Low environmental impact process for germanium recovery from an industrial residue

Abstract

This paper focused on the germanium recovery from an Integrated Gasification with Combined Cycle fly ash (IGCC FA). The global process comprised the leaching of the IGCC fly ash with an aqueous solution containing tartaric acid, retention of the germanium-tartaric chelate onto a conventional anionic resin (IRA-900) and elution of germanium. The last step consisted of the germanium precipitation which was accomplished with tannic acid. The leaching experiments were performed with tartaric aqueous solutions and with the raffinate from the subsequent ion-exchange (IX) step. Raffinate from the IX step can be reintroduced in the process as leaching solution. When the contact between FA and leaching solution was maintained for 3 h at pH = 1, the Ge leaching efficiency achieved 86%. The effect of pH, resin dosage and tartaric acid dosage on the Ge retention onto the IRA-900 resin was investigated employing a centered composite rotatable design (CCRD) for experimental design and analysis of results. The retention of Ge-tartaric acid complex onto IRA-900 was optimized using design-expert software and the optimum predicted efficiency and loading capacity were 90–98% and 3.0–3.5 mg·g−1. The experimental affinities that IRA-900 showed for the elements extracted (leached) were: Ge >> Sb > V > Ni > As > Sn > B > Zn. Different eluting solutions were tested, and more than 90% of Ge elution was achieved with 2 M HCl. Final solutions contained Ge, Sb and V. Precipitation tests focused on the optimum pH for Ge precipitation adding tannic acid to the elution solutions. A 99.3% of Ge was precipitated from eluting solution, adding 33.3 g of tannic acid per g of Ge. V also precipitated in some extent along with Ge but the rest of elements practically remained in solution.