Lead (Pb) sorption and co-precipitation on natural sulfide, sulfate and oxide minerals under environmental conditions

Even low levels of lead (Pb) contamination result in significant disruption to the surrounding ecology as Pb accumulates in soils and water and can be taken up by plants, which are then consumed by higher order animals. Understanding how Pb partitions between solids and the aqueous phase underpins prediction of bioavailability and locales of high toxicity, and the development of effective treatment options. This paper aims to unify our empirical understanding of the interaction between Pb_(aq) and various common minerals associated with many large sulfide ore-bodies mined for their base- and precious metal contents, by measuring the sorption of Pb onto hematite (Fe₂O₃), pyrite (FeS₂), chalcopyrite (CuFeS₂), bornite (Cu₅FeS₄) and barite (BaSO₄) as a function of solution pH and Pb_(aq) concentration. In general, all minerals displayed a linear relation on a log–log plot of sorbed portion versus Pb concentration in the coexisting solution (Freundlich isotherm) over a wide range of Pb concentrations at pH 6. Hematite had two different domains (dual Freundlich behaviour), with Pb_(aq) showing higher affinity for sorption at low Pb_(aq) concentrations compared to high Pb_(aq) concentrations. For the sulfide minerals (pyrite, chalcopyrite, bornite), Pb sorption/precipitation on the oxidised surface is favoured at low pH, while Pb sorption to Fe(oxyhydr)oxide and/or co-precipitation as anglesite is favoured at high pH. Isotherm modelling highlights the dual roles of Pb_(aq) concentration and pH in controlling Pb scavenging in these natural minerals, and it is important to consider these parameters when predicting the Pb-geochemical cycle and its dynamic uptake in natural and engineered systems.