Decomposition of copper concentrates at high-temperatures: An efficient method to remove volatile impurities

The thermal decomposition of three synthetic copper sulfides (chalcocite (Cu2S), chalcopyrite (CuFeS2), and enargite (Cu3AsS4)) and two commercial copper concentrates has been studied on a thermobalance (T = 1173–1773 K) and an imaging furnace (T ≈ 1914 K) in inert atmospheres. It is demonstrated that the absence of oxygen, in combination with high decomposition temperatures furthers the removal of heavy metal impurities by volatilization. Elemental analyses on residues of treated concentrates showed that removal of volatile impurities occurs in three distinct temperature ranges: Already below temperatures of 1173 K arsenic and bismuth are removed. Evaporation of cadmium and tin requires temperatures below 1673 K, while substantial evaporation of Pb and Zn only occurs at temperatures between 1673 and 1773 K. At 1773 K the removal of these elements exceeds 95%. Thermal treatment at even higher temperatures in an imaging furnace and repeated grinding of the sample resulted in a removal of between 90% and 99% of the initial amounts of arsenic, zinc, and lead within 90 s. The strong effect of grinding indicates that the elimination of volatile elements is hindered by the mass transfer from the interior of the melt to the gas phase. Furthermore, it was demonstrated that even though a slag-like phase is produced, heavy metal impurities are efficiently removed by thermal decomposition at high-temperatures.