Adsorption properties of molybdenum and vanadium on hydrous titanium (IV) oxide

The adsorption of molybdenum (Mo) and vanadium (V) from sea water on hydrous titanium (IV) oxide (HTO) was investigated. HTO as an adsorbent was prepared from the precipitation of aqueous solution of titanium (IV) tetrachloride by hydrolysis with alkaline solution at various pHs. HTOs of different crystallinities from anatase to amorphous were obtained at different precipitating pHs. The anatase type of HTO which was precipitated at low pH of the solution showed a larger capacity of adsorption for Mo than the amorphous. The capacity of adsorption for Mo on HTO increased in proportion to the crystallinity of anatase, while the one for V slightly increased. The linear relationship between log Ksub(d) and pH was obtained for the adsorption of Mo on HTO with slope of -0.9 in the range of pH 7 to 10. The enthalpy changes for the adsorption of Mo on HTO were estimated to be -2.8 kcal mol-1. Ksub(d) for the adsorption of V on HTO showed a large and constant value in the pH 6 to 10 region including natural sea water. These differences in the pH dependency of the adsorptive properties between Mo and V on HTO ware thought to be due to the difference in the adsorption mechanism for these elements, for Mo was considered to be due to an anion exchange mechanism. The adsorption isotherms for Mo and V on HTO showed the Freundlich's relationship, and the equilibrium adsorption capacities for Mo and V on HTO were measured to be 40 mu g g-1 and 240 mu g g-1, respectively. (author)