不同pH值混合螯合剂对土壤重金属淋洗及植物提取的影响

为了得出混合螯合剂（MC）淋洗去除重金属的最佳pH值以及对后续植物提取重金属的影响，用Ca(OH)2将pH值为2.75的MC提高至pH值5、7和9，对重金属污染土壤进行了盆栽淋洗试验，而后种植东南景天（Sedum Alfredii），测定淋出液及植物重金属含量。另外，通过浸提试验研究了含有不同阳离子的MC对重金属淋洗效果的影响。结果表明，pH值为5和7的MC显著提高了Cd、Pb和Cu的淋出率。与Na+、K+离子相比，Ca2+的存在能够提高MC对重金属的淋洗去除。pH值7和9的MC淋洗土壤后提高了东南景天的生物量，但是降低东南景天中Cd和Zn的浓度，导致其植物提取率低于无淋洗剂对照。在化学淋洗+植物提取联合技术中，Cd和Zn主要靠植物提取去除，植物提取率分别可达土壤Cd的30%～40%和土壤Zn的6.5%～6.9%；而Pb和Cu主要靠混合螯合剂淋洗去除，去除率分别为2.3%～2.6%和1.6%～2.0%。综合来说，如果需要同时去除Cd、Zn、Pb和Cu，降低土壤重金属有效态含量，用pH值9的MC淋洗土壤联合植物提取较为合适。

Effects of mixture of chelating agents with different pH values on phytoextraction and heavy metals removal

The mixture of chelators (MC) can remove heavy metals from contaminated soils, but the appropriate pH value and its impacts on the following phytoextraction need to be elucidated. Pot experiments were carried out to evaluate the efficiency of heavy metals removal by MC at different pH values (2.75, 5, 7 and 9). The ptytoextraction by Sedum alfredii in the soil after washing with MC were also assessed. Result showed that soil washing with MC at pH 5 and 7 significantly increased the leached Cd, Pb and Cu. Heavy metals removal enhanced by addition of Ca2+ into MC instead of Na+ or K+. The biomass of S. alfredii enhanced after soil washing with MC at pH value 7 and 9, but the concentrations of Cd and Zn in S. alfredii and phytoextraction rates reduced compared with the initial MC at pH 2.75. In this combined technology, Zn and Cd removal mainly depended on phytoextraction, its removal rates were from 30% to 40% of the total soil Cd and from 6.5% to 6.9% for Zn. Pb and Cu removal relied on soil washing, the removal rates were from 2.3% to 2.6% of the total soil Pb and from 1.6% to 2.0% for Cu. Overall, the combination of soil washing with pH value 9 MC and phytoextraction was preferred to remove simultaneously Cd, Zn, Pb and Cu from the acidic contaminated soil and to decrease its available pools in the soil.