Utilizing arsenic-containing bioleaching waste as a sulfate source in calcium sulfoaluminate cement: A self-stabilizing approach for waste valorization

The effective stabilization of arsenic-containing bioleaching waste (BW) remains a key barrier in metallurgical waste valorization. This study introduces a self-stabilizing approach in which BW serves both as a sulfate donor and an arsenic source within a calcium sulfoaluminate (CSA) cement system, enabling internal immobilization through its own reactive constituents. Experimental results showed that increasing BW content reduced ettringite formation and compressive strength, with the 1-day strength decreasing from 27.3 MPa (10 wt% BW) to 10.5 MPa (50 wt% BW). Incorporating 5 wt% carbide slag (CS) markedly enhanced hydration, increasing 1-day strength by 38.3 % and refining the pore structure by 21.6 % in total pore volume. With respect to arsenic stabilization, sequential extraction and toxicity characteristic leaching procedure (TCLP) tests indicated that over 95 % of arsenic was immobilized in the residual fraction, with leaching concentrations well below regulatory limits, and this stability was maintained even under freeze–thaw conditions. The immobilization mechanism was found to involve both physical encapsulation within a densified microstructure and chemical stabilization through arsenic incorporation into ettringite and adsorption onto C-S-H gels. Furthermore, density functional theory (DFT) calculations confirmed that AsO 4 3- and AsO 3 3- exhibit strong chemisorption onto C-S-H surfaces via Ca–O coordination, with adsorption energies reaching up to –4.98 eV. Overall, the co-utilization of BW and CS in CSA cement presents an effective and low-carbon strategy for the stabilization of arsenic-bearing wastes, offering both structural integrity and long-term environmental safety. • A self-stabilizing CSA system was developed where arsenic-containing waste acts as both contaminant and sulfate source. • Carbide slag addition enhanced arsenic immobilization by promoting ettringite and C–S–H formation. • Arsenic stabilization was confirmed by sequential extraction and TCLP under highly acidic conditions. • DFT simulations revealed strong chemisorption of arsenate/arsenite on C-S-H surfaces.