Pertechnetate (TcO4−) sequestration from groundwater by cost-effective organoclays and granular activated carbon under oxic environmental conditions

Abstract

Technetium-99 (99Tc) is a major risk driver at nuclear power plants and several US Department of Energy (DOE) sites. Pertechnetate (TcO4−), the most common chemical form present in liquid nuclear waste and the environment, displays limited adsorption onto sediments, making it highly mobile and difficult to immobilize. In this work, inexpensive organoclays and granular activated carbon (GAC) were investigated for TcO4− sequestration from artificial groundwater (AGW). The Tc adsorption capacities were 15 mg/g for organoclays and 25 mg/g for GAC from pH 3–12 AGW under oxic conditions. Competitive NO3− at two orders of magnitude greater concentration than TcO4− reduced the Tc adsorption capacity by only 9–25%. In addition, the adsorbed Tc was effectively desorbed by KI, but not Na2SO4, and the regenerated sorbents retained their Tc removal capacity. X-ray absorption spectroscopy demonstrated that the Tc species bound to the organoclays and GAC was Tc(VII) (i.e., TcO4−), rather than Tc(IV). Thus, the inexpensive organoclays and GAC are highly effective at sequestering 99Tc in its naturally existing TcO4− without requiring costly reductive systems, which may provide a practical solution for removing 99TcO4− from environmental systems.