Selective recovery of gallium with continuous counter-current foam separation and its application to leaching solution of zinc refinery residues

Abstract

Continuous counter-current foam separation with simultaneous injections of metal and surfactant solutions into the rising foam bed was applied to gallium(III) recovery from hydrochloric acid solutions. A nonionic surfactant, poly(oxyethylene) nonylphenyl ether, used in this study showed a strong affinity to gallium(III) and played a double role of foam-producer and metal collector. The method was applied to multi-metals solutions of gallium, iron, copper and zinc, and the effects of experimental parameters such as solution acidity, an air flow rate, and injection rates of metal and surfactant solutions, were discussed in terms of the percent recovery and the separation factor of gallium(III) and iron(III). Satisfactory results could be obtained in a single stage; under the optimized condition, the separation factor of gallium(III) was 67 over iron(III) and more than 1000 over the other metals, while keeping the gallium(III) recovery complete. Compared with our previous experiment of solvent extraction using the same surfactant as an extractant, where the separation factor of gallium(III) over iron(III) was found to be merely 1.2, the present method provides much better performance due to its unique contact mechanism between the metal and the surfactant. As a practical trial, the method was applied to an acid leaching solution of zinc refinery residue containing gallium along with vast amounts of zinc, iron, aluminum and arsenic. By optimizing the experimental parameters and reducing trivalent iron with the dose of ascorbic acid to the leaching solution, complete recovery of gallium was attained with negligible contamination from the other metals.