Application of sol-gel technique in radwaste fixation

Np02+can fixed in Ai(OH)3 hydrogel in spite of its relatively good solubility in neutral to slightly alkaline solutions. The loss of Np due to washing the Np-containing gel with water is below 2% . this loss is primarily caused by fine gel fragments suspended in and discharged with the wash water. the amount of genuinely dissolved Np(V) is approximately one order magnitude lower than that present in the suspended gel particles. the low concentration compared to that expected according to the solubility product is caused by strong adsorptive properties of the A1(OH)3 hydrogel. This has been proved both by leaching and loading tests. However, adsorption was found to be weaker in strong ammonia solutions than in weak ones. The adsorption mechanism is discussed. It is assumed that NP02+is attached to hydroxyl ions which on their part are bound to the gel