Chemical immobilization of 8-hydroxyquinoline and 8-hydroxyquinaldine on chitosan-silica adsorbent materials for the selective recovery of gallium from Bayer liquor

Abstract

Ion exchange is a widely used technique for the recovery of gallium from Bayer liquor of the alumina industry. However, development of cheap, selective, reusable and environmentally friendly resin materials is essential. Novel resins must be resistant to both the highly alkaline environment of Bayer liquor and the acidic media used for stripping. In this study, chitosan was combined with silica. The hybrid chitosan-silica (CS) adsorbent matrix was chemically immobilized with the organic ligands 8-hydroxyquinoline (8-HQO) and 8-hydroxyquinaldine (8-HQA), the latter being the C2-methylated analogue of the former. Adsorption of Ga(III) and Al(III) by CS functionalized with 8-HQO and 8-HQA was studied as a function of kinetics, equilibrium concentration, aqueous pH and temperature, to determine the conditions to get the highest selectivity for Ga(III). With the 8-HQA-functionalized adsorbent, selective stripping of the loaded metal ions by sulfuric acid resulted in a better Ga(III)/Al(III) separation, in comparison with 8-HQO-CS. In contrast to the resins that are currently in use, no significant loss in Ga(III) loading was observed after seven consecutive alkaline adsorption and acidic desorption cycles. It was also possible to separate Ga(III) from a synthetic Bayer solution using an ion-exchange column with 8-HQA-functionalized CS as the stationary phase. The studied adsorbents are considered promising resin materials to make gallium recovery from Bayer liquor of lower environmental impact and less expensive by significantly decreasing the resin cost.