Journal of Environmental Chemical Engineering
Effect of Mg2+-, Sr2+-, and Fe3+-substitution on 85Sr and 60Co adsorption on amorphous calcium phosphates: Adsorption performance, selectivity, and mechanism
Ivanets, Andrei; Zarkov, Aleksej; Prozorovich, Vladimir; Venhlinskaya, Ekaterina; Radkevich, Artsiom; Yang, Jen-Chang; Papynov, Evgeniy; Yarusova, Sofiya; Kareiva, Aivaras

Hydroxyapatite Ca10(OH)2(PO4)6 is a well-known efficient adsorbent of dyes, heavy metal ions, and radionuclides. Its adsorption efficacy strongly depends on crystalline/amorphous structure, defectiveness, texture characteristics, and morphology. Herein, we synthesized Mg2+-, Sr2+-, and Fe3+-substituted (5 mol%) amorphous calcium phosphates as an effective 85Sr and 60Co radionuclides adsorbents. The introduction of Mg2+-, Sr2+-, and Fe3+ ions led to the formation of amorphous calcium phosphates with particles size in the nanoscale range of approximately 10–50 nm. The features of the adsorption behavior of amorphous calcium phosphates were determined depending on the variation of the pH of aqueous, NaCl and CaCl2 solutions. Fe3+-substituted samples demonstrated the superior adsorption efficiency to 85Sr (Kd 7.77 ×103 cm3/g) and 60Co (Kd 6.84 ×104 cm3/g) radionuclides at pH of 10.0 and 4.0, respectively. The adsorption performance of obtained adsorbents slowly decreased at 0.1 M NaCl backgrounds and Kd85Sr and 60Co reached 1.67 × 103 and 2.78 × 104 cm3/g for non-substituted calcium phosphate. The dramatic decrease of calcium phosphates adsorbents efficiency to 85Sr (Kd <150 cm3/g) and 60Co (Kd <1.34 ×103 cm3/g) for 0.05 M CaCl2 model solution was established. The adsorption mechanism of dissolution-precipitation (for 85Sr) and chemisorption (for 60Co) was proposed. Fe3+-substituted calcium phosphate showed the competitive affinity and selectivity to 85Sr and 60Co comparing with described inorganic adsorbents and to be considered as prospective adsorbent for wastewater treatment in nuclear industry. © 2022 Elsevier Ltd

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