Low concentration of Fe(II) to enhance the precipitation of U(VI) under neutral oxygen-rich conditions

Yanpei Xie; Qi Fang; Mi Li; Sainan Wang; Yingfeng Luo; Xiaoyan Wu; Junwen Lv; Wenfa Tan; Hongqiang Wang; Kaixuan Tan

doi:10.1016/j.scitotenv.2019.134827

Low concentration of Fe(II) to enhance the precipitation of U(VI) under neutral oxygen-rich conditions

Sci Total Environ. 2020 Apr 1:711:134827. doi: 10.1016/j.scitotenv.2019.134827. Epub 2019 Nov 5.

Authors

Yanpei Xie¹, Qi Fang², Mi Li³, Sainan Wang¹, Yingfeng Luo¹, Xiaoyan Wu³, Junwen Lv³, Wenfa Tan³, Hongqiang Wang³, Kaixuan Tan¹

Affiliations

¹ School of Resource Environment and Safety Engineering, University of South China, Hengyang 421001, PR China.
² School of Resource Environment and Safety Engineering, University of South China, Hengyang 421001, PR China; Hengyang Key Laboratory of Soil Pollution Control and Remediation, University of South China, Hengyang 421001, PR China. Electronic address: frances2009@foxmail.com.
³ School of Resource Environment and Safety Engineering, University of South China, Hengyang 421001, PR China; Hengyang Key Laboratory of Soil Pollution Control and Remediation, University of South China, Hengyang 421001, PR China.

PMID: 32000325
DOI: 10.1016/j.scitotenv.2019.134827

Abstract

Immobilization of U(VI) by naturally ubiquitous ferrous ions (Fe(II)) has been considered as an efficient and ecofriendly method to retard the migration of aqueous U(VI) at many nuclear sites and surface environments. In this study, we conducted Fe-U coprecipitation experiments to investigate the mechanism and stability of uranium (U) precipitation induced by a small quantity of Fe(II) under oxygen-rich conditions. The experimental results suggest that the sedimentation rates of U(VI) by Fe(II) under neutral oxygen-rich conditions are more than 96%, which are about 36% higher than those without Fe(II) and 16% higher than those under oxygen-free conditions. The Fe-U coprecipitates were observed to remain stable under slightly acidic to neutral and oxygen-rich conditions. Fe(II) primarily settles down as low-crystalline iron oxide hydroxide. U(VI) mainly precipitates as three forms: 16-20% of U forms uranyl hydroxide and metaschoepite, which is absorbed on the surface of the solids; 52-56% of U is absorbed as discrete uranyl phases at the internal pores of iron oxide hydroxide; and 27-29% of U is probably incorporated into the FeO(OH) structure as U(V) and U(VI). The U(V) generated via one-electron reduction is somewhat resistant to the oxidation of O₂ and the acid dissolution. In addition, nearly 70% of U and only about 15% of Fe could be extracted in 24 h by a hydrochloric acid solution with the H⁺ concentration ([H⁺]) of 0.01 M, revealing that U(VI) immobilization by low concentration of Fe(II) combined with O₂ has potential applications in the separation and recycling of aqueous uranium.

Keywords: Coprecipitation; Fe(II); Mechanism; Oxygen; Stability; U(VI).