The sorption of caesium and strontium from its aqueous solutions by ten clinoptilolite-and mordenite-containing sedimentary materials from Slovalda, Bulgaria, Ukraine and Greece was investigated by batch-type procedure and radiotracer techniques. The concentration of the solutions, that were performed in and without the presence of competing cations (0.005 mol.dm 3 KC1) varied between 1.10 4 and 5.10 4 mol.dm 3. The uptake and distribution coefficient (Kd) values determined for the materials of the different origin, were correlated with their mineralogical composition and gross cation exchange capacity (CEC). The identification of the specific uptake sites was attempted on the basis of the sorption isotherms and the content of exchangeable cations. The experimental results provide information on the suitability of the individual materials for the treatment of radioactive wastes and their application as backfills in potential nuclear waste repositories.
The effect of humic acid addition on the capacity of inorganic sorbents to sorb radioactive cesium and strontium was studied on montmorillonites in a calcium and potassium form. The Sips isotherm for humic acid sorption and multisite distribution model of ion sorption was found to suit well for the description of mobility of ions as a function of equilibrium humic acid concentration as a single variable at given pH and type of silicate. Complexation of the ions was of minor importance at the conditions investigated. Influence of humic acid on the specific radiocesium interception potential (SRIP) was also evaluated.
The effect of Aldrich humic acid (HA) on the mobility of ~37Cs, 85Sr, ~SZEu and 239pu radionuclides was studied in Ca-montmorillonite suspensions. Verified 2-sites-2-species (2s2s) models correspond to an intensive interaction of all elements with humificated surface, what is in a remarkable contrast with the weak complexation of cesium and even strontium in solutions -the neutral ligand interaction constants 13 (1/mol) are log 13<-9.9 and 7.56+0.21 for Cs and Sr, respectively. The result for europium complexation in solution, log 13= 12.49-2-_0.18 is in a good agreement with literature data. For plutonium(IV) not only a high proton competitive constant in solution was obtained, log 13=(-0.67+ 0.32)+3pH, but also a strong chemisorption, which at high concentrations ofhumic acid (above 0.05 g/I) indicates the formation of bridge humate complexes of plutonium on the humificated surface. Logarithms of heterogeneous interaction constants (~10, I/g) of the elements with surface humic acid are 4.47+0.23, 4.39+0.08, and 6.40+0.33 for Cs, Sr, and Eu(III), respectively, and the logarithm of the proton competitive constant (~24, I/g) for Pu(IV) -3.80+0.72. Distribution coefficients of humic acid and metal humates between 0.01 g HA/1 solution and montmorillonite were derived as log Ka(AH ) =-1.04_+0.11, log Ka(EuA ) = 1.56_+0.11 and log Ka(PUA ) = 2.25+0.04, while the values for Cs and Sr were obtained with very high uncertainty. Speciation of the elements on montmorillonite surface is illustrated as a function of equilibrium concentration of humic acid in solution and ofpH.*
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