Correlation between dielectric properties and aqueous oxidation rate for pulverized sphalerites and zinc concentrates

In a previous paper the dielectric properties, including dielectric constant, dielectric loss tangent, and relaxation time, of six particulate sphalerite samples and four zinc flotation concentrates were measured using a packed bed condenser. In the current study, the same particulate samples were ground to an average size of 8.5 μm, and together with the concentrates underwent oxidation in an acidic sulfate solution, containing 100 g/dm³ H₂SO₄, 10 g/dm³ total Fe, and 30 g/dm³ Zn, at a controlled suspension potential of 0.55 V (Ptvs SCE) and at 90 °C (363 K). Under these experimental conditions, the Fe³⁺ concentration and the suspension potential had little effect on the oxidation rate. The oxidation proceeded mainly in the sulfur-forming type. The results were analyzed using a simplified kinetic expression for spherical particles with a logarithmic normal size distribution. It was found that the rate constant varied in proportion to the 0.6th power of the reciprocal of the equivalent parallel resistances for the dense substance and the packed bed. The rate constant also varied in proportion to the reciprocal of the dielectric relaxation time; however, this variation was influenced by the copper content of the samples. Formerly with National Research Institute for Metals     

Oxidation of Fe (II) in sulfuric acid solutions with dissolved molecular oxygen

The oxidation of Fe(II) with dissolved molecular oxygen was studied in sulfuric acid solutions containing 0.2 mol · dm⁻³ FeSO₄ at temperatures ranging from 343 to 363 K. In solutions of sulfuric acid above 0.4 mol · dm⁻³, the oxidation of Fe (II) was found to proceed through two parallel paths. In one path the reaction rate was proportional to both [Fe⁻²⁺]² andp _{o 2} exhibiting an activation energy of 51.6 · kJ mol⁻¹. In another path the reaction rate was proportional to [Fe²⁺]², [SO ₄ ^{2 −}], andp _{o 2} with an activation energy of 144.6 kJ · mol⁻¹. A reaction mechanism in which the SO ₄ ^{2 −} ions play an important role was proposed for the oxidation of Fe(II). In dilute solutions of sulfuric acid below 0.4 mol · dm⁻³, the rate of the oxidation reaction was found to be proportional to both [Fe(II)]² andp _{o 2}, and was also affected by [H⁺] and [SO ₄ ^{2 −}]. The decrease in [H⁺] resulted in the increase of reaction rate. The discussion was further extended to the effect of Fe (III) on the oxidation reaction of Fe (II).     

Leaching kinetics and stoichiometry of pyrite oxidation from a pyrite–marcasite concentrate in acid ferric sulfate media

A pyrite concentrate with minor marcasite was oxidized in an acidic ferric sulfate medium at temperatures from 45 to 75 °C and at constant potentials corresponding to Fe(III) to Fe(II) ratios from 10 to 300. Potassium permanganate (KMnO₄) was found to be both a suitable oxidant for controlling the solution potential and a convenient and reliable indicator of leaching progress.The stoichiometry of pyrite oxidation was found to be essentially independent of temperature and only slightly dependent on solution potential over the range of conditions studied. Each unit of sulfide sulfur oxidized yielded 64 ± 2% sulfate, the rest elemental sulfur as discrete particles approximately 2 μm in diameter.The pyrite oxidation rate was very sensitive to the temperature, giving a large activation energy (83 kJ/mol), and was proportional to the Fe(III)/Fe(II) concentration ratio to the power of 0.57. The shrinking sphere model fitted very well the changing grain topology. A single mathematical expression combines the thermal, chemical, and topological functions to predict the pyrite conversion as a function of the known temperature, ferric concentration, ferrous concentration, particle size, and time. The model predictions are excellent over the range of conditions tested.     

Microbial depyritisation of three different coals by Acidithiobacillus ferrooxidans in a batch stirred tank reactor

Abstract

The present study aimed to investigate the depyritisation potential of Acidithiobacillus ferrooxidans on two different types of coals, namely lignite and anthracite collected from three different countries (Korea, China and Indonesia). The experimental work was conducted on a batch mode in a stirred tank reactor. All the batch biooxidation of pyrite in the different coal samples were conducted in a pH controlled condition (pH?=?1·5). The growth medium employed for the batch biooxidation of pyritic coal was free from iron supplement. At. ferrooxidans oxidised mineral pyrite of Korean anthracite at a greater rate (98%) compared to 96 and 92% of pyrite oxidation for Indonesian and Chinese lignite respectively. The ratio of bioleach residue to the feed was reasonably good with range of 8·56–9·06 stating the net mass loss of 9–14. Coal depyritisation was carried out by the available Fe³⁺ ion in the inoculum producing Fe²⁺ ion as a product and this Fe²⁺ ion was further oxidised to Fe³⁺ ion by At. ferrooxidans. This Fe³⁺ ion produced by At. ferrooxidans continued the oxidation of the residual pyrite in the coal until all pyrite content was oxidised completely. The three different coals were found to be feasible for biological depyritisation of the coal could be scaled up for further studies in a continuous stirred tank bioreactor.

L’étude présente avait pour but d’examiner le potentiel d’enlèvement de la pyrite par Acidithiobacillus ferrooxidans dans deux types de charbons, soit le lignite et l’anthracite, récoltés dans trois pays, soit la Corée, la Chine et l’Indonésie. On a effectué le travail expérimental dans un mode en vrac, dans un réacteur agité. On a effectué toute la bio-oxydation en vrac de la pyrite des échantillons de charbon à un pH contrôlé de 1·5. Le médium de croissance utilisé pour la bio-oxydation en vrac du charbon pyritique ne contenait pas de supplément de fer. At. ferrooxydans oxydait le minerai de pyrite de l’anthracite coréen en plus grande proportion (98%) que l’oxydation de la pyrite du lignite indonésien (96%) ou chinois (92%), respectivement. Le rapport de résidu de biolixiviation à l’alimentation était raisonnablement bon, avec une gamme de 8·56 à 9·06, établissant la perte de masse nette de 9 à 14. L’enlèvement de la pyrite du charbon était effectué par l’ion Fe³⁺ disponible dans l’inoculum, donnant lieu à l’ion Fe²⁺ comme produit et cet ion Fe²⁺ était davantage oxydé en ion Fe³⁺ par At. ferrooxidans. Cet ion Fe³⁺ produit par At. ferrooxidans continuait l’oxydation de la pyrite résiduelle dans le charbon jusqu’à ce que toute la pyrite soit complètement oxydée. On a trouvé qu’il était possible d’effectuer l’enlèvement biologique de la pyrite des trois charbons et d’augmenter l’échelle pour des études futures dans un bioréacteur en continu agité.     

锑金精矿矿浆电解阳极区选择性氧化浸出研究

研究了锑金精矿矿浆电解过程中阳极区硫化矿物选择性氧化分解热力学基础。结果表明,黄铁矿标准氧化分解电位较辉锑矿低,从热力学角度看,黄铁矿会被优先氧化分解;当溶液中加入Cl~-以后,辉锑矿和黄铁矿氧化分解电位都呈现下降趋势,其中辉锑矿下降更为迅速;在研究条件下,当Cl~-浓度大于2.05mol/L时,辉锑矿的分解电位小于黄铁矿,在热力学上使得辉锑矿优先选择性氧化分解成为可能。矿浆电解法处理锑金精矿实验中,锑的浸出率可超过98%,而铁的浸出率在8%以下,可实现锑的选择性浸出。     

Oxidation of ferrous sulfate in weakly acidic solution by gas bubbling

The oxidation of Fe²⁺ ion in aqueous solution in a pH region between 4.7 and 5.5 was studied. By supplying dilute NaOH solution from an automatic titrator, pH of the solution was maintained constant during the oxidation. The reaction is comprised of the sequential steps of the dissolution of gaseous oxygen and the oxidation of Fe²⁺ ion by dissolved oxygen. The latter reaction proceeds along two paths: homogeneous reaction in the solution (rate constant:k) and heterogeneous reaction on the surface of ferric hydroxide precipitate (rate constant:ks). The measured time variation of the concentrations of Fe²⁺ ion and dissolved oxygen was explained by simultaneous rate equations. Linear relationships were found between logk and pH and between logks and pH having slopes of 2 and unity, respectively. An activation energy of 103 kJ/mol was obtained fork. The overall rate of oxidation of Fe²⁺ ion was chemically controlled at pH lower than 5.0 and temperature lower than 298 K. On the other hand, it was controlled by both chemical reactions and the dissolution of oxygen at higher pH and temperature.     

Leaching of chalcopyrite with ferric ion. Part II: Effect of redox potential

This paper reports the effect of redox potential (or Fe³⁺/Fe²⁺ ratio) on chalcopyrite leaching. The relationship between redox potential and other variables (iron concentration and temperature) is also evaluated. Leaching tests were performed in stirred Erlenmeyer flasks with 0.5 g of pure chalcopyrite and 100 mL of a Fe³⁺/Fe²⁺ sulphate solution. The redox potential ranged between 300 and 600 mV Ag/AgCl for the solution at a pH 1.8, 180 rpm, with temperatures at 35 °C or 68 °C. The results show that although ferric ion is responsible for the oxidation of chalcopyrite, ferrous ion has an important role in that it controls precipitation and nucleation of jarosites, which ultimately causes passivation of this sulphide. Chalcopyrite dissolves through the formation of an intermediary product (covellite, CuS) that is later oxidized by ferric ion, releasing Cu²⁺ ions.     

Solvent extraction equilibria of copper and nickel with SME 529

Distribution equilibria in the extraction of copper and nickel from 1.0 mol/dm³ aqueous ammonium nitrate solution by anti-2-hydroxy-5-nonylacetophenone oxime, the active species of SME 529, in MSB 210 diluent were studied at 30°C. The extraction equilibrium constants for copper and nickel were determined to be 1.9 × 10¹ and 3.2 × 10⁵, respectively. The aqueous solubility of the oxime was also examined, resulting in a measurement of the partition coefficient of the monomeric oxime between the aqueous and organic phases, its dissociation constant in the aqueous phase and its dimerization constant in the organic phase as 2.2 × 10^?4, 0.53 nmol/dm³ and 31 dm³/mol, respectively. It was found that the extraction of copper is decreased by the addition of p-nonylphenol due to adduct formation. The equilibrium constant of the adduct formation between the oxime and p-nonylphenol was determined to be 6.6 dm³/mol. It was observed that nickel is extracted by p-nonylphenol.     

Electrowinning of Copper in the Presence of Anodic Depolarisers - A Review

Abstract

Alternative anodic reactions have been investigated to reduce the cell voltage and hence energy consumption in the electrowinning of copper. It is necessary to avoid oxygen evolution reaction at the anode, which requires a high potential of 2 V in order to reduce the cell voltage. An extensive literature review reveals that the cell voltage can be reduced by using various ionic couples, such as Fe²⁺/Fe³⁺, Cu²⁺/Cu¹⁺. Addition of cobalt, soluble sulfites and sulfur dioxide to the electrolyte modifies the anodic reaction. Examination of several electrode materials for anodic oxidation confirms that graphite is the most suitable material. Some fundamental studies on the anodic oxidation of sulfur dioxide have also been reviewed.     

Electrochemical Phenomena in MnO2-Fes2 Leaching in Dilute HCl. Part 3: Manganese Dissolution from Indian Ocean Nodules

Abstract

The present paper deals with the kinetics and mechanism of MnO₂ dissolution from sea bed manganese nodules in the presence of pyrite. Manganese (iv) was found to dissolve mostly through reduction by ferrous ions generated by the oxidation of pyrite by ferric ions which was considered to take place through two reactions, one producing S° and the other [SO₄^2?]. These two reactions were found to take place at a mole proportion of about 20% and 80%, respectively, but in terms of electron involvement the participation of the former is insignificant. The dissolution rates obtained from leaching studies were analysed based on the kinetic expressions derived previously and were found to confirm the theoretical basis. The kinetics and mechanism vary depending on whether or not sufficient acid is present. In the presence of sufficient acid the expression {[Fe³⁺]/(Rate)² = K ₃[Fe²⁺] + K ₄} is valid and in depleted acid conditions {rate = K ₆[H⁺][Fe²⁺])^1/2} holds good.

Résumé

Le présent document traite de la cinétique et du mécanisme de dissolution, en présence de pyrite, du MnO₂ de nodules de manganèse du fond de la mer. On a trouve que le manganèse (iv) se dissolvait en grande partie par réduction par des ions ferreux générés par l'oxydation de la pyrite par des ions ferriques. On considère que ceci se produit par l'intermédiaire de deux réactions. l'une produisant S° et l'autre, [SO₄^2?]. Ces deux réctions se produisent à des proportions, en mol, d'environ 20% et 80%, respectivement, mais en ce qui a trait à l'impliçation d'électron, la participation de la première est insignifiante. On a analysé les taux de dissolution obtenus des études de lessivage en se basant sur les expresions cinétiques dérivées auparavant, confirmant la base théorique. La cine[Faac]tique et Ie mécanisme varient dépendant qu'il y a ou non suffisamment d'acide présent. En présence de suffisamment d'acide, l'expression {[Fe³⁺]/(taux)² = K ₃[Fe²⁺] + K₄} est valide et, en conditions appauvries en acide, {taux = K ₆[H⁺][Fe²⁺]^1/2} tient.     

Studies on the effect of addition of silver ions on the direct oxidation of pyrite

The nature of the reaction between Ag⁺ and pyrite in 0.25 M H₂SO₄ solutions has been investigated in order to determine whether Ag⁺ can enhance the ferric sulfate leaching of this mineral. Analysis of reacted pyrite particles using scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and low-angle X-ray diffraction (XRD) indicates that elemental silver and elemental sulfur are the primary surface species formed by this interaction. Rest potential measurements of a pyrite electrode immersed in a solution containing 10⁻² M Ag⁺ are also consistent with what is expected for the deposition of metallic silver. Furthermore, the XRD data reveal that, at the most, only minor amounts of Ag₂S are being produced. The presence of Ag₂O has also been detected, but this is due to oxidation of silver after the experiment is complete and while the particles are being transferred for surface analysis. When 1 M ferric sulfate is contacted with pyrite which has been pretreated in a AgNO₃ solution, most of the silver immediately redissolves and does not redeposit while ferric ions are present. This indicates that the kinetics of the transfer reaction between Ag⁺ and pyrite is slower than the reaction between Fe³⁺ and pyrite and suggests that Ag⁺ does not likely enhance the ferric sulfate leaching.     

Toxicity of metal extraction and flotation chemicals to Sulfolobus metallicus and chalcopyrite bioleaching

The effect of chemicals used in preparation of mineral concentrates and subsequent extraction of metals to the thermophilic, acidophilic microorganism Sulfolobus metallicus has been tested. The chemicals tested included collectors and frothers employed during flotation of the ore to produce a mineral concentrate, solvent extraction reagents used to remove metals after leaching, and thiocyanate produced as a decomposition product during cyanidation for gold recovery. The effect of these chemicals to S. metallicus depends on the conditions and time frame that the experiments were carried out due to their mode of toxicity and stability in acid pH. The metal extraction chemical that had the least effect on bioleaching was potassium amyl xanthate that increased the leaching rate, possibly due to solubilization of sulfur that can form passivation layers on the surface of minerals. The frother Flotanol C-7 decreased the chalcopyrite leaching rate, despite having no effect on Fe²⁺ oxidation by S. metallicus resting cells. This is probably due to inhibition of oxygen transfer during bioleaching that had little effect on Fe²⁺ oxidation over 20 min. Solvent extraction chemicals inhibited both Fe²⁺ oxidation and bioleaching suggesting their mode of inhibition is due to Fe²⁺ oxidation. The results suggest that relevant concentrations of metal extraction and flotation chemicals can be toxic to chalcopyrite bioleaching by S. metallicus.     

Thermal decomposition and oxidation of bastnaesite concentrate in inert and oxidative atmosphere

To clearly elucidate the oxidative roasting behaviors of the bastnaesite, the thermal decomposition and oxidation of the bastnaesite concentrate in inert and oxidative atmosphere have been investigated in detail. Experimental data indicated that the initial decomposition temperature of the concentrate under N_2 atmosphere is 150 ℃ higher than that under O_2 atmosphere,most likely because the oxidation of the cerium induces the decomposition of the concentrate. For the roasted samples under N_2 atmosphere at500 ℃ and above,the oxidation efficiency of the cerium is 19.8%-26.8% because of the fact that rareearth fluorocarbonate is first decomposed to form rare-earth oxyfluoride and CO_2, and the cerium oxyfluoride is then partially oxidized by the CO_2 gas. The rest cerium in these samples can be further oxidized in air at room temperature, with the oxidation efficiency of the cerium gradually increasing to above 80% in 7 d. This can be attributed to the obvious changes in the inner morphology of the roasted samples under N_2 atmosphere at high temperatures, which largely induce the diffusion of the air and improves the oxidation activity of CeOF, and further induces the oxidation of CeOF by the air. XRD and XPS techniques were used to further verify the significant differences in the thermal decomposition behaviors of the bastnaesite concentrate under N_2 and O_2 atmosphere. Moreover, no oxidation of Pr~(3+) to Pr~(4+) in the roasted samples under both N_2 and O_2 atmosphere is observed. This gives an overall understanding of the oxidative roasting of the bastnaesite concentrate without additives.     

Reaction mechanism for the acid ferric sulfate leaching of chalcopyrite

The acid ferric sulfate leaching of chalcopyrite, CuFeS₂ + 4Fe⁺³ = Cu⁺² + 5Fe⁺² + 2S⁰ was studied using monosize particles in a well stirred reactor at ambient pressure and dilute solid phase concentration in order to obtain fundamental details of the reaction kinetics. The principal rate limiting step for this electrochemical reaction appears to be a transport process through the elemental sulfur reaction product. This conclusion has been reached in other investigations and is supported by data from this investigation in which the reaction rate was found to have an inverse second order dependence on the initial particle diameter. Furthermore, the reaction kinetics were found to be independent of Fe⁺³, Fe⁺², Cu⁺² and H₂SO₄ in the range of additions studied. The unique aspect of this particular research effort is that data analysis, using the Wagner theory of oxidation, suggests that the rate limiting process may be the transport of electrons through the elemental sulfur layer. Predicted reaction rates calculated from first principles using the physicochemical properties of the system (conductivity of elemental sulfur and the free energy change for the reaction) agree satisfactorily with experimentally determined rates. Further evidence which supports this analysis includes an experimental activation energy of 20 kcal/mol (83.7 kJ/mol) which is approximately the same as the apparent activation energy for the transfer of electrons through elemental sulfur, 23 kcal/ mol (96.3 kJ/mol) calculated from both conductivity and electron mobility measurements reported in the literature. formerly Metallurgy Graduate Student, University of Utah.     

Enhancement of chalcopyrite leaching by ferrous ions in acidic ferric sulfate solutions

The effects of ferrous ions on chalcopyrite oxidation with ferric ions in 0.1 mol dm⁻³ sulfuric acid solutions were investigated by leaching experiments at 303 K in nitrogen. With high cupric ion concentrations, the chalcopyrite oxidation was enhanced by high concentrations of ferrous ions and copper extraction was mainly controlled by the concentration ratio of ferrous to ferric ions or the redox potential of solutions. Ferrous ions, however, suppressed the chalcopyrite oxidation when cupric ion concentrations were low. A reaction model, which involves chalcopyrite reduction to intermediate Cu₂S by ferrous ions and oxidation of the Cu₂S by ferric ions, was proposed to interpret the results.     

The leaching of chalcopyrite with ferric sulfate

The leaching kinetics of natural chalcopyrite crystals with ferric sulfate was studied. The morphology of the leached chalcopyrite and the electrochemical properties of chalcopyrite electrodes also were investigated. The leaching of chalcopyrite showed parabolic-like kinetics initially and then showed linear kinetics. In the initial stage, a dense sulfur layer formed on the chalcopyrite surface. The growth of the layer caused it to peel from the surface, leaving a rough surface. In the linear stage, no thick sulfur layer was observed. In this investigation, chalcopyrite leaching in the linear stage was principally studied. The apparent activation energy for chalcopyrite leaching was found to range from 76.8 to 87.7 kJ mol⁻¹, and this suggests that the leaching of chalcopyrite is chemically controlled. The leaching rate of chalcopyrite increases with an increase in Fe(SO₄)_1.5 concentration up to 0.1 mol dm⁻³, but a further increase of the Fe(SO₄)_1.5 concentration has little effect on the leaching rate. The dependency of the mixed potential upon Fe(SO₄)_1.5 concentration was found to be 79 mV decade⁻¹ from 0.01 mol dm⁻³ to 1 mol dm⁻³ Fe(SO₄)_1.5. Both the leaching rate and the mixed potential decreased with an increased FeSO₄ concentration. The anodic current of Fe(II) oxidation on the chalcopyrite surface in a sulfate medium was larger than that in a chloride medium.     

难浸金精矿生物浸出体系的电位-pH图分析

电位-pH图是一种重要的热力学分析方法,能够直观地反映出浸出体系中的各种热力学平衡,有助于推断出物质发生化学反应的趋势,在难处理金精矿生物浸出体系中有重要指导作用。通过热力学计算,针对生物浸出环境绘制并分析了313 K温度下,pH=0~7.0,E=-1.2~1.2 V范围内适宜生物氧化黄铁矿-水系、毒砂-水系的电位-pH图。结果表明：在酸性体系下黄铁矿的稳定区域存在于0.336 V以下,毒砂则为0.133 V以下,毒砂的稳定性比黄铁矿的稳定性低,在较低的电位条件下便会被氧化溶解。     

Jarosite pseudomorph formation from arsenopyrite oxidation using Acidithiobacillus ferrooxidans

In this work, the oxidizing action of a native strain type A. ferrooxidans on a sulphide containing a predominance of arsenopyrite and pyrite has been evaluated. Incubation of the A. ferrooxidans strain in flasks containing 200 mL of T&K medium with the ore (particle size of 106 μm) at pulp density 8% (w/v) at 35 °C on a rotary shaker at 200 rpm resulted in preferential oxidation of the arsenopyrite and the mobilization of 88% of the arsenic in 25 days. Mineralogical characterization of the residue after biooxidation was carried out with FTIR, XRD and SEM/XEDS techniques. An in situ oxidation of the arsenopyrite is suggested on the basis of the frequent appearance of jarosite pseudomorph replacing arsenopyrite, in which the transformations Fe²⁺ → Fe³⁺, S^− 2 → S^+ 6 and As^− 1 → As^+ 3 → As^+ 5 occur for the most part without formation of soluble intermediates, resulting in a type of jarosite that typically contains high concentrations of arsenic (type A-jarosite). However, during pyrite oxidation, dissolution of the constituent Fe and S predominates, which is evidenced by corrosion of pyrite particles with formation of pits, generating a type of jarosite with high quantities of K (type B-jarosite). Lastly, a third type of jarosite (type C-jarosite) also precipitated forming a thin film that covered the grains of pyrite principally.     

Visualisation of pyrite leaching by selected thermophilic archaea: Nature of microorganism–ore interactions during bioleaching

In this study, pyrite (FeS₂) was leached by Acidianus brierleyi, Metallosphaera sedula and Sulfolobus metallicus during a 60 day experimental period. Leaching occurred over a redox potential range of 800 to 860 mV (S.H.E.) and in the presence of increasing Fe³⁺ levels. A modified ferrozine assay was developed to detect the increase of iron in solution as bioleaching of the ore progressed. For the first time, the interactions of these extreme thermophiles with the metal sulfide ore particles were extensively documented using SEM and TEM. As the pyrite degraded, there appeared to be a progression of deposited structures forming, ranging from sub-micron precipitates and disc-shaped structures on the ore's surface, which ultimately were similar for all leaching cultures. Furthermore, the residues resulting from the leaching of pyrite by M. sedula, the most active thermophile, were characterised using SEM/EDX, and appeared to be dominated by iron sulfate precipitates. The nature of the deposits formed, together with our other results, indicate that A. brierleyi, M. sedula and S. metallicus acted through the ‘contact’ and ‘non-contact’ sub-mechanisms of the indirect bioleaching mechanism for the dissolution of pyrite. The role of the bioleaching microorganisms is thus to maintain sufficient levels of Fe³⁺ and acid during pyrite leaching, for maximal mineral dissolution.     

The Oxidation of Sulphur Dioxide and the Formation of Sulphuric Acid in Situ at Atmospheric Pressure in the Leaching of a Uranium Ore

Abstract

The oxidation of SO₂ to form H₂SO₄ in situ, at atmospheric pressure and temperatures from 25 to 80°C, was examined by passing a mixture of SO₂ dioxide and air for 7 hrs through a reaction vessel containing quartz- or uranium-bearing solids moistened with H₂O to 85% solids. At the end of the contact period the solution was analyzed for free acid and other constituents of SO₂ and extraction of Uranium.

In tests with quartz at 80°C, the addition of Fe₂(SO₄)₃ or Fe₂O₃ increased the amount of SO₂ converted to H₂SO₄. E.g. without Fe₂(SO₄)₃ added the conversion obtained was 2% with 0.7 and 2.3 1b/ton quartz of Fe₂(SO₄)₃ the conversions were 18 and 24% respectively.

Tests were conducted on a mixture of flotation tailings, and a residue, which contained 24.3 per cent Fe⁺⁺⁺ as oxide, derived from the roasting of a sulphide concentrate at 500°C. The tailings and sulphide concentrate were obtained from the flotation of a uranium ore containing brannerite and about 9 per cent pyrite Roasting of the sulphide concentrate yielded "160 to 180 lb per ton of ore of sulphur dioxide of which 80,to, 100 lb was introduced into the conversion system over a 7-hour period. At 80°C, 40 per cent of the sulphuric dioxide introduced was converted to sulphuric acid which dissolved 93 per cent of the uranium in the mixturet of solids.