Binding and precipitation of germanium(IV) by four hydrolyzable tannins

Abstract

The complexation conditions and complex characteristics of 1,2,3,4,6-O-galloyl-β-D-glucose (PGG), a typical hydrolyzable tannin, and Ge4+ were studied. Species of the PGG-Al3+ complex formed in various water-methanol systems (20% to 100%, v/v) were investigated. The results showed that the amount of PGG and Ge in the precipitate was substantially influenced by the initial Ge/PGG molar ratio. The highest amount of the precipitate was obtained at the initial Ge/PGG molar ratio of 1:2 and the stoichiometric ratio (Ge/PGG molar ratio) of the precipitates gradually decreased from 0.72 to 0.30 concomitant to a decrease in the initial Ge/PGG molar ratio from 1:1 to 1:4. Precipitation experiments of Ge4+ by four hydrolyzable tannins from Chinese gallnut (TA), chestnut shell (CT), Platycarya strobilacea infructescence (PT), and Valonia (VT) were compared. The results indicated that the amount of the precipitate was substantially influenced by the initial tannin/Ge ratio and pH and was slightly influenced by the reaction time. The highest amount of the precipitate was obtained at the initial tannin/Ge mass ratio of 2.3:1 and pH 7.2. Stability of the TA-Ge, CT-Ge, VT-Ge, and PT-Ge precipitates in several solutions was determined. The TA-Ge precipitates showed relatively high stability in the test solvents compared to that of other tannins.