| In order to achieve the recovery of valuable metals from the heavy-metal containing waste residues and the finally comprehensive utilization of the wastes after the separation of metals, the sulfuration of the heavy-metal containing waste residues was proposed in this research. The heavy-metals in the residues were sulfurized to man-made heavy-metal sulfides, which can be separated by flotation process, and the remaining heavy metals in the residues will be immobilized by encapsulation and solidification using sulfur to achieve not only the detoxification process of heavy-metals, but also the acquisition of sulfur construction material which has several incomparable advantages. As a branch of the project, this paper was focused on the confirming of the factors and characteristic for sulfur immobilization/stabilization process. The following results were gained:(1) The optimal technical conditions for sulfur immobilization process were confirmed. In the experiment, two kinds of sludges, including sulfuration sludge and gypsum sludge which were produced in the waste acid treatment process of a smelter factory, were used as the experiment materials. The sludges were treated for sulfur immobilization/stabilization, and the results showed that, the leaching toxicities of heavy metals, such as Zn and Cd could be reduced effectively by using elemental sulfur, and it was beneficial to the enhancement of compressive strength when gypsum sludge was added to the mixture. The compressive strength of solidified body reached 47.5Mpa with the following conditions:the sulfur addition ratio was 25% (mass ratio), the sulfuration sludge addition ratio was 55%, the gypsum sludge addition ratio was 20%, the diameter of the sludge was less than 150μm, and the skeletal material addition ratio was 15%. After the pretreatment of the sulfuration sludge with 400mL sodium sulfide solution (1 mol/L), the concentrations of Zn and Cd in the leachate of the solidified body were 1.74mg/L and 0.87mg/L, which reached the identification standards of leaching toxicity for hazardous wastes(GB5085.3-2007), and the compressive strength of solidified body was 21.9Mpa. The solidified body had a perfect appearance, sulfur and sludges were mixed to uniform state. The long-term leaching experiment result of the solidified body showed that, the leaching rates reduced to steady as the leaching time increased. The solidified body is an ideal building material as its excellent water impermeability and corrosion resistance.(2) The factors of mechanical activation for promoting and strengthening the sulfur stabilization process were studied. During the mechanical activation process, when the concentration of sodium sulfide solution was 200g/L, ball/material ratio was 3.3:1, liquid/solid ratio was 2.75:1, and the milling reaction time was 1h, the leaching toxicities of Zn and Cd were 2.85mg/L and 0.77mg/L respectively, which reached the leaching toxicities' standards(GB5085.3-2007). According to the ICP test of the leachate, all of the other heavy-metals contained in the sludges could reach the leaching toxicities' standards after the mechanical activation.(3) The characteristic of mechanical activation for promoting and strengthening the sulfur stabilization process was discussed. The sulfidation rates of the heavy-metal oxide (ZnO and CdO) could reach high values after the mechanical activation, of which the sulfidation rates of Zn and Cd reached 49.5% and 59.4% respectively. The XRD patterns of sulfidization products showed that, the peak shapes of the heavy-metal sulfides had the same trends with the chemical phase analysis results. The TG-DTA patterns of the sulfidization products showed that it had a favorable thermal stability in the high temperature. The SEM morphology indicated that the products are uniformly distributed particulate materials, whose particle size reached micrometer-level. |
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