Abstract
The precipitation of tannin complex of germanium from sulfuric solutions obtained after dross leaching was investigated. The tested solutions contained mainly zinc, germanium, indium, and tin. The influence of temperature, time, amount of added tannic acid and its purity was determined. The application of pure tannic acid allowed the precipitation of >99% of germanium and decreased its concentration in a solution <0.015 g/dm3. It required ca. 11–13 g of pure tannic acid per each 1 g of dissolved germanium. The preferred process conditions for Ge precipitation using powder tannic acid were 90 °C, 90 min, whereas for 20% aq. solution—5 min. It was found that 40% to 50% of tin coprecipitated at these conditions. Therefore, a detinning operation using hydrogen peroxide was proposed. It allowed the removal of >99% Sn and reduced its concentration in the solution below 0.025 g/dm3.
Highlights
Germanium is considered as a critical raw material by the European Union [1]
The Ge-tannin complex in aqueous solutions is formed according to the following equation [12]: Ge4+ + H2 T → (GeT)2+ + 2H+
During these tests 100 g pure tannic acid was added to 1 dm3 of the solution
Summary
Germanium is considered as a critical raw material by the European Union [1]. It is important to many different industrial sectors like optic fibers, infrared optics, electronics, photovoltaics or catalysts for polyethylene terephthalate (PET) production [2]. Ge is obtained as an accompanying element during the processing of other raw materials—mainly from coal ash and by-products of zinc production. One of the ways to process Ge is leaching in aqueous solutions of different acids (usually sulfuric, hydrochloric or oxalic). Dissolved Ge may be later precipitated from sulfuric solutions using hydrogen sulfide [3] or tannic acid, alternatively using ion-exchange resins [4,5], membranes [6], or solvent extraction [7]. Tannic acid forms a water insoluble complex with Ge, firstly described in 1938 by Davies and Morgan [9,10,11]. The Ge-tannin complex in aqueous solutions is formed according to the following equation [12]: Ge4+ + H2 T → (GeT)2+ + 2H+
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