The chemical or electrochemical dissolution of silicon-containing nuclear fuel alloys for reprocessing generates silicic acid in solution, which in turn polymerizes to polysilicic acid and may ultimately form a gel. The polymers and gels can lead to line plugging throughout the plant and emulsion stabilization in the solvent extraction columns of the reprocessing plant. Methods of control of this problem which were studied included preventing or slowing the polymerization, and using additives to accelerate the rate of polymerization so that the gel could be readily removed from solution. To study the effects of acid, tempera¬ture, salt concentration, and additives on this reaction, the gel times of solutions containing exaggerated concentrations of silicon were measured as a function of the variables. Finally, the effects were verified by measurements made with solutions of typical silicon concen¬trations. It was shown that by various mechanisms the presence of chemically inert solids or gelatin in the solution accelerated gel formation and would facilitate removal of the gel by centrifugation. Hydrogen bonding agents, which accelerated gelation in solutions of low electrolyte content, were not effective enough in the high salt, high acid solutions to be useful. Therefore, no new procedure was suggested by these studies which would satisfactorily coagulate the silica so that it would be effectively removed by filtration or sedimentation.
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