Remediation of Cr(VI)-Contaminated Soils by Washing with Low-Molecular-Weight Organic Acids Based on the Distribution of Heavy Metal Species

In this article, low-molecular-weight organic acids were applied to remediate the hexavalent chromium [Cr(VI)]-contaminated soil. The influence of different parameters (washing concentration, solid-liquid ratio, time, and pH value) on the repair effect was explored, and the form distribution and desorption kinetic experiments of the soil were performed. The results show that the pH of eluents can significantly affect the form distribution of chromium, with the exchangeable form increasing considerably at a lower pH. The kinetics of Cr(VI) desorption can be described by the pseudo-second-order kinetics equation. The best washing scheme was determined to be the citric acid as the eluent at a concentration of 0.3 mol/L, a solid to liquid ratio of 1:10, pH 4, and a washing time of 6 h. The removal rate can be as high as 73.52%. After washing, the leaching concentration of Cr(VI) in the soil was reduced from 23.76 to 1.05 mg/L, well below the regulatory constraint of 5 mg/L. Additionally, the characterizations of X-ray diffractometer and scanning electron microscope showed little effect of adopting citric acid as a washing agent on soil structure and surface morphology. This study can provide a theoretical basis for the remediation of Cr(VI)-contaminated soil at industrial sites.