The influence of pyrite pre-oxidation on gold recovery by cyanidation
ABSTRACT The influence of pyrite pre-oxidation in alkaline solutions on gold recovery by cyanidation from Twin Creek refractory gold ore in which pyrite was identified as the major sulfide mineral has been investigated with the aid of electrochemical measurements, leaching experiments, and direct analysis of reaction products for selected residues. It was found that gold recovery by cyanidation in bottle roll experiments mainly depended on the extent of pyrite pre-oxidation. The rate of pyrite oxidation in alkaline solutions measured by electrochemical measurements, including chronoamperometry and linear sweep voltammetry, increased with an increase in pH, potential, and temperature. All alkaline reagents used for the electrochemical measurements, NaOH, NH4OH, Na2CO3 and Ca(OH)2, showed a similar effect on pyrite oxidation kinetics. However, the results of alkaline pre-oxidation for pyrite of the Twin Creek refractory gold ore suggested that NaOH and Na2CO3/Ca(OH)2 were superior to Ca(OH)2. Without pre-oxidation, cyanide leachable gold was found to be only 20% which could be increased to 70% under appropriate pre-oxidation conditions. At the same time, cyanide consumption decreased from 2.5 kg/t ore to 1.5 kg/t ore.Selected residues after pre-oxidation and cyanidation were examined by X-ray diffraction. Backscattered electron images of pyrite particles in these residues were taken. The reaction products at the surface of pyrite particles were found to be iron-, silicon-, and calcium-bearing compounds with variable amounts of sulfur as determined by X-ray energy dispersion analysis. Additionally, some mineral fines, such as aluminum and/or potassium-bearing minerals, were found to be present at the partially oxidized pyrite surface.
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ABSTRACT: A detailed study on the relative importance of passivation phenomena and galvanic interactions during gold cyanidation was carried out. Mineral disc electrodes consisting of a sulfide-rich industrial ore and major sulfide components were prepared along with an Au electrode (gold/silver alloy) in use for gold leaching rate tests. These leaching tests that were conducted by hyphenating gold and mineral disc electrodes conjointly in one electrochemical cell or in two separate electrochemical cells objectified both passivation-induced setbacks as well as boosts by Au/mineral galvanic interactions on gold dissolution. To decipher the role of sulfide ores on gold cyanidation, a systematic study was performed by monitoring the leaching behavior of an Au disc electrode successively immersed in slurries of industrial ore and its major sulfide constituents, i.e., pyrite, sphalerite and chalcopyrite. The tested mineral constituents and ore exhibited an inhibiting effect on gold leaching, decreasing in the following order: chalcopyrite > sphalerite > industrial ore > pyrite. Pre-oxidation of the industrial sulfide ore prior to cyanidation improved the gold leaching rate. However, in spite of noticeable reductions in cyanide consumption, no beneficial effect of pre-oxidation on gold leaching was observed for the major sulfide (ore) constituents when tested separately. Although cooperating permanent galvanic interactions between gold and main constitutive minerals in the industrial ore prompted higher gold leaching rates, predictability of the latter from lab-controlled leach tests of the nearly pure constitutive sulfide minerals still remain premature.Hydrometallurgy. 01/2010;
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ABSTRACT: Despite the wealth of published data on the beneficial or detrimental effects of silver, lead, sulfide, and carbonaceous matter on the rate of gold cyanidation at an anode or by dissolved oxygen, the lack of comparative studies on relative effects has hampered rationalisation of the role of these activators or passivators of gold. In the present study, the published rate data per unit surface area of gold, silver, and gold–silver alloys based on electrochemical or chemical dissolution of rotating discs or foils of constant surface area in aerated cyanide solutions at ambient temperatures are analysed on the basis of the Levich equation. The current status of the reaction mechanism is also reviewed and updated on the basis of species distribution and potential–pH diagrams, stoichiometric factors, and interim chemical species of gold(I), silver(I), and lead(II). The anodic peak potentials of reported voltammograms closely follow the potential–pH lines of Au(I)/Au(0) and Pb(II)/Pb(0) couples. Despite the formation of stable complexes between lead(II), nitrate, and hydroxide ions, the total calculated soluble lead(II) in alkaline solutions of pH range 10–11 saturated with lead hydroxide is shown to beHydrometallurgy 01/2008; 90(1):46-73. · 2.17 Impact Factor
- Proceedings of XIIIth International Mineral Processing Symposium-IMPS 2012; 10/2012