoires industrielles. L'idée directrice de ce travail était d'aboutir à une meilleure compréhension sur les liens entre les mécanismes de précipitation et la stabilité de l'arsenic dans les co-précipités formés. Aussi, le rôle du design du procédé ainsi que celui des co-ions sur l'extraction, respectivement la stabilisation de l'arsenic ont fait l'objet d'un examen approfondi à court terme soit au stade de co-precipitation, respectivement à long terme durant le vieillissement de la solution. Les paramètres/facteurs étudiés incluaient le caractère continu du procédé (en comparaison avec un procédé discontinu), le nombre d'étapes (le profile pH), le recyclage des produits solides et la nature (Ca2+, Ni2+ et Al3+) des co-ions introduits dans le système. Cette étude a montré que l'utilisation d'un procédé continu (en comparaison avec un procédé discontinu) améliorait considérablement l'extraction de l'arsenic à partir de solutions aqueuses sulfatées. Aussi, la présence de calcium (introduit sous forme de chaux hydratée) s'est avérée profitable à l'extraction de l'arsenic à court et à long terme. Il a été observé que la stabilisation de l'arsenic dans le cas des expériences de vieillissement (d'une durée de 300 jours) performées à différentes températures (3, 22, 40 et 70°C) atteignait un état d'équilibre fortement influencé par le design du procédé continu ainsi que par les co-ions présents lors de la co-précipitation. Il a été mis en évidence que lors de la phase de co-précipitation, l'arsenic était réparti sous forme de de

The quest for ever stronger and tougher steels has lead to an interest in the 'Acicular Ferrite' microstructure, its chaotic and disordered morphology imparting a high degree of toughness to the steel. To date, only complex and expensive materials and manufacturing processes have formed acicular ferrite within bulk cast steel. As such, the thrust of this research is to produce a cheap steel addition, an iron - titanium oxide metal-ceramic composite, that will facilitate the formation of acicular ferrite in conventionally manufactured bulk cast steels. The Self-propagating High-temperature Synthesis (SHS) process has been utilised to manufacture the iron - titanium oxide material from compacts pressed from Fe203 + Ti powders. The fundamental reactions that occur as titanium powder and Fe203 + Ti powder compacts are heated in air and argon atmospheres have been investigated. The process’s involved are reported and have been modelled mathematically. A computer simulation of the reaction process has been developed and tested against experimental evidence. The effect of various compact parameters, the starting compact stoichiometry and other processing variables have been examined with respect to the composition of the products and their morphology.

This project presents a study of iron technology in Early Medieval (fifth to eleventh centuries AD) Britain through the examination of iron found in settlement contexts. This is a period characterized by significant cultural, political and social changes. The effect of these changes on iron technology has never been investigated on a large scale. Previous studies on iron focused either on individual sites or on single artefact types, and did not provide any clear multi-region interpretive framework. A longstanding problem has been in identifying the extent of usage of a key alloy: phosphoric iron. This research project examined iron assemblages from eight settlement sites of varying size, culture, economic and social status from across Britain. From each settlement a mixed assemblage of iron artefacts was sampled, including edged tools, items of personal adornment, construction materials, and craft tools. Analysis was by traditional archaeometallurgical techniques alongside SEM-EDS elemental analysis. Alloy usage, specifically relating to phosphoric iron, was examined and the manufacturing techniques assessed. It was shown that elemental analysis is the only reliable method to determine the presence of phosphorus in iron and demonstrated that the traditional phosphoric indicators as observed during optical microscopy are insufficient. Results were subjected to a series of comparisons based on settlement size, the inferred social status, and cultural affinities. The results demonstrate the high technological level of iron artefact production across the country. All areas had access to the full range of iron alloys and employed a highly developed range of smithing techniques. Phosphoric iron was a prevalent alloy in this period. Based on these results, a model of the Early Medieval iron industry is generated, suggesting a vibrant economy in which both local and traded irons were significant.

Pitting corrosion of iron has been studied via artificial pits. Solid corrosion products were observed within the pit, which was characterised as disordered-carbon and Fe\(_3\)C, acted as diffusion barriers for metal ions and slightly increased the solution resistance. Its formation depends upon the interfacial potential. High purity iron was used to calculate an effective diffusion coefficient for metal ions (a combination of self-diffusion and electrical migration) in different MgCl\(_2\) concentrations. The contribution of self-diffusion increases with increasing MgCl\(_2\) concentration if Mg\(^2\)\(^+\) depletion in the pit is considered. The Tafel kinetics of iron dissolution in metal ion saturated solutions was studied in different MgCl\(_2\) concentrations. The Tafel slope (56 to 70 mV/decade) was independent of MgCl\(_2\) and FeCl\(_2\) concentration when FeCl\(_2\) is saturated. The effect of nitrate on the composition/structure of salt layers was characterised. The salt layer is composed of FeCl\(_2\).4H\(_2\)O in chloride-based solutions (isotropic in HCl and anisotropic in HCl with trace nitrate), and Fe(NO\(_3\))\(_2\).6H\(_2\)O in nitrate-based solutions. The dissolution behaviour of iron in chloride/nitrate solutions was studied. Dissolution is uniform under a salt layer, but crevice formation and surface roughening. Potentiodynamic measurements can induce abrupt dissolution/ passivation transitions, resulting in deep and localised attack.

This thesis presents geochemical records of metalliferous enrichment of soils and isotope analysis of metal finds at Iron Age and Romano-British period settlements in North Ceredigion, Mid Wales, UK. The research sets out to explore whether North Ceredigion’s Iron Age sites had similar metal-production functions to other sites along the Atlantic fringe. Six sites were surveyed using portable x-ray fluorescence (pXRF), a previously unused method in the archaeology of Mid Wales. Also tested was the pXRF (Niton XLt700 pXRF) with regard to how environmentally driven matrix effects may alter its in situ analyses results. Portable x-ray fluorescence was further used to analyse testing a range of certified reference materials (CRM) and site samples to assess target elements (Pb, Cu, Zn and Fe) for comparative accuracy and precision against Atomic absorption spectroscopy (AAS) and Inductively coupled plasma mass spectrometry (ICP-MS) for both in situ and laboratory sampling. At Castell Grogwynion, one of the Iron Age sites surveyed recorded > 20 times Pb enrichment compared to back ground values of 110 ppm. Further geophysical surveys confirmed that high dipolar signals correlated to the pXRF Pb hotspots were similar to other known Iron Age and Roman period smelting sites, but the subsequent excavation only unearthed broken pottery and other waste midden development. Broken pottery remains were dated to no earlier than the medieval period suggesting a re-occupation, possibly for Pb prospection. It was established that Pb and metal rich soils within the villa footprint have similar isotope signatures to local ores found ca. 4km east, suggesting local ores were used in its construction, possibly with some evidence of in situ metal working.

The nature of Cu isotope fractionation in natural Cu-Fe-S minerals was investigated through acid ferric sulfate leaching of copper ore from Morenci, Arizona. Copper isotope composition of the derived solutions varies from δ⁶⁵Cu = 0.47‰ to 5.21‰ over the course of progressive copper extraction. High δ⁶⁵Cu values characterize solutions collected in the first half of the leach, while the solutions collected between 35% and 45% copper recovery exhibit lower δ⁶⁵Cu values. This general pattern was observed for both bacterially-mediated and abiotic leaching. Sulfate solutions derived from dissolving pure djurleite show variable Cu isotope compositions as well, although the range is protracted from δ⁶⁵Cu = 0.01‰ to 1.21‰. As the Cu:S ratio of the remaining sulfide decreases, crystal structure parameters change as mineralogy passes through a series of nonstoichiometric copper sulfides. Mineralogy converges to yarrowite near 44% copper dissolution. Crystal chemical studies show that distribution of the two copper-sulfur bond coordination geometries, triangular planar and tetrahedral, in the copper sulfides, approximately corresponds to changes in δ⁶⁵Cu of the leachates. In particular, the proportion of CuS3 relative to CuS4 groups decreases from Cu/S = 2.00 (chalcocite) to 1.40 (geerite). Between Cu/S = 1.40 to 1.00 (covellite), the relative proportion of CuS3 groups increases slightly. Connection between coordination number and Cu isotope fractionation implies affinity of CuS₃ groups for the heavier, ⁶⁵Cu, isotope. This can be justified through bond length-bond strength arguments. Solutions from bornite dissolution vary from δ⁶⁵Cu = -0.79‰ to 1.14‰, with the largest values associated with solutions from early stage of reaction (up to 15% copper removal). Around 25% dissolution, δ⁶⁵Cu of the solution approaches that of the original bornite (δ⁶⁵Cu = 0.02‰). This is explained by disappearance of all remaining CuS₃ groups. Sulfur isotope compositions of solutions and sulfides derived from djurleite leaching were determined to investigate the possibility of intra-mineral fractionation. Very soon after reaction initiation, δ³⁴S of both sulfur reservoirs reach a steady-state with sulfate solutions about 2‰ enriched in ³⁴S relative to residual sulfide. Unlike the case of Cu isotopes, the main partitioning affecting S isotopes is exchange between sulfate and sulfide.

Thesis (PhD) -- Stellenbosch University, 2014.
ENGLISH ABSTRACT: The process route for the production of base and platinum-group metals from natural sulfide ores commonly requires the conversion of high-iron furnace matte into an iron-lean converter matte. This is followed by pre-treatment through cooling of the iron-lean molten matte, physical processing of the solidified matte and hydrometallurgical metal extraction. Lonmin is the third largest producer of platinum-group metals in the world and utilizes Peirce-Smith converters for blowing high-iron furnace matte with air to a final iron concentration or endpoint. The molten matte is water granulated and solidification occurs via fast-cooling. The solidified matte is ground in a closed circuit ball mill with hydrocyclone classification and subjected to first stage atmospheric leaching. The specification of an ideal or desirable converter iron endpoint requires careful consideration. Most importantly, it must ensure the crystallization of converter matte with mineralogical qualities that are within the setpoints of the downstream unit processes and techniques. An additional consideration is for the final blown converter matte to achieve an optimum bulk concentration of the base metals Ni and Cu and platinum-group metals Pt, Pd, Rh, Ru and Ir. Mattes characteristic of variable iron endpoints were regularly produced at the Lonmin converter plant section. Uncertainty by plant metallurgists in knowing the desirable iron endpoint, particularly within the context of the Lonmin base metal refinery, and poor control has had detrimental effects on the mineralogical quality of the final matte and hence on the processing characteristics of the solidified matte particles downstream. A desirable iron endpoint required investigation, selection and implementation at Lonmin. The primary focus of this study was therefore to quantify the effect of a specific iron endpoint on the mineralogy and mineral chemistry of solidified converter matte. A fundamental examination of the solidification process upon cooling was regarded as critical to an in-depth understanding of the attained mineralogy and mineral chemistry as a function of a specific iron endpoint. It became equally important to quantify the effect of the resultant mineralogy, and hence iron endpoint, on the physical property of mineral structures in relation to downstream grinding, liberation and leaching characteristics. Despite considerable industry context, limited in-depth and coherent studies on the effect of a specific iron endpoint on fast-cooled converter matte systems were found in both industrial and scholarly literature. Previous findings in literature offered a limited quantitative understanding of the effect on mineralogy and mineral chemistry. Phase and cooling equilibria of multi-component, iron endpoint specific Ni-Cu-S matte systems were also not fully available. These would have been particularly useful in understanding the complexities of converter matte solidification as a function of iron endpoint. Physical property knowledge of converter matte mineral structures was hardly available and even less so in relation to grinding, liberation and leaching processes. A comprehensive investigation was therefore required to address these extensive knowledge gaps with respect to fastcooled converter matte systems in an industrial framework. Three Peirce-Smith converter production samples, representative of the extent in variability of iron endpoints attained at the converter plant, were used in a systematic investigation coupled to a novel combination of modern analytical techniques, computational thermochemistry and metallurgical testwork. The modern analytical techniques included the application of high resolution transmission electron microscopy and focused ion beam scanning electron microscopy tomography. Computational thermochemistry was applied through the use of MTDATA phase diagram software. Metallurgical testwork involved laboratory batch grinding at various specific energies. Closely associated leach experiments were also considered relevant to this wide-ranging investigation. The Peirce-Smith converter samples investigated were indicative of mattes that attained specific endpoints of 5.17%, 0.99% and 0.15 weight% Fe. The highest combined bulk concentration of the important base and platinum-group metals was achieved in the matte which attained a specific iron endpoint of 0.99%. The mineralogy of all three converter mattes was dominated by nickel sulfide mineral structures matched to the natural mineral of heazlewoodite. Mineral structures of copper sulfide, NiCu-alloy, spinel and OsRu-alloy were also constituents of the different converter mattes. The attainment of a specific iron endpoint was found to result in measurable mineralogical differences with respect to relative mineral abundances, external morphological characteristics and mineral chemistry. The mineralogical differences were particularly distinct between mineral structures of the high (5.17%) and low (0.99% and 0.15%) iron mattes. Subtle mineralogical differences were evident between mineral structures of the low iron mattes. The 0.99% Fe matte was characteristic of a significantly higher NiCu-alloy relative abundance, compared to the 5.17% Fe matte. The NiCu-alloy structures were found to act as the primary collectors of the economically significant platinum-group metals. Mineralogical observations were used to develop an understanding of the underlying mineralization mechanism of NiCu-alloy structures. High-fidelity color and grayscale 3D reconstructions were produced of the resultant mineralized structures. It was shown theoretically that variations in iron endpoint specific starting compositions of oxygen-free liquid matte systems alter the solidification pathway towards the eutectic. Moreover, a quantitative understanding of liquid phase solidification of the high and low iron matte systems, including oxygen, was developed to within ±2.5 oC. Most of the specific energy available for grinding was expended breaking the nickel sulfide matrix, particularly of the high iron matte. The breakage rates of copper sulfide mineral structures in the 5.17% Fe matte were calculated to be higher than in the 0.15% Fe matte at 25kWh/t specific energy. The degree of copper sulfide liberation was shown to be higher for the 5.17% Fe matte than for the 0.15% Fe matte at the same specific energy of grinding. A higher degree of Ni extraction and Cu cementation could be achieved when leaching low iron matte particles. The production of converter matte attaining a specific iron endpoint of 0.99% was found to be the most suitable with respect to endpoint selection criteria. A practical iron endpoint range of 1.6% to 1.0% was recommended for the production of converter matte with a resultant mineralogical quality within the constraints of the Lonmin base metal refinery. This study offers an integrated understanding of base and platinum-group metals production as a function of a desirable iron endpoint at Lonmin. This was not previously available in metal production literature. New technology for the monitoring and consistent control of such a practical iron endpoint range can subsequently be implemented.
AFRIKAANSE OPSOMMING: Die prosesroete vir die produksie van onedel en platinumgroepmetale uit natuurlike swawelertse vereis gewoonlik die omsetting van ’n ysterryke hoogoondmat in ’n ysterarm omsettermat. Hierna volg voorbehandeling deur die afkoeling van die ysterarm gesmelte mat, fisiese verwerking van die soliede mat, en hidrometallurgiese metaalekstraksie. Lonmin is die derde grootste produsent van platinumgroepmetale ter wêreld en gebruik Peirce-Smith-omsetters om ysterryke hoogoondmat met lug te blaas totdat dit ’n finale ysterkonsentrasie- of ystereindpunt bereik. Die gesmelte mat word met water granuleer, en solidifikasie vind deur middel van snelafkoeling plaas. Die soliede mat word in ’n geslotekringbalmeul met hidrosikloonklassifikasie gemaal en aan eerstestadium- atmosferiese loging onderwerp. Die spesifikasie van ’n ideale of gewenste ystereindpunt verg deeglike oorweging. Bowenal moet dit verseker dat die omsettermat kristalliseer met mineralogiese eienskappe wat binne die setpunte van die eenheidsprosesse en - tegnieke verder af in die prosesstroom val. ’n Bykomende oorweging is dat die uiteindelike geblaasde omsettermat ’n optimale massakonsentrasie van die onedel metale Ni en Cu en die platinumgroepmetale Pt, Pd, Rh, Ru en Ir moet bevat. Matte met die kenmerke van wisselende ystereindpunte is gereeld by die Lonminomsetteraanleg geproduseer. Die onsekerheid van metallurge by die aanleg oor die gewenste ystereindpunt – veral binne die konteks van die Lonmin-raffinadery vir onedel metale – sowel as swak beheer het ’n nadelige uitwerking gehad op die mineralogiese gehalte van die uiteindelike mat, en dus ook op die verwerkingskenmerke van die soliede matdeeltjies verder af in die prosesstroom. Die bepaling van die gewenste ystereindpunt het sorgvuldige ondersoek, seleksie en toepassing deur Lonmin vereis. Hierdie studie is dus hoofsaaklik uitgevoer om die uitwerking van ’n spesifieke ystereindpunt op die mineralogie en minerale chemie van soliede omsettermat te kwantifiseer. ’n Grondliggende ondersoek na die solidifikasieproses by afkoeling is as noodsaaklik beskou vir ’n diepgaande begrip van die verworwe mineralogie en minerale chemie as ’n funksie van ’n spesifieke ystereindpunt. Mettertyd het dit egter ewe belangrik geword om die uitwerking van die gevolglike mineralogie, en dus die ystereindpunt, op die fisiese eienskappe van minerale strukture met betrekking tot maling-, vrystellings- en loogprosesse verder af in die prosesstroom te kwantifiseer. Ondanks heelwat bedryfskonteks, het nóg bedryfs- nóg vakkundige literatuur veel diepte- en samehangende studies oor die uitwerking van ’n spesifieke ystereindpunt op snelafgekoelde omsettermatstelsels opgelewer. Vorige bevindinge in die literatuur het boonop ’n beperkte kwantitatiewe begrip van die uitwerking op mineralogie en minerale chemie getoon. Die fase- en afkoelingsekwilibriums van ystereindpuntspesifieke Ni-Cu-S-matstelsels met veelvuldige komponente was ook nie ten volle beskikbaar nie. Dít sou veral goed te pas gekom het om die kompleksiteite van omsettermatsolidifikasie as ’n funksie van ystereindpunt te verstaan. Kennis van die fisiese eienskappe van die minerale strukture van omsettermat was kwalik beskikbaar, terwyl selfs minder inligting oor maling-, vrystellings- en loogprosesse opgespoor kon word. Daarom was ’n omvattende ondersoek nodig om hierdie beduidende kennisleemtes met betrekking tot snelafgekoelde omsettermatstelsels in ’n nywerheidsraamwerk aan te vul. Drie Peirce-Smith-omsetterproduksiemonsters wat die wisselende bestek van ystereindpunte by die omsetteraanleg verteenwoordig, is in ’n stelselmatige ondersoek gebruik, tesame met ’n vernuwende kombinasie van moderne ontledingstegnieke, gerekenariseerde termochemiese bewerkings en metallurgiese toetswerk. Die moderne ontledingstegnieke sluit onder andere in hoëresolusie-transmissie-elektronmikroskopie (HRTEM) en gefokusdeioonstraalskandering-elektron-mikroskopie (FIB SEM) tomografie. Die gerekenariseerde termochemiese bewerkings is met behulp van MTDATAfasediagramsagteware uitgevoer. Metallurgiese toetswerk het die maling van laboratoriumlotte teen verskillende spesifieke energieë behels. Nou verwante loogproefnemings is ook as relevant vir hierdie omvattende studie beskou. Die bestudeerde Peirce-Smith-omsettermonsters het op matte met spesifieke eindpunte van 5.17%, 0.99% en 0.15 gewig% Fe gedui. Die hoogste gekombineerde massakonsentrasie van die belangrike onedel en platinumgroepmetale is in die mat met ’n spesifieke ystereindpunt van 0.99% gevind. Die mineralogie van ál drie omsettermatte is oorheers deur die minerale strukture van nikkelsulfied, wat met die natuurlike mineraal heazlewoodiet ooreenstem. Die verskillende omsettermatte het ook die minerale strukture van kopersulfied, NiCu-allooi, spinel en OsRu-allooi bevat. Daar is bevind dat die verkryging van ’n spesifieke ystereindpunt tot meetbare mineralogiese verskille in die relatiewe volopheid van minerale, die eksterne morfologiese kenmerke sowel as minerale chemie lei. Die mineralogiese verskille was veral duidelik te sien tussen die minerale strukture van die ysterryke (5.17% Fe) en ysterarm (0.99% en 0.15% Fe) matte. Fyn mineralogiese verskille is ook tussen die minerale strukture van die ysterarm matte bespeur. Die 0.99% Fe-mat het tipies beduidend meer NiCu-allooi as die 5.17% Fe-mat bevat. Die NiCu-allooistrukture tree oënskynlik op as die hoofversamelaars van die ekonomies belangrike platinumgroepmetale. Mineralogiese waarnemings is gebruik om ’n begrip te ontwikkel van die onderliggende mineralisasiemeganisme van NiCuallooistrukture. Die gevolglike gemineraliseerde strukture is met behulp van driedimensionele rekonstruksies met hoë kleurgetrouheid sowel as in grysskaal voorgestel. Daar is teoreties aangetoon dat variasies in ystereindpuntspesifieke beginsamestellings van suurstofvrye vloeibare matstelsels die solidifikasieroete na die eutetikum wysig. Daarbenewens is die vloeifasesolidifikasie van die ysterryke en ysterarm matstelsels, wat suurstof insluit, op sowat ±2.5 oC gekwantifiseer. Die meeste van die spesifieke energie wat vir maling beskikbaar was, is gebruik om die nikkelsulfiedmatriks te breek, veral vir die ysterryke mat. Berekeninge toon dat die breektempo’s van die minerale strukture van kopersulfied by die 5.17% Fe-mat hoër was as by die 0.15% Fe-mat teen ’n spesifieke energie van 25 kWh/t. Die mate van kopersulfiedvrystelling was hoër by die 5.17% Fe-mat as by die 0.15% Fe-mat by dieselfde spesifieke energie vir maling. ’n Hoër mate van Ni-ekstraksie en Cu-sementasie is verkry toe ysterarm matdeeltjies geloog is. Wat eindpuntseleksiemaatstawwe betref, is die produksie van ’n omsettermat met ’n spesifieke ystereindpunt van 0,99% as die mees geskikte aangewys. ’n Praktiese ystereindpuntbestek van 1.6% tot 1.0% word aanbeveel vir die produksie van ’n omsettermat met ’n gevolglike mineralogiese gehalte wat binne die perke van die Lonmin-raffinadery vir onedel metale val. Hierdie studie bied ’n geïntegreerde begrip van die produksie van onedel en platinumgroepmetale as ’n funksie van ’n gewenste ystereindpunt by Lonmin. Hierdie inligting was nie voorheen in literatuur oor metaalproduksie beskikbaar nie. Nuwe tegnologie vir die monitering en konsekwente beheer van so ’n praktiese ystereindpuntbestek kan dus op grond hiervan in werking gestel word.

Regeneration of HCl from process solutions is an important unit operation in chloride hydrometallurgy. Currently, it is accomplished by the highly capital and energy intensive technology of pyrohydrolysis. The research described in this thesis, has focused on an alternative HCl regeneration system from iron(II, III) chloride solutions that has been coined "Hydrolytic Distillation". This system relates to the earlier developed (in the 1970s) PORI Process. Basically this system involves two steps: (1) the oxidation of ferrous chloride solution by oxygen sparging under reflux conditions (atmospheric pressure) at 150ºC; and (2) the hydrolytic decomposition under atmospheric pressure of ferric chloride solution by continuous controlled water addition at 180ºC. As a result of the latter step iron is recovered as hematite and chloride units as superazeotropic (8-9 M) hydrochloric acid in the vapor phase condensate. The study on oxidation determined that 2/3 of FeCl2 is converted to FeCl3 and 1/3 to Fe2O3 at a rate that is controlled by oxygen mass transfer. The hematite product from the oxidation step proved to be crystalline but nanostructured consisting of 1-2 μm porous aggregated particles possessing 12-28 m2/g specific surface area and to be essentially pure α-Fe2O3 (70% Fe, <0.1% Cl-). With reference to the hydrolytic precipitation/distillation step it was determined that at 180ºC, the temperature at which superazeotropic HCl (8-9 M) was consistently produced, the composition of the liquid phase is "FeCl32H2O". Controlled continuous addition of H2O (or feed solution) was found to be critical in maintaining pseudo-steady state and driving the reaction to ~95% conversion efficiency. The hematite consisted of coarse spherical compact aggregated particles (~40 μm) that exhibited excellent filtration and washing properties. Its %Fe content was 68.5% and it contained ~4% H2O and ~3% Cl- that could be re
Le recyclage d'acide chlorhydrique à partir de solutions industrielles chlorées constitue une étape importante des procédés hydrométallurgiques. A l'heure actuelle cette opération est effectuée par pyrohydrolyse, une technique très couteuse d'un point de vue économique ou énergétique. La recherche présentée dans ce manuscrit se concentre sur un système de recyclage d'acide chlorhydrique à partir de solutions de chlorure de fer (II, III), baptisé "Distillation Hydrolytique". Ce système est issu du procédé PORI, préalablement développé (dans les années 1970). Le système inclus principalement deux étapes : (1) l'oxidation d'une solution de chlorure de fer (II) (FeCl2) par barbotage d'oxygène et utilisation d'une colonne à reflux (sous pression atmosphérique), à une température de 150°C ; (2) la décomposition hydrolytique sous pression atmosphérique d'une solution de chlorure de fer (III) (FeCl3) à 180 °C par ajout d'eau contrôlé et continu. A la fin de cette dernière étape, le fer est récupéré sous forme d'hématite et les dérivés chlorés sous forme d'acide chlorhydrique super-azéotropique (8-9 M) dans le condensat provenant de la phase gazeuse. L'étude sur l'oxidation a permis de déterminer que 2/3 du FeCl2 était converti sous forme de FeCl3 et le reste sous forme d'hématite Fe2O3, la vitesse de réaction étant contrôlée par le transfert de masse de l'oxygène. L'hématite produite lors de l'étape d'oxidation s'est avérée de nature cristalline, nano-structurée, constituée d'agrégats de particules poreuses, d'une taille moyenne de 1-2 μm avec une aire de surface de 12-28 m2/g et de composition chimique α-Fe2O3 quasi pure (70% Fe, < 0.1% Cl-). Quant à l'étape de précipitation/distillation hydrolytique, il a été déterminé qu'à 180°C, température à laquelle l'acide chlorhydrique super-azéotropique était continuellement produit, la compo