This work aimed to investigate dispersed gas flotation for Ga(III) removal as influenced by the speciation and solubility of Ga(III). Theoretical Ga(III) solubility was the lowest (0.615  104 mM) in pH range of 4.9–5.8, and experimental solubility of Ga(III) generally showed a good agreement with theoretical predictions.
In flotation separation, removal efficiency of Ga(III) dramatically increased from 43.0% to 87.3% as pH increased from 2.5 to 6.0. In contrast, the efficiency sharply declined to 41.4% once pH further increased to 10.3. At pH 2.5, Ga(III) removal efficiency substantially increased with increasing SDS concentration;
however, the removal efficiency slightly rose with SDS concentration at pH 6.0 and remained unchanged at pH 10.3. The clear correlation between SDS dose and Ga(III) separation efficiency showed that the electrostatic interactions resulted in flotation separation of cationic species of soluble Ga(III). In addition,
anionic SDS became adsorbed on the positively charged surface of colloidal solid Ga(III) via electrostatic force facilitated attachment of nitrogen gas and Ga(III) separation by foam. Nitrogen flow rate accelerated reaction rate of flotation process, while ionic strength slightly hindered removal efficiency of Ga(III).