Factors Affecting Ph Value During The Electrokinetic Remediation Of Cr Contaminated Soil

Recently, the serious soil pollution situation has caused widespread concern around the world, the development of technologies for cleaning up the contaminated soils is urgent needed. Studies have demonstrated that electrokinetic remediation technology is an effective way capable of removing heavy metals from soils with low permeability.Cr is one of the common contaminants in the abandoned industrial site of China, and pH value is the key factor for the removing of heavy metals from the soil by electrokinetics. To evaluate the extraction of Cr from contaminated soil by electrokinetics and study the factors affecting pH value and the transformation between Cr(VI) and Cr(III), four electrokinetic remediation experiments were performed with three different kinds of electrolytes and two types of Cr contaminated soils under constant electric potential.The results indicated that the use of different electrolytes didn’t cause significant differences among the anolyte pH value or catholyte pH value, after 25 h the maximum difference in the pH value of anolytes among the experiments with the selected electrolytes is <0.8, and it was <1.2 for the catholytes. pH value is closely related to the current, and electroosmotic flow will also make a difference to pH value. Soil pH value almost remained above 7 due to the high acid buffering capacity of the soil. When the electrolytes were ultra-pure water, 0.1 M KCl and 0.1 M citric acid,concentrations of Cr in the real contaminated soil decreased by 6.59%,-2.15% and 23.57%,respectively. Material flows show 13.07% of Cr removed out of the artificially contaminated soil. The removal efficiency of the total Cr in artificially contaminated soil is almost twice of real contaminated soil when the same electrolyte was used. Cr in the anolytes with high Cr concentration returned to the soil. Based on the mass balance analysis more Cr(VI) reduced to Cr(III) than the oxidation of Cr(III)to Cr(VI) when citric acid and ultra-pure water were used as electrolytes.A numerical model was established to predict the pH value changes of the electrolytes, and another was selected to predict the soil pH value base on the software of COMSOL Multiphysics during the electrokinetic remediation of contaminated soil, by comparing the results predicted with the experimental results the model were optimized, the optimized elecrtolyte pH value predicted model can predict the pH value of elecrtolytes during the electrokinetic remediation of Cr contaminated soil well, while the soil pH value predicted model still needs to be further optimized.