Effect of carbon black on chalcopyrite leaching in sulfuric acid media at 50 °C

Leaching experiments were performed in Erlenmeyer flasks containing sulfuric medium (200 mL) agitated on a magnetic stirrer at 50 °C. The addition of carbon black enhanced the kinetics of chalcopyrite leaching. The extraction yield of copper was 90% in 94 h in the presence of carbon black, whereas it was 28% in the absence of carbon black. The acceleration of chalcopyrite dissolution did not occur without contact between chalcopyrite and carbon black, suggesting that galvanic interaction between the two materials is related to the improvement of the leaching rate. In the presence of carbon black, the [Fe(III)]/[Fe(II)] ratio in the leaching solution decreased to below 0.1 in 1 h, whereas it was over 0.1 without carbon black. The redox potential fell to below 600 mV vs. SHE with a decrease in the [Fe(III)]/[Fe(II)] ratio, and the leaching rate of chalcopyrite increased markedly. It remained at nearly 560-570 mV during the chalcopyrite dissolution. The enhanced kinetics of chalcopyrite leaching could be attributed to dissolution reactions at the low redox potential in addition to the galvanic interaction between chalcopyrite and carbon black. The effects of several variables such as pH, dosage of carbon black, and initial concentrations of Fe(II), Fe(III), and Cu(II) on the kinetics of chalcopyrite leaching were examined.