A laboratory simulation to investigate effects of moistures on U distribution among solid phase components in army range soils

Abstract

Uranium is a naturally occurring radioactive trace element found in rocks, soils, and coals. U may contaminate groundwater and soil from nuclear power plant operations, spent fuel reprocessing, high-level waste disposal, ore mining and processing, or manufacturing processes. Yuma Proving Ground in Arizona, USA has been used depleted uranium ballistics for 36 years where U has accumulated in this army testing site. The objective of this study is to develop a laboratory scheme on the effects of soil moisture regiments on the distribution and partitioning of U in army range soil among solid phase components to mimic U biogeochemical processes in the field. Three moisture regiments were saturated paste, field capacity, and wetting-drying cycle which covered major scenarios in fields from the wet summer season to the dry winter season. Uranium in soils with different forms of U (UO₂, UO₃, uranyl, and schoepite) was fractionated into 8 operationally defined solid components with sequential selective dissolution procedure. The essences of this new development were as following:•A scheme was developed for investigation of U distribution, partitioning and transformation among solid phase components in army weapon test range soils with various U forms under 3 soil moisture regimes.•Soil moisture was one of major environmental factors in controlling biogeochemical processes and fates of U in army weapon test site.

Keywords: Biogeochemical conditions; Distribution; Fractionation; Soil moistures; U fractionation; U redistribution; Uranium; Yuma soil.

Graphical abstract

Fig. 1

Flow chart of the laboratory scale simulation on effects of soil moisture on U distribution among solid-phase components in soils. Water (H₂O): the water soluble fraction, EXC: the exchangeable, CARB: the carbonate bound, ERO: the easily reducible oxide bound, OM: the organic matter bound, AmoFe: the amorphous iron oxide bound, CryFe: the crystalline iron oxide bound, RES: the residual fraction, ICP-MS/ICP-OES: inductively coupled plasma- mass spectroscopy/optical emission spectroscopy.

Fig. 2

U distribution among solid-phase components in Yuma soils with uranyl at 100 mg/kg under saturated paste (A), field capacity (B) and wetting-drying cycle (C) moistures over 1 week, 2 weeks and 1 month of incubation. D. The comparison of U distribution among three moisture regimes at 2 weeks of incubation. H₂O: the water soluble fraction, EXC: the exchangeable, CARB: the carbonate bound, ERO: the easily reducible oxide bound, OM: the organic matter bound, AmoFe: the amorphous iron oxide bound, CryFe: the crystalline iron oxide bound, RES: the residual fraction. In Fig. 2D, difference letters in the same fraction indicate the significant difference at p = 0.05 probability among three moistures.