Lead adsorption on copper sulphides and the relevance to its contamination in copper concentrates

Abstract

Certain complex copper sulphide ores contain trace levels of radioactive elements, most of which can be separated from the copper sulphide minerals during flotation. However, the flotation process is less effective at removing some of these radionuclides, namely Pb-210. It is hypothesised that Pb-210 is interacting with copper sulphides and this interaction is contributing to flotation rejection inefficiency. Throughout this study, regular lead is used to simulate Pb-210. Cryogenic X-ray Photoelectron Spectrometry (Cryo-XPS) has been used to confirm an interaction between lead and copper sulphide minerals in which lead forms as a lead sulphide-like compound on the surface of copper sulphide minerals. Lead interacts with copper sulphide mineral surfaces via two mechanisms: chemically adsorbing to sulphur to form lead sulphide and lead sulphite species, and precipitating on the surface as various lead oxides species. The ratio of lead-sulphur species to lead-oxygen species on the copper sulphide surfaces is increased by regrinding due to the lead-sulphur species being more strongly associated with the mineral surfaces. Lead remains on the mineral surfaces during flotation and is carried to copper concentrates during cleaner flotation.