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The adsorption-desorption of copper ions and a mixture of five metal ions (cadmium, copper, nickel, lead and zinc) in aqueous solutions by a spruce sawdust column was reported. Different studies about the copper binding mechanism, the efficiency of some regenerating solutions for the copper desorption, the use of column for copper adsorption-desorption by successive cycles as well as the adsorption-desorption of a multi-component solution were investigated. An ion exchange mechanism seemed to explain the removal of copper by the natural components of sawdust, i.e., calcium, magnesium and manganese accounting for 71, 13 and 5.5% respectively of the copper binding on sawdust. But there was evidence variation in the contribution of these ions during the copper adsorption in the continuous flow process. Regeneration ofthe sawdust column was described by the efficiency sequence: H+ > Ca2+ >> Na+, where protons were the most promising regenerating agents. Adsorption-desorption cycles showed that copper binding capacity of sawdust, after a decrease of 23% between cycles 1 and 2, was stabilized at 3.1 x 10(-2) meq g(-1) for the following cycles. Adsorption of a mixture of five metal ions indicated that nickel broke through first when saturation of sawdust was reached, followed by the other metal ions in the order zinc, cadmium, copper and lead. The effects of competitive ion exchange, because of affinity differences between the metal ions for sawdust, resulting in the metals having the lower affinity being displaced by those having a higher one and to overshoot the 0.2 meq l(-1) feed solution.

The biosorption of five metal ions, cadmium, copper, nickel, lead and zinc in single component solutions and a multicomponent mixture in aqueous solutions by spruce sawdust is reported. A comparative study, performed through batch experiments, between the cationic release of sawdust in ultra pure water and in a metallic solution leads to an understanding of the heavy metal ion fixation mechanism on sawdust. An empirical model is developed in order to distinguish between a sorption phenomenon purely based on ion exchange from one in which physical adsorption is involved. Thus, the difference in cations released between the two solutions corresponds to the metal ions which bind to anionic sites by displacing protons from acidic groups and existing cations (natural components of the sawdust) from anionic sites. Metal ion binding capacities of spruce sawdust reach values ranging from 2.1 to 4.3x10(-2) meq g(-1) in single metal ion solutions with the following relative preference: Zn < Ni < Cd << Cu < Pb. Our results show variable contributions of the different cations of the sawdust in the ion exchange mechanism in which calcium, naturally present in the sawdust, accounts for about 65% of the biosorption of the metal ions studied. The study also indicates the possibility of desorbing the loaded metal ions with a calcium solution.

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