Center for Mineral Processing and Metallurgy, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Miyagi, Japan.
Department of Materials and Life Science, Faculty of Science and Technology, Seikei University, Musashino, Tokyo, Japan.
PLoS One. 2022 Mar 14;17(3):e0265451. doi: 10.1371/journal.pone.0265451. eCollection 2022.
Fluoride contamination is a major problem in wastewater treatment. Metaettringite (which has previously shown enhanced anion adsorption) was investigated as a possible adsorbent to remove fluoride from low-concentration solution (25 mg-F/L). The fluoride removal properties of ettringite and metaettringite were first compared at pH 10, and metaettringite was found to be more effective. The dominant reaction mechanism for fluoride adsorption in metaettringite was found to be recrystallization of metaettringite by rehydration; this was accompanied by precipitation of calcium fluoride. The adsorption kinetics followed the pseudo-second order model. Metaettringite was also able to remove fluoride effectively in low pH environment (i.e., at pH 3.5). The influence of coexistence of sulfate ions in solution on the fluoride removal performance was investigated, and a small decrease in performance was noted. The residual fluoride concentrations obtained with higher doses of metaettringite were lower than those specified by the Japanese effluent standard (non-coastal areas: 8 mg-F/L; coastal areas: 15 mg-F/L). The fluoride removal capacity of metaettringite was compared with those of other solid materials. The observed maximum capacity was 174.7 mg-F/g-metaettringite. In the case of high fluoride concentration solution, the main removal mechanism will be changed to calcium fluoride precipitation. In general, metaettringite is regarded as promising material for fluoride removal in wastewater treatment.
氟化物污染是废水处理中的一个主要问题。钙矾石（先前已显示出增强阴离子吸附的能力）被研究为一种可能的吸附剂，用于从低浓度溶液（25mg-F/L）中去除氟化物。首先比较了钙矾石和钙矾石在 pH 值 10 下的氟化物去除性能，发现钙矾石更有效。钙矾石中氟化物吸附的主要反应机制是通过再水合作用使钙矾石再结晶；这伴随着氟化钙的沉淀。吸附动力学遵循准二级模型。钙矾石在低 pH 环境（即 pH 3.5）中也能有效地去除氟化物。研究了溶液中硫酸根离子共存对氟化物去除性能的影响，发现性能略有下降。用较高剂量的钙矾石获得的残留氟化物浓度低于日本排放标准（非沿海地区：8mg-F/L；沿海地区：15mg-F/L）规定的浓度。钙矾石的氟化物去除能力与其他固体材料进行了比较。观察到的最大容量为 174.7mg-F/g-钙矾石。在高氟化物浓度溶液的情况下，主要的去除机制将变为氟化钙沉淀。总的来说，钙矾石被认为是废水处理中去除氟化物的一种有前途的材料。
