模拟酸雨下铅锌冶炼废渣重金属的静态释放特征

以株洲某铅锌冶炼废水中和渣为研究对象，开展不同初始pH值（3.0，4.5，5.6和7.0）模拟酸雨静态浸出实验，研究22d浸泡过程中废渣Cd、Cu、Pb和Zn等重金属的动态释放规律及其化学形态变化和矿物相变特征.结果表明，废渣具有较强的酸缓冲潜力，浸出液pH值稳定在6.20~6.66.Cu和Pb在浸泡初期释放较快，Cd和Zn释放相对较慢.浸出液Cd浓度随浸出时间增加而上升，Zn浓度呈波动变化，Cu和Pb浓度变幅较小.提高雨水酸度促进废渣中重金属的释放，浸出液Cd、Cu、Pb和Zn浓度范围分别为1.38~8.70，0~0.02，1.21~2.26和27.2~135mg/L，其中Cd、Pb和Zn浓度分别超过我国《铅、锌工业污染物排放标准》（GB 25466-2010）限值的26.6~173倍、1.42~3.52倍和17.1~89.0倍..重金属BCR顺序提取表明，浸出液中较高Cd和Zn浓度与其赋存高活性态比例一致，且酸雨促使残渣态Cd和Pb向活性态转化.XRD分析显示，pH=3.0酸雨处理22d后原废渣中Cd和Zn的赋存矿物相消失，PbSO₄谱峰增强，表明废渣重金属的释放受其赋存矿物相及次生矿物形成的影响.重金属释放率呈现出Cd （2.50%~15.8%）> Zn （0.41%~2.13%）> Pb （0.06%~0.10%）> Cu （0.0003%~0.11%）的趋势.自然堆存酸雨作用下废渣中Cd、Pb和Zn具有较大环境风险，需加强降雨淋滤污染防治管控.

Static release characteristics of heavy metals from lead-zinc smelting slag leached by simulated acid rain

The static 22 days leaching experiments of simulated acid rain with different initial pH values (3.0, 4.5, 5.6 and 7.0) were carried out to study the dynamic release of heavy metals (Cd, Cu, Pb and Zn) and their chemical speciation changes and mineral phase transformation in wastewater neutralization slag from a lead-zinc smelting plant in Zhuzhou city. The results showed that the slag had strong acid buffering potential, and there was slight change in the leachate pH value (6.20~6.66). The release of Cu and Pb was fast at the initial immersion stage of 0.5d, and Cd and Zn released slowly. The concentration of Cd in leachate was increased with the increase in leaching time and that of Zn was sharply fluctuated, while the concentrations of Cu and Pb was changed slightly during the leaching process. The concentration of Cd, Cu, Pb and Zn in leachate was 1.38~8.70, 0~0.02, 1.21~2.26 and 27.2~135mg/L, respectively. The concentration of Cd, Pb and Zn was 26.6~173,1.42~3.52 and 17.1~89.0 times higher than corresponding heavy metal threshold limit of emission standard of pollutants for lead and zinc industry (GB 25466~2010), respectively. The higher concentrations of Cd and Zn in leachates were in consistent with their higher content of active forms in slag based on BCR sequential extraction analysis. The transformation of residual fraction Cd and Pb to more active fraction was promoted by acid rain. XRD analysis showed that the mineral phases of Cd and Zn was disappeared, and the spectrum peak of PbSO₄ in slag was enhanced after 22 days leaching by acid rain of pH 3.0, indicating that the release of heavy metals in slag was affected by their existing mineral phases and the formation of secondary minerals. The release efficiency of heavy metals was followed as Cd (2.50%~15.8%) > Zn (0.41%~2.13%) > Pb (0.06%~0.10%) > Cu (0.0003%~0.11%). The results suggested that Cd, Pb and Zn in slag leached by acid rain could pose great environmental risks and need pollution control.