Flotation Separation of Soluble and Colloidal Indium from Aqueous Solution

This work investigated the speciation and solubility of indium (In) and its flotation separation from aqueous solution. Lowest theoretical In solubility was predicted for pH 5.5-8.5, and the solubility increased as it became more acidic or more alkaline. Experimentally, 20 mg/L of In completely dissolved at pH < 3.0, which agreed with theoretical prediction. At pH 3.6-9.9, In showed slightly higher solubility than predictions. There was good agreement at pH > 9.9. Flotation reaction was described by pseudo-first-order kinetic model and its reaction rate increased with increasing nitrogen flow rate. The results indicated that pH played a key for the flotation process. As pH increased from 4.0 to 6.8, removal efficiency rose from 65.0% to 95.8% when applying surfactant SDS as collector. The efficiency decreased to 56.7% at pH 9.9. Lower removal efficiency was found once using CTAB. Electrostatic interaction between collector with both soluble and colloidal In was the main mechanism for In flotation.