A THERMOANALYTICAL STUDY OF THE OXIDATION OF CHALCOCITE

A sample of chalcocite of particle size 45-75 mum has been oxidised in a TG-DTA apparatus at a heating rate of 10 deg.min-1 and the products at various temperatures characterised by XRD, SEM, FTIR and EPMA. Thi s has enabled the events in the TG-DTA record to be assigned to specif ic chemical reactions, as well as the development of a full reaction s cheme for the oxidation of chalcocite. Only minor reactions occurred u p to 430-degrees-C, but above this temperature there was significant o xidation which resulted in an exotherm and mass gain. These events wer e due primarily to the oxidation of sulfide to copper(I) oxide, and th e formation of copper(II) sulfate. The reaction then slowed, but melti ng commenced at 490-degrees-C which permitted further oxidation to tak e place with the appearance of a second exotherm and mass gain. By 570 -degrees-C, sulfide oxidation was complete, but solid-solid reactions took place between Cu2O and CuSO4 to produce CuO.CuSO4. Some conversio n of Cu2O had occurred. By 775-degrees-C, CuO and CuO.CuSO4 were the o nly phases detected. Above this temperature the latter phase was unsta ble and decomposed to the end product CuO.