Toxic Metal-Rich Extraction By-Product: Contamination Assessment and Reprocessing

The main objective of this study was to establish the contamination caused by Pb–Zn mining site of Lakhouat (NW Tunisia) and detail its spread. Samples were analyzed and the 3D toxic metals content map showed that the contamination level was relatively superficial. This is due to the transportation phenomenon which is mainly caused by the wind. The same was detected in both the nearby topsoils and the stream sediments. In order to neutralize these heavy metals, sediments containing rejects were used to produce cement. Tests reported that concentrations of leached contaminants (Pb, Zn, and Cu) decreased considerably. Indeed, 75–85% of these toxic elements were immobilized in the obtained mortars. Mining rejects-based geopolymers were also confectioned. The formulations were set by mixing commercial-grade metakaolin with Lakhouat by-products. The activation was achieved using sodium silicate/NaOH prepared solution. Si/Al ratios of 2.5 and 3.5 were studied. It appeared that at higher Si/Al ratio relatively good cohesion and mechanical strength was achieved. These obtained geopolymers could present a good candidate to immobilize the toxic metals contained in the rejects.