The release and mobility of heavy metals during mining operations raise environmental concerns. In this study, a filling cementitious material to effectively replace ordinary Portland cement (OPC) and solidify heavy metals was developed by using red mud (RM), calcium carbide slag (CS), ground granulated blast-furnace slag (GGBS), and fly ash (FA) as raw materials. The influence of heavy metal and solid waste contents on the resulting mechanical properties, leaching toxicity, hydration attributes, microstructure, chromium chemical form, and environmental safety of the heavy metal solidified composite was evaluated. The results showed that when the Cr 3+ content was 2% and the mass ratio of RM: CS: FA: GGBS was 15:15:20:50, the 28-day strength of the solidified composite of the filling cementitious material could reach 21.49 MPa, which was 109.65% higher than that of the control group. In addition, the leaching concentration of Cr 3+ was found to be inversely proportional to the strength of the solidified composite. The leaching concentration of Cr 3+ was lower than 21.71 ppb, which was significantly lower than the limit of 15 mg/L stipulated in GB 5085.3 −2007 standard. The solidification rate of Cr 3+ was above 99.998%, and Cr 3+ ions were mainly solidified by N/C−(A)−S−H ion exchange or chemical bonding, accompanied by a small amount of physical encapsulation. Furthermore, comparative analysis reveals that this filling cementitious material offers favorable economic and environmental benefits. • Cr 3+ can be solidified by RM, CS, FA and GGBS. • Adding 2% Cr 3+ can increase the UCS by 109.65%. • Cr 3+ is mainly solidified by N/C-(A)-S-H ion exchange or chemical bonding.
Pang et al. (Thu,) studied this question.