Artisanal metallurgical slag produced more than 50 years ago at a mine site in southwest Japan is rich in toxic metals and metalloids. Some of the slag remains on a waste dump and could contaminate the surrounding area through the dissolution of heavy metals and metalloids during weathering. To assess this risk, this study has investigated the behavior of the toxic elements in the smelting slag during weathering. Most of the potentially toxic elements are contained in willemite and/or matte drops. Maximum metal and metalloid concentrations in the slag are 28.1 wt % Fe, 22.7 wt % Zn, 1.63 wt % Cu, 3450 mg/kg Sn, 826 mg/kg Pb, 780 mg/kg As, and 116 mg/kg Cd. Zn is mainly contained in willemite, whereas other metals and metalloids are mainly concentrated in matte drops. The willemite and matte drops are converted to Fe-hydroxides during weathering, indicating that potentially toxic metals and metalloids contained in these phases are released by weathering processes. Therefore, weathering of the artisanal metallurgical slag, containing large amounts of willemite and matte drops, may pollute the surrounding environment.
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