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.
"This improvement could be attributed to the amelioration of the passivation effect of sulphide ion. Previous studies (Lia et al., 2006; Li et al., 2009) have confirmed the benefits of pre-oxidation/aeration on subsequent cyanide leaching of gold ores. Sceresini (2005) also reported that the addition of lead nitrate improved the extraction of gold from a copper bearing sulphide ore presumably due to the alleviation of sulphide effect. "
"At the same time, pyrite becomes more cathodic and the consumption of electrons on its surface through cathodic reactions, such as the reduction of oxygen producing hydroxyl ions, is enhanced. Collector species might not adsorb on such a surface due to the coverage of mineral with hydrophilic hdroxy-species (Li et al., 2006; Pecina-Treviño et al., 2003; Rao and Finch, 1988; Sohn and Wadsworth, 1979). "
[Show abstract][Hide abstract] ABSTRACT: Consumption of base metals has been increasing continuously in parallel with
the technological improvements over the world. This demand has resulted in the need to
enhance processing of complex sulfide ores, which are the primary sources of base metals.
Complex sulfide ores are concentrated mainly through flotation. Sulfide minerals are semiconductors,
and pyrite is the major gangue mineral associated with these ores. Main interest in
the processing of complex sulfide ores has focused on the rejection of pyrite and selectivity
problem that arises owing to the similar electrochemical behavior of pyrite to the other sulfide
minerals in a complex ore. Vast number of research has been conducted on pyrite flotation,
producing significant data on this particular matter. This review aims to gather these data with
an attempt to evaluate pyrite flotation as a whole picture. In this respect, roles of different
flotation agents, pH and electrochemical conditions on the hydrophobicity and floatability of
pyrite were discussed.
XIIth INTERNATIONAL MINERAL PROCESSING SYMPOSIUM 2010; 10/2010
[Show abstract][Hide abstract] ABSTRACT: Characterization of a pyritous mineral from a mine in the state of Sonora, Mexico, in conjunction with preliminary experimentation for the processes of simultaneous pressure oxidation and cyanide leaching was realized, modifying pressure, temperature, cyanide concentration and particle size. The results of the study and preliminary experimental tests of the simultaneous processes are shown.
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