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(NO
3)
2 solution of 4n weight normality under the condition of 75% water-cement ratio (W/C), with 4nNaNO
3, 0.5nFe(NO
3)
3, 0.5nAl(NO
3)
3, 0.2nCa(NO
3)
2, and 0.2nNaNO
3 solution respectively under the condition of 40% W/C have been determined to range from 2.7×10
-8 to 8.3×10
-7cmcm
2/sec for leaching into tap water and 1.9×10
-8 to 3.1×10
-7cmcm
2/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.
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