A sample of chalcocite of particle size 45–75 μm, 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. This has enabled the events in the TG-DTA
record to be assigned to specific chemical reactions, as well as the development of a full reaction scheme for the oxidation
Only minor reactions occurred up to 430°C, but above this temperature there was significant oxidation which resulted in an
exotherm and mass gain. These events were due primarily to the oxidation of sulfide to copper(I) oxide, and the formation
of copper(II) sulfate. The reaction then slowed, but melting commenced at 490°C which permitted further oxidation to take
place with the appearance of a second exotherm and mass gain. By 570°C, sulfide oxidation was complete, but solid-solid reactions
took place between Cu2O and CuSO4 to produce CuO·CuSO4. Some conversion of Cu2O had occurred. By 775°C, CuO and CuO·CuSO4 were the only phases detected. Above this temperature the latter phase was unstable and decomposed to the end product CuO.