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Lanthanide and Heavy Metal Adsorption Using Renewable Polysaccharides
Shir Dayan; shirdayan09@gmail.com
Prof. Adi Wolfson1, Prof. Oshrat Levy-Ontman1, Dr. Ofra Paz-Tal2 1SCE - Shamoon College of Engineering, Be’er-Sheva 2Shimon Peres Negev Nuclear Research Center, Dimona, Israel
Most domestic and industrial activities involve the generation of wastewater. Heavy metals are among the main pollutants found in industrial wastewater, including rare metals from the lanthanide group. Among the various techniques for heavy metal removal, adsorption on biological supports is very promising. The aim of this research is to examine the treatment of aqueous solutions containing lanthanide and heavy metal ions by adsorption using hydrogels )beads( of polysaccharides extracted from algae: Kappa )K( and Iota )I( from the carrageenan group, and alginate )A(. The focus was on developing a simple, eco-friendly, and cost-effective process that is easy to design and operate, enabling the recycling of both the metals and the polysaccharides. The effect of the type of cross- linking salt on the formation of the beads with the three polysaccharides was tested, along with the adsorption efficiency of various lanthanide ions. It was found that divalent/ trivalent cations formed beads with all three polysaccharides, except Mg2+ with A, whereas monovalent cations only formed beads with K and I. As expected, adsorption efficiency also varied with the type of polysaccharide following the order: A>I>K. This indicates differences between carrageenans with ester sulfate and hydroxyl groups, and A with carboxylic and hydroxyl groups- due to the different functional groups. Furthermore, when comparing the adsorption efficiency of carrageenan polysaccharides, it was found that I has a higher adsorption efficiency than K. Lastly, when comparing the different cations used as cross-linkers, the cation’s hydration radius, charge, and type of anion in the salt all influence the adsorption efficiency. Since the adsorption efficiencies of all the lanthanide ions were similar, Ce3+ was chosen as the representative lanthanide for the continuation of the study. Next, the effect of metal ion concentration on adsorption efficiency was examined. It was found that increasing the concentration of Ce3+ ions reduced the adsorption efficiency as the ratio of metal ions to polysaccharide decreases, resulting in fewer available adsorption sites per metal ion. For other heavy metal ions )Cu2+, Fe3+, Ru3+, Rh3+(, there was no consistent trend. The effect of the solution’s pH on the adsorption efficiency was also tested. For Ce3+ ions adsorbed on I polysaccharide, the adsorption efficiency increased with increasing pH, while for K and A, no significant change was observed. For other heavy metal ions, there was no consistent trend. Kinetic experiments indicated that the adsorption of all tested metals follows a pseudo-second-order kinetic model, indicating that the adsorption is mainly influenced by the chemical adsorption of cations by the functional polysaccharide groups. The adsorption of Ce3+ or Eu3+ with additional heavy
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