The kinetics of the dissolution of chrysocolla in acid solutions

Abstract

The dissolution of liberated chrysocolla particles in dilute (0.033 to 0.15 mol L−1) sulfuric acid solutions has been shown to be relatively rapid and the kinetics of dissolution are consistent with rate-determining diffusion of acid through the silica layer that is formed around the particles from which the copper has been dissolved. The rate is inversely proportional to the square of the particle size and increases linearly with increasing acidity. The effect of the addition of chloride ions on the rate is negligible at concentrations below 70 g/L chloride. Addition of sulphate ions results in reduced rates of dissolution due to complexation of the proton by sulphate ions. The effect of temperature is relatively small as expected for a process for which the rate is controlled by diffusion.The rate of dissolution in dilute acid is slower than malachite but faster than tenorite under the same conditions. These results suggest that heap leaching of chrysocolla in dilute acid may be slow relative to malachite but should present no chemical problems and that there is no advantage to be gained from the addition of chloride ions. High sulphate concentrations (100 g/L) in the raffinate solution to the heap could reduce the rate by up to one-half.