Measurements of isotope ratios of heavy elements including Cr, Cu, Fe, Ni, Pb and Zn can provide useful insights into the mechanisms controlling the release, transport and attenuation of dissolved constituents in mine wastes and remediation systems. Laboratory-based studies linking the speciation of dissolved elements and the composition and structure of secondary phases with changes in metal isotope ratios can complement field investigations. A series of synchrotron-based flow-through cell experiments was conducted to assess the changes in isotope ratios of Cr, Cu, Ni, Se and Zn associated with reaction mechanisms affecting the concentrations of dissolved elements at sites impacted by mine waste (mill tailings and waste rock) disposal and in passive remediation systems (e.g., permeable reactive barriers). Laboratory batch experiments focused on changes in Zn isotope ratios associated with precipitation of Zn hydroxide, carbonate, phosphate and sulfide indicate distinct variations in isotope ratios associated with variations in the Zn-bearing phase precipitated. Flow-through cell experiments conducted under sulfate reducing conditions show isotope fractionation that is consistent with observations from the laboratory batch experiments. Comparison of the experimental results to isotope ratio measurements derived from well-instrumented field installations can provide additional information for the interpretation of field observations. Field measurements show modest changes in Zn isotope ratios (0.25 ‰) were observed to correspond to declines in dissolved Zn concentration from 25 mg/L to 5 mg/L which were attributed to Zn adsorption onto tailings solids. At the same location, a sharp decline in dissolved Cu concentrations from approximately 600 mg/L to &lt; 10 mg/L and a corresponding change in the Cu isotope ratio (15‰ for Cu) accompanied Cu removal through formation of covellite.  Incorporating non-traditional isotope fractionation in reactive transport modelling provides an additional constraint on simulations, which can be used to distinguish reaction mechanisms and provide improved estimates of solute concentrations.

Application of non-traditional isotope measurements to studies of mine-wastes and remediation systems

2019 Spring National Meeting

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