Thermal removal of arsenic from copper concentrates: Three-dimensional isothermal predominance diagrams for the Cu-As-S-O system

Abstract The three-dimensional predominance volume diagrams (PVDs) for the system Cu-As-S-O were constructed at 900 K using P A s 4 O 6 g , P O 2 g , a n d P S O 2 g as independent coordinates. The constant total pressure surface was used to identify the equilibrium phases that are stable at 0.25 atm total pressure. The isobaric surface superimposed on the predominance diagram provides useful insights into the roasting of complex copper sulfosalts such as enargite ( C u 3 A s S 4 ) and tennantite ( C u 12 A s 4 S 13 ). There are nine interior invariant points each with four associated condensed phases at 900 K. The expanded diagrams showing the stability volumes of each individual phase are presented. According to the PVD for the Cu-As-S-O system, the transformation of enargite to copper sulfate follows the C u 3 A s S 4 → C u S → C u S O 4 or C u 3 A s S 4 → C u 2 S → C u S → C u S O 4 sequence when the pressure of A s 4 O 6 g is extremely low. At high A s 4 O 6 g pressures however, enargite can directly transform to copper sulfate.