One-Step HF-Free Synthesis of Alkali Metal Fluorides from Fluorspar

Abstract

Alkali metal fluorides (MF) are commodity chemicals currently synthesized from naturally occurring fluorite (fluorspar, CaF₂) in two steps: conversion of acid grade fluorspar (AGF) into highly hazardous hydrogen fluoride (HF) followed by neutralization with alkali metal hydroxides/carbonates. Herein, we report a one-step mechanochemical reaction that converts AGF into alkali metal fluorides under basic conditions, bypassing HF. The method consists of reacting AGF with alkali metal (hydr)oxides and titanium dioxide (TiO₂) under mechanical energy for MF formation and in situ sequestration of calcium (hydr)oxide byproducts as calcium titanate (CaTiO₃). Ca²⁺ sequestration prevents reversible CaF₂ formation upon aqueous extraction, thus enabling the isolation of alkali metal fluorides. We also demonstrate that alkali metal titanates (M₂TiO₃) are suitable reagents for both CaF₂ activation and Ca²⁺ sequestration, with K₂TiO₃ being optimal for KF synthesis.