Influence of the Organic Acids on the Heavy Metals Mobility and Distribution in the Contaminated Soils

The accumulation of heavy metals in the soil is a serious environmental problem. One of the heavy metals remediation methods from contaminated soils is the use of chelating agents, particularly organic acids. The aim of this study was to evaluate the potential of citric acid, and tartaric acid for the Cd, Zn, Cu, Pb, Ni mobility and distribution in the contaminated soils. Accordingly, soil samples were collected from contaminated soils of Charmshar Industrial Park located in Varamin city. Six samples were collected from surface (0-15 cm) in 2019. Contaminated soils were washed using 0.05M citric acid and tartaric acid using a soil: liquid ratio of 1:25. In order to understand the distribution of Zn, Pb, Cu, Ni, and Cd in soils before and after washing, a sequential extraction procedure was applied. Accordingly, five chemical fractions of the studied heavy metals were defined: exchangeable (F1), carbonate (F2), organic (F3), Fe-Mn oxide (F4) and residual (F5). Residual forms were the most important for the retention of all heavy metals. Zn and Cu had the same distribution and fractionation pattern. Cd and Pb had a strong affinity for the Fe-Mn oxide fraction. The washing efficiency varied in the order: Citric Acid˃Tartaric Acid. Citric acid removed 45.55% Zn, 31.04% Pb, 35.64% Ni, 48.7% Cu and 37.2%. Tartaric acid showed extraction efficiency of 3.42% Zn, 16.15% Pb, 26.34% Ni, 28.93% Cu and 18.76% Cd. The Cu, Cd and Ni mobility factor were observed higher than 10 %. The mobility factor for five heavy metals calculated less than 10 %, after washing by citric acid and tartaric acid. The results of this study showed that citric acid and tartaric acid have a deleterious role in the release of heavy metals, and using theses acids is recommended to contaminated soil remediation.