Comparison of Conventional Soil Washing Methods for Simultaneous Removal of Arsenic and Lead.

Soil washing is commonly considered a media transfer technology for reducing soil contamination using physical separation and chemical treatment. The present study was conducted to compare conventional soil washing techniques. Therefore, soil washing batch tests, using soil that had been co-contaminated highly with arsenic (As) and lead (Pb) were conducted using phosphoric acid (0 - 3 M) as an washing eluent and soil:solution ratios (1:5 – 1:100, g:mL) for optimizing desorption conditions. For comparison to chemical treatments, particle separation conducted within batch test. Separation processes were performed using a different size of sieve, (53, 75, 150, 250, 425 um), after agitating with deionized water and phosphoric acid (0.5 M). Each of sequential extraction procedures (Wenzel and Tessier method for As and Pb, respectively) was used to identify the distribution of elements and their mobility (fraction I + II). The removal of As and Pb increased with the concentration of the phosphoric acid up to 2 M, with no more significant difference above 2 M (p<0.05). In both As and Pb removal, the removal efficiency was the highest with a solid:solution ration of 1:40. The maximum removal efficiencies of As and Pb through chemical treatment were 40.81 and 42.19%, respectively. In the case of particle separation, the removal efficiencies increased with increasing the size of sieve, e.g. 53 to 425 µm, from 43.47 to 77.84% for As, and from 57.94 to 74.62% for Pb, when the amount of residual soil was decreased by 76.11 and 46.53%. However, there was no significant effect of changing washing solution, deionized water to phosphoric acid (0.5 M) for increasing removal efficiency (p<0.05), due to the low mobility fractions of As (1.62%) and Pb (9.73%) in soil. From these results, a physical separation method seems to be a useful tool for eliminating toxic trace elements bounded strongly.