Extraction and Separation of Gallium and Indium from Aqueous Chloride Solution Using Several Organophosphorus Compounds as Extractants

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A separation process for gallium and indium in chloride solution with organophosphorus acids as extractants is investigated. Extraction equilibrium formulations are established up to high loading ratios, and extraction equilibrium constants are determined, employing bis(2-ethylhexyl)phosphoric acid (D2EHPA), 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (EHPNA), and bis(2-ethylhexyl)phosphinic acid (PIA-226) as extractants, and kerosene as a diluent. A feature of the present extraction systems is the inclusion of chloride and hydroxyl ions in the extract entities to compensate the positive charge of the metals, especially at high loadings. With EHPNA and PIA-226, mixed complexes containing both metals in a mole ratio of 1:1 are formed at high loading ratios. This is not the case with D2EHPA, which makes D2EHPA most suitable for separation of gallium and indium. Simulation work on separation of gallium and indium by counter-current mixer-settler cascade with D2EHPA shows that separation and recovery of gallium and indium are enhanced under the conditions of high pH values of aqueous feed solution and large values of ratio of the flow rate of organic to aqueous phase, E/F. Effective separation is realized by counter-current cascade of 15 stages, and an E/F ratio of 3 with gallium purity of 99.8% and indium purity of 97.4%.
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