The interactions of radioactive lead with sulphide minerals

Highlights: • ²¹⁰Pb was hypothesised to associate with sulphide mineral surfaces in flotation. • Pb²⁺ interacted with pyrite, chalcocite and chalcopyrite surfaces, forming different lead species. • PbS was detected on all mineral surfaces and formed via Pb²⁺ adsorption to sulphur-rich sites. • Pb(OH)₂ was detected on all surfaces and formed via Pb²⁺ adsorption at hydroxide-rich sites. • PbO was detected on chalcocite surface only and formed via Pb²⁺ adsorption to Cu₂O sites. Radionuclides, specifically ²¹⁰Pb, 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 ²¹⁰Pb forms a stable PbS species on the copper sulphide surfaces allowing ²¹⁰Pb 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 ²¹⁰Pb. 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 ²¹⁰Pb recovery to concentrates.