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 delta(66/64)Zn and delta(114/110)Cd values of 0.42 per thousand and 1.04 per thousand, respectively, among all smelter samples. No significant difference is observed between the isotopic compositions of the Zn ore concentrates (delta(66/64)Zn=0.09 to 0.17 per thousand; delta(114/110)Cd=-0.13 to 0.18 per thousand) and the roasting product, calcine (delta(66/64)Zn=0.17 per thousand; delta(114/110)Cd=0.05 per thousand), due to approximately 100% recovery from roasting. The overall Zn recovery from metallurgical processing is approximately 98%, thus the refined Zn metal (delta(66/64)Zn=0.22 per thousand) is not significantly fractionated relative to the starting materials despite significantly fractionated fume (delta(66/64)Zn=0.43 per thousand) and effluent (delta(66/64)Zn=0.41 to 0.51 per thousand). Calculated Cd recovery from metallurgical processing is 72-92%, with the majority of the unrecovered Cd lost during Pb operations (delta(114/110)Cd=-0.38 per thousand). The refined Cd metal is heavy (delta(114/110)Cd=0.39 to 0.52 per thousand) 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 (delta(114/110)Cd=-0.52 per thousand) and effluent (delta(114/110)Cd=0.31 to 0.46 per thousand). 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.
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