The effect of mineralogy on the mobility of heavy metals in mine tailings: a case study in the Samsanjeil mine, Korea

This study examined the chemical speciation and mobility of As and heavy metals in a tailings impoundment in Samsanjeil mine located in Gosung, Korea, as well as the factors affecting them. XRD, SEM, and 5-step sequential extraction were used to examine the samples at two sampling sites (NN and SN sites). The pH of the tailings decreased with increasing depth at the NN site (from 7.2 to 2.8), whereas no significant differences were observed at the SN site (8.1–8.8). The samples at the SN site showed a larger amount of calcite than those at the NN site, indicating that calcite plays an important role buffering the pH in the study sites. Jarosite was found only at the lower part of the NN site, where calcite was not found. The mineralogical observation of jarosite and calcite was also confirmed by SEM. The concentrations of As and heavy metals in the tailings were as follows: Cu > As > Zn > > Pb > Co > Cr > Ni > Cd. The total concentrations of Ni, Zn, Co, and Cd were higher at the SN site than those at the NN site. On the other hand, the concentrations of As and Cr existing as oxyanions were higher at the NN site, which can be explained by the mobility changes of those elements affected by pH variations. At the NN site, the fractions of heavy metals bound to the Fe/Mn oxides, except for As and Cr, decreased, and Cu, Zn, and Co showed an increasing fraction of exchangeable metals with increasing depth. This suggests that the pH and resulting surface charge of minerals, such as goethite and jarosite, are the dominant factors controlling the chemical speciation of metals. These results highlight the importance of mineralogy in controlling the mobility and possible bioavailability of heavy metals in tailings.