Analysis and visualization of enargite and tennantite roasting using Cu-As-S-O system predominance volume diagrams

Abstract The roasting of enargite (Cu 3 AsS 4 ) in the temperature range 673 K (400 °C) to 900 K (673 °C) has been considered in the light of three-dimensional predominance volume diagrams (PVDs). Condensed phases considered were Cu, Cu 3 As, Cu 2 O, Cu 2 S, CuO, CuS, CuSO 4 , CuO·CuSO 4 , Cu 3 AsO 4 , Cu 3 As 2 O 8 , Cu 3 AsS 4 , Cu 6 As 4 S 9 , and Cu 12 As 4 S 13 . Gases considered were As 4 , As 4 O 6 , AsS, As 4 S 4 , O 2 , S 2 , SO 2 , and SO 3 . There are four line segments associated with each of the nine invariant points while each corner has three. The PVD at 900 K shows the gas composition during vacuum decomposition of tennantite with selected O 2 infiltration. Calculations show that increasing the O/Tennantite reacted ratio in the system leads to the formation of Cu 3 As 2 O 8 at 900 K and CuSO 4 at 673 K. Roasting experiments at 673 K showed that enargite transformed into tennantite (Cu 12 As 4 S 13 ) in the absence of oxygen; whereas, in the presence of oxygen it transformed into CuSO 4 and CuO·CuSO 4 . Enargite does not appear to transform directly into CuSO 4 , but follows a path that includes Cu 2 S or CuS . Sulfate formation is favored over oxide at lower roasting temperatures.