Abstract
The acid-base chemistry of Beishan (Gansu, China) granite (BS03, 600 m) was studied by potentiometric titration, and the adsorption of Eu(III) on the granite was investigated using a batch technique. It was found that the pHPZNPC of the granite is 9.4 at I = 0.1 M NaCl and decreases to 9.0 at I = 0.4 M NaCl. The profile of parallel titration curves of the granite at variable ionic strengths is roughly comparable to that of montmorillonite under similar conditions. The distribution coefficient ( K d) of Eu(III) on the granite varies with pH, ionic strength and Eu(III) concentration. The K d values of Eu(III) decrease significantly with increasing ionic strength in the low pH range, whereas the effect of ionic strength on the K d values is very weak in the high pH range. The experimental results of Eu(III) adsorption on the granite as a function of pH, ionic strength and Eu(III) concentration were quantitatively interpreted by a model with a cation exchange reaction of Eu3+ on the granite and two inner-sphere surface complexation reactions of Eu(III) on the surface hydroxyl sites. The adsorption of Eu(III) on the granite at I = 0.1 M was predicted by the proposed model, which was compared with the results of Am(III) adsorption on the granite under similar conditions reported by other groups.
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