土壤淋洗及后续措施原位修复矿区重金属污染土壤及其机理研究

In recent years, the southern Chinese red soil has being polluted seriously by metal mining. It is vital to remediate contaminated soil to food safe production and ecological civilization construction in our country. Soil washing is an effective technology to reduce the concentration levels of heavy metals in contaminated soils. However, agricultural production on the washed-soil was not feasible becauce of the residual chelatoes and metals in soil. It has been reported that the chemical immobilization and phytoextraction technologies had done well to reduce the heavy metal levels and ameliorate the soil. However, it is unclear to the mechanism of residual metal-chelates migration and transformation in washed soil with subsequent measures. This study will firstly reveal the temporal evolution rule of heavy metals species and the immobilized mechanism of residual heavy metals in washed soil with chemical amendments by incubation experiment. Secondly, some work will be done to explore the mechanism of residual metal-chelates migration and transformation in washed soil with phytoextraction by rhizosphere bag cultivation and to understand the environmental behavior of residual heavy metals in washed soil. The results could provide the theory basis for remediating contaminated soil from mining areas by combination of soil remediation technologies. Therefore, this project has important theoretical significance and practical value.

近年来金属矿开采使南方红壤区土壤重金属污染严重，矿区重金属污染农田修复对我国粮食安全和生态文明建设至关重要。土壤淋洗技术可快速降低矿区污染土壤中重金属含量，但残留的淋洗剂和重金属还将影响正常农业生产。化学改良和植物提取措施可弥补土壤淋洗技术的不足，然而后续措施对淋洗后土壤中残留重金属的迁移转化影响机制尚不清楚。本项目拟采用室内培养试验，研究化学改良对淋洗后土壤中重金属形态转化时间演变规律，揭示残留重金属的钝化机理；通过根际袋培养试验，研究植物提取对淋洗后土壤残留有机络合态重金属迁移转化的影响机制，从而深入理解淋洗后土壤中残留重金属的环境行为。项目结果将为发展实用、高效的矿区重金属复合污染土壤多技术联合修复模式提供理论依据，对推动重金属污染土壤修复治理具有重要的理论意义和实践意义。

2016年《土壤污染防治行动计划》（简称“土十条”）颁布，其中加强对重金属污染土壤治理与修复是当前土壤污染防治行动计划的重点工作之一。土壤淋洗修复技术可快速将污染物从土壤中移除，尤其对于中重度污染土壤，而且修复费用相对低廉，现已成为污染土壤快速修复技术研究的热点。然而需采取措施解决淋洗后土壤质量恢复问题，使修复后土壤得到安全利用。本项目通过批试验研究了不同淋洗剂对土壤中重金属的去除及其淋洗参数优化；通过培养试验和生物毒性试验研究了不同改良剂对淋洗后土壤中重金属形态变化和土壤质量恢复等方面研究；通过田间试验研究了淋洗后土壤上植物套种系统植物生长状况。主要研究结果如下：.（1）EDTA、GLDA和柠檬酸摩尔比为1:1:3时混合试剂（MC）对Cd和Cu的去除率与相同用量的EDTA处理差异不显著，而Zn和Pb的去除率略低。但此混合试剂减少了EDTA用量，降低了EDTA的环境风险。.（2）混合试剂淋洗时间达4h后，重金属的去除率趋于平稳，即体系达到吸附平衡。pH值为2时对Cd、Zn、Pb和Cu的去除能力最高，分别达到40%、17%、18%和16%。MC浓度为50 mmol L-1时为最佳淋洗浓度。MC相同用量的情况下（1 mol kg-1土），单次淋洗比多次淋洗对重金属的去除率高。与传统淋洗剂EDTA、FeCl3相比，MC对土壤结构、理化性质以及土壤酶活性的影响较小，是一种温和淋洗剂。.（3）与原污染土壤相比，MC淋洗后土壤中有效态Cd、Pb和Zn含量降低幅度分别为70.1%、88.2%和76.0%。改良剂能进一步是淋洗后土壤中有效态重金属含量降低，其中碳酸钙和鸡粪对交换态Cd含量的降低幅度最大，鸡粪对交换态Pb含量的降低幅度最大，碳酸钙对交换态Cu含量的降低幅度最大。改良剂使修复后的土壤性质有一定程度恢复，如碳酸钙+鸡粪处理小白菜发芽率及茎长均处于较高水平。.（4）田间试验表明，化学淋洗后土壤全Zn、Pb和Cu含量显著降低，降低率分别为37%~53%、37%~52%和15%~32%。采用石灰和有机肥改良淋洗后土壤所产两季玉米籽粒Cd、Zn、Cu含量均符合国家食品卫生标准。