One-Step HF-Free Synthesis of Alkali Metal Fluorides from Fluorspar.
Schlatzer T., Goult CA., Hayward MA., Gouverneur V.
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.