The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Gabriel Da Silva - One of the best experts on this subject based on the ideXlab platform.
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kinetics and mechanism of the bacterial and Ferric Sulphate oxidation of galena
Hydrometallurgy, 2004Co-Authors: Gabriel Da SilvaAbstract:The bacterial oxidation of galena (PbS) has been studied, largely due to its relevance to the bioleaching of sphalerite (ZnS) and other sulphide minerals. Ferric Sulphate oxidation experiments were first conducted as an analog to the indirect bio-oxidation mechanism, and the process was found to be diffusion-controlled due to the presence of a product layer. The bacterial oxidation of galena by a mixed culture of iron- and sulphur-oxidising bacterium was found to proceed according to a diffusion-controlled indirect mechanism, in which the primary role of the bacteria is the re-generation of Ferric iron. Using quantitative XRD analysis, it was demonstrated that the oxidation product layer consisted solely of lead Sulphate and elemental sulphur, in a 1:1 ratio. It was proposed that elemental sulphur and lead ions were formed in a Ferric oxidation reaction, while lead Sulphate subsequently formed via precipitation of the lead ions, consuming Sulphate ions from solution. The galena bio-oxidation experiments demonstrated considerable acid consumption, because of occlusion of the produced elemental sulphur by precipitated lead Sulphate. This reveals a new mechanism through which galena oxidation may hinder the bioleaching of other sulphide minerals.
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relative importance of diffusion and reaction control during the bacterial and Ferric Sulphate leaching of zinc sulphide
Hydrometallurgy, 2004Co-Authors: Gabriel Da SilvaAbstract:A study has been undertaken on the bacterial and Ferric Sulphate leaching of sphalerite, with the aim of observing the relative importance of both diffusion and reaction control, across a range of operating conditions. To facilitate this kinetic analysis a mixed-control rate equation was developed based upon the shrinking particle and shrinking core models, featuring both an intrinsic rate of zinc extraction and a product layer diffusion coefficient. The Ferric Sulphate oxidation of a pure sphalerite sample was first studied, and the process was found to be mainly controlled by surface diffusion, thought to be due to formation of the elemental sulphur product layer. The mesophilic bacterial oxidation of a high-grade zinc ore was studied at 35 °C, and the process was observed to be controlled by both chemical reaction and diffusion. However, during the mesophilic bacterial oxidation of a low-grade zinc ore at 25 °C, diffusion was found to be rate limiting. It was proposed that this diffusion resistance arises from an unreacted layer of gangue material.
Versiane Albis Leao - One of the best experts on this subject based on the ideXlab platform.
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the leaching kinetics of a zinc sulphide concentrate in acid Ferric Sulphate
Hydrometallurgy, 2007Co-Authors: Adelson Dias De Souza, Pablo Dos Santos Pina, Versiane Albis Leao, Carlos Antonio Da Silva, Priscila De Freitas SiqueiraAbstract:Abstract This work examines the dissolution kinetics of an iron–rich zinc sulphide concentrate in acid Ferric Sulphate medium. The effects of temperature, Ferric ion and sulphuric acid concentrations, agitation speed and particle size on the leaching kinetics were investigated. The leaching process could be separated into two stages. Initially, the dissolution kinetics was controlled by the chemical reaction at the surface of the zinc sulphide particles followed by a second step where the reaction was controlled by diffusion of the reagents or products through the elemental sulphur (ash) layer. The activation energy of the chemical controlled step was 27.5 kJ/mol and the value determined for the diffusion controlled step was 19.6 kJ/mol. The reaction order with respect to Ferric ion and sulphuric acid concentrations were approximately 0.50 and 1.00, respectively. Analysis of the unreacted and reacted sulphide particles by SEM-EDS showed a progressive increase of the thickness of the elemental sulphur layer on the solid surface. The development of this sulphur layer is further evidence of the change on the rate-controlling step as the reaction progress.
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the role of sodium chloride on surface properties of chalcopyrite leached with Ferric Sulphate
Hydrometallurgy, 2007Co-Authors: M F C Carneiro, Versiane Albis LeaoAbstract:Abstract Leaching of chalcopyrite in oxidizing conditions usually results in low copper extraction due to mineral passivation. It has been proposed that sodium chloride has a positive effect on chalcopyrite dissolution increasing copper extraction. Aiming to bring further insight into this topic, the present work seeks to evaluate the influence of sodium chloride on the leaching of chalcopyrite focusing on surface area and porosity of the reaction products formed during leaching. A finely ground ( d 50 = 5.5 μm) chalcopyrite concentrate assaying 25.2% iron, 30.9% sulphur and 27.5% copper was leached in oxygenated Ferric Sulphate solutions at atmospheric pressure and 95 °C. It has been observed that although sodium chloride favoured natrojarosite precipitation, which reduced the total iron concentration during leaching, copper extractions as high as 91% were accomplished as compared to 45% copper extraction in the absence of NaCl. It is suggested that sodium chloride reduces chalcopyrite passivation and complexes Cu(I) ions adding a second redox couple to the system. Furthermore, morphologic characterization of the reaction products performed by SEM analyses as well as specific surface area and porosity measurements have confirmed that NaCl increases surface area and porosity of the product layer, which explains the high copper extractions observed in the presence of the salt.
Aleksandar N Nikoloski - One of the best experts on this subject based on the ideXlab platform.
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Leaching of brannerite in the Ferric Sulphate system — Part 1: Kinetics and reaction mechanisms
Hydrometallurgy, 2015Co-Authors: Rorie Gilligan, Aleksandar N NikoloskiAbstract:The uranium titanate mineral brannerite, UTi2O6 is the most common of the uranium minerals which is considered refractory. Ore containing brannerite mineralisation has been mined and processed in several locations around the world. Under typical uranium ore processing conditions, brannerite is often lost to tailings. In order to design an effective process for the leaching of high-brannerite uranium ores, it is first necessary to understand the mechanism of the chemical processes through which brannerite dissolves in the absence of interferences from the host rock. In the present study, a specimen of brannerite obtained as a single crystal was leached in sulphuric acid (10-200 g/L) and Ferric Sulphate (2.8 g/L Fe3 +) solution at 25-96°C for 5 h. The rate of titanium dissolution was monitored along with uranium. Comparisons between the rates at which these two elements dissolved and the morphological changes that were observed to take place during the dissolution process indicated two different sets of leaching reaction mechanisms. At low temperatures, uranium dissolved at a much higher rate than titanium initially, leaving titanium rich areas on the brannerite particles similar to observations reported in earlier investigations which suggest incongruent dissolution. The calculated activation energies for uranium and titanium dissolution were 36 and 48 kJ/mol respectively. At higher temperatures, uranium and titanium dissolved at similar rates in constant proportions suggesting congruent dissolution. The calculated activation energy for this reaction was 23 kJ/mol. The transition between incongruent and congruent dissolution took place at lower temperatures when the acid concentration was higher. Titanium appeared to undergo hydrolysis after dissolution, forming anatase. This side reaction was most favourable at lower acid concentrations and high temperatures.
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leaching of brannerite in the Ferric Sulphate system part 1 kinetics and reaction mechanisms
Hydrometallurgy, 2015Co-Authors: Rorie Gilligan, Aleksandar N NikoloskiAbstract:The uranium titanate mineral brannerite, UTi2O6 is the most common of the uranium minerals which is considered refractory. Ore containing brannerite mineralisation has been mined and processed in several locations around the world. Under typical uranium ore processing conditions, brannerite is often lost to tailings. In order to design an effective process for the leaching of high-brannerite uranium ores, it is first necessary to understand the mechanism of the chemical processes through which brannerite dissolves in the absence of interferences from the host rock. In the present study, a specimen of brannerite obtained as a single crystal was leached in sulphuric acid (10-200 g/L) and Ferric Sulphate (2.8 g/L Fe3 +) solution at 25-96°C for 5 h. The rate of titanium dissolution was monitored along with uranium. Comparisons between the rates at which these two elements dissolved and the morphological changes that were observed to take place during the dissolution process indicated two different sets of leaching reaction mechanisms. At low temperatures, uranium dissolved at a much higher rate than titanium initially, leaving titanium rich areas on the brannerite particles similar to observations reported in earlier investigations which suggest incongruent dissolution. The calculated activation energies for uranium and titanium dissolution were 36 and 48 kJ/mol respectively. At higher temperatures, uranium and titanium dissolved at similar rates in constant proportions suggesting congruent dissolution. The calculated activation energy for this reaction was 23 kJ/mol. The transition between incongruent and congruent dissolution took place at lower temperatures when the acid concentration was higher. Titanium appeared to undergo hydrolysis after dissolution, forming anatase. This side reaction was most favourable at lower acid concentrations and high temperatures.
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uranium extraction from a pure natural brannerite mineral by acidic Ferric Sulphate leaching
Minerals Engineering, 2013Co-Authors: Allan Costine, Aleksandar N Nikoloski, Micheal Da Costa, Kok Fung Chong, Ralph HacklAbstract:Brannerite is a refractory uranium mineral from which it is very difficult to liberate the uranium. Hence in commercial mineral processing operations, brannerite often reports to the residue. This paper will show that for a pure form of natural brannerite nearly complete extraction of uranium (∼99%) is achievable under practical conditions. The efficient extraction of uranium from ores containing brannerite requires a detailed understanding of the fundamental mechanisms governing the rate and extent of dissolution. These mechanisms are often complicated by the presence of gangue minerals which consume reagents and impact on the solution chemistry. In this study, the acidic Ferric Sulphate leaching of an exceptionally pure, natural brannerite mineral (35.8% U, 20.1% Ti) was investigated under atmospheric conditions. Hence the variation in mineral composition was not present as a complicating factor and the results were able to identify some of the inhibiting mechanisms, and also the preferred conditions for the leaching of brannerite in an acidic Ferric Sulphate system. The effects of temperature (40-80 C), Ferric ion concentration (0-100 g/L), H2SO4 concentration (10-200 g/L), redox potential (424-752 mV vs. Ag/AgCl), and particle size on uranium and titanium extractions were studied for leach times up to 48 h. Under relatively mild conditions (40 C, 24 h leach time, 40 g/L H2SO4), the extent of uranium extraction was 94.4%. The extractions improved with the use of a higher temperature, a finer particle size, and a longer leach time. The presence of Ferric iron was essential for enhanced dissolution rates, but had only a minor effect on the final uranium extractions, particularly at 60 C and 80 C. All of the leach residues studied had some crystalline anatase (TiO2) and lead Sulphate (anglesite) present. A strong correlation was found between the concentrations of unleached uranium and the amount of titanium precipitated in the residues, which could be explained by the observation of a Ti-enriched diffusion layer on the surface of the dissolving grains of brannerite, which hindered the extraction process. These findings further the current understanding of the extraction process and lead a step closer to elucidation of the mechanism of the extraction process.
Teófilo A. Graber - One of the best experts on this subject based on the ideXlab platform.
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The ternary system arsenic pentoxide + Ferric Sulphate + water : Solubility, density and refractive index of saturated solutions at 323.15 and 343.15K
Fluid Phase Equilibria, 2008Co-Authors: María E. Taboada, Patricia C. Castillo, Elsa K. Flores, Teófilo A. GraberAbstract:Abstract The present study includes measurements on the solubility, density, and refractive index of saturated Ferric Sulphate–arsenic oxide–water solutions at 323.15 and 343.15 K for different mass fractions of arsenic and iron. The phase diagram was determined at 323.15 and 343.15 K and its regions were defined. The most important salt precipitated at both temperatures was Fe(H2AsO4)3·5H2O (kaatialaite). Equations are proposed which correlate the equilibrium and physical property data of the ternary systems as a function of the mass fraction of iron. These equations allowed determination of invariant points (double salt saturations) for both temperatures studied. Finally, the solubility of Fe(H2AsO4)3·5H2O in aqueous solution was determined in order to evaluate the feasibility of its use as a stable (non-leaching) waste disposal alternative.
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the ternary system arsenic pentoxide Ferric Sulphate water solubility density and refractive index of saturated solutions at 323 15 and 343 15k
Fluid Phase Equilibria, 2008Co-Authors: María E. Taboada, Patricia C. Castillo, Elsa K. Flores, Teófilo A. GraberAbstract:Abstract The present study includes measurements on the solubility, density, and refractive index of saturated Ferric Sulphate–arsenic oxide–water solutions at 323.15 and 343.15 K for different mass fractions of arsenic and iron. The phase diagram was determined at 323.15 and 343.15 K and its regions were defined. The most important salt precipitated at both temperatures was Fe(H2AsO4)3·5H2O (kaatialaite). Equations are proposed which correlate the equilibrium and physical property data of the ternary systems as a function of the mass fraction of iron. These equations allowed determination of invariant points (double salt saturations) for both temperatures studied. Finally, the solubility of Fe(H2AsO4)3·5H2O in aqueous solution was determined in order to evaluate the feasibility of its use as a stable (non-leaching) waste disposal alternative.
Rorie Gilligan - One of the best experts on this subject based on the ideXlab platform.
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leaching of brannerite in the Ferric Sulphate system part 1 kinetics and reaction mechanisms
Hydrometallurgy, 2015Co-Authors: Rorie Gilligan, Aleksandar N NikoloskiAbstract:The uranium titanate mineral brannerite, UTi2O6 is the most common of the uranium minerals which is considered refractory. Ore containing brannerite mineralisation has been mined and processed in several locations around the world. Under typical uranium ore processing conditions, brannerite is often lost to tailings. In order to design an effective process for the leaching of high-brannerite uranium ores, it is first necessary to understand the mechanism of the chemical processes through which brannerite dissolves in the absence of interferences from the host rock. In the present study, a specimen of brannerite obtained as a single crystal was leached in sulphuric acid (10-200 g/L) and Ferric Sulphate (2.8 g/L Fe3 +) solution at 25-96°C for 5 h. The rate of titanium dissolution was monitored along with uranium. Comparisons between the rates at which these two elements dissolved and the morphological changes that were observed to take place during the dissolution process indicated two different sets of leaching reaction mechanisms. At low temperatures, uranium dissolved at a much higher rate than titanium initially, leaving titanium rich areas on the brannerite particles similar to observations reported in earlier investigations which suggest incongruent dissolution. The calculated activation energies for uranium and titanium dissolution were 36 and 48 kJ/mol respectively. At higher temperatures, uranium and titanium dissolved at similar rates in constant proportions suggesting congruent dissolution. The calculated activation energy for this reaction was 23 kJ/mol. The transition between incongruent and congruent dissolution took place at lower temperatures when the acid concentration was higher. Titanium appeared to undergo hydrolysis after dissolution, forming anatase. This side reaction was most favourable at lower acid concentrations and high temperatures.
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Leaching of brannerite in the Ferric Sulphate system — Part 1: Kinetics and reaction mechanisms
Hydrometallurgy, 2015Co-Authors: Rorie Gilligan, Aleksandar N NikoloskiAbstract:The uranium titanate mineral brannerite, UTi2O6 is the most common of the uranium minerals which is considered refractory. Ore containing brannerite mineralisation has been mined and processed in several locations around the world. Under typical uranium ore processing conditions, brannerite is often lost to tailings. In order to design an effective process for the leaching of high-brannerite uranium ores, it is first necessary to understand the mechanism of the chemical processes through which brannerite dissolves in the absence of interferences from the host rock. In the present study, a specimen of brannerite obtained as a single crystal was leached in sulphuric acid (10-200 g/L) and Ferric Sulphate (2.8 g/L Fe3 +) solution at 25-96°C for 5 h. The rate of titanium dissolution was monitored along with uranium. Comparisons between the rates at which these two elements dissolved and the morphological changes that were observed to take place during the dissolution process indicated two different sets of leaching reaction mechanisms. At low temperatures, uranium dissolved at a much higher rate than titanium initially, leaving titanium rich areas on the brannerite particles similar to observations reported in earlier investigations which suggest incongruent dissolution. The calculated activation energies for uranium and titanium dissolution were 36 and 48 kJ/mol respectively. At higher temperatures, uranium and titanium dissolved at similar rates in constant proportions suggesting congruent dissolution. The calculated activation energy for this reaction was 23 kJ/mol. The transition between incongruent and congruent dissolution took place at lower temperatures when the acid concentration was higher. Titanium appeared to undergo hydrolysis after dissolution, forming anatase. This side reaction was most favourable at lower acid concentrations and high temperatures.