Summary of Adsorption Capacity and Adsorption Kinetics of Uranium and Other Elements on Amidoxime-based Adsorbents from Time Series Marine Testing at the Pacific Northwest National Laboratory

Abstract

The Pacific Northwest National Laboratory (PNNL) has been conducting marine testing of uranium adsorbent materials for the Fuel Resources Program, Department of Energy, Office of Nuclear Energy (DOE-NE) beginning in FY 2012. The marine testing program is being conducted at PNNL's Marine Sciences Laboratory (MSL), located at Sequim Bay, along the coast of Washington. One of the main efforts of the marine testing program is the determination of adsorption capacity and adsorption kinetics for uranium and selected other elements (e.g. vanadium, iron, copper, nickel, and zinc) for adsorbent materials provided primarily by Oak Ridge National Laboratory (ORNL), but also includes other Fuel Resources Program participants. This report summarizes the major marine testing results that have been obtained to date using time series sampling for 42 to 56 days using either flow-through column or recirculating flume exposures. The major results are highlighted in this report and the full data sets are appended as a series of Excel spreadsheet files. Over the four year period (2012-2016) that marine testing of amidoxime-based polymeric adsorbents was conducted at PNNL's Marine Science Laboratory, there has been a steady progression of improvement in the 56-day adsorbent capacity from 3.30 g U/kg adsorbent for the ORNL 38H adsorbent to the current best performing adsorbent prepared by a collaboration between the University of Tennessee and ORNL to produce the adsorbent SB12-8, which has an adsorption capacity of 6.56 g U/kg adsorbent. This nearly doubling of the adsorption capacity in four years is a significant advancement in amidoxime-based adsorbent technology and a significant achievement for the Uranium from Seawater program. The achievements are evident when compared to the several decades of work conducted by the Japanese scientists beginning in the 1980's (Kim et al., 2013). The best adsorbent capacity reported by the Japanese scientists was 3.2 g U/kg adsorbent for a 180 day deployment at temperatures between 15 and 25 °C (Kim et al., 2013) The majority of the capacities the Japanese scientists reported were less than 2 g U/kg adsorbent (Kim et al., 2013). Repeated time series measurements of a common formulation of amidoxime-based adsorbent, the ORNL AF series, by both flow-through column (3.91 ± 0.11 g U/kg adsorbent). and recirculating flume exposures (4.03 ± 0.12 g U/kg adsorbent) produced 56-day adsorption capacities that agreed extremely well. This excellent agreement generates confidence that the testing procedures are accurate and reliable and moreover, that the technology to produce the adsorbents is highly reliable and reproducible, lending additional confidence of the robustness and homogeneity of the production technology.

Extraction and adsorption of U(VI) from aqueous solution using affinity ligand-based technologies: an overview

“…This work is followed by substantial research focusing on amidoxime-based adsorbents (Zhuang et al 2018;Wu et al 2018;Zhao et al 2014b;Yuan et al 2016;Wang et al 2018b;Cheng et al 2019), and numerous reviews on amidoxime-based adsorbents for uranium harvest (Abney et al 2017). So far, the countable marine experiments have all involved amidoxime-based polymer adsorbents (Gill et al 2016;Ladshaw et al 2017).…”

Amidoxime Polymers for Uranium Adsorption: Influence of Comonomers and Temperature

“…Since then, the U.S. Department of Energy (DOE) has sought to continue research into uranium recovery by supporting multidisciplinary research into materials development, advanced characterization, and the development of high performance computational models [ 8 ]. DOE support of amidoxime research has, in turn, led to the development of materials with more than three times the adsorption capacity of the Japanese materials, increasing from 1.8 mg U/g adsorbent to 6.56 mg U/g adsorbent after 56 days of exposure [ 9 ].…”

“…Along with its relatively low recovery rates, solvent extraction [ 18 , 19 ] is further harmed by solvent losses through entrainment and dissolution, making the process cost prohibitive [ 4 ]. Despite having higher recovery rates, flotation techniques [ 20 , 21 ] are undesirable due to surfactant losses [ 9 ] and the time needed to obtain high recovery rates [ 3 ]. Compared to the previously mentioned techniques, the application of magnetic adsorption [ 14 ] to uranium recovery from seawater has received relatively little attention, though recovery from other aqueous solutions has been reported [ 22 , 23 ].…”

“…The application of ATRP to amidoxime polymer synthesis was investigated by Brown and coworkers using an amidoxime-acrylic acid copolymer grafted to Poly (vinyl chloride)-co-chlorinated Poly (vinyl chloride) fibers [ 40 ]. Flow-through column experiments showed a uranium recovery rate of 6.56 mg U/g adsorbent after 56 days in contact with seawater, which is the highest adsorption capacity observed to date [ 9 ]. The use of alternative alkaline conditioners, such as sodium hydroxide (NaOH), has also been considered to replace KOH conditioning.…”

“…Adsorption experiments with three different adsorbents (38H, AI8, and AF1) are examined to quantify the impact of temperature on uranium uptake capacities. While these materials have essentially the same types of active surface ligands for capturing uranium, prior studies have noted that they have different uranium capacities from both laboratory and seawater experiments [ 9 , 37 , 38 , 39 ]. The major difference between these materials is the acid comonomers used in the grafting of the ligands.…”