Immobilization of heavy-metal containing waste residue using sulfur to make construction materials

Based on the analysis of the leaching toxicity and compressive strength, the sulfuration slag and gypsum slag which were produced during the treatment process of waste acid in a smelter, were used as experimental materials. The optimal conditions for sulfur immobilization were studied. The results show that the leaching rate of sulfuration slag is higher than that of gypsum slag, and the leaching toxicity of zinc and cadmium is 1 547.0 mg/L and 104.4 mg/L, respectively. Increasing of sulfur content and adding of gypsum slag are beneficial to the decrease of leaching toxicity. The concentration of zinc and cadmium in the leachate of the solidified body is 1.74 mg/L and 0.87 mg/L respectively with a pretreatment of sodium sulfide at the concentration of 1 mol/L, which is lower than the identification standards of leaching toxicity for hazardous wastes (GB 5085.3-2007). When the particle size of sulfuration slag is less than 150 μm, the gypsum slag adding ratio is 20% and the aggregate adding ratio is 15%, and the compressive strength of solidified body will reach the maximum value as 47.5 MPa, which reaches the level of C47 concrete strength according to the standard of inspection and assessment of concrete strength (GBJ 107-87).