Immobilization of Saccharomyces cerevisiae on a natural zeolite for the biosorption of radioisotopes

Abstract

In recent years, intensive attempts have been made to remove toxic heavy metals and radionuclides from wastewater. Uranium is one of the most threatening elements due to its radioactivity and high toxicity. Significant amounts of uranium are released into the environment throughout the nuclear fuel cycle. Biosorption technology offers the advantages of low operating costs and high efficiency for metal removal from aqueous solutions. In this work, the sorption of uranyl ions from aqueous solutions by Saccharomyces Cerevisiae (SC) as free cells and in an immobilized form on Zeolite Clinoptilolite was investigated. First, a characterization of the natural zeolite was carried out by classical chemical analysis, XRD, FTIR, and TG/DTG, and then the influence of solution pH, temperature, contact time, and initial concentration on uranyl sorption was investigated. The concentration range of uranyl in the solution was between 0.02 and 1 mmol L-1, which was determined by the ICP-OES method. In addition, the immobilization of 17.1 × 108 cells ml-1 number of yeast cells on clinoptilolite was optimized and observed using an SEM. More results demonstrated that metal binding was carried out extracellularly at the cell wall surface and the rate of uranyl ion uptake by free yeast cells of SC is rapid. The equilibrium adsorption ratio for all samples was calculated and showed that the points corresponding to initial concentrations lower than about 0.1 mmol L-1 have a higher and closer absorption fraction. Moreover, at concentrations higher than 0.2 mmol L-1, the adsorption rate decreases compared to low concentrations.