Tailoring of organically modified silicas for the solid-liquid extraction of actinides

Hybrid materials with complexing properties toward lanthanides(III), americium(III), and plutonium(IV) are described. These new silica-based materials, containing malonamide ligands, have been prepared by sol-gel hydrolysis and condensation of a silylated tetraeth-ylmalonamide in the presence of tetraethoxysilane (TEOS). A family of these hybrid materials was obtained by varying the amount of TEOS, the catalyst, and the R-w ratio (amount of water added per Si-O bonds). The porous hybrids exhibited BET surface areas up to 300 m(2) g(-1) with the average pore diameter ranging from 30 to 90 A. The new hybrids were used as solid phase extractants in batch experiments for the extraction of americium and plutonium from high-level liquid wastes. The hybrids were shown to be highly efficient materials in solid-liquid extraction, exhibiting distribution coefficients up to 10(4) and loading capacities up to 0.46 mequiv/g. They compared favorably to related silica-based material containing malonamide immobilized by classical techniques. The sol-gel approach allows one to adjust the ligand loading and to achieve some control and some tuning of the ligand environment since the oxide matrix is built around the complexing moieties. The use of templating techniques was also studied to enhance the extracting properties.