Modeling of organic and inorganic cation sorption by illite

Sorption of several organic and inorganic cations on illite (Clay Minerals Society Source Clay Imt-2) was determined experimentally and results compar ed to model calculations. The cations studied were crystal violet (CV+), be nzyltrimethylammonium (BTMA(+)), benzyltriethylammonium (BTEA(+)), Ca2+, Mg 2+, K+, Na+, Cs+, and Li+. The adsorption-model calculations involved a sol ution of the electrostatic Gouy-Chapman equations. The model considered spe cific adsorption and sorption/exclusion in the double-layer region in a clo sed system. Model calculations considered the simultaneous presence of four to six cations in the system. The adsorption of CV included formation of n eutral and charged complexes. The adsorption attained 0.37 mol kg(-1) or 15 0% of the cation exchange capacity (CEC) of illite in aqueous suspension. T he adsorption of BTMA and BTEA did not exceed the CEC and was reduced with an increase in ionic strength. The sorption of CV below the CEC was rather insensitive to the ionic strength because of the large binding coefficients and was only slightly reduced in NaCl, CsCl, or Na2SO4 solutions. When add ed in amounts exceeding the CEC in high ionic strength, 0.667 M NaNO3, NaCl , or CsCl solutions, the adsorbed quantities of CV increased to three times the CEC. At high sulphate concentrations (0.333 M Na2SO4), the adsorption was below the CEC. Model calculations yielded satisfactory Simulations for the adsorption, particularly for cations added in amounts approaching or ex ceeding the CEC. The binding coefficients for formation of neutral complexe s followed the sequence: CV > Ca > BTMA > BTEA > Cs > Mg > K > Na > Li. Mod el calculations also suggested that sites were present which bound exchange able cations, particularly K+, Na+, and Mg2+, very tightly.