ABSTRACT

Lead-zinc tailings represent an important source of Cd and other heavy metals in the environment. The active geochemical process in the tailings plays a critical role in these heavy metals’ fate and ecological risk. However, a substantial study gap occurs in carbonate-rich Pb-Zn tailings compared to carbonate-poor ones. In this contribution, we conducted XRD mineralogy, particle distribution, ICP-MS and ICP-AES bulk chemical analyses, and BCR geochemical fractions for Niujiaotang Cd-rich Pb-Zn tailings to decipher the geochemical process operating in the tailings. The result demonstrates that dolomite and pyrite dominated the mineralogy of tailings with an average pH of 6.36. The average Cd, Zn, and Pb in 17 contents tailings samples are 141, 8118, and 340 mg/kg, respectively. The significant correlation between Cd vs. Zn and Zn vs. Pb and varied Zn/Cd and Zn/Pb ratios in the four BCR fractions from the tailings samples were revealed. Pyrite weathering and associated dissolution and oxidation of sphalerite are responsible for the release of Cd and Zn from the tailings. Dolomite dissolution and associated acid neutralization caused Cd and Zn attenuation by the formation of carbonate minerals. The differences in weathering and oxidation rates of sulfide minerals and the pH-dependent geochemical behavior of secondary minerals lead to varied mobility among Pb, Zn, and Cd. We proposed that these geochemical processes operating in the tailings significantly lowered the ecological risk of heavy metals. This contribution sheds new insight into heavy metal pollution control for Pb-Zn tailings from carbonate-rich deposits.