Composite gels of calcium alginate containing iminodiacetic type resin were prepared as a chemical analogue of biological tissues and membrane such as the cell wall. This chemical model was applied in copper biosorption from synthetic aqueous solutions. Experimental data on the composite were compared to those obtained for the biopolymer and the iminodiacetic-type resin separately and fitted into the ion exchange equilibrium model proposed in this work, which basically assumes that metal retention is the sum of the metal loaded onto the biopolymer and onto the resin. This model is tested with experimental data on copper biosorption on composite gels, including the equilibrium expressions of all the ionic species that are present in the system, the fraction of metal enclosed in the gel fluid, the gel volume variation, and the Donnan equilibrium theory. Another simplified model that only requires one equilibrium constant for each metal in the resin is shown to fit the results of the experiment fairly well, but it proves necessary to include an empirical parameter n into the equilibrium equation of copper in the resin to obtain the best fit of experimental data. References: 22
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