SELECTIVE ION EXCHANGE REACTIONS FOR CESIUM AND STRONTIUM BY SOIL MINERALS
The basis for discharge of low and intermediate activity wastes into the ground is the retention of the nuclides, particularly cesium and strontium, by ion exchange on the soil particles. Studies at Oak Ridge have shown that minerals with the mica structure are efficient in selectively sorbing cesium. For the low concentration of cesium generally found in wastes, ion-exchange capacity is seldom the controlling parameter for its removal. Biotite, a primary mica mineral, will sorb cesium even more efficiently than vermiculite even though biotite has about 1% the exchange capacity of vermiculite. In a demineralized water system, montmorillonite with 90-meq-per-100 g exchange capacity give a distribution coefficient (Kd) of 1700 ml per g, whereas illite with 20-meq-per- 100 g gave a Kd of 49,000. In the acidic pH range, ion exchange originating from isomorphous substitutions is the dominant mechanism for strontium removal by soils. In neutral and alkaline systems, additional reactions may occur. Hydrous oxides of iron and aluminum show high selectivities for strontium in this pH region. A Conasauga shale soil did not sorb as much strontium after being subjected to free iron oxide removal in spite of an increase in capacity resulting from the removal of the iron coating. An aluminum saturated montmorillonite showed the lowest removal of strontium at pH 6.0: when the pH was raised to 10, this sample removed more strontium than potassium, sodium, or calcium saturnted samaples. Knowledge of the mechanlsms responsible for selective ion exchange reactions made possible the preparations of materials that show even greater selectivities than their natural counterparts. Thus, in solutions high in sodium nitrate concentrations, montmorillonite heated to 600 deg C and vermiculites saturated with potassium ions remove more cesium than the natural minerals. Gibbsite, an aluminum hydroxide mineral commonly found in soils, was made 50 times more selective for strontium by heating to temperatures that decomposed the mineral to the oxide. (auth)
- Research Organization:
- Oak Ridge National Lab., Tenn.
- NSA Number:
- NSA-18-017344
- OSTI ID:
- 4065619
- Journal Information:
- Colloq. Intern. Retention Migration Ions Radioactifs Sols, Saclay, 1962, Journal Name: Colloq. Intern. Retention Migration Ions Radioactifs Sols, Saclay, 1962
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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SORPTION OF CESIUM BY SOILS AND ITS DISPLACEMENT BY SALT SOLUTIONS
STRUCTURAL IMPLICATIONS IN CESIUM SORPTION
Related Subjects
ADSORPTION
ALUMINUM HYDROXIDES
ALUMINUM OXIDES
ALUMINUM SILICATES
BIOTITE
CESIUM
CLAYS
DISTRIBUTION
EFFICIENCY
GIBBSITE
ILLITE
ION EXCHANGE
ION EXCHANGE MATERIALS
IRON OXIDES
IRON SILICATES
LATTICES
MAGNESIUM SILICATES
MATERIALS TESTING
MICA
MINERALS
MONTMORILLONITE
POTASSIUM SILICATES
REACTION KINETICS
SODIUM NITRATES
SOILS
STRONTIUM
VERMICULITE
WASTE DISPOSAL AND PROCESSING
WASTE SOLUTIONS