EFFECT OF IONIC-STRENGTH AND ION-PAIR FORMATION ON THE ADSORPTION OF NICKEL BY KAOLINITE

Adsorption of Ni(II) by Ca- and Na-saturated kaolinites was studied in equilibrating solutions with total Ni concentrations ranging from 118 to 946 mu g/liter. Background electrolytes used in these experiments were 0. 005, 0. 01, 0. 025, and 0. 5 M Ca(NO//3)//2, 0. 002 and 0. 005 M CaSO//4, 0. 01 and 0. 1 M NaNO//3, and 0. 005 and 0. 05 M Na//2SO//4. Ion speciation in equilibrium solutions was calculated by the computer program GEOCHEM. Computed Ni**2** plus concentrations and activities at equilibrium were correlated with total Ni adsorbed by kaolinite. Increasing ionic strength resulted in decreasing Ni adsorption. Adsorption of Ni was greater from solutions when NO//3 was the dominant anion. Based on adsorption data in SO//4 medium, the standard free energy of adsorption of Ni**2** plus ion on kaolinite was computed to be minus 27 kJ/mole. Refs.