A study of recovery of copper and cobalt from copper–cobalt oxide ores by ammonium salt roasting

Copper and cobalt recovery from a copper–cobalt ore of Democratic Republic of Congo (DRC) by ammonium chloride roasting is studied. The effects of roasting temperature, roasting time, and the dosage of ammonium chloride on the leaching rate of copper and cobalt are investigated. The results show 90% copper and 95% cobalt recovery under the optimal experimental conditions of average particle diameter 0.10 mm and 1:2 ammonium chloride to ore mass ratio at a roasting temperature of 300 °C for 3 h. After adjusting the pH of the leaching solution to 7 by ammonia addition, the copper and cobalt in the solution were precipitated by ammonium bicarbonate at 60 °C for 40 min. Ammonium chloride crystals obtained after absorbing the exhaust gas and filtration of the scrub liquor could be reused for the roasting process. With X-ray diffraction analysis on the calcined ore at different temperatures, the roasting mechanism of copper–cobalt oxide ores with ammonium chloride was investigated. Co(NH3)6CuCl5 was found to be the main intermediate compound formed at roasting temperatures below 320 °C, above which it was further decomposed to CoCl2 and CuCl2.