Study On Soil Washing Technology Of Multi-heavy Metals Contaminated Coastal Saline-alkali Soil

Soil is a key natural factor in human production and life,which can also be the ultimate recipient of more than 90%of pollutants in the environment.Land developments and utilizations are prone to different degrees of soil pollution,especially the increasingly prominent heavy metal pollution problem.Chemical soil washing technology has attracted extensive attention from scholars at home and abroad in recent years due to its short engineering cycle,high removal rate and the stabilized ability to separate pollutants.Based on soil washing tests,we determined the combination and proportion of complex washing agents,and explored the effect of compound washing on the speciations of heavy metals.Through the optimization of the washing conditions,the main influencing factors of the washing process were studied.The effects of washig on soil properties were studied and the mechanism of action was analyzed.Through the systematic study of soil leaching process,it is expected to provide theoretical basis and reference for soil treatment of multi-heavy metal pollution in typical saline-alkali land.（1）Among 9 kinds of washing agents,the removal of As exhibited as CA>OA>KH₂PO₄>Fe Cl₃>GLDA;while Cr showed quite different as Fe Cl₃>CA>OA>Humic Acid>Na₂EDTA.When washing with CA+KH₂PO₄（4:1）,the removal rate of As was 68.26±0.59%,and Cr was 37.21±1.86%,showing a certain degree of synergistic effect.After CA+KH₂PO₄ compounding washing,heavy metals in the soil were mostly in an unstable state（about 60-70%）tested with BCR sequential extraction method.（2）The optimal conditions predicted by response surface optimization analysis were:CA and KH₂PO₄ concentration=0.54 M（3.5:1）,reaction time=11.6 h.The actual removal rate of As was 90.82±0.37%and Cr was 58.13±2.19%.The amount of heavy metal washing was significantly reduced.The results of seed germination test and soil enzyme activity were significantly decreased after compound washing.Therefore,the changes in soil properties such as p H and nutrients caused by soil washing may have a greater impact on the ecological effects of the soil.