Polyethyleneimine gel-coat on silica. High uranium capacity and fast kinetics of gel-coated resin

A new process has been developed for gel-coating a weak-base resin polyethyleneimine (PEI) as a thin layer on high surface area silica using preloaded Cu(II) as the host ion on silica and glutaraldehyde as the cross-linking agent, followed by removal of the host ion by leaching with acid. The >NCH(OH) group introduced by the reaction with glutaraldehyde is found to enhance both U and Fe sorption, the effect, however, being relatively more pronounced on the latter. An $\text{O}\text{N}$ mole ratio ∼0.70 of the gel-coated PEI resin is found to be optimum for U sorption. In U sorption from dilute (0.1–0.4 mM) aqueous solutions of UO₂SO₄ at pH 4–5, the gel-coated resin exhibits several times higher capacity than a conventional bead-form resin Dowex-1X8. However, the capacity of the resin-coated silica sorbent, containing a large percentage of low-capacity silica, is only comparable to that of the bead-form Dowex resin at low solution concentrations. The gel-coated resin also exhibits a significantly faster rate of attainment of equilibrium sorption as compared to the bead-form Dowex resin, the sorption kinetics being diffusion-controlled with a high value of 8.4 × 10⁻⁶ cm²/s for the product of distribution coefficient and effective diffusivity. The stripping of the sorbed U from the gel-coated sorbent with 2 N H₂SO₄ is nearly instantaneous.