Heavy metal biosorption by gellan gum gel beads

The Ni^2+ accumulation in batch mode from diluted solutions by gel beads of gellan gum (GG), alginate, (kappa)-carrageenan, agar, agarose, silica gel, polyacrylamide and two mixtures of GG+agar was investigated. All polymeric materials studied accumulated Ni^2+, but gel beads of GG were stable, easily obtainable and showed the highest Ni^2+ accumulation. The pH of the Ni^2+ solution was not critical for Ni^2+ accumulation. Accumulation of metals Cu^2+, Co^2+, Ni^2+, Pb^2+, Cd^2+ and Zn^ 2+ by GG gel beads reached the equilibrium after 24 h. The removal of Pb^2+ and Cu^2+ from the aqueous solution was very efficient, with maximum metal uptake (qmax) of 0.85 and 0.75 mmol/g dw GG, respectively. The general qmax sequence was Pb>Cu>Ni~Zn=Co>Cd. In an equimolar metal mixture sorption experiment a clear reduction in accumulation was observed, except for Pb^2+ (30%). Heavy metals were desorbed with 100 mM sodium citrate.