Quantitative metal and metaloid distribution in primary and secondary phases in historical lead-silver smelting slags from Rammelsberg ore deposit (Germany) and implications for their recovery

Abstract

Historical slags from primary Pb/Ag and Cu smelting can have high contents of valuable metal(loid)s. So far, there are hardly any studies that provide quantitative information on metal(loid) partitioning (deportment) between all slag phases based on automated mineralogy which is important for designing metal recovery from such slags. In this study, slags from the Kanstein Pb/Ag smelter, belonging to the Rammelsberg ore deposit, were studied by SEM-based automated mineralogy (here MLA), EPMA, and LA-ICP-MS on polished sections and by XRF and LA-ICP-MS on sieve fractions of bulk samples. The slags are rich in Fe (21–32 wt%), Zn (7.9–19 wt%), Pb (1.8–3.3 wt%), Cu (0.7–1.4 wt%) with slightly elevated concentrations of Co (309–586 ppm), Sb (155–459 ppm), Sn (84–204 ppm), Ag (19–115 ppm), In (18–64 ppm), Ga (15–25 ppm), Bi (2–20 ppm). A Ba-S-rich slag and a SiO2-rich slag can be distinguished; the first probably formed under more reducing conditions, at higher temperatures (>1200 °C) and without roasting. The weathering phases are the main carriers of all metal(loid)s (up to 45–94 % of total metal(loid) content in individual samples). Larger amounts of up to 13–83 % can be contained in glass (Ga, Sn, Zn, Fe, Ag, In, Co, Ge, Sb, Cu, Pb, Ni), pure metals and intermetallic compounds (Bi, Ag, Sb), sulphides (esp. sphalerite; Zn, Cu, Ag, In, Co), silicates (esp. fayalite; Ni, Co, Zn, Fe, Ga, Ag, In, Sn, Ge), or oxides (esp. wüstite; Fe, Co, Ge, Zn, In, Ga), if their modal proportions in the slags are high enough. Due to the complex and variable metal deportment, processing of the entire slag using leaching or pyrometallurgy is most promising for recovery.