Zhao Qing-Yuan, Li Xiao-Ming, Yang Qi, Chen Can, Zhong Zhen-Yu, Zhong Yu, Chen Fei, Chen Xun-Feng, Wang Xiang
College of Environmental Science and Engineering, Hunan University, Changsha 410082, China.
Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China.
Huan Jing Ke Xue. 2018 Jan 8;39(1):389-398. doi: 10.13227/j.hjkx.201705273.
In this study, three kinds of amendments including superphosphate, humic acid, and fly ash and their complex combination were adopted to passivate the artificially simulated Pb-and Cd-containing soils. The passivation efficiency evaluation was performed via the CaCl and triethylenetriaminepentaacetic acid (DTPA) extraction method as well as a BCR morphological classification experiment. The microstructures and structures of the soil were explored further via X-ray diffraction (XRD) and scanning electron microscopy with X-ray energy dispersive spectroscopy (SEM-EDS) to elaborate the passivation mechanism. The results demonstrated that all passivation processes, excluding single humic acid addition, could reduce the CaCl and DTPA extraction contents of Pb and Cd in soils, where the optimal efficiency could be achieved by the sequential addition of superphosphate and humic acid, followed by fly ash. There was a weakly positive correlation between soil pH and CaCl/DTPA extraction content of Pb, a negative correlation between soil pH and CaCl/DTPA extraction content of Cd, and a significantly negative correlation between available phosphorous content and CaCl/DTPA extraction contents of Pb and Cd, suggesting the crucial role of available phosphorous contents to control the activities of Pb and Cd. In the presence of phosphate, humic acid, and fly ash, the Pb and Cd could convert from active weak acid extraction to low-activity residual speciation, resulting in effectively reducing Pb and Cd transferability. Throughout the XRD and SEM-EDS analyses, it was found that ion exchange was the predominant mechanism in heavy metal passivation by single superphosphate, wherein the heavy metals were transformed into an insoluble Ca-containing phosphate mixture. The dissolving/precipitation or surface adsorption could be concluded as the main mechanism in the combination of the three passivation agents that converted heavy metals to lead phosphate precipitate[(Pb(PO)] or mixed heavy metal mineral[PbFe(SO)(PO)(OH)], so as to obtain superior heavy metal passivation achievement.
在本研究中，采用过磷酸钙、腐殖酸和粉煤灰三种改良剂及其复合组合对人工模拟的含铅镉土壤进行钝化处理。通过氯化钙和三乙烯四胺五乙酸（DTPA）提取法以及BCR形态分类实验进行钝化效率评价。通过X射线衍射（XRD）和带X射线能谱的扫描电子显微镜（SEM-EDS）进一步探究土壤的微观结构和结构，以阐明钝化机制。结果表明，除单一添加腐殖酸外，所有钝化处理均能降低土壤中铅和镉的氯化钙和DTPA提取含量，其中过磷酸钙和腐殖酸依次添加后再添加粉煤灰可达到最佳效果。土壤pH值与铅的氯化钙/DTPA提取含量之间呈弱正相关，土壤pH值与镉的氯化钙/DTPA提取含量之间呈负相关，有效磷含量与铅和镉的氯化钙/DTPA提取含量之间呈显著负相关，表明有效磷含量对控制铅和镉的活性起着关键作用。在磷酸盐、腐殖酸和粉煤灰存在的情况下，铅和镉可从活性弱酸提取态转化为低活性残留形态，从而有效降低铅和镉的迁移性。通过XRD和SEM-EDS分析发现，离子交换是单一过磷酸钙钝化重金属的主要机制，其中重金属转化为不溶性含钙磷酸盐混合物。溶解/沉淀或表面吸附可被认为是三种钝化剂组合将重金属转化为磷酸铅沉淀[Pb₃(PO₄)₂]或混合重金属矿物[PbFe₃(SO₄)(PO₄)₂(OH)]的主要机制，从而获得优异的重金属钝化效果。
