INTERACTION OF LIGHT-METALS AND PROTONS WITH SEAWEED BIOSORBENT

Based on their displacement by protons, the following ascending order of light metals affinity toward Sargassum fluitans biomass was observe d: Na+ less than or equal to K+ < Mg2+ < Ca2+ < Al3+. Higher biomass-m etal affinities resulted in lowering the leaching tendency of (polysac charidic) biomass components during the sorption process. More than 12 % weight loss of protonated biomass occurred during 2 min of sorption, which should be considered in all stoichiometric and sorption calcula tions. The rate of proton uptake for Na-loaded and Ca-loaded S. fluita ns biomass at pH 4.5 was lower than the rate of desorption at pH 1.1. In the case of Na-loaded S. fluitans, the predominant proton uptake ra te was of a zero order. Na uptake by protonated S. fluitans biomass di d not take place at all in the presence of Ca and Al ions. However, it increased in the absence of other light metals. Since the affinity of Ca2+ for the biomass was much greater than that of Na+, the three-com ponent system of Na+, H+ and Ca2+ could be simplified into proton-calc ium ion exchange. The initial rate of Ca uptake with protonated S, flu itans biomass at pH 4.5 was lower than that of proton release from bio mass. Approximately 20% of Ca2+ sorbed was bound to the binding site a s a mono-valent ion. Titration and stoichiometric indications pointed to the fact that Al was being sorbed as a hydroxyl complex. (C) 1997 P ublished by Elsevier Science Ltd.