It is important to assess the effects of ionic strength and type of anion when studying adsorption of metals on soils and soil components because the background salt may complex metals and compete for adsorption sites. Four experiments were carried out to determine the effect of ionic strength and anions on Zn adsorption by two soils and to determine the effects of these two factors on the pH‐adsorption relationships. Zinc adsorption using NO ‐ 3 at ionic strengths of 0.005 and 0.01 mol L −1 was the same but the adsorption at 0.05 and 0.1 mol L −1 was lower than for the other ionic strengths. The SO 2‐ 4 ion produced higher adsorption than NO ‐ 3 or Cl ‐ ions which yielded the same isotherm at pH 6. Increased ionic strength had similar effects at all pH levels studied. The three anions had no effect on the pH‐adsorption curves which were exactly the same within a soil type. Plotting the activity of the free Zn in the systems vs. adsorbed Zn gave much the same results as when concentration data were used. In general, ionic strength and anions had no influence on the shape of the isotherms, showing that the same relationships would be found regardless of ionic strength or anion. The absolute values of the adsorption maxima were different in some cases.
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L. M. Shuman (1986) studied this question.