Comparison of ion exchange and Donnan equilibrium models for the pH-dependent adsorption of sodium and calcium ions onto kraft wood pulp fibers

The ion exchange and Donnan equilibrium models were compared for predicting the multi-component adsorption of hydrogen, sodium and calcium ions onto kraft wood pulp fibers. At pH 2.7-6, the Donnan model predicted the adsorption of Na and Ca ions onto both bleached and unbleached wood fibers better than the ion exchange model. The Donnan model assumed a non-site specific distribution of metal ions between charged fiber and external solution phases and and a carboxylate site specific adsorption of hydrogen ions.