Properties and Mechanism of Molybdenum and Zirconium Adsorption by a Macroporous Silica‐Based Extraction Resin in the MAREC Process

Abstract

To achieve effective separation of molybdenum and zirconium in the MAREC process, the adsorption properties and mechanism of Mo(VI) and Zr(IV) with a macroporous CMPO/SiO2‐P (CMPO: octyl(phenyl)‐N,N‐diisobutylcarbamoylmethylphosphine oxide) extraction resin have been studied. By investigating the influence of the aqueous concentrations of H+ and NO3 − on the adsorption of Mo(VI), the composition of complex of Mo(VI) and CMPO/SiO2–P is determined as H2MoO4 · 2CMPO/SiO2–P for dilute aqueous HNO3 and H2MoO3 (NO3)2 · 2CMPO/SiO2–P for concentrated aqueous HNO3, respectively. Similarly, the composition of Zr(IV) and CMPO/SiO2–P is determined as ZrO(NO3)2 · 2CMPO/SiO2–P or Zr(NO3)4 · 2CMPO/SiO2–P in 0.3–4.0 M HNO3, while ZrO2 · 2H2O · 2CMPO/SiO2–P is assumed for lower HNO3 concentration. Based on the compositions of Mo(VI) and Zr(IV) with CMPO/SiO2–P and the elution behavior of Mo(VI) and Zr(IV) by using 0.05 M diethylenetriaminepentaacetic acid (DTPA) at 0.01–1.0 M HNO3, a dynamic interconversion equilibrium between the complexes of Mo(VI) or Zr(IV) and CMPO/SiO2–P is demonstrated to take place in the elution process. To verify the adsorption mechanism, the adsorption and elution behavior of Mo(VI) and Zr(IV) with 0.05 M DTPA‐pH 2.0 was performed from a simulated high level radioactive liquid waste (HLLW) containing Pd(II), Gd(III), Y(III), Eu(III), Sm(III), Mo(VI), and Zr(IV). The results indicate that Mo(VI) and Zr(IV) not only can be efficiently eluted with 0.05 M DTPA‐pH 2.0, but also the elution efficiency is much better than that of 0.5 M H2C2O4 previously used in the MAREC process. The reverse equilibrium of complexes between Mo(VI) or Zr(IV) and CMPO/SiO2–P in high and low acidity was demonstrated, respectively.