Optimizing soil washing remediation of mercury contaminated soil using various washing solutions and solid/liquid ratios

Most of the artisanal and small-scale gold miners in Indonesia as in the case of those who are in Banten Province, still use the amalgamation process in the gold extraction process. Therefore, mercury contamination could not be avoided. As a result, it was found that the concentration of mercury-contaminated soil in Lebak, Banten Province was detected as high as 136,9 mg/kg. Since the contamination process occurred for a long time, making the formation and mobility of complex mercury in soil increased by time. Soil washing is one remediation technology that can be applied in the recovery of mercury-contaminated soil. This study aims to determine the optimum conditions of the soil washing process: effect of pH, the concentration of washing solutions and ratio of solid/liquid. Furthermore, the value of the distribution coefficient, desorption of mercury in the soil and fractionation of mercury in the soil were also observed. Potassium Iodide was found to be the best washing solution among others used in this study. The optimum condition was obtained at pH 2, the concentration of washing solution at 0.25 M and the solid/liquid ratio of 1:15. Under these conditions, mercury desorption efficiency reached 86.9% with the value of the distribution coefficient of 0.185. Mercury fractionation analysis in the contaminated soil showed that the mobile > semi-mobile > non-mobile fractions. Potassium iodide was able to desorb at about 84% of mobile fractions, 97% of semi-mobile and 25% non-mobile mercury.