The interactions of radioactive lead with sulphide minerals

Radionuclides, specifically Pb-210, can be recovered to copper concentrates potentially by associating with copper sulphide surfaces. This presents regulatory and health issues around radionuclide activity in concentrates. It is hypothesised that Pb-210 forms a stable PbS species on the copper sulphide surfaces allowing Pb-210 to be carried through the flotation process. It is the presence of such a species that this paper seeks to confirm. The minerals examined in this study are chalcocite (Cu2S), chalcopyrite (CuFeS2) and pyrite (FeS2) with lead nitrate providing Pb2+ to simulate Pb-210. Thermodynamic modelling and Cyclic Voltammetry studies indicate that PbS does form on the mineral surfaces with Cryogenic X-ray Photoelectron Spectroscopy confirming its presence. The mechanism of PbS formation is via the adsorption of Pb2+ to sulphur-rich regions on the mineral surfaces and subsequent reaction to form PbS. Various oxygen-associated lead species were also detected, forming via the interaction of Pb2+ with mineral oxidation products. Total lead on the mineral surfaces was 9.69 at%, 19.62 at% and 12.62 at% for pyrite, chalcocite and chalcopyrite, respectively. The ratio of lead-sulphur species to lead oxygen species was 0.27, 0.84 and 1.00 for pyrite, chalcocite and chalcopyrite, respectively. Under flotation conditions, PbS is a stable species, meaning that it likely remains on mineral surfaces throughout the flotation process, facilitating Pb-210 recovery to concentrates.

Automated summary

The study demonstrates that stable lead sulphide species can form on copper sulphide surfaces, aiding in the recovery of Pb-210 to copper concentrates. Thermodynamic modelling and experimental studies provide evidence for this phenomenon.