| Chalcopyrite can be hydrothermally converted to copper-rich sulfides, covellite (CuS) and digenite (Cu{dollar}sb{lcub}1.8{rcub}{dollar}S), a defect structure of chalcocite, by controlled oxygen injection. Close control of oxygen injection, according to reaction stoichiometries, provides unique conditions of E{dollar}sb{lcub}rm h{rcub}{dollar} under which enrichment is favored. Enrichment occurs by the simultaneous containment of copper in the solid phase and rejection of iron (Fe{dollar}sp{lcub}++{rcub}){dollar} and sulfur (SO{dollar}sb4sp=){dollar} to the liquid phase.; The kinetic behavior of chalcopyrite enrichment by means of constant low oxygen injection was examined. The effects of oxygen feed rate, particle size, temperature, acid concentration and ferrous ion concentration on the conversion rate were determined. An electrochemical mechanism in which chalcopyrite first reacts to form covellite and secondly forms digenite is proposed. Chalcopyrite reacts anodically: (UNFORMATTED TABLE OR EQUATION FOLLOWS){dollar}{dollar}eqalign{lcub}&rm CuFeSsb2+4Hsb2O=CuS+Fesp{lcub}++{rcub}+SO4sp=+8Hsp++8esp-crcr &rm CuS+2Hsb2O={lcub}1over2{rcub}Cusb2S+{lcub}1over2{rcub}SO4sp=+4Hsp++3esp-crcr &rm CuFeSsb2+6Hsb2O={lcub}1over2{rcub}Cusb2S+Fesp{lcub}++{rcub}+{lcub}3over2{rcub}SO4sp=+ 12Hsp++11esp-cr{rcub}{dollar}{dollar}(TABLE/EQUATION ENDS)Similarly, rapid stoichiometrically controlled oxygen injection was carried out and shown to be kinetically more favorable than the case of slow continuous oxygen injection. In this case released copper reacts with chalcopyrite according to the enrichment reaction: {dollar}{dollar}rm 5CuFeSsb2+11Cusp{lcub}++{rcub}+8Hsb2O=8Cusb2S+5Fesp{lcub}++{rcub}+2SO4sp=+16Hsp+{dollar}{dollar}The rate is controlled by a mixed potential related to cathodic discharge reaction of oxygen and anodic interfacial enrichment reactions.; A rate equation, considering particle size, oxygen feed rate, temperature and reaction stoichiometry, is developed based on the proposed electrochemical model. Using the proposed rate equation, stoichiometric factors under various experimental conditions were determined. The stoichiometric factor did not vary appreciably with particle size and reaction temperature, but varied greatly with oxygen feed rate. The experimentally determined activation energy and the enthalpy of activation were 58.6 kJ/mole (14.0 kcal/mole) and 108.0 kJ/mole (25.8 kcal/mole), respectively. |
