Estimation of Rh, Ru, and Ir leaching kinetics during the sulfuric acid pressure leaching of Ni–Cu matte as a function of temperature, pressure, and acid concentration

In order to develop an improved understanding of the leaching behaviour of base metals and platinum group metals in a high pressure sulfuric acid leaching system, bench scale batch tests were performed to evaluate the effects of temperature, pressure, acid concentration, and solid-to-liquid ratio on the system. The precipitation and leaching kinetics of the other precious metals (OPMs: rhodium, ruthenium, and iridium) were influenced primarily by the leaching temperature, while the copper leaching kinetics were mostly dependent on the initial acid concentration. ons describing the leaching behaviour were proposed based on the experimentally determined leaching kinetics data. Cationic exchange reactions between digenite and dissolved OPMs and between polydymite and dissolved OPMs resulted in OPM precipitation during the initial leaching stages. Copper leaching reactions preferentially consumed the available oxygen during the initial leaching stages. The experimental data were used to determine the rate constants of the reactions describing the leaching behaviour. This was done by means of the method of least squares, considering the differences between the predicted concentrations and the concentrations measured over time at different operating conditions. The dissolution rates of the OPM compounds increased in the order: oxides < alloys < sulfides.