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 μ g/liter. Background electrolytes used in these experiments were 0.005,0.01,0.025, and 0.5 M Ca(N0 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 2 SO 4 , Ion speciation in equilibrium solutions was calculated by the computer program GEOCHEM. Computed Ni 2+ 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+ ion on kaolinite was computed to be —27 kJ/mole.