Cesium Ion Exchange
Authors: John Willey, John Schmoker
Abstract
The U.S. Department of Energy’s Hanford Reservation was established in the early 1940’s as a secret
government project to enrich uranium for nuclear weapons. As a result of over 50 years of nuclear fuel
production, the Hanford Reservation has the largest repository of untreated nuclear waste in the world.
Over 55 million gallons of highly toxic and radioactive waste is contained in 177 underground tanks
(Burgeson et al, 2006). Many of the tanks are currently leaking into the surrounding area. The U.S.
Department of Energy has contracted with outside vendors to engineer and build a state-of-the-art
vitrification facility to suspend the liquid radioactive waste in silicate glass for indefinite storage. The
vitrification facility utilizes two primary methods for separating radioactive materials from the bulk
waste, which are ultrafiltration and ion exchange. Our project focuses on the ion exchange process. Our
intention is to develop mass transfer and reactor design models to accurately describe the ion exchange
process. To summarize our goals for this project, the following issues will be addressed:

Model the ion flux and concentration gradient throughoutthe reactor using the spherical nature of
the resin beads.

Determine the rate equation associated with the ion exchange reaction.

Size the ion exchange column according to required radioactivity levels for Low Activity
Wastefeed.

Determine loading time for lead column.
Researching these issues will help us and our classmates better understand the overall ion exchange
process, which is a separation process widely used throughout industry.
Support for Issue Research
Process Overview
The primary concern for our process is the separation of radioactive Cesium-137 from the nonradioactive substituents in the waste stream. Hanford’s Pretreatment Facility utilizes ResorcinolFormaldehyde Resin to exchange 137Cs+ atoms for Na+ inside a series of packed ion exchange columns.
Figure 1 illustrates the overall ion exchange process.
137
Cs
Lead
Lag
Upflow Reagents
NaOH, HNO3, H20
Polish
Resin Rejuvenation
Na+ Form
Loading - Low Activity Waste (LAW)
Elution – Highly Concentrated 137 Cs to High Level Waste (HLW)
Figure 1: Cesium Ion Exchange Process
Theuntreated waste enters the lead column and flows through lag and polishing columns before
concentrated Cesium is sent to the High Level Waste (HLW) facility. The remaining waste is sent to the
Low Activity Waste (LAW) melters for vitrification.The fourth column is kept in reserve in order to
keep throughput constant while resin rejuvenation is being performed on fully loaded columns.
Mass Transfer
Resorcinol-Formaldehyde resin is comprised of resorcinol (1,3-dihydroxybenzene) units linked with
methylene bridges as shown in Figure 2.
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Figure 2: Resorcinol-Formaldehyde Resin Functional Groups (King et al, 2005)
The combination of hydroxyl and alkyl groups activates the benzene ring toward electrophilic
substitution reactions (King et al, 2005). Each resorcinol molecule has two available groups for cation
exchange.Figure 3 describes the general reaction.
Figure 3: General Electrophilic Ion Exchange Reaction
The primary ion exchange reaction is accomplished between di-sodium substituted (Na form) resin and
aqueous cesium.The resin is highly spherical and consistently sized as seen infigure 4 (King 2007). As a
result, we will develop a mass transfer model for ion exchange around a sphere as a function of
concentration. The concentration gradient between the Na+resin and 137Cs+in the waste feed will cause
diffusion to occur between the two species, leaving 137Cs on the surface of the resin beads while Na+
atoms flow out the Low Activity Waste Stream.
Figure 4: Spherical Resorcinol-Formaldehyde Resin (King 2007)
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Reactor Design
Although the exact configuration and internal structure of Hanford’s cesium ion exchange columns is
proprietary, we will model our reactors after traditional packed bed reactors. As a result, we will
consider the effects of concentration and pressure changes on the reaction rate as waste travels through
the columns. The process is considered isothermal so temperature variations will not be considered. A
reaction rate model will be developed to describe the kinetics inherent to the ion exchange process.
Due to radioactivity requirements for the LAW feed, a majority of the radioactive cesium must be
removed prior to exiting the polishing column. We will determine the required size of the ion exchange
columns in order to meet this specification and the associated loading time for the lead column.
Issue Justification
Treatment and storage of nuclear waste is a continuing problem. The Hanford site has the largest
stockpile of untreated nuclear waste in the world (Burgeson et al, 2006). The U.S. Department of
Energy is committed to the safe cleanup and disposal of Hanford’s nuclear waste, as evidenced by the
creation of the vitrification plant. Our project focuses on the most important part of pretreating the
waste prior to vitrification. Researching this process allows us to develop models for both mass
transport and reactor design. Modeling the diffusion within the column and determining the packed bed
reactor specifications are directly related to our curriculum and provide benefits to ourselves as well as
our classmates. Nuclear waste treatment is an example of ion exchange application in the real world.
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Appendix A
References
Burgeson, I. E. , Deschane, J.R. , Cook, B. J. , Blanchard Jr. , D. L. and Weier, D. L. (2006) ‘Evaluation
of Elution Parameters for Cesium Ion Exchange Resins’, Separation Science and Technology, 41: 11,
2373 – 2390.
Fiskum, S. K. , Steele, M. J. , Blanchard, D. L. Jr. , (2006) ‘Small Column Ion Exchange Testing of
Spherical Resorcinol-Formaldehyde Resin for 137Cs Removal from Pre-Treated Hanford Tank 241-An102 Waste’, Battelle – Pacific Northwest Division, Richland Wa.
Hassan, N. M. , McCabe, D. J. , King, D. W. , Hamm, L. L. , Johnson, M. E. , (2002) ‘Ion Exchange
Removal of Cesium From Hanford Tank Waste Supernates With SuperLig 644 Resin’ Journal of
Radioanalytical and Nuclear Chemistry, Vol. 254, No. 1, pp. 33-40.
King, D. W., (2007) ‘Literature Reviews to Support Ion Exchange Technology Selection for Modular
Salt Processing’, Savannah River National Laboratory, Westinghouse Savannah River Company, Aiken,
SC.
King, D. W., et al, (2006) Reactivity of Resorcinol Formaldehyde Resin with Nitric Acid, Savannah
River National Laboratory, Westinghouse Savannah River Company, Aiken, SC.
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