Fluoride Sorption Performance of a Layered Double-Hydroxide–Based Adsorbent Using Soil Extract Solution as the Solvent

Rocks and soil excavated at construction sites can contain naturally occurring toxic substances. One low-cost means of managing the environmental burden posed by leaching of these substances is the attenuation layer method, which uses an adsorbent positioned between the fill and ground. Evaluation of adsorbent performance based on sorption tests is important for designing and optimizing attenuation layer methods; however, few studies have examined the effect of coexisting ions on sorption performance. Here, we examined the effects of these ions contained in soil extract solutions on the fluoride sorption performance of a commercial layered double-hydroxide (LDH)–based adsorbent used in the attenuation layer method. Batch and column sorption tests showed that the distribution coefficients in the presence of coexisting ions were 29%–72% lower than those in tests conducted without coexisting ions. Furthermore, the results of a solid-state analysis and various ion analyses suggest that competition for the sorption sites of LDH by sulfate ions in the soil extract solution was the cause of the reduced sorption performance. These findings imply that reliance only on deionized water-based sorption tests may overestimate the real-world sorption performance of LDH-based adsorbents.