Adsorption of Uranium from Solutions by Montmorillonite; Compositions and Properties of Uranyl Montmorillonites

A. Tsunashima1, G. W. Brindley and Marija Bastovanov
Materials Research Laboratory and Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802
1 Present address: Department of Applied Chemistry, Hokkaido University, Sapporo, 060 Japan.

Abstract: Wyoming montmorillonite, <2-µm particle size, saturated with Na, K, Mg, Ca, and Ba ions, was reacted with uranyl nitrate solutions in the concentration range 1–300 ppm uranium. With constant amounts of clay and solution volume, the adsorption isotherms of uranyl ions on the clay followed Langmuir-type curves with increasing concentration of uranium. The maximum adsorption derived from linear Langmuir plots corresponds to the exchange capacity of the clay. Experiments with solutions of constant volume and constant ionicity, but with variable proportions of uranyl and other cations, showed that uranyl ions were strongly preferred by the clay to Na+ and K+, but less strongly than Mg2+, Ca2+, and Ba2+.

Chemical analyses of uranyl montmorillonites prepared with nitrate solutions, 0.05 M and pH ∼ 2.0, gave interlayer cations (UO2)0,094H0,12. Addition of NaOH to the uranyl nitrate solution to increase the pH to 4.0 gave a montmorillonite with interlayer cations (UO2)0,083Na0,12H0,04. A fully exchanged uranyl montmorillonite was prepared with 0.05 M uranyl acetate solution, pH ∼ 4.0, followed by further treatment with 1.25 × 10−5 M solution, pH ∼ 4.5. The resulting interlayer composition was (UO2)0,19(H2O)1.15 which corresponds with the hexahydrate ion, [(UO2)−6H2O]. X-ray powder diffraction and thermal data are recorded for the fully exchanged uranyl montmorillonite.

Key Words: Adsorption • Cation exchange • Interlayer cations • Montmorillonite • Uranium • Uranyl montmorillonite

Clays and Clay Minerals; February 1981 v. 29; no. 1; p. 10-16; DOI: 10.1346/CCMN.1981.0290102
© 1981, The Clay Minerals Society
Clay Minerals Society (www.clays.org)