Reaction pathway and kinetics of the thermal decomposition of synthetic brochantite

The reaction pathway of the thermal decomposition of synthetic brochantite, Cu₄(OH)₆SO₄, to copper(II) oxide was investigated through the detailed kinetic characterization of the thermal dehydration and desulferation processes. The dehydration process was characterized by dividing into two overlapped kinetic processes with a possible formation of an intermediate compound, Cu₄O(OH)₄SO₄. The dehydrated sample, Cu₄O₃SO₄, was found first to be amorphous by means of XRD, followed by the crystallization to a mixture of CuO and CuO-CuSO₄ at around 776 K. The specific surface area and the crystallization behaviour of the amorphous dehydrated compound depend largely on the dehydration conditions. The thermal desulferation process is influenced by the gross diffusion of the gaseous product SO₃, which is governed by the advancement of the overall reaction interface from the top surface of the sample particle assemblage to the bottom.