The Science & Technology
Cambridge - Monday 4th to
Wednesday 6th September 2017
article posted 22 May 2017
Paul Bingham joined Sheffield Hallam University in January 2012 as a Senior Lecturer in Materials Engineering, and became a Reader in Materials Engineering in 2015. He contributes to
teaching across Materials Engineering, with specific focus on materials composition / structure / property relations; and glass and ceramic technology. Paul is also actively involved with
student groups and is the SHU-IOM3 Materials Society Academic Liaison.
To date Paul has published over 70 research papers in the fields of glasses; glass-ceramics; energy and the environment; waste management and nuclear and toxic waste treatment. He has
co-edited and co-authored a book on the subject of low-energy, environmentally-friendly glasses and he currently holds a number of active research grants.
Paul is a Fellow of the Society of Glass Technology and sits on its Basic Science and Technology Committee. He is a Fellow of the Higher Education Academy and is also a member of the
Institute of Physics and the Association for the History of Glass. He is a reviewer for over 10 international journals and a member of several international committees.
Modelling the sulphate capacity of simulated radioactive waste borosilicate glasses
P.A. Binghama,*, S. Vaishnava, S.D. Fordera, A. Scrimshirea, J.C. Marrab, K.M. Foxb, E.M. Piercec,
P. Workmanb, J.D. Viennad
Sulphur can be a problematic component of certain civil and defence radioactive wastes that are destined to be converted into wasteforms by vitrification. The presence of sulphur
can pose problems for safe, cost-effective waste vitrification due to its low (< ca.1 wt% SO3
) capacity in the alkali borosilicate glasses that are used globally as radioactive waste
host matrices. If the sulphate capacity limit of an oxide glass is exceeded during melting, a molten salt or “gall” layer forms on the melt surface. This is highly undesirable: radionuclides
such as 135,137
Tc and 90
Sr migrate into this water-soluble sulphate layer during melting and the salt layer can thereby provide a pathway for these radionuclides to readily be
released into the environment following contact with water in a geological waste repository. Operators therefore focus on maintaining sulphate levels below their capacity limit in the
glass melt. This can restrict the types and concentrations of waste that can be vitrified, ultimately increasing the costs and timescales associated with waste vitrification, interim
storage and final geological disposal.
In this study, the capacity of simulated high-level radioactive waste borosilicate glasses to incorporate sulphate has been examined as a function of glass composition. Combined
Fe Mössbauer and literature evidence supports the attribution of coordination numbers and oxidation states of constituent cations for the purposes of modelling, and results
confirm the validity of correlating sulphate incorporation in multicomponent borosilicate radioactive waste glasses with different models. A strong compositional dependency is observed
and this is described by an inverse linear relationship between incorporated sulphate (mol% SO42-
) and total cation field strength index of the glass,
), with a high goodness-of-fit (R2
∼ 0.950), as shown in Figure 1. Similar relationships are also obtained if theoretical optical basicity,
∼ 0.930) or non-bridging oxygen per tetrahedron ratio, NBO/T (R2
∼ 0.919), are used. Results support the application of these models, and in particular ∑(z/a2
as predictive tools to aid the development of new glass compositions with enhanced sulphate capacities.
Figure 1. Retained sulphate, SO42-
, as a function of total cation field strength, ∑(z/a2).
Materials and Engineering Research Institute, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK
Savannah River National Laboratory, Savannah River Site, 999-W, Aiken, SC 29808, USA
Oak Ridge National Lab, Biological and Environmental Science Directorate, Oak Ridge, TN 37831, USA
Pacific Northwest National Laboratory, Nuclear Sciences Division, Richland, WA 99352, USA