Precipitation behavior of Ca(OH)2, Mg(OH)2, and Mn(OH)2 from CaCl2, MgCl2, and MnCl2 in NaOH-H2O solutions and study of lithium recovery from seawater via two-stage precipitation process

This study describes a hydrometallurgical process to investigate the recovery of lithium from seawater using devised total process including an adsorption process with manganese oxide adsorbent and a precipitation process. First, precipitation experiments on Ca(OH)2, Mg(OH)2, and Mn(OH)2 from CaCl2, MgCl2, and MgCl2 in NaOH-H2O solutions were carried out under various conditions of reaction temperature (25–90 °C), NaOH concentration (7–14 pH), and initial amount of CaCl2, MgCl2, and MnCl2 (10 and 100 mmol/dm3). The obtained results showed that there was a need to divide the precipitation process into two steps based on the precipitation characteristics of the target elements in NaOH (or HCl)-H2O solutions. These two steps consist of a first stage with precipitation of Ca(OH)2, Mg(OH)2, and Mn(OH)2 by NaOH and a second stage with Li2CO3 recovery by neutralization using HCl, carbonation using Na2CO3, and concentration using evaporation. Chemical modeling with OLI-Systems® software was used to interpret the precipitation behavior of target elements in the first and second stages; it was compared with available experimental data and good agreement was found. On the basis of the above data, it was possible to separate Ca, Mg, and Mn under pH values ranging from 11.5 to 12.5 in the first stage after the process of seawater adsorption with manganese oxide adsorbent and to recover crystalline Li2CO3 with high purity (over 99%) carbonated by Na2CO3 in the second stage, involving neutralization by adjusting the pH value in the range of 6–8 and evaporation at 100 °C to obtain the product with high yield.