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

Alkali metal fluorides (MF) are commodity chemicals currently synthesized from naturally occurring fluorite (fluorspar, CaF) 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 (TiO) under mechanical energy for MF formation and sequestration of calcium (hydr)oxide byproducts as calcium titanate (CaTiO). Ca sequestration prevents reversible CaF formation upon aqueous extraction, thus enabling the isolation of alkali metal fluorides. We also demonstrate that alkali metal titanates (MTiO) are suitable reagents for both CaF activation and Ca sequestration, with KTiO being optimal for KF synthesis.