Recycling of arsenic-containing biohydrometallurgy waste to produce a binder for cemented paste backfill: Influence of additives

Biohydrometallurgy waste (BW) was used as sulfate sources for supersulfated cement (SSC) production with the aim of providing an alternative binder for cemented paste backfill (CPB). Additives, including carbide slag (CC), Al2(SO4)3 (AlS) and Na2SO4 (NaS), were used to modify the binder properties, when considering the poor mechanical strength at the early curing ages. The reaction kinetics of binder modified by additives were studied via isothermal calorimeter test; mechanical strength and hydration products modifications due to the addition of additives were also explored. Additionally, arsenic (As) leaching from the binders was tested and the immobilization mechanism was explored using density functional theory (DFT) calculation. The results showed that the addition of CC increased the early strength strongly, but higher amount of CC restricted the strength development after curing for a long time; NaS presented marginal influence on the binder properties. The coupling addition of 25 wt% CC and 1 wt% AlS showed the best performance; the compressive strength after curing for 3 and 28 days reached around 13.67 MPa and 36.97 MPa, which was increased by about 47.69% and 18.34%, respectively, compared to the control sample. The superior performance was attributed to the generation of more reaction gels, especially ettringite (AFt). Rising in the AFt content contributed to better immobilization effects on As, because that it led to lower pore volume and permeability; besides, AFt showed higher immobilization effects according to the DFT calculation.