A cross scale investigation of galena oxidation and controls on mobilization of lead in mine waste rock

Highlights: • Cross-scale techniques are integrated to investigate galena oxidation. • Synchrotron-based measurements indicate the formation of covellite on the galena surface. • Lead released by galena oxidation accumulates as cerussite and shannonite in the neutral-pH environment. • Secondary covellite occurs intergrown with Pb-bearing carbonates on the galena surface. • Increasing effluent Pb concentrations are likely over the long term in the absence of remedial actions. Galena and Pb-bearing secondary phases are the main sources of Pb in the terrestrial environment. Oxidative dissolution of galena releases aqueous Pb and SO₄ to the surficial environment and commonly causes the formation of anglesite (in acidic environments) or cerussite (in alkaline environments). However, conditions prevalent in weathering environments are diverse and different reaction mechanisms reflect this variability at various scales. Here we applied complementary techniques across a range of scales, from nanometers to 10 s of meters, to study the oxidation of galena and accumulation of secondary phases that influence the release and mobilization of Pb within a sulfide-bearing waste-rock pile. Within the neutral-pH pore-water environment, the oxidation of galena releases Pb ions resulting in the formation of secondary Pb-bearing carbonate precipitates. Cerussite is the dominant phase and shannonite is a possible minor phase. Dissolved Cu from the pore water reacts at the surface of galena, forming covellite at the interface. Nanometer scale characterization suggests that secondary covellite is intergrown with secondary Pb-bearing carbonates at the interface. A small amount of the S derived from galena is sequestered with the secondary covellite, but the majority of the S is oxidized to sulfate and released to the pore water.