Summary The equilibria as well as the rates of adsorption and desorption of the ions Pb 2+ , Cu 2+ , Cd 2+ , Zn 2+ , and Ca 2+ by soil organic matter were determined in batch experiments as a function of the amount of metal ions added to an aqueous suspension of HCl‐washed peat. Simultaneous determination of the metal ions and hydrogen ions in the solution by atomic absorption spectrophotometry and pH‐measurements showed that the adsorption of one divalent metal ion by peat was coupled with the release of two hydrogen ions. Since this equivalent ion‐exchange process causes a corresponding increase of the electric conductivity of the solution, the rates of the adsorption and desorption processes were determined by an immersed conductivity electrode. The distribution coefficients show that the selective order for the metal adsorption by peat is Pb 2+ > Cu 2+ > Cd 2+ ≌ Zn 2+ > Ca 2+ in the pH range of 3·5 to 4·5. The slope of ‐2, as observed in a double logarithmic plot of the distribution coefficients versus the total solution concentration confirms the equivalence of the ion‐exchange process of divalent metal ions for monovalent H 3 O + ‐ions in peat. The absolute rates of adsorption, as well as the rates for the fractional attainment of the equilibrium, increase with increasing amounts of metal ions added. This behaviour is also observed for the subsequent desorption of the metal ions by H 3 O + ‐ions. At a given amount of metal ions added, the absolute rates of adsorption decrease in the order Pb 2+ > Cu 2+ > Cd 2+ > Zn 2+ > Ca 2+ , while the rates for the fractional attainment of the equilibrium decrease in the order Ca 2+ > Zn 2+ ≌ Cd 2+ > Pb 2+ > Cu 2+ . The half times for adsorption and desorption were in the range of 5 to 15 sec.
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Bunzl et al. (1976) studied this question.