The immobilization of hazardous wastes in ordinary Portland cement (OPC)-based materials has been widely studied and implemented. OPC-based materials have a high carbon footprint associated with their production and geopolymer materials are a sustainable and eco-friendly alternative. Therefore, this work aimed to immobilize two hazardous industrial wastes: copper wastewater sludge and phosphogypsum in one-part geopolymer materials. For that purpose, the precursor was partially substituted by these wastes (5, 10 and 20 wt.%) in the formulations. The geopolymer fresh and hardened state properties were evaluated, and the immobilisation of pollutants was determined through leaching tests. In phosphogypsum pastes (PG5, PG10 and PG20) it was observed that the compressive strength decreased with the increase in its amount, varying between 67 MPa and 19 MPa. In copper sludge pastes, the compressive strength of the specimens (CWS5 and CWS10) reached ~50 MPa. The mortars, MPG10 and MCWSs10, had compressive strengths of 13 MPa and 21 MPa, respectively. Leaching tests showed that pastes and mortars immobilise the hazardous species of the wastes, except for As from copper sludge, whose the best result was found in the compact paste (CWSs10) that leached 2 mg/kg of As. Results suggest that optimized compositions are suitable for the construction sector.

Gas scrubbing sludge (SS) and fine dust of converters (SC) are wastes generated in the off-gas cleaning system of smelting and converting processes. Both wastes are considered hazardous materials due to their high metal contents and leaching characteristics. The main purpose of this study was to gain essential knowledge on the recovery of valuable elements contained in these wastes. Thus, an exhaustive characterization was carried out to determine the composition, mineral phases, particle size, and leachability of both wastes (SS and SC) as a preliminary step to select the most appropriate applications and treatment for them. These wastes are composed of fine particles (~ 95% < 63 µm), mainly containing Pb (> 20%) as anglesite (PbSO 4), while SS presents a high concentration of Se (34%), which is mainly identified as metallic selenium. Therefore, these residues could be used as secondary sources of Pb and Se. The recovery of Se by roasting process and Pb recovery by hydrometallurgical route seem to be the best options for the management of these wastes.

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