Browsing by Author "Kolusheva T."

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    Study of the complex equilibrium between titanium (IV) and tannic acid
    (2014-01-01) Surleva A.; Atanasova P.; Kolusheva T.; Costadinnova L.
    Titanium-tannin (Ti-TA) complex is used in the modern leather technology as an alternative of chromium tannage and as an effective modification of vegetable tanning. The ratio between metal and tanning reagent is a key factor for minimizing the unused quantities of tannic acid that could reach the environment by waste waters and cause damages on aqueous ecosystems. However, a lack of reliable data about Ti-TA complexation limits the possibility for fine tuning of the composition of tanning solutions. This study is aimed at characterization of titanyl-tannin complex: its structure, stoichiometry and stability constant. The data of alpha-coefficient of titanyl-hydroxocomplexation at different pH values were also presented.The results obtained showed that in the concentration interval 5×10-6 - 2×10-5 M and pH 4, the main titanium IV species in titanyl/tannin/formate solutions is titanyl-hydroxo-tannin complex TiO(OH)TA. It was proved by UV-Vis and IR spectrometry that the aromatic carboxylic oxygen (Ar-C=O) and probably phenolic oxygen of tannin are involved in the coordination of titanyl ion. The stability constant of TiO(OH)TA was estimated: lgβ = 16.53. The obtained molar ratio curves and the calculated values of the equilibrium constants could be used in leather technology for selecting an appropriate composition of tanning solutions.