Recovery of fluoride as perovskite-like minerals from industrial wastewater

• Fluoride was recovered as peroskite-like minerals from wastewater.
• Both pH and molar ratio are critical parameters for fluoride removal and minerals recovery.
• Elpasolite and cryolite could be easily separated via gravity.
• The method is simple and energy-efficient.

This study investigated the recovery of fluoride (626.5 mg/L) from an industrial wastewater as perovskite-like minerals. Effects of equilibrium pH (pHeq), molar ratio of Na to F (Na/F), and types of pH reagents were examined. Fluoride was recovered and confirmed by XRD as elpasolite (K2NaAlF6) when pH reagent was KOH. High fluoride removal efficiency (>94.7%) was found at Na/F of 3/6, Al/F of 1/6, room temperature, and pHeq range of 4.2–5.7. Satisfactory K2NaAlF6 recovery and fluoride removal were found as Na/F reduced to 1/6. Fluoride was recovered as cryolite (Na3AlF6) when NaOH was the pH reagent at Na/F of 12/6, Al/F of 1/6 and pHeq range of 5.5–7.2, and good fluoride removal efficiency (>94.5%) was found. Size analysis and sedimentation test showed that both K2NaAlF6 and Na3AlF6 could be easily separated from water. The current study demonstrated simple and energy-efficient alternatives for fluoride recovery as potentially reusable minerals from wastewater.