知识与财富的链接
为研究土壤淋洗技术对锑矿区周边高浓度锑(Sb)、砷(As)污染土壤的修复效果,筛选生物降解性能良好的淋洗剂,以广西河池市南丹县某锑矿区周边高浓度Sb、As污染土壤为研究对象,考察了不同低分子有机酸及淋洗条件(浓度、固液比、淋洗时间和淋洗级数)对Sb、As淋洗效率的影响,利用Wenzel连续形态提取法比较淋洗前后土壤中Sb、As形态变化,并结合扫描电子显微镜-X射线能量色散谱(SEM-EDS)、X射线光电子能谱(XPS)等分析方法初步探索了淋洗去除土壤Sb、As的反应机理.结果表明:由于草酸(oxalic acid,OA)具有较强的酸性及还原性,其对Sb、As的淋洗效率最高,且在最佳淋洗条件下Sb、As淋洗效率分别可达91.18％、97.63％.高浓度污染土壤中Sb、As主要以铁铝氧化物结合态形式存在,占Sb、As总量的70％以上;OA淋洗后,土壤中结合态、残渣态的Sb、As向吸附态Sb、As转化.OA淋洗去除Sb、As的反应机理主要包括三方面:①OA的含氧官能团与Sb、As含氧阴离子竞争土壤颗粒中铁(氢)氧化物表面的吸附位点,发生配位交换,从而解吸出Sb、As;②OA的有机配体吸附在铁(氢)氧化物表面的Fe结构上,生成有机酸与Fe的络合物,破坏矿物表面结构,促进Sb、As的解吸溶解;③通过OA还原作用形成的Fe与S的络合物吸附在土壤颗粒表面,进一步降低Sb、As在土壤中的吸附.研究显示,在淋洗修复锑矿区高浓度Sb、As污染土壤时,可选用OA作为环境友好型淋洗剂,虽然低分子有机酸淋洗后土壤有机质、阳离子交换量增加,但土壤酸化明显、剩余重金属生物可利用性增强,因此淋洗后的土壤还需结合相应风险管控目标作进一步处理.
In order to study the remediation effect of soil washing on high-level antimony (Sb) and arsenic (As) contaminated soil and to select biodegradable washing agents, high-level Sb and As contaminated soil from an antimony mine in Nandan, Hechi City, Guangxi was selected in this study. The impacts of low-molecular organic acids and washing conditions (agent concentration, solid-liquid ratio, time and frequency) were explored to optimize the washing efficiency of Sb and As. Wenzel sequential extraction procedures were conducted to compare the metal speciation changes before and after soil washing. Scanning electron microscope coupled energy dispersive spectrometer (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphology and elemental composition of soil particles during the remediation. The results showed that oxalic acid (OA) had higher washing efficiency for Sb and As than other organic acids due to its higher acidity and reducing properties. Under the optimum washing conditions, the washing efficiency of Sb and As could reach 91.18% and 97.63%, respectively. Sb and As mainly associated with Fe-Al oxides in high-level contaminated soil, accounting for more than 70% of the total metals in the soil. The mechanisms of Sb and As removal by OA included three aspects: (1) The OA competed with Sb and As anions for the adsorption sites on the surface of iron (hydro) oxides, resulting in the desorption of Sb and As from the oxide surface. (2) The OA organic ligands were adsorbed on the surface of iron (hydro)oxide, forming Fe(Ⅲ)-organic acid complex. This facilitated the desorption and dissolution of Sb and As. (3) The reduction product i.e., Fe(Ⅱ)-S produced by the OA reduction reaction can be adsorbed on the surface of soil particles, thereby preventing the re-adsorption of Sb and As to the soil. The results show that the OA can be used as an environmentally friendly washing agent in the remediation of high-level Sb and As contaminated soil in mining areas. Soil organic matter and cation exchange capability increase after OA washing, so the problems of soil acidification and the increased bioavailability of residual metals in the soil need to be addressed when reutilizes the washed soil.
