Removal and recovery of gallium from aqueous solutions by complexation with sodium di-(n-octyl) phosphinate

A new precipitation process is reported for the removal and recovery of gallium (III) from aqueous solutions using sodium di-(n-octyl) phosphinate. The complexes formed have low solubility in water and the ligand is easily regenerated, as previously reported for the precipitation of lead and zinc. The effects of different ligand-to-gallium mole ratios, pH and temperature are studied. Essentially complete removal of gallium was obtained at 22 °C using a ligand-to-gallium mole ratio of 3 and pH between 2 and 7.5. The effects of competing ions, such as SO42−, Cl−, Na+ and Ca2+, are documented. While there is a clear selectivity of gallium over Ca2+, the presence of Na+ cation and anions such as SO42− and Cl−, instead of NO3−, decreases the efficiency of the process. Gallium is recovered from the insoluble complexes using diethyl ether or chloroform in contact with an aqueous solution at different values of pH. While gallium is solubilized in the aqueous phase, the ligand is extracted into the organic phase. The ligand is recovered by evaporating the organic solvent.