Germanium recovery from gasification fly ash: Evaluation of end-products obtained by precipitation methods

In this study the purity of the germanium end-products obtained by two different precipitation methods carried out on germanium-bearing solutions was evaluated as a last step of a hydrometallurgy process for the recovery of this valuable element from the Puertollano Integrated Gasification Combined Cycle (IGCC) fly ash. Since H2S is produced as a by-product in the gas cleaning system of the Puertollano IGCC plant, precipitation of germanium as GeS2 was tested by sulfiding the Ge-bearing solutions. The technological and hazardous issues that surround H2S handling conducted to investigate a novel precipitation procedure: precipitation as an organic complex by adding 1,2-dihydroxy benzene pyrocatechol (CAT) and cetyltrimethylammonium bromide (CTAB) to the Ge-bearing solutions. Relatively high purity Ge end-products (90 and 93% hexagonal-GeO2 purity, respectively) were obtained by precipitating Ge from enriched solutions, as GeS2 sulfiding the solutions with H2S, or as organic complex with CAT/CTAB mixtures and subsequent roasting of the precipitates. Both methods showed high efficiency (>99%) to precipitate selectively Ge using a single precipitation stage from germanium-bearing solutions.