Quantitative determination of phases present in oxidised chalcocite

Abstract

A sample of chalcocite (Cu₂S) of particle size 45–75 μm was heated in air at 10°C min⁻¹ in a simultaneous TG-DTA apparatus. The phase compositions of the products at various temperatures were quantitatively determined by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and wet chemical analyses. Copper(II) sulfate, of amount 1.7% by mass, was observed at 435°C and increased rapidly in concentration to 56% at 570°C. From 570–670°C, there was a rapid decrease in CuSO₄ content to 9.8% as the phase converted to CuSO₄·CuO, with the CuSO₄ not being detected at 775°C. From 435–570°C, Cu₂O formed, but at a rather slower rate, reaching 47% at 570°C. The Cu₂O level then decreased to 38% over the range 570–670°C. CuSO₄·CuO was first detected at 570°C by FTIR, although it was not detected by XRD at this temperature. The content of this species reached 41% at 670°C, decreased to 24% at 775°C, and was not detected at 840°C. CuO first appeared at 670°C and rose steadily in concentration until at 840°C it was the only compound present.