Binding of Toxic Metal Ions to Alginate Natural Polyelectrolyte

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Alginate is an important carboxyl group containing natural polysaccharide component of many biosorbents. Protonation and the effect of pH on the binding of metal ions Pb (II), Zn (II) and Cd (II) of the alginate were studied at room temperature. Mass average molecular weight and average size of the alginate were obtained from static and dynamic light scattering studies (337±18 % kDa and 126.8 nm) . Protonation constant was obtained from pH metric titration curves by using the Henderson-Hasselbalch equation (logKH=3.53, I=0.1 M, KNO3) . Binding of metal ions was studied at a constant concentration of the ligand (0.25 g/liter) by increasing the concentration of the metal ions from 10-5 to 10-3 M, at the pH values of 3, 4 and 5, at I=0.1 M, KNO3. Concentrations of the free metal ions [M2+] were obtained from a direct DC polarographic study of the equilibrium systems by applying the concept of mean diffusion coefficient. Formation constants of the M2+ -alginate complexes were calculated for each pH from the obtained ligand saturation vs. [M2+] curves evaluated by the equation of binding derived from equilibrium principles.
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