Predominance Area Diagrams Bounding the Cu-As-S-O System’s 3D Predominance Diagram at 900 K (627 °C)

Abstract

The two-dimensional predominance area (Kellogg) diagram (PAD) surfaces bounding the three-dimensional Cu-As-S-O system were constructed at 900 K. The computations employed gases As₄O_6(g), O_2(g), and SO_2(g) as the independent coordinate species to generate diagrams of As₄O_6(g) − O_2(g),O_2(g) − SO_2(g), and As₄O_6(g) − SO_2(g), while the third gas (As₄O₆, O₂, or SO₂) was fixed. The results indicate that there is no shared boundary between enargite (Cu₃AsS₄) and copper sulfate (CuSO₄); however, at ${\mathrm{P}}_{{\mathrm{O}}_2}<{10}^{-6}$atm, ${\mathrm{P}}_{{\mathrm{As}}_4{\mathrm{O}}_6}<{10}^{-10}$ atm, and ${\mathrm{P}}_{{\mathrm{SO}}_2}>{10}^{-4}$ atm, CuSO₄ is the stable phase at 900 K. The chemical driving force for oxidation of intermediate phases between enargite and copper sulfate is substantial except for basic sulfate (CuO · CuSO₄).