Mechanochemical Processing of enargite (Cu₃AsS₄)

A commercial enargite (Cu3AsS4) concentrate was mechanically milled in inert and oxidising atmospheres for up to 50 h. No substantial effect was observed in either an inert atmosphere or in air other than a broadening and weakening of the diffraction peaks. Milling in oxygen was dramatic with significant reaction evident even after 1 h. The products were As2O3 and CuSO45H2O, both of which are readily soluble; a small amount of SO2 was also formed. Dissolution in acid left CuS as the major phase; this phase was thermodynamically predicted to be a minor phase during the oxidation process and appeared to be
stable for long periods under milling. Milling for 1 h at 100 C resulted in the same products but showed a greater extent of oxidation. The small fraction of tennantite in the sample was comparatively resistant to oxidation.