P 78 Podval'naya, N. V. Hydrolytic Precipitation of Calcium Polyvanadates from Vanadium(IV) and Vanadium(V) Solutions / N. V. Podval'naya, V. L. Volkov // Russian Journal of Inorganic Chemistry. - 2007. - Vol. 52, № 9. - P1468-1473 : il. - Bibliogr. : p. 1473 (13 ref.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): ГИДРОЛИТИЧЕСКОЕ ОСАЖДЕНИЕ -- ПОЛИВАНАДАТ КАЛЬЦИЯ Аннотация: The effect of VO2+ ions on the composition and kinetics of calcium polyvanadate precipitation from solutions with 1.5≤pH≤9 at 80–90°C has been studied. For 1.5≤pH < 3 and V(4+)yV(5+) = 0.11–9, the precipitated compounds have the general formula CaVxV(4+)yV(5+)12-yO31–δ· nH2O (0.8 ≤ x ≤ 1.06, 2 ≤ y ≤ 3, 0.94 ≤ δ ≤ 1.5). The maximum vanadium(IV) proportion (y = 3) in the precipitates is achieved when V4+/V5+ = 0.5–1.0 in the solution and pH is 3. Polyvanadate precipitation at pH 1.7 has a long induction period (up to 30 min), which is not observed for V4+/V5+ > 0.1. Precipitation in solutions with pH 3 occurs only when VO2+ ions are added, with a maximum rate near V4+/V5+ = 0.2 and in presence of chloride ions. The processes are controlled by a secondorder reaction on the polyvanadate surface Полный текст |