Advantages of pH and Temperature Control in the Carbonation Stage for Li2CO3 Production with Sulphated Liquors

This work addresses the carbonation of an aqueous solution that simulates leach liquor with sulphuric acid, a chemical system that is seldom studied, and the subsequent precipitation of Li2CO3 via evaporation of the diluent water. New details were revealed on the automatic control of pH and temperature to optimizes the carbonation operation conditions and the quality of the products. Among the relevant findings are: a) the carbonation stage was optimized at pH 12 and 35 °C because, under these conditions, the redox potential (100–200 mV) promotes the carbonates stability, b) the carbonation reaction in sulphated solutions has zero order and its activation energy is 6.81 kJ/mol, suggesting that the reaction is controlled by diffusion, and c) At pH 8 and 20 °C the maximum purity (99.9 % Li2CO3) was precipitated. Additionally, other carbonate based secondary phases were precipitated together with Li2CO3. The chemical stability of these secondary phases is pH dependent and are discussed in detail. In the production of Li2CO3, the automatic control of pH and temperature optimizes the carbonation stage of a leach liquor with sulphuric acid and defines the recovery rate and the purity of the products, during the evaporation stage. The carbonation stage was optimized at pH 12 and 35 °C, but at pH 8 and 20 °C the maximum purity (99.9 % Li2CO3) was obtained.