Page 23 - חוברת תזות הנדסה ירוקה 2024

Removal of Europium from wastewater by renewable polysaccharides-based hydrogels
Shir Nagar1; Shirngrr@gmail.com
Prof. Adi Wolfson1, Dr. Ofra Paz-Tal2, Dr. Oshrat Levy-Ontman1 1Shamoon College of Engineering, Be’er-Sheva, Israel. 2Negev Nuclear Research Center, Israel.
The advancement of recent technologies has led to a significant rise in the demand for heavy and radioactive metals, particularly lanthanides. Consequently, the volume of industrial wastewater containing harmful heavy metals has also increased, posing threats to ecosystems and human health, necessitating effective treatment methods, such as adsorption.
Polysaccharides derived from biological sources present a promising solution due to their renewable nature, biodegradability, and inherent hydrophilic properties. These polymers feature diverse functional groups, enabling their versatile use in various applications, including as adsorbents for heavy metal ions, particularly lanthanide ions.
In this study, polysaccharides extracted from algae were employed for the adsorption of europium ions )Eu3+( from aqueous solutions. Three polysaccharides were used: iota )I(; kappa )K(, containing hydroxyl and sulfate ester groups; and alginate )A(, with hydroxyl groups and carboxylic acid. The adsorbent was prepared by the dropwise addition of a polysaccharide solution into a salt solution, serving as a cross-linking agent. This process resulted in the formation of spherical hydrogels )beads( that could be easily separated from the solution and employed as adsorbents.
In general, bead formation was found to be dependent on the type and amount of functional groups in the polysaccharides, together with the type, and especially the valence, of the cation serving as a cross-linking agent. Additionally, all the synthesized beads, prepared from these three polysaccharides using various salts, effectively adsorbed Eu3+ ions, although the adsorption yield varied widely. Furthermore, a comparison of the adsorption performances of the beads derived from polysaccharides K and I, revealed, as expected, that the higher sulfate ester groups led to higher adsorption yields. When comparing the different cations used as cross-linkers in the bead preparation step, it was observed that the hydration radius, charge of the cation, and type of anion in the salt play crucial roles that affect Eu3+ ion adsorption yield.
Analyses of beads formed from I with monovalent cations )Li+, Na+, and K+( before and after adsorption of Eu3+ ions, revealed that all cation adsorption occurs primarily in the sulfate ester groups. Moreover, higher monovalent cation concentrations yielded stiffer beads and, thus, decreased the Eu3+ ion adsorption yield. It was also found that lower Eu3+ ion concentrations or higher amounts of polysaccharide )during the adsorption step( resulted in higher adsorption yields. Furthermore, at higher I polysaccharide concentrations, more thermally stable beads were formed and they were more ordered.
Kinetic experiments revealed that the pseudo-second order model aptly describes the adsorption kinetics of Eu3+ ions onto I beads prepared with LiCl or CaCl2 salts. This suggests that the process
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