Synergistic extraction of Li/Rb and simultaneous removal of Si from the lithium concentrate via a novel alkaline method

The alkali method has been proven to be an effective approach for lithium (Li) and rubidium (Rb) extraction; however, the significant dissolution of silicon (Si) remains a challenging issue. A high Si concentration in the leachate can cause filtration difficulties and pipeline blockages, while also negatively affecting phase separation during the subsequent extraction of Rb. Additionally, since the leachate needs to be recycled, the removal of Si from the leach liquor is essential. This study introduces an innovative approach of adding Al(OH) 3 for Si removal during the alkali leaching of lithium concentrate. Preliminary single-factor experiments demonstrate that Al(OH) 3 effectively reduces the Si concentration in leach liquor but also consumes NaOH, leading to a decline in Li and Rb leaching efficiency. Given the interaction between Al(OH) 3 addition and NaOH concentration on element leaching, Response Surface Methodology was employed to predict and optimize the parameters of the leaching process. Under the optimal parameters of 290 g/L NaOH concentration, 39 % Al(OH) 3 addition, and 120 °C leaching temperature, the experimental leaching efficiencies of Li, Rb, and Si were 99.8 %, 87.9 %, and 4.1 %, respectively. Subsequently, Rb was separated with Li via solvent extraction under high alkaline conditions. The single-stage extraction efficiency of Rb was 82.8 % at optimized conditions, and after four-stage countercurrent extraction, the overall Rb recovery could reach 99.2 %. The innovative alkali method proposed not only enables the synergistic extraction and separation of Li and Rb but also achieves effective Si removal and its utilization.