Abstract

Molybdenite flotation concentrate was leached with sodium dichromate-sulfuric acid solutions in order to remove the copper sulfide impurities. The experimental results indicated that the temperature has a large influence on the copper dissolution. The concentration of dichromate has also a pronounced effect for concentrations under 0.10 M, while sulfuric acid concentration over the stoichiometric value has a deleterious effect on the copper dissolution. The purification of molybdenite concentrates by this method is feasible, and the best results were obtained by leaching the concentrate with the stoichiometric concentration of H2SO4 and 0.12 M Na2Cr2O7 solution for 90 min at 100°C. Under these conditions, about 95% of the copper was dissolved with little dissolution of molybdenum. The kinetic study showed that the dissolution of copper from the concentrate is well represented by a shrinking core model controlled by diffusion through a porous layer, 1/3 ln(1 - ?) - [1 - (1 - ?)-1/3] = kt. The apparent activation energy obtained was 40 kJ/mol for the temperature range 50 to 100°C. © 1998 Elsevier Science B.V.