575. セメント固化体中<SUP>137</SUP>Csの浸出に対する固化物の化学的特性および浸出条件の影響

Abstract

The leaching characteristics of 137Cs from wastes solidified with cement were studied. The principal results are as follows.The diffusional leaching rate is a little lower in sea water than in tap water.The diffusion coefficients of 137Cs for leaching from waste solidified with Ca(NO3)2 solution of 4n weight normality under the condition of 75% water-cement ratio (W/C), with 4nNaNO3, 0.5nFe(NO3)3, 0.5nAl(NO3)3, 0.2nCa(NO3)2, and 0.2nNaNO3 solution respectively under the condition of 40% W/C have been determined to range from 2.7×10-8 to 8.3×10-7cmcm2/sec for leaching into tap water and 1.9×10-8 to 3.1×10-7cmcm2/sec for that into sea water.The diffusion coefficients diminish by about 60% when the leaching water temperature is lowered by 20° to 30°C. The coefficients are also reduced by about 50% with increase in pressure from 1 to 300 atm.More than half of the 137Cs coprecipitated with nickel ferrocyanide is turned to leachable ionic state in cement pastes as a result of alkali decomposition of the precipitate.In a cement milk, vermiculite and glauconite are capable of maintaining a high selective exchange capacity for caesium. Then about 98% of the 137Cs adsorbed onto vermiculite can be retained in a cement paste after hardening.