Adsorption of Heavy Metal Ions from Multi-Ion Solutions Using Polysaccharide Hydrogels

Adsorption has been found to be highly effective for removing heavy metals from polluted industrial wastewater. Adsorbents of biological origin, such as negatively charged polysaccharides, e.g., alginate and carrageenan, have attracted a lot of attention recently. In this study, these three polysaccharides were used to adsorb different heavy metal ions from aqueous solutions. The results showed that the sorption yields of various lanthanides with the kappa and iota carrageenan were similar, though the sorption yields of the iota beads were higher. Also, the iota and the kappa beads had higher sorption yields for Ru³⁺ and Rh³⁺ than they did for the lanthanides. In general, the presence of light metal ions in the solution affected the sorption yields of the heavy metal ions, depending on the type and concentration of the light metal ions. All three polysaccharides were also capable of adsorbing mixtures of lanthanides and heavy metal ions. In binary solutions that contained both lanthanide ions (Ce³⁺ or Eu³⁺) and transition heavy metal ions (Ru³⁺ or Rh³⁺), differences in sorption yields were observed, with all polysaccharides exhibiting higher selectivity for Ru³⁺ and Rh³⁺. Finally, FTIR, SEM/EDS, and TGA analyses confirmed that all metal ions were adsorbed onto both types of carrageenan.