Understanding the affinity of Cyphos Nitrate for Zr(IV) over other metal ions present in simulated high level liquid waste compositions

Abstract

The presence of Zr(IV) in the spent nuclear fuel (SNF) is an hindrance for a smooth and safe reprocessing of actinides and other fission products. The separation of Zr(IV) from nitric acid feed through solvent extraction route is a challenging task as far as its aqueous chemistry and the selectivity of the proposed extractants for it is concerned. In this context, we employed a strongly hydrophobic and sustainable quarternary alkyl phosphonium-based ionic liquid (IL): Tri(hexyl)tetradecylphosphonium nitrate ([P₆₆₆₁₄][NO₃]) (or cyphos nitrate) for the extraction of Zr(IV) from a broad range of acidic feed and evaluated the feasibility of its selective separation from a Fast Reactor Simulated High Level Liquid Waste (FR-SHLLW) solution (Burn up: 80 GWd/Te). The extraction factor of [P₆₆₆₁₄][NO₃] was compared with that observed in other classes of ILs in their undiluted condition. The efficient extraction of Zr(IV) without any additional ligand in IL phase by adopting simple complexation mechanism infers the novelty of [P₆₆₆₁₄][NO₃]. High asymmetricity and bulkiness of IL cation enables more freedom to its anion (NO₃^-) to coordinate with Zr(IV), thereby realizing high extraction factors as compared to other ILs having different cations (or anions). The novelty was further clarified from the notable extraction efficiency by consuming very less IL volume (low IL to aqueous phase ratio). The radiation stability of cyphos nitrate was affirmed from the extraction factors at different exposed doses. The uniqueness of [P₆₆₆₁₄][NO₃] for Zr(IV) over the co-extracting Pd(II) was assured using an aqueous soluble complexing agent for the later to be trapped in the raffinate phase of SHLLW solution. At end, a schematic flow-sheet was proposed for selective separation of Zr(IV) from SHLLW solution.