Feasibility of soil washing agents to remove fluoride and risk assessment of fluoride-contaminated soils

Purpose The objectives of this study are to find the most suitable soil washing agent and the optimal concentration for fluoride removal and to further provide insights into fluoride-contaminated soil washing. Methods The effects of the washing solution, the concentration, and the particle size of soil on the fluoride removal efficiency were investigated. Evaluation of the feasibility of ZrO2 to treat soil-washing wastewater and risk assessment of fluoride contaminated soil before and after soil washing were also conducted. The fluoride concentration in soil was measured following the standard method, and the fluoride concentration in solution was measured following 2-(parasulfophenylazo)-1,8-dihydroxy-3,6-naphthalene-disulfonate (SPADNS) spectrophotometric method. Results Sulfuric acid (H2SO4) showed the highest fluoride removal efficiency. The dominant fraction of F was the residual fraction before and after soil washing. ZrO2 injection showed 97.9% of fluoride removal efficiency in the post-treatment of soil-washing wastewater. The hazard quotient for non-carcinogenic risk was 1.12 x 10(-2) for adults and 1.04 x 10(-1) for children, respectively. Conclusion The results indicated that 1 M of H2SO4 could meet Korean soil standard (400 mg/kg) as soil washing solution. These results indicated that the soil washing of fluoride-contaminated soil with H2SO4 could be a feasible technique for soil remediation.