Leaching of CuFeS₂ by aqueous FeCl₃, HCl, and NaCl: Effects of solution composition and limited oxidant

Abstract

Batch leaching experiments were performed in which the initial amounts of chalcopyrite and ferric chloride were selected to ensure that the oxidant was significantly depleted over the course of an experiment. Solution samples were analyzed for Cu(II) and Fe(III) by visible spectrophotometry and for total copper and total iron by atomic absorption, making it possible to measure changes in the solution component concentrations as leaching progressed. For selected samples, the solution potential was also measured. In all experiments, the Cu(II) concentration passed through a maximum and, simultaneously, the Cu(I) concentration increased very sharply. An acceleration in the total rate of leaching was normally observed at the same time. Early in a leach, the solution potential was too high for the reduction of Cu(II) to Cu(I) to take place at the time of the increase in the overall leaching rate, however, the solution potential dropped sharply during a span of a few hours, reaching a value low enough that reduction of cupric ion became possible. The amount of Cu(I) present at the completion of a leach was dependent on the total chloride concentration of the system. The highest Cu(I)/Cu ratios were observed in systems with the highest chloride concentrations. The ultimate extent of CuFeS₂ leaching was dependent on the initial FeCl₃ and total chloride concentrations; the FeCl₃ was virtually completely consumed and the total chloride concentration controlled the extent to which Cu(II) was reduced by reaction with chalcopyrite.