Investigating the behaviour of PGEs during first-stage leaching of a Ni-Fe-Cu-S converter matte

Abstract

In a first-stage atmospheric leach in a Sherritt Ni-Cu matte leach process, a Ni-Cu-Fe-S Peirce-Smith converter matte is contacted with recycled aqueous copper sulphate/sulphuric acid solution (spent solution) with the purpose of dissolving nickel, while simultaneously removing copper (via metathesis and cementation reactions) from solution. While the iron content has been found to have a significant impact on the first-stage leach, a previously expected relationship between copper and PGM behaviour has not been established clearly. For this study, a converter matte consisting mainly of heazlewoodite (Ni3S2), chalcocite (Cu2S), and awaruite (Ni3Fe) was leached in a laboratory-scale batch reactor. The temperature, acid, and copper concentration under both oxidative and non-oxidative conditions were varied, while the copper, iron, and PGEs were tracked and the pH and Eh measured. Palladium was generally found to be closely related to the behaviour of copper, while platinum did not leach. The other platinum group metals such as iridium and rhodium were found to precipitate only with accelerated precipitation being observed during Fe precipitation reactions.