Immobilization of Cr(VI)-containing tailings by using slag-cementing materials for cemented paste backfill: influence of sulfate and limestone addition.

Abstract

Heavy metals in mine tailings lead to serious environmental problems. Cemented paste backfill (CPB) is widely used for treating the mine tailing. The high cost of ordinary Portland cement (OPC) reduces the profit of mine production. The work investigates the treatment of Cr(VI)-containing tailings by using slag-based cementitious materials for CPB. Flue gas desulfurization gypsum (FGDG) and limestone were used to modify the properties of samples. Results showed that the coupling addition of 6 wt% FGDG and 3 wt% limestone (A6L3) led to the highest compressive strength of CPB samples, which also presented satisfactory immobilization effects for Cr(VI). The compressive strength of CPB samples using A6L3 as a binder was comparable to the OPC-based sample, reaching about 5.53MPa; the immobilization efficiency for Cr(VI) was about 99.5%. The effects of FGDG and limestone were twofold: the addition of FGDG favored the formation of ettringite and then contributed to a more compact structure; besides, incorporating limestone increased the packing density of the CPB system by decreasing the loosening and wedge effect.