Uranium uptake onto Magnox sludge minerals studied using EXAFS

A Van Veelen,G T W Law,J R Bargar,D K Shuh,J Rogers,R Copping,A J Smith,R A Wogelius

doi:10.1180/minmag.2012.076.8.24

Abstract

AbstractAround the world large quantities of sludge wastes derived from nuclear energy production are currently kept in storage facilities. In the UK, the British government has marked sludge removal as a top priority as these facilities are nearing the end of their operational lifetimes. Therefore chemical understanding of uranium uptake in Mg-rich sludge is critical for successful remediation strategies. Previous studies have explored uranium uptake by the calcium carbonate minerals, calcite and aragonite, under conditions applicable to both natural and anthropogenically perturbed systems. However, studies of the uptake by Mg-rich minerals such as brucite [Mg(OH)2], nesquehonite [MgCO3·3H2O] and hydromagnesite [Mg5(CO3)4(OH)2·4H2O], have not been previously conducted. Such experiments will improve our understanding of the mobility of uranium and other actinides in natural lithologies as well as provide key information applicable to nuclear waste repository strategies involving Mg-rich phases. Experiments with mineral powders were used to determine the partition coefficients (Kd) and coordination of UO22+ during adsorption and co-precipitation with brucite, nesquehonite and hydromagnesite. The Kd values for the selected Mg-rich minerals were comparable or greater than those published for calcium carbonates. Extended X-ray absorption fine structure analysis results showed that the structure of the uranyl-triscarbonato [UO2(CO3)3] species was maintained after surface attachment and that uptake of uranyl ions took place mainly via mineral surface reactions.

Highlights

LARGE quantities of sludge wastes derived from nuclear power are currently housed in storage facilities around the world
Synthesized minerals The protocols developed for synthesizing the minerals brucite, nesquehonite and hydromagnesite were successful and their powder patterns were verified by X-ray diffraction (XRD) (Fig.1)
The most intense artinite peak (2 ̄01) could be resolved; the peak width relative to the nesquehonite peaks suggested it to be poorly crystalline, and the relatively low intensity indicates a minor component of the synthesized solid

Summary

Introduction

LARGE quantities of sludge wastes derived from nuclear power are currently housed in storage facilities around the world. In the UK, over 1000 m3 of radioactive waste from the first generation Magnox fuel cans are currently stored under water. As a result the fuel cladding became extensively corroded and instead of an easy removal of the fuel rods from the cladding, a complex and highly contaminated waste has been produced. In the absence of waste management, significant amounts of intermediate-level waste have accumulated creating some of the most complex radiological remediation and clean up challenges in the world (Topping and Bruce, 2006). Limited records exist of what exactly was stored in these facilities, due to changing priorities at the time (Horsley and Hallington, 2005)

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Results

Conclusion