One- and Two-step Coagulation Treatment of Radioactive Wastes

The removal of long-life fission-products, especially of 137Cs, 90Sr and 106Ru was studied by jar-testers and slurry recirculation type flocculators. (1l/min, ACCELATOR) Bentonite-polyelectrolyte coagulation was found most effective for 137Cs removal, phosphate coagulation for 90Sr removal and sulfide coagulation for 106Ru removal. Any coagulant employed can remove 144Ce end 95Zr significantly. Better removal of contaminants from mixtures of 137Cs, 90Sr and 106Ru were obtained by two-step coagulation with the combination of bentonite-polyelectrolyte and phosphate and/or sulfide. The best is the phosphate coagulation followed by bentonitepolyelectrolyte coagulation. Slurry recirculation type flocculator can remove contaminants with less chemicals compared with jar-tester. With this flocculator less than 1 hr was necessary to restore the slurry state from the disturbance caused by wrong feeding of chemicals. Various processes were applied to the reduction of sludge volume produced by coagulation, and freezing treatment was found most effective to reduce the volume to 1% or less of the original waste volume.