Immobilization of uranium from aqueous solutions by room-temperature precipitation of pyromorphite [Pb5(PO4)3Cl]

• Published in: Polyhedron 2024-04, Vol.252, p.116891, Article 116891
• Main Authors: Sordyl, Julia, Chamberlain, Carmen E., Sweet, Teagan F.M., Burns, Peter C., Cronberger, Karl, Manecki, Maciej
• Format: Article
• Language: English
• Subjects: Apatite; Autunite; Incorporation; Removal; Synthetic
• ISSN: 0277-5387; 1873-3719
• DOI: 10.1016/j.poly.2024.116891

The present work demonstrates the efficient removal of uranium supported by the addition of lead through the rapid precipitation of a crystalline powder. [Display omitted] U(VI) in natural pyromorphite reaches 0.5 wt%. However, this depends on concentration of U in source solutions and the upper limit of incorporation of uranyl into pyromorphite at low temperature is unknown. If U(VI) incorporation capacity in the structure is high enough, Pb-apatite could be used in radioactive waste remediation. In this study, eight compounds were synthesized from aqueous solutions containing Pb2+, (UO2)2+, (PO4)3- and Cl- ions in a still water column under ambient conditions. In each synthesis, the molar ratio of (UO2)2+:Pb was varied, targeting composition Pb5-x(UO2)x(PO4)3Cl. The final solutions were analyzed with inductively coupled plasma optical emission spectroscopy (ICP-OES) for Pb and U(VI) concentrations, while dried solids were analyzed using powder X-ray diffraction (PXRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), wavelength dispersive X-ray spectroscopy (WDS) using an electron microprobe, and Raman spectroscopy. Synthesis products are synthetic analogs of pyromorphite containing (UO2)2+, partially substituting Pb2+. For the higher initial concentration of U, coprecipitation of a second phase/phases was observed. U was removed from the solution at levels ranging from 74.3 % (σ = 1.5) to 88 % (σ = 2), and Pb was removed at levels ranging from 91 % (σ = 2) to 96.8 % (σ = 1.9). Precipitation of pyromorphite from uranyl-contaminated solutions may immobilize uranyl in the form of highly insoluble, stable, crystalline Pb phosphates.