Dissertations / Theses on the topic 'Zinc leaching'

Studies were conducted into the mechanism and kinetics of the dissolution of synthetic zinc sulfide and zinc concentrate in aqueous solutions containing sulfur dioxide.Experiments at ambient temperature established that the dissolution of ZnS in aqueous solutions of sulfur dioxide proceeds via acidic non-oxidative dissolution and not by direct reaction of the sulfide with S02(aq). The non-oxidative dissolution reaction generates H2S(aq) or HS-(aq) species which are thought to rapidly react with sulfurous acid species, S02(aq) or HS03-(aq), to possibly produce initially sulfane monosulfonates as intermediates, followed by sulfane disulfonates and elemental sulfur. The formation of sulfane monosulfonates is postulated based upon inhibition observed in ZnS / S02 leaches which is not attributable to either H2S(aq) or occlusion elemental sulfur.At elevated temperatures (100oC - 200oC) the rate of ZnS dissolution in sulfurous acid is affected by the thermal decomposition of sulfurous acid, which produces sulfuric acid, which leaches the mineral non-oxidatively. Increasing the temperature increases the rate of thermal decomposition of sulfurous acid and consequently, the rate of sulfuric acid formation, increasing the rate of ZnS dissolution.The kinetics of the dissolution of ZnS in solutions of sulfuric acid and sulfur dioxide were investigated at temperatures up to 200oC. At 100oC and 150oC, the dissolution of ZnS in H2SO4 was found to obey the relationd[Zn2+]/dt = kfAs[H+] krAs[H2S(aq)]1/2[Zn2+]1/2and equilibria and rate constants for the ZnS / H2S04 reaction were obtained over the range, 100oC to 200oC. The activation energies of the forward and reverse reactions were found to be 56 +/- 11 kJ mol-1 and 45 +/- 15 kJ mol-1, respectively. The equilibrium constants were 4.99x10-4, 1.26x10-3 and 2.83x10-3 at 100oC, 150oC and 200oC, respectively.In the presence of added S02, at low ZnS pulp density (0.5 g L-1), the rate of ZnS dissolution in sulfuric acid increased due to the removal of H2S(aq) by reaction with S02(aq) or HS03-(aq). However the increase in rate was much less than that expected for the complete removal of H2S(aq). As with leaches of ZnS in sulfurous acid at ambient temperature, the inhibition was not attributable to the presence of residual H2S(aq) or to occlusion of unreacted ZnS by elemental sulfur, but is thought to be due to aqueous species that are like "H2S", in that they may react with Zn2+ to reprecipitate W.To this end, sulfane monosulfonates have again been postulated. The rate of ZnS dissolution, under conditions of low pulp density, was independent Of S02 concentration, suggesting that under these conditions the rate of the H2S / S02 reaction is also independent of the S02 concentration.At higher pulp densities (200 g L-1), similar to those expected in an industrial application, synthetic zinc sulfide leached rapidly in H2S04 / S02 solutions to approximately 60% zinc extraction, but was then inhibited by the large amounts of sulfur that formed. These caused agglomerates of zinc sulfide and elemental sulfur to form, even at temperatures below the melting point of sulfur, reducing the surface area of zinc sulfide available for reaction.Leaches of zinc concentrate at low pulp densities in H2S04 / S02 solutions and at temperatures above sulfur's meting point, were inhibited by the formation of molten sulfur. In contrast to synthetic zinc sulfide, zinc concentrate is readily wet by molten sulfur. Three surfactants orthophenylenediamine, quebracho and sodium ligninsulfonate were found to be reasonably effective in preventing molten sulfur from occluding the mineral surface. At high pulp densities, the H2S04 / S02 leach solution was unable to effect, the extraction of zinc from a zinc concentrate beyond approximately 10%.Integral S02 / H2S04 leaching of zinc concentrate was found not to be a commercial prospect. However, sidestream processing of zinc concentrate in an acid leach stage followed by reaction of generated H2S with S02 from the roasting stage to produce elemental sulfur may be viable.

Studies were conducted into the mechanism and kinetics of the dissolution of synthetic zinc sulfide and zinc concentrate in aqueous solutions containing sulfur dioxide.Experiments at ambient temperature established that the dissolution of ZnS in aqueous solutions of sulfur dioxide proceeds via acidic non-oxidative dissolution and not by direct reaction of the sulfide with S02(aq). The non-oxidative dissolution reaction generates H2S(aq) or HS-(aq) species which are thought to rapidly react with sulfurous acid species, S02(aq) or HS03-(aq), to possibly produce initially sulfane monosulfonates as intermediates, followed by sulfane disulfonates and elemental sulfur. The formation of sulfane monosulfonates is postulated based upon inhibition observed in ZnS / S02 leaches which is not attributable to either H2S(aq) or occlusion elemental sulfur.At elevated temperatures (100oC - 200oC) the rate of ZnS dissolution in sulfurous acid is affected by the thermal decomposition of sulfurous acid, which produces sulfuric acid, which leaches the mineral non-oxidatively. Increasing the temperature increases the rate of thermal decomposition of sulfurous acid and consequently, the rate of sulfuric acid formation, increasing the rate of ZnS dissolution.The kinetics of the dissolution of ZnS in solutions of sulfuric acid and sulfur dioxide were investigated at temperatures up to 200oC. At 100oC and 150oC, the dissolution of ZnS in H2SO4 was found to obey the relationd[Zn2+]/dt = kfAs[H+] krAs[H2S(aq)]1/2[Zn2+]1/2and equilibria and rate constants for the ZnS / H2S04 reaction were obtained over the range, 100oC to 200oC. The activation energies of the forward and reverse reactions were found to be 56 +/- 11 kJ mol-1 and 45 +/- 15 kJ mol-1, respectively. The equilibrium constants were 4.99x10-4, 1.26x10-3 and 2.83x10-3 at 100oC, 150oC and 200oC, respectively.In the presence of added S02, ++
at low ZnS pulp density (0.5 g L-1), the rate of ZnS dissolution in sulfuric acid increased due to the removal of H2S(aq) by reaction with S02(aq) or HS03-(aq). However the increase in rate was much less than that expected for the complete removal of H2S(aq). As with leaches of ZnS in sulfurous acid at ambient temperature, the inhibition was not attributable to the presence of residual H2S(aq) or to occlusion of unreacted ZnS by elemental sulfur, but is thought to be due to aqueous species that are like "H2S", in that they may react with Zn2+ to reprecipitate W.To this end, sulfane monosulfonates have again been postulated. The rate of ZnS dissolution, under conditions of low pulp density, was independent Of S02 concentration, suggesting that under these conditions the rate of the H2S / S02 reaction is also independent of the S02 concentration.At higher pulp densities (200 g L-1), similar to those expected in an industrial application, synthetic zinc sulfide leached rapidly in H2S04 / S02 solutions to approximately 60% zinc extraction, but was then inhibited by the large amounts of sulfur that formed. These caused agglomerates of zinc sulfide and elemental sulfur to form, even at temperatures below the melting point of sulfur, reducing the surface area of zinc sulfide available for reaction.Leaches of zinc concentrate at low pulp densities in H2S04 / S02 solutions and at temperatures above sulfur's meting point, were inhibited by the formation of molten sulfur. In contrast to synthetic zinc sulfide, zinc concentrate is readily wet by molten sulfur. Three surfactants orthophenylenediamine, quebracho and sodium ligninsulfonate were found to be reasonably effective in preventing molten sulfur from occluding the mineral surface. At high pulp densities, the H2S04 / S02 leach solution was unable to effect, the extraction of zinc from a zinc concentrate beyond approximately ++
10%.Integral S02 / H2S04 leaching of zinc concentrate was found not to be a commercial prospect. However, sidestream processing of zinc concentrate in an acid leach stage followed by reaction of generated H2S with S02 from the roasting stage to produce elemental sulfur may be viable.

In the field of hydrometallurgy, the industrial uptake of leaching models has been overlooked partially due to the lack of universal models. A model developed for one plant cannot easily be transferred for the application of a different plant without redesigning the leaching kinetics in the code. The Multiple Convolution Integral (MCI)-based model developed in this thesis has the ability to be universally applied by user-controlled inputs. Chemical reactions can be selected while the modeling software calculates the mass and energy balances. Residence times, operating conditions, and the rate-limiting reagents can also be defined to calculate a precise fraction reacted (leach extent) for sulphide minerals. The ability of the using the MCI model for predicting sphalerite leaching is examined in comparison to hydrometallurgical plant data collected from a Canadian pressure leach operation. The results are promising, showing that the model can predict plant Zn extraction data to within an error of 1.5 %. The model is further verified through bench scale pressure leaching experiments where 94 % of the zinc is extracted within 90 minutes using a concentrate sample from the same industrial plant. The effect of temperature is analyzed and the activation energy is calculated to be 40.8 kJ/mol. Interesting discoveries with respect to the reagent concentrations and their effect on the overall fraction reacted are also explored from the model results. In addition, the limitations of the MCI model are explained along with suggestions for improvement.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

The main objectives of this Thesis were the determination of the reaction kinetics of the dissolution of zinc-ferrite particles ((Zn$ sb{1-x}$, Fe$ sbsp{x}{2+}$)$ rm Fe sbsp{2}{3+}O sb4$, x $ le$ 0.4) in hot aqueous solutions of sulphuric acid, and the development of a mathematical model for the prediction of the performance of a series of continuous stirred-tank reactors where zinc ferrite is leached.
Well-characterised, porous zinc-ferrite particles of industrial origin were subjected to controlled leaching experiments at temperatures close to 373 K in sulphuric acid solutions of concentration higher than 0.25mol L$ sp{-1}$. The dissolution process was found to be described most adequately by the grain model with surface reaction being the rate-controlling step. After analysing the experimental results through this model, a unique rate equation for zinc-ferrite dissolution as a function of temperature and solution composition, was obtained.
Based on this rate equation, a mathematical framework was built for the analysis of the start-up and the steady-state of reactor cascades where zinc ferrite is continuously leached. This framework consisted of population-balance and mass-balance equations, which were solved analytically or numerically. Computer simulation results, which were obtained by this reactor model, showed very good agreement with actual industrial data.

In this thesis, it was aimed to select and propose a feasible method, or series of methods, for the recovery of zinc (Zn) and lead (Pb) that are present in disposed Ç
iNKUR leach residues having 12.43 % Zn, 15.51 % Pb and 6.27 % Fe. Initially, physical, chemical and mineralogical characterizations of the leach residues were done. Results of these analyses showed that lead was present as lead sulfate (PbSO4), and zinc was present as zinc sulfate heptahydrate (ZnSO4.7H2O), zinc ferrite (ZnFe2O4) and zinc silicate (2ZnO.SiO2) in the leach residues. Initially, water leaching experiments were carried out to determine water soluble amount of blended leach residue, and the maximum zinc recovery was obtained as 18 %. After these trials, sulphuric acid and brine leaching were used to recover zinc and lead, respectively. Firstly, due to the insufficient recovery in water leaching trials acid leaching experiments were done for zinc recovery and the parameters studied were acid concentration, reaction duration, leaching temperature and solid-liquid ratio (pulp density). About 72 % Zn was recovered after hot acid leaching by using 150 g/l H2SO4 at 95 oC in 2 hours with a pulp density of 200 g/l. For lead recovery brine leaching experiments were done with the secondary leach residue obtained after H2SO4 leaching. In brine leaching experiments, NaCl concentration, pulp density (solid/liquid ratio), reaction duration and leaching temperature were chosen as variables. Effect of HCl addition was also investigated. In brine leaching while lead recoveries up to 98 % could be attained at a low pulp density in laboratory scale, the maximum recovery obtained was 84.9 % at a high pulp density (200 g/l) with 300 g/l NaCl concentration in 10 minutes at 95 oC.

Due to the increasing usage of Sn in different electronics, such as solders and in touchscreens, together with Boliden Rönnskärs increased intake of electronic waste as a secondaryraw material, a Zn-containing product called Zn-clinker has increasing amounts of Sn. TheZn-clinker is shipped to Boliden Zn-smelter in Odda, where the Zn-clinker is mixed in withcalcine (roasted concentrate) and leached in several steps. Since Zn-clinker is a product froma halogen removal in a clinker-furnace, the feed material (Mixed Oxide), for this furnace, wasalso investigated since there are plans to replace clinkering with soda-washing in the future.Most of the Sn ends up in the leaching residue which then is deposited in the mountaincaverns close by the Boliden Odda smelter. Boliden is studying the possibility to recoverPb/Ag and Sn content from the leaching residue and create a valuable by-product. Bystudying how the leaching of Sn behaves, together with a characterization of the materials, thefollowing question should be answered: “During which sulphuric acid leaching conditions, ofZn-clinker and Mixed Oxide, is the leaching of Sn minimized?” The leaching results for Zn-clinker showed that 8-10% Sn will leach out, despite changingtemperature, redox potential, time and pH. A characterization of the material with SEM-EDSand XRD-analysis was also conducted to see if Sn could be identified in any phases in thematerials. The studies provided enough evidence that Zn2SnO4 could be concluded to be themain phase in the leaching residue for Zn-clinker, a form that would not leach underconditions presented in this project. However, 8-10% of the Sn will come together with Feand when Fe leach out, so does Sn. The leaching results for Mixed Oxide pointed towards that different phases from them foundin Zn-clinker was present. Sn losses varied between 10-20% but raised to 47% whentemperature was changed to 80 °C during leaching. The SEM-EDS analysis showed that theidentified Sn-phases contained more Sn than in Zn-clinker and together with the leachingresults, a conclusion that Sn would mainly be found as SnO2 or SnO in the Mixed Oxide, butthere is still uncertainty about the distributions of these forms. Unfortunately half of the As leached out during the soda-washing for Mixed Oxide, creating aleachate with Cl, F and As that need to be taken care of. This could be challenging andpresenting a costly side-project for the route different from the Zn-clinker route used today.Another observation was that PbCO3 formed during the soda-washing, a phase that willconsume more sulphuric acid during leaching.

Magister Scientiae (Medical Bioscience) - MSc(MBS)
Mercury (Hg) is an example of a toxic metal that is not essential for nutrition. It exists in organic and inorganic forms in seafood and vapour from dental amalgam fillings respectively. Elemental mercury (Hg0) from dental amalgam was the focus of this study. Dental amalgam is one of the most commonly used dental filling materials and has been used for over 150 years. It is composed of Hg0 (approximately 50%) combined with other metals such as copper and zinc (Zn). These fillings give off Hg0 vapour throughout their existence, and is further enhanced by activities such as chewing, grinding of teeth and drinking hot liquids. Mercury consumption can lead to Zn loss or deficiency, and is reported to displace Zn and copper. Several European nations have outlawed the use of amalgam as a restorative material due to controversies regarding its safety in children, women of childbearing age and individuals with renal disease. Moreover, various studies have reported correlations between the number of amalgam fillings and Hg concentration in blood plasma, urine, faeces, saliva and different organs. Blood, urine, and hair mercury levels are used to predict possible health effects that may be caused by the different forms of Hg. Urine Hg is used to test exposure to metallic Hg0 vapour and inorganic Hg forms. This study aimed to evaluate the effects of Hg0 from dental amalgam restorations on the status of Zn in the urine. This was done by determining the concentrations of Hg0 in urine, buccal cells and the oral cavity, and its relationship with urinary Zn concentrations in the same individuals. Samples of urine, buccal tissues, chewing gum and completed questionnaires were collected from the participants (women and men) at the dental clinics in Tygerberg Hospital (TBH), Cape Town. Samples were analyzed using inductively coupled plasma mass spectrometer (ICP-MS). Findings from this study show that there was a correlation between levels of urinary Hg0 and urinary Zn (p=0.02). However, urinary Hg0 did not predict the amount of urinary Zn. Also, no relationship was found between levels of Hg0 in buccal swab or the chew test samples and urinary Zn level. There was a significant difference between females and males in the level of urinary Zn, men had higher levels of Zn excreted in the urine than females (p=0.05). However, there was no significant difference in the level of urinary Hg0 between males and females. The number of fillings (4-7) and age of fillings were significantly associated with urinary Hg0 level (p˂0.05), while smoking ˃15 cigarettes/day increased the level of Hg0 in buccal swab samples (p=0.002). We were not able to demonstrate a causal effect of Hg0 leaching on urinary zinc levels.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES.

A novel system for leaching of reconstituted cores of soils taken from horizons of Calluna moorland podzol profiles derived from granites has been used to see if absolute, or at least, relative, weathering rates assessed by simple leaching techniques and by using the PROFILE model agreed. Initial base cations are first removed by leaching with ammonium acetate. Agreement was reasonable, but the results highlighted problems posed by mineralization effects in column-based procedures. A successful attempt was made to develop a procedure to overcome this problem, based upon pre-oxidation with H₂O₂. This procedure was tested on a selection of B and C horizon soils from podzol profiles, and shown to give weathering rates which correlated well with those derived using the PROFILE model. The equilibrated soil cores remaining at the end of the study were then used for testing the effect of acidification of infiltrating water upon weathering rates of base cations. Weathering rate did not increase regularly to combat the acid input. Intact soil core microcosms, fitted with rhizon samplers at three depths and subjected to appropriate simulated precipitation, have been used to elucidate how land use influences the mobility of copper and zinc. Three land uses were considered, improved pasture, semi-improved pasture, and Calluna moorland. Copper and zinc concentrations were also measured in river water samples collected at 59 points from throughout the River Dee network under diverse flow conditions, with a view to elucidating catchment factors influencing the mobilisation of these two elements into river water. The results demonstrated large inputs of copper arising as a consequence of arable land use, and suggested that TOC in drainage water from moorland soils mobilises copper from mineral sediments in the river network. Both zinc and copper concentrations were increased under high discharge conditions.

A \"Região dos Lagos\" de Santa Gertrudes é um exemplo das muitas áreas contaminadas com metais pesados existentes no Estado de São Paulo e no Brasil. O pólo de Revestimentos Cerâmicos de Santa Gertrudes dispôs inadequadamente seus resíduos sólidos e águas residuárias diretamente no solo por mais de três décadas, contaminando uma área de 1,5 km2. A despeito das incertezas que cercam e que prejudicam a plena compreensão de um processo de bioremediação de um solo contaminado, esta pesquisa avalia a influência do pH inicial e da adição de inoculo e nutrientes sobre a eficiência de remoção de chumbo (Pb) e zinco (Zn) de um latossolo vermelho, submetido à biolixiviação com Acidithiobacillus ferrooxidans e Acidithiobacillus thiooxidans. Este solo apresenta elevados teores de óxidos de ferro (8,3 %) e alumínio (16,8 %), argila (57 %), chumbo (717 mg/kg) e zinco (181 mg/kg). Os experimentos foram conduzidos em reatores em batelada, monitorados durante 30 dias e resultaram na solubilização de até 3,6 mgPb/L e 50,0 mgZn/L. Constatou-se que para este solo e sob as condições experimentais utilizadas, não foi necessária a redução inicial do pH; a solubilização do chumbo foi inexpressiva, provavelmente, devido à sua precipitação na forma de PbSO4; a do zinco decorreu, principalmente, da liberação de íons H+, produzidos durante a dissociação dos nutrientes, em particular o FeSO4, que promoveram a acidificação do meio. Embora a lixiviação química tenha sido o principal mecanismo de solubilização do zinco, a biolixiviação devido a Acidithiobacillus ferrooxidans indígenas foi registrada e incrementou em até 17 % a lixiviação deste elemento, a partir do décimo dia de experimentação.
The \"Lake Region\" of Santa Gertrudes is one of several contaminated sites with heavy metals in São Paulo State, Brazil. As in other regions of this country, in the 1970\'s the ceramic industries of Santa Gertrudes disposed their solid wastes and wastewaters directly in soil and contaminated an area of 1.5 km2. Biological solubilization of lead (Pb) and zinc (Zn) from soil of the Lake Region was tested in batch reactors. The biological process used the leaching capacity of Acidithiobacillus ferroxidans and Acidithiobacillus thiooxidans. Tests were performed to determine the influence of initial pH, the percentage of inoculum and the addition of nutrients on the efficiency of removal of these metals. The soil contained high concentration of iron oxides (8.3 %) and aluminum (16.8 %), clay (57 %), lead (717 mg/kg) and zinc (181 mg/kg). It was not necessary to reduce the initial pH of soil. Solubilization of lead (up to 3.6 mg/L) and zinc (up to 50 mg/L) was obtained, but the solubilization of Pb was low, probably because the element was precipitated as PbSO4. The solubilization of zinc was strongly correlated with the release of H+ ions produced from nutrient dissociation, particularly FeSO4, which promoted the acidification of solution. Although chemical solubilization was the main mechanism of Zn removal, biological solubilization by indigenous Acidithiobacillus ferroxidans was detected, reaching up to 17 % of the total element leached after 10 days of testing.

This research covers the fundamental aspects of the direct leaching of sphalerite by considering the dissolution of silver, lead, and copper contents and their effects on the process. The effects of independence variables such as sodium hydroxide, potassium permanganate, hydrogen peroxide, lead nitrate, sodium chloride, dissolved oxygen, temperature, glycine concentration, dissolution time, and particle size on the process were investigated. All the outputs have been modelled and optimised through the analysis of variance.

The major aim of this study was to investigate various leaching methods for the recovery of zinc and lead from blended neutral leach residues of Ç
inkur having a composition of 12.59 % Zn, 15.21 % Pb, 6.45 % Fe, 0.054 % Cd. Initially water leaching tests were performed at various conditions of leaching temperature, reaction time and particle size. The optimized conditions for water leaching were found to be 2 h, 95&
#61616
C and 250 g/l pulp density with a final pH of 5.9. However, the zinc recovery value of 10.26 % was not adequate for industrial scale operations itself. In acid leaching trials
acid concentration, temperature, reaction time and particle size were the chosen variables. At the optimized condition of 150 g/l H2SO4, 95&
#61616
C, 2 h at 250 g/l pulp density with a final pregnant solution pH of 4.2, the extraction values were determined as 74.87 % for Zn and 39.59 % for Fe. These recovery values were evaluated as suitable for industrially feasible operations while creating a secondary leach residue of a composition of 4.10 % Zn, 19.17 % Pb, 5.52 % Fe and 85 ppm Cd that would not be suitable for pyrometallurgical lead production. After recovering zinc in considerable amount by hot sulphuric acid leaching, NaCl leaching experiments for the extraction of lead were done on the secondary leach residue by taking temperature, time and pulp density into account. The most promising conditions of brine leaching for lead recovery were found as 300 g/l NaCl, 20&
#61616
C, 15 minutes and 20 g/l pulp density that gave approximately 82 % lead recovery with a final residue of 7.87 % Pb, 6.86 % Zn, 8.79 % Fe.

Previous studies from laboratory experiments and a similar process at a plant in Switzerland, led to the pilot plant project at Renova AB, which will be described in this master thesis. In cooperation with Götaverken Miljö AB it was investigated if fly ash, produced at the Renova Waste-to-Energy plant in Gothenburg, could be treated with own scrubber liquids in order to recover zinc. If successful, Renova might build this tested pilot process in to a big scale. The pilot plant has a scale of 16 times smaller than a future big scale process. The goal of the project is to leach zinc from fly ash and gain a fly ash residue, which is classified as non-hazardous waste. The filtrate from the leaching campaign is treated so that the containing zinc is recovered. The zinc cake end product shall has a quality so that it can be sold to other industries or upgraded to high purity zinc metal. The evaluation of the experiments showed that the pilot plant process was successful. It was possible to leach out zinc by a maximum quote of 74%. The total recovery of zinc could be achieved by a maximum of 72%. The final zinc cake product was achieved through a precipitation and filtration campaign. This thesis evaluates, which process set-ups for zinc recovery through leaching and precipitation & filtration are the best and can be recommended for a big scale process. In addition, it briefly analyses the zinc product quality. Future studies will be necessary within: cost analysis of the process, zinc product quality and an analysis of the ash residue.

I nanocompositi di gomma (NC) sono materiali comunemente usati nell’industria degli pneumatici. Le proprietà meccaniche dipendono sia dall’aggiunta delle nanoparticelle (NP) di filler rinforzanti e dal processo di vulcanizzazione. La reazione di vulcanizzazione a base zolfo si basa sulla formazione di un reticolo chimico tra le catene di polimero attraverso ponti mono-, bi- e poli-sulfurei. L’incremento della velocità di reazione e dell’efficienza di reticolazione è consentito da un complesso sistema catalitico, composto da acceleranti (ad esempio sulfenammidi), attivatori (ossidi metallici) e co-attivatori (acidi grassi). L’ossido di zinco (ZnO) è il principale attivatore usato industrialmente; un ruolo fondamentale è assegnato agli ioni zinco, in grado di influenzare aspetti cinetici e meccanicistici, come il processo di accorciamento dei ponti sulfurei nei prodotti di reticolazione (associato a maggiori densità di reticolo). Ciononostante, la bassa dispersione dell’ossido di zinco, dovuta ad una bassa affinità verso il polimero, porta ad un uso ingente di ZnO nelle gomme (3-5 parti per cento di gomma) e a problemi ambientali, connessi al rilascio dello zinco durante il ciclo di vita degli pneumatici. In questo quadro, lo scopo del progetto di dottorato è stato lo sviluppo di attivatori innovativi a base zinco per il processo di vulcanizzazione, per ridurre il quantitativo di ZnO micro-cristallino nel processo industriale e diminuire il rilascio di zinco, mantenendo un’elevata efficienza del processo. A tal scopo, l’introduzione di siti reattivi di zinco è stata indagata. Partendo da NP di ZnO ancorate sulla superficie della silice (ZnO/SiO2), siti singoli di zinco (Zn/SiO2) dispersi su silice sono stati sintetizzati, sfruttando i vantaggi derivanti da una maggiore dispersione dello zinco nel composito e incrementando la reattività e disponibilità dell’attivatore nella reazione. Inizialmente, la sintesi dei due materiali e le loro proprietà sono state studiate, tramite analisi strutturali, morfologiche e di superficie. NP di ZnO amorfe, con dimensioni e percentuali di carico su silice variabili, sono state sintetizzate utilizzando una procedura ottimizzata di tipo sol-gel, basata sul fenomeno di idrolisi e condensazione di un precursore di zinco in ambiente basico. Inoltre, centri isolati di zinco (II) sono stati preparati in una reazione a due fasi, in cui la silice è pre-funzionalizzata con un agente ancorante (3-amminopropil)trietossisilano, APTES) e in seguito fatta interagire con un precursore di zinco. La caratterizzazione sperimentale ha suggerito che ogni centro di zinco isolato fosse coordinato con due gruppi amminici e due gruppi labili (idrossidi o nitrati), che potessero promuovere una maggiore reattività. I test in NC di gomma, comparati con NC preparati con ZnO micro-cristallino, hanno dimostrato maggiori efficienze di vulcanizzazione, migliorate proprietà meccaniche, elevate densità di reticolo e maggiore rinforzo in presenza dei due attivatori, usando metà del quantitativo tradizionale di ZnO. La cinetica di reazione è stata studiata tramite un approccio modello (Model Compound Vulcanization, MCV), evidenziando una migliore cinetica di processo e differenti meccanismi di reazione per ZnO/SiO2 e Zn/SiO2. Inoltre, i centri di zinco isolati hanno dimostrato di comportarsi da siti catalitici eterogenei, con una potenziale riduzione del rilascio di zinco e conseguenze dirette sulla distribuzione della reticolazione nel composito vulcanizzato, evidenziato tramite analisi avanzate di tipo morfologico e meccanico. Infine, la modulazione dei parametri strutturali degli attivatori e il loro uso in sistemi non convenzionali, che includono compositi rinforzati da filler anisotropici e polimeri modificati organicamente, hanno dimostrato la possibile regolazione della reattività e l’alta versatilità dei due attivatori per applicazioni in diversi sistemi.
Rubber nanocomposites (NCs) are commonly used materials in tyres industries. Their mechanical properties are the combined result of the addition of reinforcing filler nanoparticles (NPs) and the vulcanization process. Sulphur vulcanization reaction is based on the formation of a chemical cross-link between polymer chains through mono-, bi- and poly-sulphide bridges. The enhancement of the vulcanization rate and cross-linking efficiency is achieved thanks to a complex catalytic system, composed of accelerators (as sulphenamides), activators (metal oxides) and co-activators (fatty acids). Zinc oxide (ZnO) is the primary industrial activator and a main role is recognized to zinc ions, able to influence both kinetic and mechanistic aspects of the reaction, through the shortening of sulphur bridges in the products (associated to higher cross-linking densities). Nevertheless, some drawbacks are connected to the low dispersion of ZnO, because of the low affinity with the rubber, such as the use of high ZnO amount in rubber (3-5 parts per hundred rubber) and environmental issues, due to zinc release during the lifecycle of tyres. In this scenario, the aim of the PhD project is the development of innovative zinc-based activators for rubber vulcanization process, to reduce the amount of microcrystalline ZnO used in the industrial process and to decrease the zinc leaching during the preparation and use of the material, keeping a high vulcanization efficiency. Thus, the introduction of more active zinc species in the form of reactive sites has been proposed. Starting from nanosized ZnO particles anchored onto surface silica particles (ZnO/SiO2), single zinc sites (Zn/SiO2) dispersed on silica were synthesized, to exploit the advantages derived from the higher distribution, while increasing the availability and reactivity of the activator towards the other vulcanization reagents. In the first part, the syntheses of the materials were studied and their properties deeply investigated, through structural, morphological and surface analyses. The formation of amorphous ZnO NPs with tunable zinc loading and size on silica was achieved exploiting an optimized sol-gel procedure, based on hydrolysis and condensation of a zinc precursor in a basic environment. Besides, isolated zinc(II) centres anchored to silica were synthesized in a two-step reaction, in which silica was pre-functionalized with a grafting agent ((3-aminopropyl)triethoxysilane, APTES) and then reacted with a zinc precursor. The experimental characterization suggested the coordination of each zinc isolated centres to two amine groups and two labile groups (hydroxide or nitrate), promoting a higher reactivity. Both ZnO/SiO2 and Zn/SiO2 were tested as activators in rubber NCs and compared to microcrystalline ZnO; higher vulcanization efficiencies and improved mechanical properties were achieved, with increased cross-linking densities, using half of the conventional amount of ZnO. Lately, the kinetic of the vulcanization reaction was studied thanks to a model approach, called “Model Compound Vulcanization” (MCV). This study highlighted that the vulcanization process proceeded with an improved kinetic and following different reaction mechanisms. In particular, Zn centres were proved to behave as heterogeneous catalytic sites during the reaction, with a potential impact on the reduction of zinc leaching from rubber NCs and a direct consequence on the cross-linking distribution of the vulcanized rubber NCs, evidenced through advanced morphological and mechanical analyses. Finally, the modulation of the structural parameters of the activators and the use into non-conventional systems, including anisotropic NPs reinforced NCs and organically modified polymers, demonstrated the possible modulation of their reactivity and the high versatility of the materials for applications into different systems.

Entre le milieu du XIXème et du XXème siècle, le secteur sidérurgique a été l’une des principales sources de richesse en France. Toutefois, la production de ferromanganèse a généré une quantité considérable de déchets, notamment lors du lavage des fumées des hauts fourneaux. Ces boues d’épuration, riches en zinc (Zn), manganèse (Mn) et plomb (Pb) (5 à 40% en masse), ont été déposées dans des bassins de décantation en périphérie des sites sidérurgiques. Depuis la fermeture des usines, ces terrains sont restés en l’état et certains, comme à Pompey (Lorraine), ont été progressivement colonisés par la végétation. Compte tenu des risques sanitaires liés aux concentrations en métaux, une décontamination semble inévitable. Néanmoins, on prend conscience aujourd’hui de l’épuisement des ressources, et ces bassins apparaissent comme un gisement de ressources secondaires. Ce travail vise à développer un procédé hydrométallurgique pour extraire Zn, Mn et Pb de ces résidus, dans l’optique de récupérer ces métaux sous forme pure et revalorisable, tout en décontaminant ces sites. Tout d’abord, les expériences ont permis déterminer les conditions optimales (quantité d’acide, temps, température, ajout de réactifs, densité de pulpe) pour parvenir à extraire sélectivement Zn et Mn contenus dans les boues et former un résidu riche en Pb. Le Zn a été ensuite récupéré sous forme de ZnO ou ZnS par précipitation ou sous forme métallique par électrodéposition. Enfin, le Mn a été précipité sous forme de MnCO3 avec une concentration acceptable en impuretés. Une étude technico-économique a été réalisée pour évaluer l’intérêt de l’industrialisation du procédé
During the XIXth and XXth centuries, steel industry has been one of the main sources of wealth in France. However, ferromanganese manufacturing has produced huge quantities of wastes, for instance after blast-furnace gas washing. The residual sludge, containing high concentrations of zinc (Zn), manganese (Mn) and lead (Pb) (5 to 40 wt %), has been deposited in ponds, in the vicinity of steel-making plants. Since plant closure, these fields have been left untouched; some of them, like in Pompey (Lorraine) have been colonized by vegetation. These sites may be considered as a threat to health and environment and should be cleaned up. Nevertheless, with awareness of metal shortage, these ponds may be considered as deposits of secondary resources. This works aims at designing a hydrometallurgical process to extract Zn, Mn and Pb from these residues and recover them in a valuable form, while decontaminating the sites. At first, experiments have enabled us to determine the optimal conditions (acid concentration, duration, temperature, reactant addition, pulp density) to extract selectively Zn and Mn from the sludge and leave a Pb-rich residue. Then, Zn was recovered as ZnO or ZnS after precipitation or as Zn after electrowinning. Mn was recovered as MnCO3 at an acceptable purity. A technico-economic study has been done to assess the industrial interest of the process

O presente trabalho determinou a concentração dos metais zinco, manganês, cádmio, chumbo, níquel, cobre e cromo no efluente e solo de quatro colunas de latossolo indeformadas. Duas colunas foram contaminadas por pilhas do tipo zinco-carbono e duas colunas foram utilizadas como referência, além de pilhas isoladas, foram todas lixiviadas por uma solução \"água de chuva\" (HNO3 + H2SO4, pH 4,0). Os metais no efluente e no solo foram determinados pela técnica de ICP-OES. A avaliação do efluente e do solo das colunas contaminadas pelas pilhas mostrou um incremento das concentrações dos metais, principalmente de zinco, manganês e chumbo. A sequência das massas acumuladas dos metais no efluente e no solo da coluna contaminada apresentaram uma sequência semelhante a da lixiviação isolada da pilha (Zn > Mn > Pb > Cr > Cu > Ni > Cd), confirmando a influência da pilha nas concentrações dos metais no efluente e solo das colunas. Observou-se também que a contaminação de Zn e Mn tende a migrar da camada superior da coluna de solo para as camadas inferiores. O estudo mostrou que as pilhas podem causar uma contaminação significativa do solo para os metais Zn, Mn e Pb e possivelmente também para Cd. Esta contaminação do solo poderia vir a causar uma contaminação da água subterrânea para os metais Zn, Mn e Pb, dependo das características do perfil do solo.
The aim of the present study was to determine the concentration of Zn, Mn, Pb, Cd, Cu, Cr, and Ni in an oxisol column contaminated with zinc-carbon batteries. Two control and two contaminated columns, and batteries alone were leached for a periods of six months and one year with aqueous solution of HNO3 and H2SO4 (1:1, pH 4,0) to simulate rainwater. The metal concentrations in effluent and soil were measured by means of ICP-OES technique. Results from the contaminated column showed enhanced concentrations in both effluent and soil (mainly zinc, manganese and lead). In addition, the total amount of metals in effluent and soil showed similar sequence order as observed for batteries alone (Zn > Mn > Pb > Cr > Cu > Ni > Cd) indicating that batteries can be considered the main source of contamination. We also observed migration of Zn and Mn from the top to the lower layers of the soil columns. The study gives further evidence that batteries can significantly contaminate the soil with metals like Zn, Mn and Pb, and maybe Cd too. This soil contamination combined with the enhanced concentrations found in the effluent can point out a probable groundwater contamination.

Les rejets des Usines à Zinc de Kolwezi contiennent majoritairement du zinc sous forme réfractaire (ferrite) au traitement hydrométallurgique conventionnel. Ils contiennent d’autres métaux « lourds » qui les rendent dangereux vis-à-vis de l’environnement dans lequel ils sont actuellement entreposés. Ces métaux, dont la plupart peuvent être valorisés, font de ces rejets un véritable gisement secondaire. Il est donc impératif de mettre au point un procédé adéquat de valorisation ;d’où le thème de la présente thèse :« Etude de valorisation des rejets des Usines à Zinc de Kolwezi, RDC ».

A l’aide des techniques modernes de caractérisation (physico–chimique, minéralogique et morphologique), nous sommes arrivés à cibler, à adapter et à justifier l’utilisation d’une technique de valorisation des matières minérales existantes. Les minéraux utiles contenus dans les rejets UZK ont été sulfatés par digestion et sélectivement mis en solution après un grillage. La sulfatation s’est avérée l’étape déterminante du procédé et un intérêt particulier a été focalisé sur cette étape en réalisant une étude cinétique approfondie.

Les données et informations récoltées tout le long de cette recherche nous ont permis de réaliser une simulation du procédé par le logiciel ASPEN PLUS. Ce qui a permis de faire une ébauche d’un schéma de traitement industriel. Ce dernier s’est avéré souple vis-à-vis de l’utilisation d’autres matières comme les calcines des concentrés sulfurés cuivre-zinc.

Residues from the Kolwezi Zinc Plant (Usines à Zinc de Kolwezi UZK) essentially contain zinc in a refractory (ferrite) form, which is difficult to recover by conventional hydrometallurgical methods. « Heavy» metals are also present that make them hazardous towards the environment in which they are currently stored. Most of these metals are valuable; thus, the UZK residues are a real secondary deposit. It is therefore imperative to develop an appropriate method of treatment, hence the theme of the present thesis: « Recovery study of values metals from Kolwezi Zinc Plant residues, DRC ».

Using modern techniques of characterization (physical and chemical, mineralogical and morphological), we focused, adapted and justified the use of a technique for efficient recovery of the existing valuable minerals. The minerals contained in UZK residues have been sulphated by digestion and thereafter selectively dissolved after roasting. Sulphatation proved to be the decisive step of the process and a particular attention has been given to this step by performing a detailed kinetic study.

The data and information collected throughout this research allowed a simulation of the developed method by using the « Aspen Plus » software. This allowed us to propose a draft scheme of industrial processing. The latter proved flexible towards the use of other materials such as calcines of copper-zinc sulphide concentrates.

Doctorat en Sciences de l'ingénieur
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Ce travail traite d’un problème de pollution liée à la présence de métaux de base dans des passifs environnementaux issus d’un traitement métallurgique des minerais sulfureux cuivre – zinc provenant de la mine de Kipushi en République Démocratique du Congo. L’objectif principal de ce travail a été d’arriver à proposer des scénarios de gestion durable au passif environnemental de la filière présentant les risques environnementaux les plus élevés. Pour cela, on a d’abord procédé à une identification des différents problèmes environnementaux tout au long de la filière de traitement sur les quatre sites d’exploitation. Ensuite on a prélevé des échantillons puis procéder par des tests de disponibilité à la lixiviation à l’eau déminéralisée pour évaluer les fractions solubles des métaux de base présents et aussi par des tests de conformité de mise en décharge afin de classer ces rejets conformément à la directive européenne 2003-33-CE. Ainsi, les rejets Ex – UZK ont été identifiés comme les plus dangereux de la filière au regard de cette directive, car les quantités lixiviées de cuivre et de zinc dans ces rejets ont dépassé largement les limites fournies par la directive, et donc ils ne peuvent même pas être mis en décharge de classe I sans traitement métallurgique préalable pouvant permettre leur dépollution.

Par contre, les autres rejets de la filière, en l’occurrence les rejets de flottation de Kipushi et les scories de fusion pour matte de cuivre, peuvent eux être acceptés en décharge de classe I, sans traitement préalable au regard des limites fournies par la même directive. Les procédés de lixiviation acide chaude et de digestion ont été proposés et retenus comme scénarios de gestion durable à appliquer à ces rejets Ex – UZK, car ils se réalisent tous deux en milieu acide sulfurique d’une part et d’autre part leur application et surtout leur faisabilité en République Démocratique du Congo reste possible ;en outre ils aboutissent à des nouveaux rejets contenant le fer sous forme d’hématite, pouvant être stocké aisément et durablement dans la nature, ce qui est conforme au principe du développement durable. Nous avons tenté de modéliser ces deux scénarios en discutant et comparant la circulation des flux de matière dans les deux procédés, d’abord autour de chaque opération métallurgique unitaire, et ensuite sur l’ensemble du procédé. Ainsi nous avons pu chiffrer tous les flux entrant et sortant dans le système étudié, en considérant 1000 kg de rejets Ex –UZK alimentés. Cette quantification nous a permis de comparer les coûts opératoires de ces deux procédés. Les résultats obtenus dans la présente étude sont encourageants et nous ont permis de formuler des recommandations pour les études ultérieures éventuelles dont les résultats pourront l’enrichir davantage, notamment sur les aspects technologiques, économiques et environnementaux, de manière à faciliter les applications sur terrain.

This work deals with environmental liabilities consisting of base metals pollution due to metallurgical processing of copper – zinc sulphide ores in Kipushi mine in Democratic Republic of Congo. The main objective of this work was to propose sustainable management scenarios for the most important environmental liabilities from metallurgical sector. For this purpose, liabilities were first identified on four metallurgical plants. Then, leaching tests with deionized water were carried out to assess the soluble fractions of base metals. These effluents were also classified according to the test described in european decision 2003-33-EC, which determines the conformity of waste to landfill. Ex – UZK effluents are the most dangerous from this sector, according to this directive, since the quantities of leached copper and zinc were far beyond the limits :they cannot be sent to class I landfill without prior metallurgical processing. However, other effluents like flotation wast and Lubumbashi slag originating from melting for copper matte, are acceptable without prior treatment. Hot acid leaching and digestion were proposed as sustainable management scenarios for to these Ex – UZK waste because :both can be performed in sulfuric acid and they are feasible in Democratic Republic of Congo. They also lead to an iron – rich waste consisting of hematite that can be stored easily and sustainably in nature, which is consistent with the principle of sustainable development. We have modeled these two scenarios by discussing and comparing the flows in both processes, first for each individual metallurgical unit process, and then for the whole chain of value. So we could assess all the inputs and outputs of the studied system, expressed per ton of Ex – UZK waste. The operating costs of both processes were calculated and compared. The results are encouraging. Recommendations were proposed for further studies, in order to investigate more deeply the technological, economical and environmental aspects, to facilitate the final application.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Etude dans le cadre de l'extraction de cu des minerais de type chalcopyrite. Lors de l'attaque des minerais de type chalcopyrite par des solutions de cu(ii) en milieu fortement chlorure, les metaux presents dans le minerai sous forme de sulfures passent en solution soit partiellement soit en totalite, et s elementaire precipite. Mise au point du dosage polarographique des ions cu, pb, zn et fe dissous. L'electrolyse de solutions a teneur elevee en cu(i) et contenant pb(ii), zn(ii) ou fe(ii) a mis en evidence un phenomene de codeposition de pb avec cu lorsqu'on opere a des densites de courant elevees, tandis que ni zn ni fe ne se codeposent avec cu

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the Degree of Master of Science in Engineering.
Laboratory experimentation were conducted to investigate the regeneration and recycling of nitric acid during leaching in froth (LIF) processing of Gamsberg zinc sulphide concentrate. Two experiments were performed in a mechanically stirred batch reactor at 80- 90°C to determine the leaching kinetics of the zinc sulphide concentrate. 93 to 97% of zinc was extracted into spent zinc sulphate electrolyte containing 30 to 40g/1 nitric acid during 40 to 60 minutes of leaching without regeneration of nitric acid. Between 60.72. and 97.79% of the consumed nitric acid was regenerated after 45 minutes of batch L/F experiments carried out at 80·90oC and 50kPa. The results show that the degree of nitric acid regeneration is inversely proportional to the concentration of nitric acid in the leaching solution. Zinc extraction ranged between 56.31 and 78.37% whilst 40.29 to 50.99% of the initial sulphide sulphur was oxidised to elemental sulphur. In the continuous L/F experiments conducted at 80- 90°C and 100·200kPa, the degree of nitric acid regeneration varied from 33.63 to 97.22%. Overall zinc extraction was about 62% whilst 47% of the sulphide sulphur reported as elemental sulphur after 60 minutes of processing. A five-stage L/F processing of the concentrate was carried out in which the flotation phenomenon was used for selective separation of the floatable fraction from the nonfloatable fraction. About 40 to 80% of the consumed nitric acid was regenerated, 88.94% of zinc was extracted whilst 55.65% of the sulphide sulphur reported is elemental sulphur after 77 minutes of processing. The recoveries of zinc and elemental sulphur increased to over 92% and 58% respectively when the leach residue was subsequently leached in the batch reactor.
Andrew Chakane 2019

Thesis (MTech. degree in Metallurgic Engineering)--Tshwane University of Technology, 2008.
The purpose of this study is to develop a feasible process for extracting gold and silver from an electrolytic zinc refinery residue. Composite samples of electrolytic zinc refining lead-silver residues containing traces of gold (1.35 g/t) and significant amounts of silver (155 g/t) were subjected to batchwise cyanide leaching to assess the feasibility of extracting gold and silver. This project was concluded with a recommendation that a pilot Residue Leach Plant should be commissioned to beneficiate gold and silver from the residue dam for a better estimation of lime, cyanide consumptions and gold and silver recoveries. The return on capital investment will be high at current gold price and operational cost is low. It is also recommended to investigate the economics of cyanide leaching of a pre-concentrate obtained from froth flotation.

碩士
國立成功大學
資源工程學系碩博士班
100
Crude zinc oxide is the product of the Waelz kiln process for the processing of EAF dust. With increasing amount of EAF dust produced in Taiwan, many company jump into the production and sale of crude zinc oxide to downstream firms for manufacturing of zinc oxide. Crude zinc oxide is a valuable resource with high zinc content (〉40%). it also contains other valuable metals such as lead and iron. Usually the zinc in crude zinc oxide was recovered by sulphuric acid leaching and filtration. However, the filterability of leachate produced by sulphuric acid leaching is very poor. Therefore, the objective of this study focused on the filterability improvement of leachate produced by sulphuric acid leaching. The filterability was evaluated by parameters such as the residue particle size analysis and Specific Resistance to Filtration(SRF). The results of this study show that using 0.6 N of HCl can destroy the structure of zinc-iron spinel in leachate and the size of residued PbSO4 particles is mainly distributed around 10 μm. The ZnFe2O4 particles mainly distributed in the sze range of 1 ~ 5μm, and is the main cause of poor filterability.

碩士
國立屏東科技大學
環境工程與科學系所
97
The electric arc furnace steel-making process generate a large amount of waste known as electric arc furnace flue dust. The current treatment is still limited to pyrometallurgical smelter to recover zinc oxide while dump the residues of other heavy metals oxide directly to landfill which already cause a serious threat to the environment. Due to the surging raw materials prices and shortage of mineral resources for Taiwan, how to effectively recover almost all metals would be an important issue to be addressed. The hydrometallurgical techniques could be the promising candidate. The experiment in this study was designed to perform in two stages: leaching and electrolysis. In the leaching stage, temperature, leaching time, alkaline solvent concentration, and solid-liquid ratio were the four parameters to pursue to find the optimum condition to maximize the recovery of zinc. The leaching efficiency of zinc significantly increased with the increasing temperature until 90℃. No more zinc leached out would be observed after the reaction time of 2 hours. In the range of 10％-40％, the leaching efficiency of zinc also increased with the increasing NaOH concentrations. No significant change could be found for the solid-liquid ratio within the 1:5-1:25. In the electrolysis stage, 80％ zinc could be recovered in 10 minutes and more than 95％ zinc would deposit on the cathode plate with the purity of 88％ zinc.

The objective of the International Kinetic Database (IKD) is to characterize bulk reaction rates in alkaline, neutral, and acidic minesite drainage. The IKD currently contains 307 kinetic tests from around the world, and is growing. Of the 307 tests, 185 provided leaching rates for copper and zinc. Scatterplots of these rates against pre-test parameters such as solid-phase copper and acid-base accounting failed to reveal any clear relationships. Consequently, leaching rates cannot be predicted accurately from pre-test characterization of a sample. Some correlation was noted among leaching rates, sulfate (acid) production, neutralization rate, and aqueous pH. However, the strength of these correlations was too weak to allow the accurate estimation of one parameter from another. All these observations point to the importance of kinetic testing in the assessment and prediction of mine drainage, and the inability to estimate rates prior to testing.

During the production of ferrochrome in electric arc furnaces, a dust is captured in baghouse filters as a means of air pollution control. This dust contains various metals such as chromium, zinc, iron, aluminium and magnesium. Due to the presence of hexavalent chromium in the dust, which is both toxic and carcinogenic, it requires disposal at a hazardous waste disposal site, entailing high cost. The possibility exists that these costs could be reduced if metals such as zinc can be recovered from the dust through, inter alia, leaching. Experiments were performed to determine suitable conditions for the leaching of zinc from such a baghouse dust. A two step leaching procedure was followed which prevented the formation of silica gel. The most favourable conditions for zinc extraction was with a sulphuric acid concentration of 336 g/l and an acid to dust ratio of 0,56. Under these conditions zinc was selectively leached with regard to iron and aluminium. The percentage recovery for zinc was 71,2%, aluminium 1,8% and iron 0,1%. It was concluded that the second step (dilution) of leaching did not have a significant influence on the percentage extraction of metals from the dust. Consideration of the chemical treatment cost of waste streams produced led to the conclusion that zinc recovery from baghouse dust is not an economically feasible project viewed in isolation. However, compared to disposal at a hazardous waste disposal site such as Holfontein, approximately R467 054,00 per annum (based on a seven day week and baghouse dust production of 3 600 kg/day) can be saved.
Dissertation (MEng (Environmental Engineering))--University of Pretoria, 2006.
Chemical Engineering
unrestricted

A cement-stabilised waste was subjected to batch, column, and dynamic leaching tests, and the leaching behaviour of arsenic, copper, lead, selenium, and zinc was investigated. Batch tests included the Australian Bottle Leaching Procedure (ABLP, AS 4493.3-1997), Toxicity Characteristic Leaching Procedure (TCLP, USEPA Method 1310); column testing included small columns (internal diameter = 24mm) and a large column (internal diameter = 500mm); and dynamic leaching tests were run with both short (1 hour) and long (4 hour) leachant renewal frequencies. A maximum availability test was used to indicate maximum leaching potential for the metals under investigation.

The role of the surfactants lignin sulfonic acid, cocoamido hydroxyl sulfobetaine (CAHSB), tallow amido hydroxyl sulfobetaine (TAHSB), cocoamido betaine (CAB), naphthalene sulfonic acid-formaldehyde condensates and orthophenylene diamine (OPD) in the liquid sulfur-aqueous zinc sulphate-zinc sulfide mineral system has been studied. The effect of the various surfactants on the liquid sulfur-aqueous system interfacial tensions and the liquid sulfur-mineral contact angle were measured in a high temperature-high pres-sure apparatus. In the absence of any surfactant, the liquid-liquid interfacial tension measured 54±1 mN/m, and the liquid sulfur-mineral contact angle was 80±5°. In the presence of 0.3 g/L lignin sulfonic acid, the interfacial tension decreased to about 29±1mN/m; the interfacial tension was not sensitive to any further increase in the surfactant concentration. The contact angle measured 145±5° in the presence of 0.07-0.3 g/L of the surfactant. The presence of OPD in the solution did not have any effect on the liquid sulfur-aqueous solution interfacial tension but increased the contact angle to about130±5°. At a concentration of 0.1 g/L, naphthalene sulfonic acid-formaldehyde con-densates decreased the interfacial tension to 21±1 mN/m. Beyond this concentration, the liquid-liquid interface was not sensitive to any further increase. The contact angle increased to 155±5° even at concentrations as low as 0.05 g/L. CAHSB exhibited just about the same efficiency as lignin sulfonic acid. TAHSB and CAB required higher concentrations in order to effect any substantial changes in the liquid sulfur-aqueous solution interfacial tension. They also effected a contact angle increase to 135±5°. With the exception of OPD, all the surfactants adsorbed at both the liquid-liquid and aqueous-solid interfaces. OPD, on the other hand adsorbed at only the aqueous-solid interface. When introduced into leaching systems, the surfactants influenced the metal extraction to different extents. OPD and lignin sulfonic acid were the most efficient surfactants (or dispersants for liquid sulfur). The extent of zinc extraction was enhanced to about94 % for lignin sulfonic acid and over 99 % for OPD under both low or high pulp density conditions. The other surfactants were unable to enhance zinc extraction even under low pulp density conditions. Application of metaphenylene diamine as dispersant for liquid sulfur under both low and high pulp density leaching conditions resulted in zinc extractions in excess of 98 %. A combination of the interfacial studies and the leaching experiments indicates that the most important characteristic for any effective surfactant under pressure leaching conditions is for the surfactant to adsorb at the aqueous phase-solid interface and increase the liquid sulfur-mineral contact angle. Infrared spectral analysis of both sphalerite leach residue and pulped sphalerite indicates that the lignin sulfonate ions are adsorbed both physically and chemically by the mineral. The chemically adsorbed species form a Zn(II)-based complex that has an organic portion similar to the bulk surfactant structure. OPD, on the other hand, is adsorbed chemically through the interaction of the C-N functional group with the metal ions forming a metal-amine complex.

В представленной работе на тему «Исследование комбинированной технологии переработки медно-цинковых промпродуктов» произведены теоретические и лабораторные исследования по определению оптимальной технологии переработки медно-цинковых сульфидных промпродуктов гидрометаллургическим способом. Рассмотрены две эффективные технологии, проведено сравнение по объективным показателям, сделаны экологоэкономический и экономический расчеты.
In this study, entitled "Study of the combined technologies of processing of copper-zinc middlings" produced theoretical and laboratory studies to determine the best technology processing of copper-zinc sulphide middlings hydro- metallurgical method. Two efficient technologies are considered, compared to objective indicators, are made of ecological, and economic calculations.