As application of multiple metal isotopes can effectively constrain geochemical behavior of contaminants and assess contamination sources and pathways, field-scale studies on the geochemically interlinked fractionation of Zn and Cd isotopes in groundwater are needed. In this study, we collected groundwater samples from multi-level samplers downstream of tailings dumps as well as surface water, ore mineral, precipitate, and tailings samples at the Sambo and Buddeun metallic ore mines in South Korea, and analyzed their Zn, Cd, Pb, and sulfur isotopic compositions. Furthermore, isotopic ratios of ore mineral samples from additional four mines in South Korea (Dangdu, Dongbo, Gomyeong, Samgwang) were compared. A dual isotopic approach using Zn and Cd isotopes was used to assess fractionation processes, and Pb isotopic signatures reflecting their sources were assessed. Increasing trends of δ66Zn and δ114Cd with decreasing Zn and Cd concentrations were observed in groundwater, which was saturated with respect to ZnS (amorphous and sphalerite) and CdS (greenockite). Moreover, for some groundwater samples, δ66Zn showed a positive relationship with δ34SSO4. These results suggest that Zn and Cd are precipitated as sulfide following sulfate reduction. In the plot of δ66Zn against δ114Cd, relatively high and/or increasing δ66Zn in groundwater suggested the effect of fractionation due to sulfide precipitation, while variable and high δ114Cd values suggested the fractionation by adsorption and/or sulfide precipitation, which were based on positive fractionation factors for δ66Zn and δ114Cd during sulfide precipitation and mostly negative and positive fractionation factors for δ66Zn and δ114Cd, respectively, during adsorption. This study shows that the combined use of Zn and Cd isotopes in groundwater can effectively differentiate between adsorption and sulfide precipitation following sulfate reduction in groundwater. Additionally, the 208Pb/206Pb ratios of most water samples reflected those of ore and tailings samples, which verified usefulness of Pb isotopes in water in investigating Pb contamination sources.
Bibliographical noteFunding Information:
This work was initially supported by a research fund (to S.T. Yun) from the Korea Mine Reclamation Corporation (MIRECO) funded by the Ministry of Trade, Industry, and Energy . Students at the Chemical Oceanography Laboratory in Chungnam University and at the Environmental Geochemistry Laboratory in Korea University, as well as Ji-Hye Hong at MIRECO, assisted the authors with well installation, field work, and data preparation. The completion of this work was partially supported by the Korea Environmental Industry & Technology Institute (KEITI) through the Subsurface Environment Management (SEM) Project, funded by the Korea Ministry of Environment (MOE). Special thanks go to four anonymous reviewers for providing critical and constructive comments and suggestions that helped to significantly improve the manuscript.
© 2021 Elsevier B.V.
- Mining area
- Sulfide precipitation
- Zn and Cd isotopes
ASJC Scopus subject areas
- Environmental Engineering
- Environmental Chemistry
- Waste Management and Disposal