Author
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Laird, David |
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Submitted to: Clay Minerals Society Meeting
Publication Type: Abstract Only Publication Acceptance Date: 6/15/1996 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: A model for the interaction between crystalline swelling and cation exchange selectivity is proposed. In the model, selectivity influences the mix of cations present in the interlayers, the mix of cations in the interlayers influences the extent of crystalline swelling, and the extent of crystalline swelling influences selectivity. The model treats changes in basal spacing that occur during an ion exchange reaction as phase changes for the smectite. Such phase changes require irreversible work to effect mass transfer, and are therefore inherently hysteretic. The model qualitatively predicts cation ordering, the influence of layer charge on selectivity, non-ideal exchange behavior, hysteresis in cation exchange, demixing phenomena, and fixation of K, NH4, Rb, and Cs. The model was evaluated by investigating the relationship between crystalline swelling and cation exchange selectivity for a synthetic F-hectorite. Samples of Ba- and Mg-saturated synthetic F-hectorite were equilibrated with mixed BACl2 and MgCl2 solutions (0.01 M) using a dialysis technique. Adsorbed Ba and Mg levels were determined by ICP-AES. Basal spacings of the F-hectorite samples in their respective equilibration solutions were measured by X-ray diffraction using a liquid sample cell and symmetrical transmission geometry. Barium was preferred over Mg for all samples. Vanselow selectivity coefficients (Kv) for Ba were an order of magnitude smaller for samples with 16 A basal spacings than for samples with 18 A basal spacings, and there was a strong correlation between basal spacing and Kv (r2=0.85, p<0.001). Results for the experiment demonstrate a relationship between crystalline swelling and cation exchange selectivity that is consistent with the proposed model. |
