SIMULATED TRANSPORT OF 3 CATIONS THROUGH POROUS-MEDIA - EFFECT OF DIFFERENT APPROACHES TO MODELING CATION-EXCHANGE REACTIONS

Batch cation exchange and column experiments were conducted to evaluat e selectivity coefficients which have been suggested for describing ca tion exchange reactions in solute transport models. Vanselow selectivi ty coefficients,were calculated for cation exchange equilibria with a cation resin and for equilibria reported in the literature with a Yolo loam soil. Experimental column data were compared with data from simu lations generated by a numerical solute transport model to evaluate Va nselow, Gaines-Thomas, and statistical thermodynamic selectivity coeff icients. With the cation resin, the statistical thermodynamic selectiv ity coefficient gave the most reliable estimate of column effluent cat ion concentrations. In a column packed with the Yolo loam soil, the Va nselow selectivity coefficient gave the most accurate prediction of co lumn response. Use of variable (as opposed to fixed) Vanselow selectiv ity coefficients gate more accurate predictions of column experiments. The use of ternary cation exchange data did not improve predictions o f column response.