ADVANCED OXIDATION: OXALATE DECOMPOSITION TESTING WITH OZONE Page: 2 of 12
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WM2012 Feb 26 - Mar 1, 2012, Phoenix, Arizona, USA
Oxalate Decomposition Testing with Ozone - 12534
E. Ketusky, K. Subramanian
Savannah River Remediation, LLC
Aiken, SC 29808
At the Savannah River Site (SRS), oxalic acid is currently considered the preferred agent for
chemically cleaning the large underground Liquid Radioactive Waste Tanks. It is applied
only in the final stages of emptying a tank when generally less than 5,000 kg of waste solids
remain, and slurrying based removal methods are no-longer effective. The use of oxalic acid
is preferred because of its combined dissolution and chelating properties, as well as the fact
that corrosion to the carbon steel tank walls can be controlled.
Although oxalic acid is the preferred agent, there are significant potential downstream
impacts. Impacts include:
" Degraded evaporator operation.
" Resultant oxalate precipitates taking away critically needed operating volume.
" Eventual creation of significant volumes of additional feed to salt processing.
As an alternative to dealing with the downstream impacts, oxalate decomposition using
variations of ozone based Advanced Oxidation Process (AOP) were investigated. In general
AOPs use ozone or peroxide and a catalyst to create hydroxyl radicals. Hydroxyl radicals
have among the highest oxidation potentials, and are commonly used to decompose
organics. Although oxalate is considered among the most difficult organic to decompose, the
ability of hydroxyl radicals to decompose oxalate is considered to be well demonstrated. In
addition, as AOPs are considered to be "green" their use enables any net chemical additions
to the waste to be minimized.
In order to test the ability to decompose the oxalate and determine the decomposition rates,
a test rig was designed, where 10 vol% ozone would be educted into a spent oxalic acid
decomposition loop, with the loop maintained at 7000 and recirculated at 40L/min. Each of
the spent oxalic acid streams would be created from three oxalic acid strikes of an F-
area simulant (i.e., Purex = high Fe/Al concentration) and H-area simulant (i.e., H
area modified Purex = high AI/Fe concentration) after nearing dissolution
equilibrium, and then decomposed to < 100 Parts per Million (ppm) oxalate. Since AOP
technology largely originated on using ultraviolet (UV) light as a primary catalyst,
decomposition of the spent oxalic acid, well exposed to a medium pressure mercury vapor
light was considered the benchmark. However, with multi-valent metals already contained in
the feed, and maintenance of the UV light a concern; testing was conducted to evaluate the
impact from removing the UV light. Using current AOP terminology, the test without the UV
light would likely be considered an ozone based, dark, ferrioxalate type, decomposition
Specifically, as part of the testing, the impacts from the following were investigated:
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Ketusky, E. & Subramanian, K. ADVANCED OXIDATION: OXALATE DECOMPOSITION TESTING WITH OZONE, article, February 29, 2012; United States. (digital.library.unt.edu/ark:/67531/metadc844989/m1/2/: accessed January 18, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.