Tesi sul tema "Slags"

Slags plays a significant role at high temperature processes. The estimation of the slag viscosity is vital for the safe run of e.g. entrained flow gasifiers. One opportunity of determination is rotational viscometry. This technique is disadvantageous in view of elevated temperatures, applied materials and the necessary time. Additionally, the viscosity can be predicted by the help of viscosity models, where viscosity is a function of slag composition and temperature. Due to changing slag properties within the technical processes, the calculated viscosities can hugely differ from measured ones. In this work, the viscosities of 42 slags where measured up to 100 Pa s and temperatures up to 1700 °C. Oxidizing and reducing conditions were applied. Additionally, selected slag samples were quenched at defined temperatures to qualitatively and quantitatively determine the formed minerals by X-ray diffraction (XRD). Differential temperature analysis (DTA) was applied to find the onset of crystallization for the complementation of investigations. The Einstein-Roscoe equation was chosen to improve the classic viscosity models. Reducing atmosphere decreased viscosity and the number of formed minerals was increased. Slags show a shear-thinning behavior above ca. 10 vol.-% of solid mineral matter. Also, Newtonian behavior was observed up to 60 vol.-%. To overcome problems with the kinetic cooling behavior of the slags, a viscosity approximation method was applied afterwards. This can result in optimized viscosity predictions when several preconditions are fulfilled.

The objective of this research work was to develop a methodology for experimentally estimating the interfacial properties at slag-metal interfaces. From previous experiments carried out in the division, it was decided to use surface active elements like sulfur or oxygen to trace any motion at the interface. For this purpose the following experimental investigations were carried out. Firstly the density of slag was estimated using the Archimedes Principle and the Sessile Drop technique. The density of the slag would give the molten slag height required for the surface active element to travel before reaching the slag-metal interface. Diffusivity measurements were uniquely designed in order to estimate the sulfur diffusion through slag media. It was for the first time that the chemical diffusivity was estimated from the concentration in the metal phase. Experiments carried out validated the models developed earlier. The density and diffusivity value of sulfur in the slag was used to accurately capture the time for sulfur to reach the slag-metal interface. The oscillations were identified by calculating the contact angle variations and the interfacial velocity was estimated from the change in the surface area of the liquid iron drop. The interfacial tension was estimated from the contact angles and the interfacial dilatational modulus was calculated. Based on cold model experiments using water as well as mercury, an equation of the dependence of the interfacial shear viscosity on the interfacial velocity and interfacial tension was established. This paved way for the estimation of the interfacial shear viscosity at the slag-metal interface. The present study is expected to have a strong impact on refining reactions in pyometallurgical industries where slag/metal interfaces play an important role. From a fundamental view point, this provides a deeper insight into interfacial phenomena and presents an experimental technique to quantify the same.
QC 20101130

Surface treatment processes of stainless steel, such as pickling, produces acidic waste water consisting of Na⁺, Cl⁻, F⁻, NO⁻3, SO42-, PO43-, Fe3+, Cr6+ and Ni2+. At Sandvik ABs steel works in Sandviken, this waste water is treated and neutralized using slaked lime before being released into the lake Storsjön. The aim of this report was to make a literary review of previous work in using slag as a neutralizing agent for acidic waste water. Furthermore, to see if it’s possible to replace some or all of the slaked lime in the neutralization process with slag and to study what slag that might be suitable to use. Since the waste water contains HF acid, the focus of this report was on different materials used for fluoride adsorptions. The literary study showed that the fluoride adsorption process with BOF slag, quick lime and magnesium oxide as adsorbents were endothermic. Therefore, it benefitted from an increased temperature. Furthermore, the literature study showed that many materials follow a pseudo-second-order kinetic model as well as a Langmuir or Freundlich isotherm for a fluoride adsorption. A previous experiment showed that a mixture of BF slag and slaked lime had the best HF acid neutralization among the tested materials. A fluoride adsorption experiment was made at different temperatures (25 – 55 °C) by using a slag from an aluminium reduced steel melt and a slag from a silicon reduced steel melt from the AOD converter in Sandviken. The silicon reduced steel melt slag showed an increase of fluorides in the solution, due to the presence of calcium fluoride in the slag. This was observed for all temperatures. The aluminium reduced steel melt slag also increased the fluoride content in the solution at 25 and 30 °C. At higher temperatures the fluoride content in the solution decreased with 93.6 to 94.9 %. Na⁺, Cl⁻, F⁻, NO⁻3, SO42-, PO43-, Fe3+, Cr6+, and Ni2+

In the present work the mixing between the metal and slagphase during the ladle refining process from tapping from theelectric arc furnace to casting in two different Swedish steelplants has been studied.

Three slag models and the sulphur-oxygen equilibrium betweenslag and steel was used together with the dilute solution modelfor the liquid steel phase to predict the equilibrium oxygenactivity in steel bulk and metal droplets in top slag inequilibrium with the top slag. The predicted oxygen activitieswere compared with measured oxygen activities from the steelbulk. The results show significant discrepancies between thecalculated and measured oxygen activities and the reasons forthe differences are discussed.

Metal droplet distribution in slag samples have also beendetermined using classification according to the Swedishstandard SS111116. It was found that most metal droplets arefound in the slag samples taken before vacuum degassing. Thetotal area between steel droplets and slag has been determinedto be 3 to 14 times larger than the projected flat interfacearea between top slag and steel. The effect of slag viscosityand reactions between steel and slag on the metal dropletformation in slags is also discussed.

The chemical composition of the metal droplets in the topslag was determined and possible reactions taking place betweenthe steel droplets and the slag was studied. Differencesbetween steel droplet compositions and the bulk steelcomposition are discussed. The results show significantdifferences between steel droplet and bulk steelcomposition.

Key words:oxygen activity, metal droplets, sulphur,slag, ladle, refining, distribution.

There are a number of impurity elements present in sulphide ores that can have a deleterious effect on the properties of the final copper metal product. In this thesis, an equilibrium distribution technique was used to determine the thermodynamic behaviour of selenium and tellurium in molten slags used in copper production. Calcium ferrite based slags and copper or silver alloy were equilibrated in magnesia crucibles at temperatures of 1200 to 1400 °C and oxygen partial pressures of 10-11 to 10-0.68 atm. Under conditions typical of those employed during copper converting, the minor elements were found to enter the slag as negatively charged species. The partitioning of selenium and tellurium to the slag was greatest at high temperature, low oxygen partial pressure and at highest concentration of basic oxide (CaO or BaO). The experimentally derived data were combined with published information to calculate the selenide and telluride capacities of the slag, and also to generate fundamental thermodynamic activity data for selenium and tellurium in the slag phase. It was found that the activity coefficients of selenium and tellurium were independent of their concentration in the slag over the range studied, but were strongly dependent on the temperature, slag chemistry and oxidation state of the slag. Experiments were also designed and carried out to determine what effect the presence of iron oxide and its oxidation state has on the behaviour of selenium in the slag. A series of experiments involving iron oxide additions to a calcium aluminate slag was conducted under increasingly oxidising conditions to assess the effect of total iron on the selenide capacity as the dominant oxidation state of iron in the slag changed. It was shown that at a constant ratio of CaO:Al2O3, the selenide capacity increased with total iron in the slag. However, the effect on the selenide capacity did not appear any more significant as the Fe3+:Fe2+ ratio changed in a particular direction. 4 Another series of experiments was carried out with iron calcium silicate slags to determine the stability of phases within the slag, and how this affected the equilibrium distribution and activity coefficient of selenium in the slag. A number of solid phases were identified and their composition determined by scanning electron microscopy, energy dispersive spectroscopy and electron microprobe analysis. The composition and minor element content of the remaining liquid was calculated using a thermodynamic model. From this it was found that the capacity of the liquid slag has a region of independence against slag chemistry, before increasing strongly with increasing lime content to the calcium ferrite composition. Some of the implications of this work are discussed with reference to the practicality of adjusting the process variables in a large-scale industrial process for the purpose of managing minor element content of the molten phases. Considerations include the effect on copper recovery and rate of wear of furnace refractory materials.

The influence of basicity, heat treatment as well as different oxygen partial pressures on the phase relationships in the CaO-MgO-SiO2-Cr2O3 slags was studied with a view to control the precipitation of Cr-spinel in the slag phase. The equilibrium phases in CaO-MgO-SiO2-Cr2O3 slag system in the range on 1673-1873 K have been investigated under low oxygen partial pressure as well as in as air atmosphere. In low oxygen partial pressure experiments, a suitable mixture of CO and CO2 was used to control the oxygen partial pressure. The oxygen partial pressure was kept at 10-4 Pa. The Cr2O3 and MgO contents in the slag were fixed to be 6 and 8wt% respectively. The basicity (CaO/ SiO2) of the slag was varied in the range 1.0-2.0. Gas/slag equilibrium technique was adopted to synthesize the slag at a suitable temperature above the liquidus point. One heat treatment procedure is that the samples were heated to and soaked at 1873 K for 24h in order to achieve the equilibrium state and subsequently quenched in water. The other is that the samples were heated to and soaked at 1873 K for 24h, then slow cooled to 1673 K and soaked at this temperature for additional 24h in order to achieve the equilibrium state at lower temperature before quenching in water. The chromium distribution and phase compositions in the quenched slag were studied using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction techniques (XRD). FACTsage software was used for the phase equilibrium calculations. The experimental results obtained from the present work are compared with the calculation results from FACTsage software as well as with results from samples directly quenched after soaking at 1873K. It is found that the spinel formation at 1873 K in air atmosphere is favored in the slag basicity range of 1.0 to 1.6. The size of spinel crystals increased drastically after slow cooling followed by annealing compared to samples being quenched after soaking at 1873 K. The amount of foreign elements dissolved in the spinel phase, and matrix phases decreased after slow cooling followed by annealing at lower temperature, resulting in purer phases with less defects. It was found that the amount of foreign elements in the spinel phase, and other phases decreased after soaking at very low PO2. The size of the spinel crystals was found to be larger in samples with low basicity. Spinel phase precipitation has improved in the samples with higher basicities compared to the results obtained in air.
QC 20111208

Digestion of titaniferous slag (Sorelslag) with sulphuric acid was studied in an effort to optimise the process and develop a better understanding of its chemistry.
Thermodynamic analysis of the digestion reaction was performed using the program F*A*C*T. A laboratory reactor was built to simulate the operation of an industrial slag digestion reactor. Microstructure examinations of digestion samples revealed the main phases present.
Statistically designed experiments using the Box-Behnken technique were performed in the laboratory to correlate the responses (digestion yield, maximum temperature, solidification time, degree of Ti$ sb2$O$ sb3$ oxidation, sulphuric acid loss in the gas, active acid/titanium ratio and cake height) to the four experimental variables (particle size of the slag, acid concentration, acid/slag weight ratio and baking time).
Model equations successfully tested were obtained for each response. The analysis of the figures obtained from those equations revealed the relative importance of the variables evaluated. In complement to these experimental results the qualitative mass and heat balances were calculated.

The American Society of Civil Engineers’ (ASCE’s) “2013 Report Card for America’s Infrastructure” estimated that “32% of America’s major roads are in poor or mediocre condition.” An estimated $100 billion dollars are needed to maintain that condition, and an additional $79 billion is needed to improve the quality of American roadways to an acceptable level. In many regions around the US, the service lives of concrete pavements are limited by the damage caused by freezing and thawing of pore solution inside the pavements. Alkali-activated slags (AAS) are produced from ground granulated blast furnace slag (GGBFS), a byproduct of iron production, and exhibit cementitious properties. AAS concretes have been shown to have improved corrosion and freeze/thaw resistance compared to traditional cementbased concretes. A Guarded Longitudinal Comparative Calorimeter (GLCC) was used to determine when the freezing and thawing of internal water occurs in three AAS mortars using solutions of NaOH, Na2CO3, or waterglass compared to a control Ordinary Portland Cement (OPC) mortar. AAS mortars using NaOH and Na2CO3 showed comparable thermal properties to the OPC mortar using the GLCC, and the AAS mortar using waterglass was shown to have higher heat capacity compared to the other AAS mixes. The compressive strengths varied by the alkaline solution used, with AAS with Na2CO3 showing inferior compressive strength to OPC, AAS with NaOH showing similar compressive strength to OPC, and AAS with waterglass showing superior compressive strength to OPC, but poor workability. A computer model of the GLCC testing procedure was created and showed good agreement with the experimental data. The GLCC model can be modified to approximate the results of the GLCC using a wider range of materials and internal solutions, like PCMs.

Bibliography: p. 219-226.
This thesis details an investigation into the factors affecting the electrical conductivity of slags containing some or all of the following components: Ah03, cae, Cr203, FeOx, MgO and Si02. The interest in the electrical properties of these slags originated from problems being experienced in the electrical control of the melter type furnaces of the platinum producers in South Africa. A large amount of literature on the electrical conductivity of slags was collected and analysed. The key research areas identified through the literature review were: the effect of iron oxide on slag conductivity in terms of ionic and electronic mechanisms, the effect of oxidation state on the conductivity of iron-containing slags and the effect of chromium on the electrical conductivity of melter type slags. Measurements of the electrical conductivities of various slags were conducted in order to gain an understanding of these effects.

Steel slags are by-products of the steelmaking process. To avoid unnecessary disposal, e.g. into landfill, their chemical and physical properties should be exploited to support alternative uses. Steel slags can be recycled within the steel plant or used as construction material in roads, hydraulic engineering and different types of barriers, including landfill covers. A landfill cover consists of several layers, including a liner with low water and gas permeability in order to reduce methane and leachate emissions. Several studies have demonstrated that steel slags have good potential to fulfil such an application. However, there are questions regarding the stability of the slag minerals over long periods of time. A landfill cover must function well for many decades and centuries. In order to predict the long-term stability of steel slags as a landfill liner, laboratory experiments have been performed to study the effects of accelerated ageing of steel slag under controlled conditions. The factors investigated in the storage atmosphere were carbon dioxide content, relative humidity and temperature. The influence of leachate contact and ageing time were also assessed.This thesis reports the study of electric arc furnace slags and ladle slag from the production of high-alloyed tool steel after accelerated ageing for periods of three months and ten months. Mineralogy and leaching were studied using two different leaching tests, thermal analysis, acid-neutralization capacity assays and X-ray diffraction. For the ageing periods considered, the exposure of the slags to an atmosphere enriched with carbon dioxide had the greatest impact on leaching. In general, calcium, aluminium, sulphur and sodium leached from the slag matrix to the greatest extent while other metals such as chromium, nickel, lead and zinc were found at very low levels in the leachate. The leaching of calcium and aluminium reduced with increasing carbon dioxide level. Thermal analysis revealed the decomposition of carbonates. Weight and enthalpy changes were evaluated between 100 and 1000 °C. The buffer capacity of the steel slags, represented by the acid neutralization capacity (ANC 4.5) was not reduced after 10 months of ageing. However, the division of the titration into two steps revealed a shift of buffering zones for more highly aged samples, probably due to the formation of carbonates. The mineralogy of the investigated steel slags was complex with a large variety of mineral phases, principally calcium silicates, monticellite, periclase and a spinel phase. Other possible phases were gehlenite, merwinite, akermanite and iron. The existence of different solid solution is likely among the slag phases and can cause shifting of peaks in the X-ray diffractogram. Also, calcite was identified. Short-term carbonation has not shown significant impact on mineralogy despite of calcite formation. The results of the study contribute to a better understanding of the chemical and mineral stability of electric arc furnace slag and ladle slag in the environment of a landfill liner. The consequences of slag ageing include reduced leaching rates for certain elements. To predict the long-term behaviour of aged slag, the results of this study should be combined with data from two other sources - an ongoing ageing experiment that includes mechanical tests and a full scale field test at the Hagfors landfill. Additional analytical methods that can better characterise the mineralogy, for example scanning electron microscopy (SEM) and energydispersive X-ray spectroscopy (EDX), should also be applied to better quantify the mineralogical phases and to determine which trace elements are most abundant in specific minerals.
Stålslagg är en restprodukt som kommer från ståltillverkningen. Den har kemiska och fysikaliska egenskaper som bör utnyttjas och som gör den lämplig för återanvändning, samtidigt som onödig deponering kan undvikas. Stålslagg kan återanvändas inom ståltillverkningen eller så kan den användas som konstruktionsmaterial i väg- och vattenbyggnadskonstruktioner eller i olika typer av barriärkonstruktioner som till exempel deponisluttäckningar. En deponisluttäckning består av flera skikt där tätskiktet ska ha en låg vatten- och gaspermeabilitet för att minska metan- och lakvattenutsläpp. Flera studier visar att stålslagg uppfyller dessa egenskaper och har potential att kunna användas i deponitäckning. Men det finns fortfarande oklarheter angående slaggmineralernas stabilitet över en längre tid. En deponitäcknings funktion förväntas vara stabil i många tiotals eller hundratals år. För att kunna förutsäga det långsiktiga beteendet för stålslagg i ett tätskikt genomfördes ett laboratorieexperiment vars syfte var att studera effekterna av accelererad åldring under kontrollerade förhållanden. De faktorer som studerades var koldioxidhalten, relativa luftfuktigheten, temperaturen, kontakten med lakvatten samt åldringstiden. I denna avhandling presenteras undersökningen av ljusbågsugnsslagg och skänkslagg, från framställning av höglegerat verktygsstål, efter tre respektive tio månaders accelererad åldring. Mineralogin och lakningsegenskaperna studerades genom två typer av laktester, termiska analyser, analys av syraneutraliserande kapacitet samt röntgendiffraktion. För de studerade åldringstiderna var det exponeringen av stålslaggen för en koldioxidrik atmosfär som hade den största inverkan på lakningsegenskaperna. Kalcium, aluminium, svavel och natrium var de ämnen som uppvisade den högsta utlakningen från slaggen medan metaller som krom, nickel, bly och zink endast fanns i väldigt låga koncentrationer i lakvattnet. Utlakningen av kalcium och aluminium minskade med en ökande halt av koldioxid. Termiska analyser visade på en nedbrytning av karbonater. Vikt- och entalpiförändringar mellan 100 och 1000°C utvärderades. Stålslaggens buffertkapacitet, representerad av den syraneutraliserande kapaciteten (ANC pH 4,5), reducerades inte efter tio månaders åldrande. Däremot visade uppdelningen av titreringen i två steg på en förskjutning av buffertområdena för de prover som åldrats tio månader, förmodligen på grund av karbonatbildning. Mineralogin för de undersökta stålslaggerna var komplex med en stor variation av mineralfaser, främst kalciumsilikater, monticellit, periklas och en spinellfas. Andra möjliga mineralfaser var gehlenit, merwinit, åkermanit och järn. Förekomsten av olika fastfaslösningar i stålslaggsmineralerna är sannolik vilket kan orsaka förskjutningar av topparna i diffraktogrammen. Kalcit identifierades också. Karbonatisering under en kort tid visade sig inte ha någon signifikant inverkan på mineralogin, förutom en viss kalcitbildning. Resultaten från studien bidrar till en bättre förståelse av stabiliteten för ljusbågsugns- och skänkslagg i den miljö som finns i ett tätskikt. Åldringen av slaggen resulterade i en reducerad utlakning av vissa element. För att kunna förutsäga det långsiktiga beteendet för åldrad slagg bör resultaten från den här studien kombineras med data från ett pågående åldringsförsök som inkluderar mekaniska tester samt ett fullskaligt fältförsök på Hagfors deponi. Analysmetoder som mer detaljerat kan karaktärisera mineralogin, till exempel svepelektronmikroskopi (SEM) och energidispersiv röntgenspektroskopi (EDX), bör också användas för att bättre kunna kvantifiera mineralfaserna och bestämma vilka spårelement som är vanligast i specifika mineraler.
Godkänd; 2009; 20090320 (sildie); LICENTIATSEMINARIUM Ämnesområde: Avfallsteknik Examinator: Professor Anders Lagerkvist, Luleå tekniska universitet Tid: Fredag den 24 april 2009 kl 14.15 Plats: F 664f, Luleå tekniska universitet

The inorganic chemistries of coal and petroleum differ because of their disparate geologic environments of formation, the physical state of the fuels, and the type and quantity of minerals and organic compounds in the fuels. Commercial coals typically contain 2 to 25% ash (average ~ 10%) while petroleums contain 0.003 to 0.07% ash (average ~ 0.01 %). Globally averaged, coal ash is dominated by Si, Fe, Ca, AI, and S, whereas petroleum ash contains significant quantities of V, Ni, S, Fe, Ca, Na, K, Mg, Si and AI. This larger number of important elements causes petroleum combustion slags to have more complex phase assemblages. The high vanadium contents of petroleum-based combustion feedstocks yield numerous crystalline V -oxides with stoichiometric amounts of Ca, Fe, Mg, AI, Ni andlor Na in the resulting slags. Slightly lower nickel contents yield abundant NiFe and Ni sulfides. The dominance of metals over silicon results in the formation of crystalline silicates following metal saturation of immiscible Si-rich glasses. High gasification temperatures (1200 - 1500°C) promote the development of equilibrial assemblages. Chemical variations between individual feedstock cokes coupled with nonuniform operational conditions result in three principal categories of petroleum coke slag; 1) sulfide dominant, 2) silica dominant, and 3) oxide dominant. Sulfide dominant slags are not necessarily derived from feedstocks with high sulfur contents, instead they appear to derive from feedstocks rich in chalcophile elements, predominantly Fe and Ni, by attracting sulfur otherwise lost by volatilization. Slagging additives can change the chemical categorization of resulting slags through phase modifications and the formation of new phases; this in tum can strongly alter the physical behavior of the slags. Compositionally diverse spinel oxides are the most common crystalline slag phase because of their wide thermal and compositional stability ranges, refractory nature, and rapid growth kinetics. Spinel compositions are strongly influenced by the inorganic chemistry of the feedstock, the composition of host phases, and the composition of additives. Coke slag spinels are generally enriched in AI, Fe, V, Mg, and Ni, and often contain Cr that is derived from reaction with refractory material.
Ph. D.

Titaniferous magnetite (titanomagnetite) offers a unique opportunity for the production of three valuable products from one resource. It generally contains economically appreciable reserves of vanadium and iron as well as significant contents of titanium. Titanomagnetite is typically smelted in blast or electric furnaces in the presence of reductant and fluxes (dolomite and quartz) to produce a valuable vanadium bearing pig iron and a virtually valueless titaniferous slag. The titaniferous slag by-products are generally defined by the Ca-Mg-Al-Si-Ti-O system. These fluxed slags can contain as high as 20-40wt% TiO2 (titania). The lack of interest in processing titaniferous slags to produce saleable titania materials is attributed to the presence of chemically inert phases, like the spinel solid solution [Mg(Al,Ti,V)2O4] that cannot be handled by the available titania slag upgrading technologies. The understanding of phase relations in titaniferous slags is thus important in order to be able to implement a suitable fluxing strategy for the production of a treatable titaniferous slag with no inert spinel phase. The available phase equilibria data established in air for titaniferous slags is inconclusive about the possible crystallisation of the detrimental spinel. However, literature on phase compositions of plant titaniferous slags are conclusive about the crystallisation of Mg(Al,Ti,V)2O4 in high MgO and Al2O3 bearing slags. It is thus clear that the understanding of phase relations in titaniferous slags requires further development. The objective of the current project was to investigate the phase equilibria and beneficiation of titaniferous slags to produce a saleable titania product. As a development to previous work, the composition of the slag for review was based on the available work, namely; TiO2 = 37.19wt%, SiO2 = 19.69wt%, and Al2O3 = 13.12wt%, at varying proportions of CaO (30- 0wt%) and MgO (0-30wt%). The phase equilibria studies followed a systematic approach involving the review and validation of the available equilibrium phase diagram produced in air, followed by the determination of updated phase equilibria at low oxygen partial pressures (pO2) of 10-16 atm applicable to titanomagnetite smelting. The generic approach of studying phase equilibria in multicomponent systems was followed, namely; (1) literature survey of the available thermodynamic and phase equilibria data applicable to the reviewed system, (2) calculation and re-drawing of the equilibrium phase diagrams using FactSage thermochemical software, and (3) equilibration-quench-(electron probe micro analysis) (EPMA) experiments to the validate calculated equilibrium phase relations. A titaniferous slag with little crystallisation of the inert spinel phase, based from the best fluxing strategy with an MgO-free limestone, was produced by smelting in conventional (using alumina crucible) and cold copper crucible induction furnaces for subsequent beneficiation using the established Upgraded Slag (UGS) process. A conceptual flowsheet for the production of vanadium, steel and titanium products was therefore designed and subsequently subjected to economic evaluation using the discounted cash flow (DCF) modelling approach. Thermodynamic and phase equilibria literature for the Ca-Mg-Al-Si-Ti-O system demonstrated that this system and some subsystems are well researched in air, and not as much in low pO2 atmospheres applicable to smelting operations. The FactSage software used in the current study for the calculation of phase equilibria in the Ca-Mg-Al-Si-Ti-O system applicable to titaniferous slags does not have tialite (Al2TiO5) modelled as a component in the customary pseudobrookite solution database - Al2TiO5 is a component of the pseudobrookite solution reported in literature for the current system. Hence, a private pseudobrookite solution database applicable to the reviewed system, i.e. MgTi2O5-Al2TiO5-Ti3O5, was developed and incorporated into FactSage before any calculation could be conducted. Thermodynamic modelling of the MgTi2O5-Al2TiO5-Ti3O5 system was conducted through the CALculation of PHase Diagram (CALPHAD) method. The sublattice model coupled with compound energy formalism (CEF) and Redlich-Kister polynomial were adopted. The model information was incorporated into FactSage to create a private database for subsequent calculations of phase equilibria of titaniferous slags. The equilibrium phase diagram for the Ca-Mg-Al-Si-Ti-O system in the same compositional range as in the available literature was then calculated in air. The liquidus surfaces and phase relations in the equilibrium phase diagrams of available literature and FactSage calculation are fairly comparable. However, at high MgO concentrations: FactSage calculation predicts that Mg(Al,Ti)2O4 is the primary phase, followed by successive crystallisation of pseudobrookite solid solution (MgTi2O5-Al2TiO5) and forsterite (Mg2SiO4); and the available literature reports MgTi2O5-Al2TiO5 as the primary phase, followed by Mg2SiO4. The crystallisation of spinel phase in the available phase diagram produced in air is not predicted. The crystallisation of the spinel solid solution phase in titaniferous slags is extensively reported in the open literature. Equilibration-quench-EPMA experimental results produced in air generally compared well to the FactSage calculations. The inability of the available phase diagram to predict spinel phase crystallisation was attributed to the lack of sensitive analytical techniques in the late 1960s, when the available phase diagram was developed. The phase equilibria of titaniferous slags were further calculated at low pO2 atmospheres of 10-16 atm. In the reviewed compositional range of titaniferous slags, the liquidus surface and Ti3+/Ti4+ mass fraction ratio increased with decreasing the pO2. There was no significant difference in terms of the crystallisation of phases between the calculated results in air and at pO2 of 10-16 atm, except that the size of the primary phase field at higher MgO concentrations than the composition for the minimum liquidus temperature increased and the pseudobrookite solution included Ti3+ bearing phase, i.e. MgTi2O5-Al2TiO5-Ti3O5. Equilibration-quench-EPMA experimental results produced at pO2 of 10-16 atm generally compared well to the FactSage calculations. The new phase equilibria at low pO2 of 10-16 atm shows that the crystallisation of the chemically inert Mg(Al,Ti)2O4 in titaniferous slags would occur if the slag contains high Al2O3 concentration and MgO concentration of 2wt% and above. However, the crystallisation of Mg(Al,Ti)2O4 in titaniferous slag is not significantly sensitive to variation in the TiO2 concentration in, and basicity of the slag. To produce a titaniferous slag with minimum possible inert spinel content for subsequent beneficiation, the South African Main Magnetite Layer (MML) titanomagnetite concentrate was smelted in the presence of an MgO-free lime and low ash Sasol carbon (SASCARB) reductant. This smelting approach would produce a titaniferous slag with about 4wt% MgO, which would come from the titanomagnetite - based on the phase equilibria, this slag should crystallise a small amount of the inert spinel. When the smelting was conducted in an alumina crucible placed inside a conventional induction furnace, the slag was inevitably contaminated by Al2O3 from the refractory container. This slag crystallised a significant Mg(Al,Ti)2O4 with the content approximated by the MgO concentration - the significant Mg(Al,Ti)2O4 crystallisation was attributed to the Al2O3 saturation in the titaniferous slag. A titaniferous slag containing a treatable ulvospinel phase was produced in a cold copper crucible induction furnace - the crystallisation of the ulvospinel, instead of the chemically inert spinel solid solution was attributed to the saturation of the slag by iron from the incomplete reduction process due to the inevitable stoppage of the heat supply to the induction furnace as soon as the susceptor iron metal and produced pig iron settled at the bottom of the copper crucible. For the purpose of demonstrating the feasibility of producing titania products from titaniferous slags, this slag was also subjected to beneficiation using UGS process. The current study successfully demonstrated that the titaniferous slags can be beneficiated to saleable titania products using the UGS process: the TiO2 in the Mg(Al,Ti)2O4 bearing waste titaniferous slag produced by the defunct Evraz Highveld Steel and Vanadium Corporation (EHSV) was upgraded from about 33wt% to 75wt%, while the TiO2 in the titaniferous slags produced in conventional and cold crucible induction furnaces were upgrade from about 30wt% to 67wt% and 22.00wt% to 90.45wt%, respectively. The remaining impurities in the 75wt% and 67wt% TiO2 UGS products were mainly MgO and Al2O3 contained in the refractory spinel solid solution. In the case of the 67wt% TiO2 product, there was excess Al2O3 in the spinel structure - the excess Al2O3 remained in the glass phase. Though the 90.45wt% TiO2 product is attractive for use as feedstock for the production of the preferred chloride pigment, this product however contained finer PSD and higher concentrations of impurities such as SiO2, Al2O3, and CaO, than the specification for the chloride process feedstock. This product was thus not a suitable feedstock for the chloride pigment production. Further optimisation of the UGS conditions has a potential to reduce the concentrations of impurities to levels suitable for feedstock for the preferred chloride pigment production process. Further investigations are also required to study the feasibility of the chlorination of micro-pellets of the UGS product. Since the UGS product is mainly composed of rutile structure, it would not be a suitable feed for the sulfate pigment production as the sulfuric acid lixiviant is unable to dissolve the rutile structure. Only if soluble in sulfuric acid, this high TiO2 bearing UGS product produced from titaniferous slags could be used as advantageous feedstock for the sulfate pigment production in terms of the minimization of the reagent consumption and the amount of the toxic sulfate waste. Based on the work of the current study, literature data and Pyrosim simulations, a conceptual process flowsheet for the production of vanadium slag, steelmaking pig iron and titania product was proposed. The economic modelling of the conceptual flowsheet for a 20 year operational projection showed that the process is economically viable. The process economic viability is sensitive to variation in the Opex and Revenue. In addition, additives, such as the amount and type of reductant, fluxes, and reagents account for about 75% of the Opex. It is possible that the additives are overestimated in the process as the recycle streams were not included in the proposed process and economic model. At the same time, the economic model does not consider the environmental and waste management costs. Hence, the economic analysis is considered to be preliminary in nature, or indicative at best. The current study has demonstrated that (1) a titaniferous slag containing little or no inert spinel phase that is suitable for upgrading can be produced when the MgO content in the slag is below 2wt% - the best approach to producing a slag with minimum possible MgO content would be to smelt the titanomagnetite in the presence of an MgO-free limestone flux and low ash reductant, and (2) it is technically and economically feasible to produce three products, i.e. V slag, steelmaking pig iron, and titania product, from titanomagnetite.

Avsikten med denna studie har varit att undersöka pedagogers samtal och utsagor kringestetiska arbetsformer och ämnesöverskridande arbetsområden i relation till utformandet av en”öppen ateljé” på skolan. Frågorna jag ställde mig var; Hur legitimerar pedagoger behovet aven ”öppen ateljé” på skolan? Vilka samband ser pedagoger mellan lärmiljöers utformning ochvilka läraktiviteter som kommer till uttryck? Vilka tolkningsrepertoarer om lärande ochlärmiljöer kommer till uttryck i dessa sammanhang och hur kan de förstås ur ett makt- ochkontrollperspektiv? Jag valde en kvalitativ metod med en diskursanalytisk ansats, som byggdepå fokusgruppssamtal genomförda på en mindre fristående F-9 skola i norra Sverige. En skolasom med utgångspunkt för sin verksamhet tagit ställning för att låta sig genomsyras av ReggioEmilias pedagogiska filosofi. Jag har i min studie tyckt mig finna ett antal diskurser på dennaskola, där en stor diskurs representerande skola, undervisning och lärarroll är överordnad ochdär några mindre tycks bjuda den större motstånd. Dessa diskurser kommer till uttryck i detolkningsrepertoarer pedagogerna använder för att legitimera utformandet av en öppen ateljépå skolan. Samtidigt som erkännandet av en mer progressiv filosofi tycks innebära ettdiskursivt dilemma på denna skola, tycks det också innebära att utrymmet för möjligahandlingar breddas något i det diskursiva glapp som här uppstår. Avslutningsvis för jag ettresonemang kring en additiv syn på lärande och estetik och om en motståndets diskurs.

Thesis (M.S.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains vii, 38 p. : ill. Includes abstract. Includes bibliographical references (p. 29-30).

Thesis (MScIng)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: This thesis details results obtained in an experimental study conducted to determine the effects of operating temperature, oxygen partial pressure, bulk chromium oxide content and bulk FeOx/MgO ratio on the solubility of chromium oxide in melter type slags in the platinum industry. Two PGM-containing layers in the Bushveld Complex in South Africa, the Merensky and UG2 reefs, are currently being mined for the extraction of base metals and platinum group metals (PGM). While the Merensky reef is a pyroxenitic layer, the UG2 reef is a platiniferous chromitite seam. Due to a gradual depletion in Merensky ore reserves, platinum producers have been moving towards the processing of more UG2 concentrates, which are higher in chromium oxide content. The technical difficulties associated with the smelting of concentrates with high chromium oxide contents is a matter of concern. The formation of chromite spinels in melts increases liquidus temperatures and viscosities and subsequently hampers tapping of slags and mattes from furnaces. Bottom build-up from the smelting of high chromium oxide containing concentrates could reduce effective furnace volume. From the literature reviewed it was found that very few published investigations covered melt compositions and oxygen partial pressures similar to those encountered in the platinum industry. Relevant studies were found to deal with significantly lower bulk chromium oxide and iron oxide contents. It became clear that a need exists for information on the behaviour of chromium oxide and its effects on phase chemistry and stability in melter slags. It was decided to study the phase equilibria through drop-quench experiments using six synthetic slags with bulk FeOx/MgO ratios between 0.6 and 1.9 and bulk chromium oxide contents between 1.2 and 7 wt%. Temperatures investigated were 1400, 1500 and 1600°C. The oxygen partial pressure was varied between 6.8x10-10 atm at 1400°C to8.3x10-5 atm at 1600°C. Experiments were conducted in a sealed vertical tube furnace and the required oxygen partial pressure in the furnace tube was maintained by controlling the flow rates of purified CO and CO2 gas mixtures through the tube. Reaction products were quenched after a reaction time of between 20 and 24 hours, depending on temperature, and the phase compositions were analysed by microprobe. The experimental study revealed that chromium oxide partitions very strongly into the spinel phase relative to the liquid phase, especially at lower temperatures, and higher oxygen partial pressures and bulk chromium oxide contents. The solubility of chromium oxide in the liquid phase was found to increase with increasing temperature and decreasing oxygen partial pressure. An increase in bulk chromium oxide contents of 1 wt%, under otherwise constant conditions, resulted in an increase in slag liquidus temperature of approximately 100°C over the range of temperatures investigated. At 1500°C and bulk chromium oxide contents of 3.7 and 6.4 wt% a reduction in oxygen partial pressure from 1.1x10-5 to 1.1x10-7 atm resulted in increases in soluble chromium oxide of 0.9 and 2.0 wt%, respectively. A further decrease in oxygen partial pressure to 6.7x10-9 atm resulted in increases in soluble chromium oxide of 2.8 and 4.7 wt%, respectively. Experimental results were compared to values predicted by the multi-phase equilibrium (MPE) model developed by CSIRO, and found to agree well. Slag basicity was not varied experimentally and therefore the model was used to predict its effect on the solubility of chromium oxide in the liquid phase and the stability of crystalline phases. At constant temperature, an increase in basicity resulted in a decrease in the solubility of chromium oxide in the liquid phase as well as stabilisation of the spinel phase. It was concluded that practicable combinations of one or more of four main factors, namely increased operating temperature and decreased bulk chromium oxide content, slag basicity and oxygen partial pressure, should be applied and evaluated in a plantenvironment to optimise furnace operation. The MPE model would be a valuable tool in predicting the outcomes of such investigations.
AFRIKAANSE OPSOMMING: Hierdie tesis detaileer die resultate wat verkry is uit ‘n eksperimentele studie uitgevoer om die effek van bedryfstemperatuur, die parsiële druk van suurstof, die algehele chroomoksied inhoud en die algehele FeOx/MgO verhouding op die gedrag van chroomoksied in smelter slakke in die platinum industrie te bestudeer. Twee PGM-bevattende ertslae in die Bosveldkompleks in Suid Afrika, die Merensky en UG2 riwwe, word huidiglik gemyn vir die ekstraksie van basismetale en platinumgroep metale (PGM). Die Merensky rif is ‘n piroksenitiese laag terwyl die UG2 rif ‘n platinumbevattende chromitiet laag is. As gevolg van ‘n geleidelike afname in reserwes van Merensky erts beweeg platinumprodusente al meer na die verwerking van groter hoeveelhede UG2 erts. Die tegniese probleme wat gepaard gaan met die smelting van konsentrate met hoë chroomoksied inhoud kan ‘n rede tot kommer wees. Die vorming van chromiet spinelle in die slak- en matfases verhoog likuidus temperature en viskositeite en bemoeilik die tap van hierdie fases uit oonde. Die opbou van soliede fases verlaag ook die effektiewe oondvolume. Uit die literatuurstudie is gevind dat gepubliseerde studies waarin slak samestellings en parsiële suurstofdrukke wat betrekking het op die platinumindustrie bespreek is, baie beperk is. Dit is gevind dat relevante navorsing gedoen is met aansienlik laer algehele chroom- en ysteroksied konsentrasies. Gevolglik het dit duidelik geword dat ‘n behoefte bestaan vir inligting oor die gedrag van chroomoksied in oonde en die effekte daarvan op fasechemie en –stabiliteit in smelter slakke. Daar is besluit om eksperimente uit te voer deur die gebruik van ses sintetiese slakke met algehele FeOx/MgO verhoudings tussen 0.6 en 1.9 en algehele chroomoksied konsentrasies tussen 1.2 en 7.0 % (op ‘n massabasis). Temperature van 1400, 1500 en 1600°C en suurstof parsiële drukke tussen 6.8x10-10 atm by 1400°C en 8.3x10-5 atm by 1600°C is ondersoek. Eksperimente is uitgevoer in ‘n geseëlde vertikale buisoond en dievereiste suurstofdruk in die oond is gehandhaaf deur beheer van die vloeitempos van gesuiwerde CO en CO2 gas deur die oond. Reaksieprodukte is in water geblus na ‘n reaksietyd van tussen 20 en 24 ure, afhangende van die reaksietemperatuur. Fasesamestellings is bepaal deur mikrosonde analises. Die eksperimentele studie het bewys dat chroomoksied baie sterk in die spinelfase konsentreer relatief tot die vloeistoffase, veral by laer temperature, suurstofdrukke en algehele chroomoksied konsentrasies. Dit is gevind dat die oplosbaarheid van chroomoksied in die vloeistoffase toeneem met toenemende temperatuur en afnemende suurstofdruk. ‘n Toename in die algehele chroomoksied konsentrasie van 1 massa%, onder andersins onveranderde toestande, het ‘n toename van ongeveer 100°C in likuidus temperature veroorsaak tussen 1400 en 1600°C. By 1500°C en algehele chroomoksied konsentrasies van 3.7 en 6.4 massa%, het ‘n verlaging in suurstofdruk vanaf 1.1x10-5 tot 1.1x10-7 atm respektiewelike toenames in die chroomoksied oplosbaarheid van 0.9 en 2.0 massa% veroorsaak. ‘n Verdere verlaging in suurstofdruk tot 6.7x10-9 atm het respektiewelike toenames in chroomoksied oplosbaarheid van 2.8 en 4.7 massa% veroorsaak. Eksperimentele resultate is vergelyk met waardes wat voorspel is deur die multifase ewewigsmodel (MPE), ontwikkel deur CSIRO, en goeie ooreenstemming is gevind. Verskillende slak basisiteite is nie eksperimenteel ondersoek nie en daarom is die model gebruik om die effek daarvan op die oplosbaarheid van chroomoksied in die vloeistoffase asook die stabiliteit van kristallyne fases te bepaal. By konstante temperatuur het ‘n toename in slak basisiteit ‘n afname in chroomoksied oplosbaarheid veroorsaak en die spinelfase gestabiliseer. Die aanbeveling is gemaak dat ‘n kombinasie van een of meer van vier hooffaktore, naamlik hoër bedryfstemperature en laer algehele chroomoksied konsentrasies, slak basisiteit en suurstofdruk, in die praktyk toegepas en geëvalueer moet word om sodoendeoptimum bedryfkondisies te bepaal. Die multifase ewewigsmodel is ‘n nuttige instrument wat gebruik kan word om die resultate van sulke ondersoeke te voorspel.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
A metalurgia é a ciência que estuda os diversos meios para a transformação dos metais em materiais úteis à sociedade. A metalurgia do ferro representa a maior fatia da aplicação dos metais. Por ser tão representativa é chamada de Siderurgia. Dentre as diversas rotas para a transformação do ferro em aço, as usinas semi-integradas apresentam um forte apelo ecológico, pois utilizam a sucata, oriunda da reciclagem de ferro, e o ferro gusa como matérias-primas para a fusão no Forno Elétrico a Arco. Naturalmente, em todo processo industrial há a geração de resíduos e, neste caso, o principal é a escória, composta de óxidos formados e adicionados ao longo da fusão. Seus principais constituintes são: CaO, SiO2, FeO, MnO, MgO, Al2O3 e P2O5. No entanto, ainda há a presença de Ferro Metálico, um fato indesejável, pois atua negativamente no rendimento metálico e, consequentemente, aumenta o custo do aço. Toda escória gerada é beneficiada com o intuito de recuperar a parte metálica. Este material beneficiado retorna para as usinas como sucata metálica, contendo teores definidos de ferro metálico. O teor de ferro presente na sucata recuperada é avaliado pelas empresas processadoras de escória de maneira indireta por um ensaio de densidade específica. Havia dúvidas se a sucata recuperada da escória do forno apresentava teores de ferro que justificasse seu emprego como matéria-prima ferrosa. Assim sendo, foi proposta uma rota de processamento capaz de mensurar o teor de ferro presente e permitir a comparação com os teores obtidos com o ensaio de densidade. Os resultados mostram que i) é possível calcular o impacto no rendimento, ii) que as sucatas recuperadas apresentam valores inferiores ao esperado, iii) que a equação de densidade superestima o teor de ferro e iv) que modificações propostas nos coeficientes da equação vigente melhoram seu grau de assertividade. Estes resultados foram comprovados em 3 plantas siderúrgicas.
Metallurgy is the science that studies the various processes for the transformation of metals into society useful materials. The iron metallurgy represents the largest body of the metals application, hence it is called Steel industry. Among the various routes for the transformation of iron into steel, semiintegrated plants have a strong ecological appeal due to their extensive use of scrap, derived from the recycling of iron, and pig iron as raw materials for the Electric Arc Furnace. Of course, industrial processes generate waste. The major waste of the Electric Arc Furnace is the slag, a mixture of oxides produced during the process, containing CaO, SiO2, FeO, MnO, MgO, Al2O3 e P2O5. However, there is also the presence of metallic iron, a fact undesirable, because it acts negatively on the metallic yield and therefore increases the cost of steel. All slag generated is processed in order to recover the metallic iron. The slag beneficiation returns to the mills a material containing defined levels of iron. The content of recovered iron is assessed by slag processing companies indirectly by a specific gravity test. There have been doubts whether the recovered scrap iron content justify its use as raw ferrous materials. Therefore, it is proposed a processing route capable of measuring the amount of iron present in the recovered scrap. The measured iron content is also compared with the levels obtained from the test density. The results show that i) it is possible to calculate the impact on iron yield, ii) the recovered iron content is lower than expected, iii) the density equation overestimates the amount of iron and iv) a correction is proposed to improve the assertiveness of the density equation. Three steel plants confirmed the results from this research.

Les principaux objectifs étaient d'évaluer la stabilité de l'environnement des scories métallurgiques de Cu résultant de différentes périodes d'activités industrielles et de différentes technologies de fusion. Parmi les scories étudiées, on retrouve: les scories historiques cristallines (SH) ainsi que modernes: les scories de four vertical (SFS), les scories granulées (GS) et les scories de plomb (LS). Les différentes approches adoptées dans ce travail de thèse ont tenu compte de: i) la composition chimique et la phase minérale des scories, ii) la sensibilité à la lixiviation des scories sous l’exposition à différentes conditions de pH en mode statique, iii) l’altération des scories sous exposition aux acides organiques couramment trouvés dans l'environnement du sol, iv ) la bio-altération des scories par les bactéries (Pseudomonas aeruginosa) et v) l’application future de la récupération des métaux provenant des scories étudiées en mettant en œuvre la méthode de lixiviation biologique. Résultats cruciaux: Les résultats des tests de lixiviation dépendant du pH ont montré une libération de métal plus élevée dans des conditions fortement acides (pH 2 et 4), alors que la lixiviation dans des conditions alcalines (pH 10.5) était moins importante pour toutes les scories analysées. L'effet de l’altération par le sol a été démontré, la dissolution des scories est notamment sensible à la présence d'exsudats racinaires artificiels (ARE), d’acides humiques (HA) et d’acides fulviques (FA), la contribution des ARE étant la plus forte. Selon les données recueillies, la dissolution relative des scories est strictement liée à leurs caractéristiques (composition chimique et minéralogique) en fonction des différentes conditions étudiées. L'étude concernant l’effet de l’altération biologique a révélé que Pseudomonas aeruginosa améliore considérablement la libération des éléments majeurs (Si et Fe) et métalliques (Cu, Zn, Pb) par rapport aux effets des facteurs abiotiques, indépendamment de la chimie et de la structure des scories. En outre, une récupération élevée (jusqu'à 90%) des métaux (Cu, Zn, Fe) pourrait être obtenue grâce à la lixiviation avec Acidithiobacillus thiooxidans dans des conditions de laboratoire. Conclusions générales : La stabilité des scories dans l'environnement dépend à la fois des caractéristiques chimiques et de la minéralogie. Cependant, les phases minérales hébergeant les métaux sont les facteurs les plus déterminants concernant l'intensité de la lixiviation des métaux. Pour cette raison, l'examen individuel du comportement des scories est important pour empêcher la contamination de l'environnement et devrait être considéré comme une priorité pour la gestion durable des scories. L’optimisation des paramètres de fonctionnement pour le biolessivage et le développement de la technologie à l'échelle industrielle pourrait permettre une bien meilleure gestion (voir l’exploitation) des scories métallurgiques de Cu
Problem statement: Copper pyrometallurgical slags are inevitable waste by-products of Cu smelting operations. These waste are considered to be important due to their production volume and high residual metal content that are inefficiently recovered during industrial process. Due to the lack of sustainable practices in the past, tremendous volumes of Cu-slags have been disposed in many industrial districts, regardless of the weathering and associated environmental risk. Consequently, there are many areas where slags have been proven to be a source of metallic pollution for the surrounding environment. At the present time, the outstanding contradiction between the sustainable development and environmental pollution encourages to undertake the action regarding this aspect. For this reason, slags are currently being used as supplementary materials for civil engineering purposes (e.g. cement and concrete additives, road bed filling materials, hydraulic construction materials) rather than disposed. Additionally, modern-day management strategies require slags to be thoroughly evaluated with respect to their environmental stability prior undertaking any reuse action. Main objectives were to evaluate environmental stability of Cu-metallurgical slags resulting from different periods of industrial activities and different smelting technologies. Those included: historical crystalline slag (HS) as well as modern: shaft furnace slag (SFS), granulated slag (GS) and lead slag (LS). Different approaches undertaken in this PhD work considered: i) chemical and mineral phase compositions of slags, ii) leaching susceptibility of slags under exposure to different pH-stat conditions, iii) slags weathering under exposure to organic acids commonly found in soil environment, iv) bacterially (Pseudomonas aeruginosa) mediated weathering of slags and v) future application of studied slags for metal recovery by implementing the bioleaching method. Crucial results: The results of the pH-dependent leaching tests showed a higher metal release in strong acidic conditions (pH 2 and 4), whereas leachability at alkaline conditions (pH 10.5) revealed a lower importance for all the slags analyzed. The study considering soil weathering scenario demonstrated that Cu-slags are susceptible to dissolution in the presence of artificial root exudates (ARE), humic (HA) and fulvic acids (FA), whereby ARE were found to have stronger contribution than HA and FA. According to data collected, the different behavior of individual slags is strictly related to their characteristics (chemical and phase composition) reflecting various susceptibilities to dissolution under the investigated conditions. The study considering bio-weathering scenario revealed that Pseudomonas aeruginosa considerably enhances the release of major (Si and Fe) and metallic (Cu, Zn, Pb) elements compared to the effects of abiotic factors, regardless of the slags chemistry and structure. Furthermore, a high gain (up to 90%) of metals (Cu, Zn, Fe) could be credited to bioleaching with Acidithiobacillus thiooxidans under laboratory conditions. General conclusions: The environmental stability of slags depends on both, their bulk chemistry and mineralogy. However, mineral phases harbouring the metals are the key players in metal leachability intensity. For, this reason consideration of individual slags behaviour is important for preventing environmental contamination and should be regarded as priority branch of sustainable slag management. Optimization of operating parameters for bioleaching following development of industrial scale technology is an incentive scheme for future management of Cu-metallurgical slags

The high temperature microstructure of the solid phases within the electric arc furnace (EAF) slag has a large effect on the process features such as foamability of the slag, chromium recovery, consumption of the ferroalloys and the wear rate of the refractory. The knowledge of the microstructural and compositional evolution of the slag phases during the EAF process stages is necessary for a good slag praxis.

In supplement 1, an investigation of the typical characteristics of EAF slags in the production of the AISI 304L stainless steel was carried out. In addition, compositional and microstructural evolution of the slag during the different EAF process stages was also investigated. Computational thermodynamics was also used as a tool to predict the equilibrium phases in the top slag as well as the amount of these phases at the process temperatures. Furthermore, the influence of different parameters (MgO wt%, Cr₂O₃ wt%, temperature and the top slag basicity) on the amount of the spinel phase in the slag was studied. In supplement 2, a novel study to characterize the electric arc furnace (EAF) slags in the production of duplex stainless steel at the process temperatures was performed. The investigation was focused on determining the microstructural and compositional evolution of the EAF slag during and at the end of the refining period.

Slag samples were collected from 14 heats of AISI 304L steel (2 slag samples per heat) and 7 heats of duplex steel (3 slags sample per heat). Simultaneously with each slag sampling, the temperature of the slag was measured. The selected slag samples were studied both using SEM-EDS and LOM. In some cases (supplement 2), X-ray diffraction (XRD) analyses were also performed on fine-powdered samples to confirm the existence of the observed phases.

It was observed that at the process temperature and at all process stages, the stainless steel EAF slag consists mainly of liquid oxides, magnesiochromite spinel particles and metallic droplets. Under normal operation and at the final stages of the EAF, 304L steelmaking slag contains 2-6 wt% magnesiochromite spinel crystals. It was also found that, within the compositional range of the slag samples, the only critical parameter affecting the amount of solid spinel particles in the slag is the chromium oxide content. Petrographical investigation of the EAF duplex stainless steelmaking showed that, before FeSi-addition, the slag samples contain large amounts of undissolved particles and the apparent viscosity of the slag is higher, relative to the subsequent stages. In this stage, the slag also includes solid stoichiometric calcium chromite. It was also found that, after FeSi-injection into the EAF and during the refining period, the composition and the basicity of the slag in the EAF duplex steelmaking and EAF stainless steelmaking are fairly similar. This indicates that, during the refining period, the basic condition for the utilization of an EAF foaming-slag praxis, in both austenitic and duplex stainless steel cases, is the same. Depending on the slag basicity, the slag may contain perovskite and/or dicalcium silicate too. More specifically, the duplex stainless steel slag samples with a higher basicity than 1.55 found to contain perovskite crystals.

The Swedish steelmaking industry produces large amounts of by-products. In 2008, the total amount of slag produced reached approximately 1,300,000 metric tons, of which 20% was deposited. Due to its strength, durability and chemistry, steel slag is of interest in the field of construction, since it has similar or better qualities than ordinary ballast stone, which makes it a competitive construction material. However, some steel slags face an array of quality concerns that might hinder their use. These concerns generally involve the following physical and chemical properties:Volume expansion Disintegration Leaching of metalsBy controlling and modifying process parameters during slag handling in liquid state, the physical and chemical properties of steel slags can be adequately modified to obtain a high-quality product for external application. The present work was undertaken as a research project within the Minerals and Metals Recycling Research Centre, MiMeR. The major goal of this work has been to investigate how different treatment methods including hot stage processing, cooling rates, ageing time and chemical composition influence the final properties of the slag. Analysis techniques used in this investigation include: thermodynamic calculations using FactsageTM, X-ray diffraction analyses (XRD), scanning electron microscopy (SEM), leaching tests (EN12457-2/3) and thermo-gravimetric analyses (TG).The results from this study show that it is possible to control/change the properties of the final product by additions to the liquid slag, thereby changing the chemical composition, as well as by varying the rate and method of cooling. The mineralogical composition, the size of the crystals and the composition of some solid solutions are affected by the cooling rate. The solubility of elements such as chromium and molybdenum varies, probably due to their presence in different minerals. The reactivity of the investigated slag samples increases as the cooling rate increases.When steel slags are aged, the leaching properties of the materials are changed. The total leachability and the pH decrease for all the investigated samples. All elements except magnesium decrease in leachability. As the slags are aged CaCO3 is formed on the slag surfaces. The degree of carbonation differs between different slags, due to the presence of different calcium-rich minerals in the slag. In order to form CaCO3, the calcium-containing mineral must be dissolved. This means that the solubility of the calcium-containing mineral will affect the outcome of the carbonation. The rate of dissolution for six typical slag minerals was investigated in order to distinguish the difference in solubility between the different minerals. Acidic to alkaline pHs (4, 7 and 10) were selected to investigate the solubility of the minerals under conditions comparable to those prevailing in newly produced slags and the potential future pH values obtained under acid conditions. It can be concluded that all six minerals behave differently when dissolving and that the rate of dissolution is generally slower at higher pH. At pH 10, the solubility of merwinite, akermanite and gehlenite is considered slow. The dissolution of γ-Ca2SiO4 is not affected in the same way as the other minerals when the pH is changed.
Godkänd; 2010; 20101213 (fren); DISPUTATION Ämnesområde: Processmetallurgi/Process Metallurgy Opponent: Professor Pekka Taskinen, Dept. of Materials Science and Engineering, Aalto University, Finland Ordförande: Professor Bo Björkman, Institutionen för TKG, Avd för mineralteknik och metallurgi, Luleå tekniska universitet Tid: Fredag den 4 februari 2011, kl 10.00 Plats: F341, Luleå tekniska universitet

There are many kinds of elements, especially heavy metallic elements, presentin the industrial slags. These elements bring big environmental problems ifthey are directly used in land filling. And the recovery of these elements canalso have benefits for the resource conservation. This paper reports the use ofelectrochemical method to extract the metal elements from both industrial slagand pure oxide. The mixture of NaCl-KCl was used as the electrolyte for thisprocess. Some proposals are alsomentioned for the further work.

Electric arc furnace (EAF) slags are basic characteristic slags that include approximately 40 % iron oxide compounds. Iron oxide can be recycled and re-used in the process to decrease amount of waste product besides reducing loss of raw materials. According to result of survey performed by The European Association Representing Metallurgical Slag Producers and Processors (EUROSLAG) in 2010, 8.5 million tons of EAF slag is produced in Europe. High percentage of EAF slag is re-used in road construction as aggregate. However it can be re-cycled in the internal use for metallurgical processes as well. In order to re-use EAF slag in the process as a raw material, direct reduction is a new approach. Direct reduction is reduction of iron containing raw materials with gas or solid reductants without melting of charge. In this study, reduction conditions of 39 % Fe2O3 containing EAF slag in tube furnace was examined. As the reducing agent, metallurgical coke was used. EAF slag was milled and pelletized in raw material preparation step. Pellets were charged to fixed bed type tube furnace in a graphite boat at 1050, 1100 and 1150°C respectively with 150 and 200% of stoichiometrically required amount of metallurgical coke. 5, 10, 15, 30, 60, 90 and 120 minutes process durations were performed. Direct reduced pellets were milled to be characterized by using X-Ray Diffraction (XRD) and chemical analysis methods. Results indicate that increased temperature, process duration and stoichiometry have a positive impact on direct reduction of EAF slag in terms of iron metallization. 90 % metallization degree has been achieved as the result of the study with the process conditions of 200 % stoichiometry and 90 minutes process duration at 1150 °C.

In the present thesis a study of the mechanisms of hydrogen control pickup during ladle treatment was undertaken. Previous studies showed that the presence of hydroxyl ions in the ladle slag resulteds in hydrogen transfer from the slag back into the steel bath. The main focus of the present work was therefore to gain deeper knowledge of the ladle slag, its properties and impact on hydrogen concentration in the liquid steel. For this purpose a number of slag compositions were examined in order to clarify whether these slags were single liquids at 1858 K. 14 out of 27 compositions in the Al2O3-CaO-MgO-SiO2 system werewas completely melted, while the rest had solid shape present . These results were in disagreement with the existing phase diagram.   Water solubility measurements were carried out by employing a thermo gravimetric technique. The temperature was found to have negligible effect in the water solubilities. The experimental results showed that the water capacity values varied between 1·103 and 2·103 in the majority of the composition range. However, for compositions close to CaO saturation the water capacity value could reach higher than 3·103. The experimental determined water capacity was further used to develop a water capacity model for the quaternary slag system Al2O3-CaO-MgO-SiO2. The model was constructed by considering the effects of the binary interactions between the cations in the slag on the capacity of capturing hydroxyl ions. The model calculations agreed reasonably well with the experimental results as well as with the literature data.   The water capacity model was used in the last part of the present thesis in order to determine the major source for hydrogen pick-up of the steel after vacuum degassing but before casting. For this purpose, samples of slag and metal were taken at different stages ofduring ladle treatment at SSAB. Hydrogen increase after vacuum treatment was observed. Moisture contents of the industrial slag were analysed and the water capacities of the slags were calculated. It could be seen that the hydrogen increase was correlated to the amount of moisture in the slag and the water capacity. The study showed that the slag containing most water was also the heat having the largest hydrogen increase. The slag with most water had the highest water capacity. It could be concluded that the major source for hydrogen coming back into the steel was due to the slag-metal reaction. A tentative process model to predict the final contents of hydrogen and nitrogen after tundish process was attempted. More work is needed to improve the model.

QC 20150825

Understanding the effects of the process parameters on the distribution behaviour of antimony between metal and slag in the iron blast furnace is critical to develop a universal method of controlling temper embrittlement in commercially pure low alloy steels.

In the copper smelting processes, the viscosity of the matte and the slag is an important factor for establishing efficiency. Impurities in the concentrates affect the viscosity not only by changing the melt structure but also by promoting precipitation of solid phase which sharply rises it. In this master thesis, a comprehensive methodology was established to study the MgO effects on the properties of a copper smelting slag. Thus, glassy samples were obtained and after confirmation of the composition and the glassy structure with EDS, SEM, and XRD analysis, they were examined through Ramanspectroscopy to study their glassy structure. Moreover, Mössbauer spectroscopy was used to determine the amount of Fe3+ in the samples. Models from the literature were compared to the experimental data. Coherence with the literature was found with the effect of MgO as a network modifier of the oxide melt structure and a promoter of high coordinated structures. Estimations through models were performed to study the iron redox equilibria of the melt and were compared with experimental data, but it was not possible to find the limit of Fe3+ at which precipitation of solid phase initiates.
I kopparsmältningsprocesserna är mattans och slaggens viskositet en viktig faktor för att uppnå effektivitet. Föroreningar i koncentraten påverkar viskositeten inte bara genom att ändra smältstrukturen utan också genom att främja utfällning av fast fas som kraftigt höjer den. I denna magisteruppsats fastställdes en omfattande metod för att studera MgO-effekterna på egenskaperna hos en kopparsmältningsslagg. Således erhölls glasiga prover och efter bekräftelse av kompositionen och den glasiga strukturen med EDS-, SEM- och XRD-analys undersöktes de genom Ramanspektroskopi för att studera deras glasstruktur. Dessutom användes Mössbauerspektroskopi för att bestämma mängden Fe3+ i proverna. Modeller från litteraturen jämfördes med experimentella data. Överensstämmelse med litteraturen hittades med effekten av MgO som ett nätverksmodifierare av oxidsmältstrukturen och en promotor för högkoordinerade strukturer. Uppskattningar genom modeller utfördes för att studera smältans järnredoxjämvikter och dessa jämfördes med experimentella data, men det var inte möjligt att hitta gränsen för Fe3+ vid vilken utfällning av fast fas initierades.

The solubility of cobalt in non-ferrous smelting slags has been studied at 1573 K. The study involved both sulfur-free and sulfur-containing systems. In the sulfur-free systems, the solubility of cobalt in slag was examined by equilibrating iron silicate slag with liquid Co-Au-Fe or solid Co-Fe alloys under an oxygen pressure of either 10^-9 or 10^-10 atmospheres as controlled by mixture of CO/CO2 gas. Three series of experiments were carried out to evaluate the respective effects of cobalt content, iron/silica ratio and oxide additives on the solubility of cobalt in slags. The melts were contained in either silica, alumina, cobalt or magnesium oxide crucibles. The cobalt solubility in slag was interpreted in terms of an activity coefficient of cobalt oxide, calculated from a knowledge of the activity of cobalt in the alloy, the oxygen pressure in the gas phase and the temperature of equilibration. The activity coefficient of ferrous oxide in the slag was calculated in a similar way. In the systems containing sulfur, a novel experimental method was employed to study the effect of sulfur on the activity coefficient of cobalt oxide in slag at 1573 K. Iron silicate slag was equilibrated with a liquid Co-Au-Fe alloy and a cobalt matte, with the oxygen and sulfur pressures controlled by mixtures of CO/CO2/SO2 gas at 1573 K. The method was novel since the presence of a low sulfur alloy phase, in addition to matte, allowed the metal activities in the system to be defined. In this way, the activities of cobalt oxide and the activity of cobalt sulphide could be calculated when the respective oxygen and sulfur pressures were defined. Thermodynamic analysis indicated that the solubility of cobalt in slag containing sulfur could be attributed to a solubility of cobalt sulphide in addition to cobalt oxide. The respective activity coefficients of these species were calculated for the slag along with the activity coefficient of cobalt sulphide in the matte. The data were combined to quantify the distribution coefficient of cobalt between slag and matte as a function of mole fraction of cobalt sulphide in matte as well as the sulfur and oxygen partial pressures. The effect of iron/sulfur ratio in nickel matte on the distribution coefficients of both cobalt and nickel was investigated finally by the equilibration of nickel matte (with minor cobalt), iron silicate slag and a Ni-Co-Fe-Au alloy, system was allowed to find its own equilibrium under argon, but the oxygen pressure was calculated indirectly and correlated with the change in matte composition.