Page 63 - חוברת תזות הנדסה ירוקה 2023

Removal of uranyl from aqueous solutions by means of renewable polysaccharides
Yaron Alfi1; alfiyaron79@gmail.com
Prof. Adi Wolfson1, Dr. Oshrat Levy-Ontman1, Dr. Ofra Paz-Tal2 1Sami Shamoon College of Engineering, Be’er-Sheva 2Nuclear Research Center Negev
The discharge of industrial wastewater containing heavy metals, particularly uranium, into the environment affects ecosystems and public health. Such metals may be separated from aqueous solutions by the use of various processes. In recent years, bio-based materials, made of renewable and biodegradable compounds, have been used more widely for the adsorption of certain heavy metals, among them polysaccharides produced by various microorganisms. Along with the environmental benefits of these substrates, their adsorption efficiency depends on the amounts and types of functional groups on the molecules and their physicochemical properties.
In this study, we examined the structural-functional relation of various groups regarding their ability to adsorb uranyl ions )UO22+(. The tested polysaccharides were: iota )I( and kappa )K( from the carrageenan family, that contain hydroxyl and ester sulfate groups; xanthan gum )X( and alginate )A(, with hydroxyl and carboxylic acid groups; and guar gum )G(, with hydroxyl groups only. During the first step, the adsorption yield was tested in a system in which an aqueous solution of polysaccharide was mixed with an aqueous solution of uranyl acetate. Adsorption with all the polysaccharides was carried out at pH=5 in the range of 5-60 min, and it was found that the adsorption yield reached its maximum value after 30 min. The adsorption yields of the different polysaccharides decreased in the following order: A > X / K > I / G; and stood at 98.2%, 89.7%, 85.2%, 79.1%, and 77.1%, respectively. It was also found that lowering the acidity in the system decreased the adsorption of all the tested polysaccharides, while reducing the ratio between the amount of uranyl ions and the amount of polysaccharides increased the adsorption yields of the different polysaccharides.
FTIR, SEM-EDS and TGA analyses were performed. A comparison between the FTIR spectra of the polysaccharides, before and after adsorption, showed changes in the peak characteristics of the hydroxyl groups, indicating the involvement of the hydroxyl in uranyl adsorption. For I and K, changes were observed in the ester sulfate bonds, as well. While for X and A, such peaks were found to shift around the region of the carboxyl group. Moreover, after the adsorption of uranyl into G, X and A, a new peak was observed, perhaps indicating the presence of uranyl. SEM-EDS analyses verified the presence of uranyl in the polysaccharides, where the weight composition of the uranium, after adsorption into polysaccharides X, K, I, G and A, was 30.2%, 31.1%, 33.1%, 38.1% and 40.5%, respectively.
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