Experimental weathering of historical slags exposed to rhizosphere-like organic acids and various pH conditions

Abstract

The long-lasting mining and smelting activity that took place in southern Tuscany since the 1st millennium BCE has left several remains of metallurgical interest, along with metallurgical slags. Over the centuries, these materials were treated as wastes and dumped close to the industrial sites, with no specific disposal or confinement from the surrounding environment. We performed leaching experiments on slag samples from two selected sites, applying conditions to test the effects of various pH conditions, as well as their behavior following the addition of organic acids to simulate a rhizospheric environment. The samples, a crystalline Pb slag and a glass-rich Cu slag, showed a different leachability depending upon their physical and mineral-chemical characteristics, such as the size of the fragments used in the experiments, the mineralogical composition, and the bulk content of metals in the samples. The crystalline Pb slag showed a higher susceptibility to leaching (e.g., 31 % Cu and 65 % Zn) under acidic inorganic conditions, compared to the glass-rich Cu slag, which was prone to organic mediated dissolution (14 % Cu and 6 % Zn). The highest metal mobilization occurred during the pH-dependent leaching experiments at pH 1, reaching 92 % (of leached Pb) and 65 % (Zn) for lead slag and copper slag, respectively.