Contaminant release from massive copper metallurgical slags: Insights from long-term monolithic leaching tests

Compared to compliance leaching tests performed on granular materials, leaching experiments on monolithic slags are more suitable for predicting the contaminant release when large boulders or poured slag layers are submerged in water, a specific environmental scenario typical for many smelting sites. We conducted EN 15863 dynamic monolithic leaching tests on massive copper slags over a prolonged period of 168 d. The patterns of the major contaminant (Cu, Co) fluxes indicated an initial diffusion process followed by the dissolution of primary sulfides with the maximum cumulative releases attaining 75.6 mg/m2 Cu and 4.20 mg/m2 Co. A multi-method mineralogical investigation showed that lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) started to form on the slag surface already after 9 d of leaching and partly immobilized Cu (but not Co). Vanadium and other trace elements (Zn, Pb, Cd) were leached to a much lower extent, initially controlled by diffusion followed by depletion and/or sorption to Fe oxyhydroxides. The results of the long-term leaching of the monolithic slag provide new information about the key processes affecting the release of metal (loid) contaminants under specific submerged conditions and have implications for the environmental management of slag disposal sites and/or potential reuse of slags in civil engineering.