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 observed: Na+ K+ < Mg2+ < Ca2+ < Al3+. Higher biomass-metal affinities resulted in lowering the leaching tendency of (polysaccharidic) 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 calculations. The rate of proton uptake for Na-loaded and Ca-loaded S. fluitans 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 rate was of a zero order. Na uptake by protonated S. fluitans biomass did 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-component system of Na+, H+ and Ca2+ could be simplified into proton-calcium ion exchange. The initial rate of Ca uptake with protonated S. fluitans biomass at pH 4.5 was lower than that of proton release from biomass. Approximately 20% of Ca2+ sorbed was bound to the binding site as a mono-valent ion. Titration and stoichiometric indications pointed to the fact that Al was being sorbed as a hydroxyl complex.