Hydrolyzable Tannins Complex And Precipitate With Germanium:quantitative Relationship And Influencing Conditions

Germanium is a rare dispersed metal element.China is the world's largest producer and exporter of germanium products.At present,extensive mining and inefficient smelting have led to low comprehensive utilization of germanium,serious environmental pollution and waste of energy.This thesis focuses on the key step of germanium precipitation,tannin complex germanium,which is widely used in germanium mining and smelting.It is hoped that on the basis of the existing technological process,the quantitative relationship and influencing factor of plant tannins complex and precipitatewith germanium will be clarified,and the reaction conditions will be optimized to improve the recovery and comprehensive utilization of germanium and provide theoretical basis with reference value for the development of new tannin germanium precipitating agent.The author first established the scientific research method of germanium metal complex reaction by taking the model tannin,1,2,3,4,6-penta-O-galloyl-?-D-glucose(PGG)as the object.According to the UV-Vis spectrum of the reaction between PGG and germanium and the software of Reactlab Equilibrium,the stoichiometric ratio and the complexation constant of the complexation of tannin and germanium were obtained.The phenolic hydroxyl groups in tannic acid are first deprotonated and then coordinated with germanium ions.And the p H of the solution has a great influence on the reaction.It was concluded that not all phenolic hydroxyl groups in tannic acid are prone to deprotonation.The spectral data of the reaction were analyzed by job's method reasonably.It was determined that Ge PGG and Ge₂PGG species were established at p H 6.0 and only Ge PGG was established at p H 4.0 under the test conditions.The conditional log Ks were calculated to be 5.32±0.04 and 9.81±0.12 for Ge PGG and Ge₂PGG complexes at p H 6.0,respectively.A small log K(6.50±0.07)was calculated for the Ge-PGG complex at p H 4.0,indicating weak binding between Ge and PGG at low p H values,and the optimal p H for the formation of germanium-PGG complex is about 6;the precipitation ability of tannin to precipitate germanium depends on the properties of tannin and reaction conditions:germanium precipitation by PGG was sensitive to the presence of solvents in the reaction mixture and the effects of solvent on the stability of germanium-PGG complexes can be ranked as follows:acetone,ethanol,and methanol;the presence of zinc ions in the mixture was unfavorable to germanium precipitation by PGG and that the suppression ability decreased as the zinc concentration increased;the germanium/PGG ratio was also an important factor that affected the complex,and the present study shows that more than a 3:1 germanium/PGG ratio is essential for precipitation at the stated experimental conditions;the reaction time has little impact on the precipitation of PGG-germanium.On the basis of PGG-Ge reaction,the research direction is provided for further screening of germanium precipitating agent by tannin,and a set of transportable comparison method for the performance of germanium precipitating agent by tannin is established.On this basis,taking Chinese gallnut tannin as a contrast,three kinds of hydrolyzable plant tannins were selected:valonea shell tannin,chestnut shell tannin,and fragrant fruit tannin.Further experiments on complex and precipitation germanium were carried out.Considering the influence of tannin/Ge mass ratio,reaction solvent system,p H,stability of germanium precipitate,valonea tannin has stronger germanium precipitation ability than other three kinds;at p H 7.2 at the initial tannins/Ge mass ratio of approximately 2.3:1,which was in agreement with the results of the PGG-Ge precipitation experiment described above;the Ge-tannin precipitates were more stable in EDTA-2Na than in three others tested solutions(water,50%CH₃COOH and CH₃COOH).