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Résumé :
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A method is proposed to establish useful operation conditions for solid separation of materials having different acidities. The effect of ligand acidity on competitive adsorption and desorption of metal salts was studied by using copper sulfate and sulfuric acid as model electrolytes. Adsorption equilibria with four commercial N-donor chelating adsorbents, WP-1 (functional group branched poly(ethyleneimine)), CuWRAM (functional group 2-(aminomethyl)pyridine), Reillex HP (functional group poly(4-vinylpyridine)), and Dowex M 4195 (functional group bis-2-(pyridylmethyl)amine) were measured using potentiometric and batch uptake methods. Moreover, formation of the complexes in the solid phase was studied with reflection UV―vis spectroscopy. Experimental data were correlated with a nonideal competitive adsorption (NICA) model, and the obtained parameters were used in mapping the operation conditions for the studied adsorbents. Acidity of the adsorbents was proved to increase in the order WP-1 < Reillex HP < CuWRAM < Dowex M 4195, and their apparent acidities increase with temperature. Acidity is shown to have a remarkable effect on conditions where metal adsorption and desorption can take place. Correlation of the acidity parameters and copper adsorption parameters by linear free energy relations is also discussed. According to the results, WP-1 is useful only for highly diluted copper solutions, and desorption of the adsorbed copper takes place readily with 0.1―I M H2SO4. The exploitable acid concentration range of Reillex HP is identical. Due to the lower metal affinity, it is less suitable for adsorption at low copper concentrations. Dowex M 4195 has the widest operation range and is suitable for very acidic copper separations. The only disadvantage seems to be that complete desorption of copper with acid is impossible. At moderately acidic solutions, CuWRAM offers the best balance between adsorption and desorption, because copper desorbs with 5 M H2SO4 solution.
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