Removal of TcO₄⁻ ions from solution: materials and future outlook

Abstract

Technetium mainly forms during artificial nuclear fission; it exists primarily as TcO4(-) in nuclear waste, and it is among the most hazardous radiation-derived contaminants because of its long half-life (t1/2 = 2.13 × 10(5) years) and environmental mobility. The high water solubility of TcO4(-) (11.3 mol L(-1) at 20 °C) and its ability to readily migrate within the upper layer of the Earth's crust make it particularly hazardous. Several types of materials, namely resins, molecular complexes, layered double hydroxides, and pure inorganic and metal-organic materials, have been shown to be capable of capturing TcO4(-) (or other oxoanions) from solution. In this review, we give a brief description about the types of materials that have been used to capture TcO4(-) and closely related oxyanions so far and discuss the possibility of using metal-organic frameworks (MOFs) as next-generation ion-exchange materials for the stated application. In particular, with the advent of ultra-stable MOF materials, in conjunction with their chemical tunability, MOFs can be applied to capture these oxyanions under real-life conditions.

Removal of Pertechnetate‐Related Oxyanions from Solution Using Functionalized Hierarchical Porous Frameworks

“…As such, room for improvement exists in terms of capacity, kinetics, and selectivity . Stable, hierarchical functionalized porous frameworks such as members of crystalline metal organic frameworks (MOFs), covalent organic frameworks (COFs) and amorphous porous aromatic frameworks (PAFs) offer several advantages over traditional ion‐exchange materials, such as resins, including structural rigidity, modularity and functionalizable pore surfaces (Scheme ) . MOFs or PAFs with appropriate functional groups have shown excellent ion‐exchange capacity, kinetics and selectivity for a range of industrially important ions.…”

Metal–Organic Frameworks for Separation

“…Besides organic ions, many inorganic anions and cations are responsible for water pollution too. Among many types of ionic contaminants, a particular class is inorganic ions with radioactive component such as UO 2 2+ , TcO 4 − , which have attracted much attention lately . For example, 99 Tc comes from the production of weapon grade plutonium ( 239 Pu) during irradiated uranium fuel cell reprocessing, and primarily exists in the form of TcO 4 − in nuclear waste .…”

Selective Anion Extraction and Recovery Using a FeII4L4 Cage

“…Because of its similar structure and almost identical charge density, perrhenate is also used as a nonradioactive surrogate for pertechnetate ( 99 TcO 4 − ), which is an important radiopharmaceutical and one of the most problematic radioactive ions in nuclear waste . Significant advances have been made in designing sorbent materials for removing ReO 4 − /TcO 4 − from aqueous solution by liquid–solid extraction . These solid materials take up anionic targets from water via anion exchange.…”