Sorption of lead, copper, and cadmium by calcium alginate. Metal binding stoichiometry and the pH effect.

Binding of heavy metal ions by calcium alginate has been described in the literature with many different models. In the present study, two most basic models were used to systematically compare their simultaneous description of metal uptake dependence on pH and metal ion concentration in the bulk solution. The experimental datasets corresponding to the binary sorption systems containing protons and heavy metal ion (cadmium, lead, or copper) were taken from the literature. The applicability and limitations of both models are discussed. Neither of the models gave a completely satisfactory description of all data. The two-site occupancy model yielded better results compared to the one-site occupancy model when considering the coherence of the parameters (e.g., affinity constants) but the quality of the obtained fits is similar in both cases.