Ion exchange properties of crystalline bismuth molybdenum hydrous oxide and its intercalates. Equilibrium and kinetics of UO22+ ions on the crystals

The sorption of uranyl ions on crystalline bismuth molybdenum hydrous oxide and its intercalates were investigated from point of view of both equilibrium and kinetics. Ion exchange isotherms of uranyl ions on the crystals were obtained, and ionic sieve effect was employed to describe the characteristics of ion exchange isotherms. The best fitting for sorption of uranyl ions on BMHO was achieved by means of the Langmuir isotherm, while the Freundlich isotherm appeared to best fit for its intercalates. The slightly negative free-energy change indicates that, thermodynamically, the crystals behave less favourable for uranyl ions. The equation derived from SN2 chemical reactions was proved to fit the rate curves, and the rate constants were determined. The comparison between the calculated and observed pH values as a function of time further verified the chemical reaction mechanism. (author)