Abstract
Covellite is a secondary copper sulfide, and it is not abundant. There are few investigations on this mineral in spite of it being formed during the leaching of chalcocite or digenite; the other investigations on covellite are with the use of mineraloids, copper concentrates, and synthetic covellite. The present investigation applied the surface optimization methodology using a central composite face design to evaluate the effect of leaching time, chloride concentration, and sulfuric acid concentration on the level of copper extraction from covellite (84.3% of purity). Copper is dissolved from a sample of pure covellite without the application of temperature or pressure; the importance of its purity is that the behavior of the parameters is analyzed, isolating the impurities that affect leaching. The chloride came from NaCl, and it was effectuated in a size range from –150 to +106 μm. An ANOVA indicated that the leaching time and chloride concentration have the most significant influence, while the copper extraction was independent of sulfuric acid concentration. The experimental data were described by a highly representative quadratic model obtained by linear regression (R2 = 0.99).
Highlights
Covellite is not an abundant, but it may be found in many copper deposits as a supergenic mineral, usually as a coating in the sulfide enrichment zone
This agrees with the results of other research [24], which indicates that CuS oxidation to CuS2 is possible with any chloride concentration, but the oxidation of CuS2 is only possible with very high potential or high chloride concentrations [25]
The highest copper extraction rate was obtained with the highest concentrations of chloride, and the main findings of this investigation were: 1
Summary
Covellite is not an abundant, but it may be found in many copper deposits as a supergenic mineral, usually as a coating in the sulfide enrichment zone. The following reactions occur with the main secondary copper mineral, chalcocite, when the temperature is high (Equation (1)), and the sulfur is in the form of sulfate and not of elemental sulfur, as in natural conditions (Equations (2) and (3)) [5]: Cu2 S(s) + Fe2 (SO4 )3(aq) = Cu2+ (aq) + SO4 2− (aq) + CuS(s) + 2FeSO4(aq). The creation of synthetic covellite is from a stoichiometric mixture of high-purity copper and elemental sulfur, with the application of high temperature and vacuum sealing over long periods (approximately 3 days) for its formation. We leached pure covellite in a chloride medium with the incorporation of oxygen This was performed at ambient temperature and pressure to determine the relevance of the sulfuric acid and sodium chloride concentration, followed by the dissolution time. The data were used to make a statistical analysis through a representative quadratic model of copper extraction
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