Recycling arsenic-containing bio-leaching residue in cemented paste backfill after thermal treatment: Structure modification, binder properties and environmental assessment

The substantial arsenic (As) content present in arsenic-containing bio-leaching residue (ABR) poses significant environmental challenges. Given its elevated calcium sulfate content, ABR exhib-its considerable promise for industrial applications. This study delved into the feasibility of utilizing ABR as a source of sulfates for producing super sulfated cement (SSC), offering an innovative bind-er for cemented paste backfill (CPB). Thermal treatment at varying temperatures of 150 °C, 350 °C, 600 °C, and 800 °C was employed to modify ABR's performance. The investigation encompassed the examination of phase transformations and alterations in the chemical composition of As within ABR. Subsequently, the hydration characteristics of SSC utilizing ABR, with or without thermal treatment, were studied, encompassing reaction kinetics, setting time, strength development, and microstructure. The findings revealed that thermal treatment changed the calcium sulfate structure in ABR, consequently impacting the resultant sample performance. Notably, calcination at 600 °C demonstrated optimal modification effects on both early and long-term strength attributes. This en-hanced performance can be attributed to the augmented formation of reaction products and a densi-fied microstructure. Furthermore, the thermal treatment elicited modifications in the chemical As fractions within ABR, with limited impact on the As immobilization capacity of the prepared bind-ers.