# Precipitation of Germanium from Sulphate Solutions Containing Tin and Indium Using Tannic Acid
## 4 Discussion  
During the tests on the precipitation of Ge-tannin complex from the solution containing Sn, it was found that Ge was almost completely precipitated. However, Sn and In were also present in the precipitate. Sn was present in the solution in divalent form, because its tetravalent form is not soluble in weak sulfuric acid. Divalent Sn was partially precipitated by tannic acid. In is not precipitated by tannic acid [20]. Therefore, its presence may be explained by adsorption of In on precipitate surface. The highest Ge precipitation yield was at 90 \({}^{\circ}\)C. It may be explained by an increase of tannic acid solubility and reaction rate. Detinning of the solution with H\({}_{2}\)O\({}_{2}\) allowed almost complete removal of Sn from the solution. Sn was oxidized to its tetravalent state, which precipitated from weakly acidic sulfate solution. During precipitation, parts of Ge and In were coprecipitated on the surface of the tiny SnO\({}_{2}\) precipitate. In the case of detinned solution, it was noticed that less tannic acid was consumed to precipitate \(>\)99% Ge. It was due to the lower Ge and Sn content in the detinned solution. Original leachates contained 6.3-7.8 g/dm\({}^{3}\) Ge, while the detinned one contained 5.6 g/dm\({}^{3}\). Part of the tannin was also used for Sn precipitation. Therefore, in the first case, tannic acid consumption was 100 g/dm\({}^{3}\), whereas in the second one, it was 60 g/dm\({}^{3}\). To achieve \(>\)99% Ge precipitation yield and Ge concentration \(<\)0.05 g/dm\({}^{3}\), ca. 11-13 g of pure tannic acid should be used per each 1 g of dissolved Ge. This level of tannic acid consumption was achieved for Ge concentration level \(>\)5 g/dm\({}^{3}\). For lower Ge concentrations more tannin should be used--e.g., it was reported that for 0.06 g/dm\({}^{3}\), 10 g of tannic acid was needed to precipitate 0.02811 g Ge [12]. The form of tannic acid had an influence mainly on the process kinetics. When 60 g of tannic acid solution was added at once, over 95% of Ge was precipitated after just 5 min. For the powder form, more than 60 min was required to achieve a similar result. It is connected with the availability of tannic acid molecules. When the dissolved form is used, the reaction takes place almost immediately, whereas the powder form is first dissolving and then dissolved molecules react with Ge. Slight differences in Ge precipitation yields were observed, when smaller amounts of tannic acid were applied. However, the differences decrease as more acid was added. The purity of tannic acid also had an influence on the precipitation yield of Ge. Technical tannic acid contained 80% of active compounds. It was noticed that if 60 g/dm\({}^{3}\) tannic acid was added to the pure one, \(>\)99% Ge was precipitated, while for the technical one it was 71%. The presence of In in the precipitate may be explained by the high concentration of the precipitate in the suspension and high moisture (ca. 55%) of the filtered solid. It was not possible to remove whole In during post-filtration washing. Based on the results of the tests, the following procedure for leachate processing may be proposed. Firstly, solution is detinned using H\({}_{2}\)O\({}_{2}\) and heated to 70 \({}^{\circ}\)C to remove any H\({}_{2}\)O\({}_{2}\) remaining in the liquid and filtered. Then tannic acid is added to the solution at 80-90 \({}^{\circ}\)C while mixing. The process is carried out for at least 90 min. The selection of the tannic acid form should depend on several factors. The solution may be used to reduce process time; however, the amount of generated effluents would increase. Technical tannic acid may be also used to reduce process costs; however the final Ge-tannin precipitate will contain less Ge than one precipitated with pure tannic acid.