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研究报告

Experimental study on the performance of chromium removal from soil by citric acid leaching

摘要：铬渣污染场地常常对其周边的土壤及地下水造成严重污染,因此,亟需探索修复铬污染土壤及地下水的技术方法.本文以某典型铬渣堆存场地内采集的污染土壤为研究对象,配置了浓度分别为0.01、0.05和0.1 mol·L^-1的柠檬酸溶液,通过振荡洗脱批实验和淋洗柱实验对柠檬酸去除土壤中铬的效果和机理进行探讨.实验结果表明,柠檬酸对土壤中可还原态与可氧化态铬的淋洗效果显著优于去离子水,其对土壤中总铬的淋洗率可达80.7%,而去离子水仅为49.9%;在振荡洗脱批实验初期,土壤中50%左右的铬可以快速扩散到溶液中,且不同淋洗剂间淋洗效果无显著差异;柠檬酸的存在,使得反应体系中的六价铬逐渐被还原为三价铬,且还原速率随柠檬酸浓度的升高而增大;pH并非影响柠檬酸去除土壤中铬效果的唯一主要因素,柠檬酸对土壤中铬的去除机制还缘于其对土壤中三价铬的解吸作用.

Abstract：Storage piles of chromium slags in the natural environment could cause serious chromium contamination in soil and groundwater, therefore should be solved urgently. To understand the chromium-removing effect and mechanism in soil by leaching of citric acid, batch and column tests were conducted with citric acid concentration of 0.01, 0.05 and 0.1 mol·L^-1. Contaminated soil samples were taken from a typical chromium slag storage site. The test results indicate that citric acid has a better performance than deionized water in removing reduced-state and oxidized-state chromium in soil, with chromium removal of 80.7% in comparison with 49.9% of deionized water. For all tested flushing agents, there is no obvious difference in initial stage and nearly half of chromium in soil can be quickly desorbed into the solution. The existence of citric acid causes gradual reduction of Cr (Ⅵ) to Cr (Ⅲ), and the rate increases with the increasing concentration of citric acid. The pH value is not the only major factor that influences the chromium-removing effect by citric acid. The desorption of Cr (Ⅲ) by citric acid also contributes to the removal of chromium in soil.