Surfactant-modified siliceous zeolite Y for pertechnetate remediation

Abstract

Separation of pertechnetate (99TcO4−) from contaminated groundwater and nuclear waste streams remains a technical challenge for the long-term management of 99TcO4− released to the environment. Herein, a siliceous zeolite Y phases(s) were modified with cationic surfactant and subsequently used to sequester TcO4− from acidic aqueous solution containing competing ions. Pristine and modified zeolite Y phase(s) were characterized with X-ray diffraction, X-ray absorption spectroscopy (XAS), sorption isotherms, zeta potential, and BET surface area measurements. Measured TcO4− sorption capacity of the modified zeolite Y (MSAV) was 337 mg/g, which was in good agreement with modeled estimates, 357 mg/g. The Langmuir and the pseudo-second-order models adequately described the sorption of TcO4−on the modified zeolite Y phases. Kinetic data suggest that liquid film diffusion and intraparticle diffusion were the rate-limiting steps governing TcO4− sorption. Analyses of the XAS spectra data revealed that ReO4−, a chemical analogue for TcO4−, was associated with the modified zeolite Y phase(s) as an inner-sphere complex of ReO4− possibly incorporated into a structural cavity, and there was no evidence of the reduced form of Re(IV). The modified zeolite Y exhibited fast sorption kinetics, significant sorption capacity, and robust uptake performance in acidic conditions (pH 3–5) and in the presence of high concentrations of competing anions. An important attribute of this remediation technology is that it sequesters TcO4− (Tc oxidized form) that exists naturally in most surface environments and waste streams, and it provides an effective alternative to the existing reductive precipitation technologies that have limited long-term environmental applications.