Modelling copper mobilisation from low-grade ore controlled by mineral surface reactions

Abstract

Many metals of economic value are commonly recovered from low grade ores through heap leaching at mine sites. The recovery of metals in heaps is often limited for multiple reasons including mineral overgrowth of targeted minerals resulting in suboptimal mineral dissolution rates. Chalcopyrite is a major copper iron sulphide mineral found in copper sulfide ores and its dissolution is controlled by multiple dissolution reaction mechanisms and potential mineral overgrowth. Traditional continuum scale reactive-transport models including those applied to simulate heap leaching do not account for local, mineral surface-controlled processes which may have implications for large-systems such as copper recovery in heaps. A new finite element, multicomponent reactive-transport model was developed and enabled the simulation of concurrent reactions at the discrete chalcopyrite surface and its surrounding gangue mineral and the fluid phase. The model predicts the rate of chalcopyrite dissolution controlled by different reaction mechanisms (proton- and ferric-iron promoted) as well as the rate of secondary mineral formation (jarosite) at the mineral surface. The latter may increasingly inhibit copper mobilisation over time through surface passivation. The onset and growth of the surface passivation layer is largely controlled by the surrounding fluid composition and ion transport through the gangue mineral. The reduction in porosity of the surface passivation layer leads to the breakdown of ionic transport to the chalcopyrite surface and associated copper mobilisation. Maximum copper recovery is achieved by high ferric iron concentrations and low pH and by preventing the formation of a passivation layer by keeping the sulphate concentration low.