Abstract
Although a powdered form of hydroxyapatite (p-HdA) has been studied for the adsorption of heavy metals that contaminate the restoration sites of decommissioned nuclear power plants, most of the studies are limited in the laboratory due to the head loss and post-separation in practical applications. Herein, we fabricated a porous bead form of HdA (b-HdA) as a novel adsorbent for removing radionuclides from aqueous environments via a facile synthesis by mixing the p-HdA precursor and polyvinyl butyral (PVB) as a binder and added a sintering process for the final production of a porous structure. The spherical b-HdA with an approximate diameter of 2.0 mm was successfully fabricated. The effectiveness of the b-HdA at removing Co(II) was investigated via the adsorption equilibrium at various experimental temperatures. The b-HdA exhibited the adsorption capacity for Co(II) ions with a maximum of 7.73 and 11.35 mg/g at 293 K and 313 K, respectively. The experimental kinetic data were well described using a pseudo-second-order kinetic model, and the adsorption mechanisms of Co(II) onto the b-HdA were revealed to be a chemisorption process with intraparticle diffusion being the rate-limiting step. In addition, the competitive adsorption onto the b-HdA with the order of U(VI) > Co(II) > Ni(II) > Sr(II) > Cs(I) was also observed in the multi-radionuclides system. Considering the advantages of the size, applicability to the continuous-flow column, and the easy separation from treated water, the b-HdA can be an excellent absorbent with high potential for practical applications for removing radionuclides.
Highlights
In recent years, increasing attention has been paid to the removal of radioactive pollutants from aquatic ecosystems due to their frequent and widespread detection [1,2]
Among the various noxious radionuclides, 137 Cs, 60 Co, 63 Ni, 55 Fe, 90 Sr, 226 Ra, 232 Th, and 238 U were reported as the key artificial radioactive contaminants [1,2,3]
Adsorption has been widely investigated as the most cost-effective, environmentally friendly method and the easiest technique for industrial application [9,10]
Summary
In recent years, increasing attention has been paid to the removal of radioactive pollutants from aquatic ecosystems due to their frequent and widespread detection [1,2]. Given the harmful nature of such radionuclides, various methods have been proposed and developed to effectively control radionuclide ions in contaminated water, including reverse osmosis, membrane separation, adsorption, biological treatment, and electrodialysis [3,5,7,8]. Adsorption has been widely investigated as the most cost-effective, environmentally friendly method and the easiest technique for industrial application [9,10]. In this regard, various types of adsorbents, including biomass, clays, activated carbon, hydroxyapatite, metal particulates, and metal oxides functionalized with bio-based substances have been used to separate contaminants during water treatment [1,5,11]
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