Removal of fluoride ions from aqueous solution by metaettringite

PLoS One. 2022 Mar 14;17(3):e0265451. doi: 10.1371/journal.pone.0265451. eCollection 2022.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adsorption
  • Calcium Fluoride
  • Fluorides / chemistry
  • Hydrogen-Ion Concentration
  • Kinetics
  • Water Pollutants, Chemical* / analysis
  • Water Purification*

Substances

  • Water Pollutants, Chemical
  • Calcium Fluoride
  • Fluorides

Grants and funding

Atsushi Iizuka, 16SW-361, Steel Foundation for Environmental Protection Technology, http://www.sept.or.jp/index.html, The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Atsushi Iizuka, no grant number, Arai Science and Technology Foundation, http://www.arai-f.or.jp/index.html, The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.