Feasibility of soil washing agents to remove fluoride in soils

Abstract

luorine contamination in soil is receiving increasing attention due to increasing interest in agriculture soil qualities after hydrofluoric acid leakage accident. It occurred on September 2012 in Gumi, Korea, and affected the surrounding soils and plants1). Fluoride in groundwater could be leached from fluorine-containing soil (Maximum concentration limit: 1.5 mg/L)2). The excess concentrations of fluoride could react with calcium in teeth and bones due to strong electronegativity of fluoride3). Soil washing is widely used to remediate contaminated soils. The process can extract a variety of organic or inorganic contaminants adsorbed or precipitated onto the surface of the solid particles. Selection of the appropriate extraction solution is critical for improving the extraction effectiveness. The type of washing solution depends on the target contaminants, the bonding/chelating strength of the extraction solution, and the soil characteristics4). This study investigates the feasibility of soil washing to remove fluorine in soil and characterize fluorine contamination with soil particle size and chemical fractionation. The concentration of 760 mg/kg fluoride was detected in size of 46-84 μm soil particle, fluoride tended to accumulate in the fine fractions. Residual fraction is dominant fluoride bound form in contaminated soil. Three kind of acid (HCl, HNO3, H2SO4) applied as soil washing agent. Sulfuric acid (H2SO4) showed highest fluoride removal efficiency. Effect of washing agent concentration, contact time, and solid/liquid ratio were also investigated. The results of this study could be utilized to select proper washing agent for fluorine contaminated soils.