Salinity dependence of 226Ra adsorption on montmorillonite and kaolinite
The effect of NaCl concentration (10.0–1,000 mM) on 226Ra adsorption was investigated in the presence of montmorillonite and kaolinite. A positive correlation was observed between the dissolved 226Ra and NaCl concentrations in the presence of these adsorbents. Distribution coefficients decreased from the order of 104 to 100 (mL g−1) with an increase in NaCl concentration. Although the coefficients were higher for montmorillonite than kaolinite at lower NaCl concentrations, the trend was reversed at higher NaCl concentrations (≥500 mM) owing to the sharper reduction of the coefficient for montmorillonite with the increase in NaCl concentration. The rapid reduction was ascribed to higher negative charge density of montmorillonite, which leads the Ra2+ adsorption mechanism to approach charge-compensating ion exchange.
KeywordsRadium Adsorption Montmorillonite Kaolinite Salinity Distribution coefficient
We thank M. Fuchizaki, Kanazawa University, for the XRD spectral measurements. T. Murakami, Kanazawa University, is acknowledged for valuable comments in the interpretation of the experimental results.
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