Distribution characteristics, release, environmental behavior and risk assessment of cadmium in Zn-Pb mine tailings

Anguran-Zanjan lead and zinc mine is the largest producer of lead and zinc in Iran and the Middle East. The volume of tailings produced by this mine is very large, which unfortunately is accumulated in different parts of Zanjan province without any protection operations. These tailings contain a variety of heavy metals, especially cadmium, whose disposal or spread into the environment can have very hazardous effects on soil and water resources. The present study investigates the concentration, distribution, leaching behavior and release of cadmium from Zn-Pb mine tailings (S1 and S2). In order to investigate the distribution of cadmium among different tailings components sequential extraction method and to classify the tailings in terms of environmental risk level, leaching protocols include toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), field leach test (FLT) and leaching extraction procedure (LEP) was used. The effect of contact time, particle size, liquid to solid ratio and pH on cadmium release from tailings was also studied. The results showed that the cadmium release was the same in different particle size ranges and with the increase in leaching time, the release of cadmium almost reaches a constant value. It was also found that the cadmium release behavior was cationic and solubility controls the concentration of cadmium in the leaching solution. Both tailings were classified as highly hazardous residues based on the mobility index. The results of the TCLP test also show that tailings are one of the substances that should be protected by very good management practices because they have a high potential for contaminating the soil and water resources.