Carrageenan‐Based Hydrogels for High‐Capacity Sorption of Transition Metals

ABSTRACT Transition metals are among the main pollutants found in industrial wastewater and can be removed by adsorbing them on biological supports. The treatment of aqueous solutions containing lanthanides and other representative transition metal ions by adsorption, using polysaccharide hydrogel beads of kappa ( K ) and iota ( I ) from the carrageenan group, was examined. In general, I shows higher adsorption efficiency for lanthanides than K (~ up to 2 fold) due to the larger amount of ester sulfate groups on I . Furthermore, when comparing the different cations used as crosslinkers, their hydration radius, charge, and the type of anion influence the sorption yield. In general, the sorption yields of Ru 3+ /Rh 3+ are higher (up to 2.2 fold) than those of the various lanthanides, whereas the sorption yields of Cu 2+ /Fe 3+ are lower. The FTIR analysis supported the hypothesis of chemical adsorption and shows that while the lanthanide ions are adsorbed via both ester sulfate and hydroxyl groups, the adsorption of Ru 3+ and Rh 3+ occurs mainly via the hydroxyl groups. The TGA analysis shows that the adsorption of the transition metals reduces the thermal stability of the I . The new adsorbents show high potential for the sorption of a variety of heavy metal ions.