Evaluation of zinc, cadmium and lead isotope fractionation during smelting and refining

To evaluate metallurgical processing as a source of Zn and Cd isotopic fractionation and to potentially trace their distribution in the environment, high-precision MC-ICP-MS Zn, Cd and Pb isotope ratio measurements were made for samples from the integrated Zn–Pb smelting and refining complex in Trail, B.C., Canada. Significant fractionation of Zn and Cd isotopes during processing of ZnS and PbS ore concentrates is demonstrated by the total variation in δ66/64Zn and δ114/110Cd values of 0.42‰ and 1.04‰, respectively, among all smelter samples.No significant difference is observed between the isotopic compositions of the Zn ore concentrates (δ66/64Zn = 0.09 to 0.17‰; δ114/110Cd = − 0.13 to 0.18‰) and the roasting product, calcine (δ66/64Zn = 0.17‰; δ114/110Cd = 0.05‰), due to ∼ 100% recovery from roasting. The overall Zn recovery from metallurgical processing is ∼ 98%, thus the refined Zn metal (δ66/64Zn = 0.22‰) is not significantly fractionated relative to the starting materials despite significantly fractionated fume (δ66/64Zn = 0.43‰) and effluent (δ66/64Zn = 0.41 to 0.51‰). Calculated Cd recovery from metallurgical processing is 72–92%, with the majority of the unrecovered Cd lost during Pb operations (δ114/110Cd = − 0.38‰). The refined Cd metal is heavy (δ114/110Cd = 0.39 to 0.52‰) relative to the starting materials. In addition, significant fractionation of Cd isotopes is evidenced by the relatively light and heavy isotopic compositions of the fume (δ114/110Cd = − 0.52‰) and effluent (δ114/110Cd = 0.31 to 0.46‰). In contrast to Zn and Cd, Pb isotopes are homogenized by mixing during processing. The total variation observed in the Pb isotopic compositions of smelter samples is attributed to mixing of ore sources with different radiogenic signatures.