2 research outputs found
A cross scale investigation of galena oxidation and controls on mobilization of lead in mine waste rock.
Abstract 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
Evaluating zinc isotope fractionation under sulfate reducing conditions using a flow-through cell and in situ XAS analysis
A flow-through cell experiment was conducted to evaluate Zn isotope
fractionation during ZnS precipitation under microbially-mediated
sulfate-reducing conditions. Synthetic groundwater containing 0.90 mM Zn
was pumped through a cell containing creek sediment that was
biostimulated to promote sulfate reducing conditions. Real-time, in situ
X-ray absorption spectroscopy (XAS) was applied at the Zn K-edge to
collect spectra via a Kapton (R) window in the front of the cell over
the course of the experiment. Aqueous effluent samples were collected
and analysed to determine concentrations of anions and cations, and Zn
isotope ratios. The flow rate was increased step-wise during the
experiment to modify the residence time and produce changes in the
extent of sulfate reduction, which in turn controlled the extent of ZnS
precipitation. Greater enrichment in the heavier isotope in the aqueous
phase relative to the input solution was associated with more extensive
Zn removal. A Rayleigh curve was fit to the isotope data, where epsilon=
-0.27 +/- 0.06% ( 2 sigma). Evaluation of Zn isotope fractionation under
controlled flow conditions is critical to improve the efficacy of this
powerful analytical technique when applied to natural systems or
remediation projects in the field