Gallium recovery from aluminum smelting slag via a novel combined process of bioleaching and chemical methods

Smelting slag generally contains a large number of heavy metals. In this study, the separation and selective recovery of gallium from aluminum smelting slag was studied deeply. Processes for bioleaching and recovering gallium from aluminum smelting slag have been executed. Under the condition of 2% pulp density, the Ga dissolution reached 505 mg/L, with a Ga bioleaching efficiency close to 100%. Ion exchange resin, fractionation precipitation, and milk of lime were assessed to test their efficiency in the separation and selective recovery of Ga from bioleachate. The results show ion exchange resin does not have selectivity to separate Ga from metals-based pregnant bioleachate. In addition, due to the similar properties between Ga and Al elements, copercipitation reaction occurred, consequently resulting in the failure of chemical fractionation precipitation to separate and recover Ga. However, under the optimized experimental conditions, the milk of lime technique yielded the maximum recovery of 60.6%, proving that the method is superior to the first two methods. Therefore, a combined process development of bioleaching and milk of lime can be considered high-efficiency, economically and environmentally friendly for separating and selective recovery of Ga from aluminum smelting slag.