Lithium extraction from Zimbabwean petalite using ammonium bifluoride

Abstract

Extraction of Li2CO3 from Zimbabwean petalite, from the Bikita deposit, was studied using ammonium bifluoride (ABF) digestion at temperatures ranging from room temperature to 600 oC, and gram quantities of ore. ABF digestion bypasses the conventional high-temperature conversion of the mineral to β-spodumene before acid roasting. The process reaction takes place at surprisingly low temperatures—even at room temperature with slurry formation due to the release of water. Below the melting point of ABF, the main products are LiF, AlF3, K2NaAlF6, and (NH4)2SiF6. (NH4)2SiF6 decomposes readily to form ammonia and gaseous SiF4. At higher temperature the products are cryolithionite (Li3Na3Al2F12) and eucryptite (LiAlSiO4). The fluoride solids are not readily soluble in water, and may be roasted in sulfuric acid at relatively mild conditions for a few tens of minutes, then water leached, with 99 % pure lithium carbonate easily recovered from the aqueous phase.