Investigations of Pb and Ni uptake in cementitious environments
File(s)
Author(s)
Plausinaitis, Kristijonas
Type
Thesis
Abstract
In this work, Pb and Ni uptake in a highly alkaline near-field cementitious environment is
investigated. Significant quantities of Pb occur in intermediate-level radioactive wastes (ILW)
that will be held in a UK geological disposal facility (GDF). Pb is chemotoxic and a priority for
risk assessments as part of the GDF safety-case. Ni will occur in nuclear waste as radioactive isotopes 59Ni and 63Ni. Therefore, it is important to understand their migration and
retardation behaviour within the engineered barriers of a GDF. Specifically, in the
cementitious material which might be used to backfill the ILW vaults. One such material is the
Nirex Reference Vault Backfill (NRVB).
In this work, three aspects of NRVB behaviour were investigated: the amount of Pb and Ni
ions adsorbed by NRVB, whether that adsorption is reversible, and the phases in NRVB that
primarily control the uptake. To reflect the GDF scenario, batch sorption analysis was
performed of Pb and Ni uptake onto hydrated NRVB. Pb batch sorption experiments were
also carried out on constituent components (CEM-1, Ca(OH)2, CaCO3) and calcium silicate
hydrate (C-S-H) gels. The results indicate Langmuir-type sorption onto the NRVB. Desorption
experiments suggested that, on these experimental timescales, Pb sorption is reversible, in
contrast to previous studies where Pb was introduced during cement curing. Surface analysis
techniques found that Pb is homogeneously distributed on the NRVB surface, suggesting that
the dominant sorbent phase is C-S-H gel; a hypothesis consistent with the batch sorption
measurements. X-ray absorption spectroscopy (results suggest that Pb is linked to the C-S-H
gel through Si–O–Pb bonds. In contrast, Ni sorption investigations were complicated by the
extremely low solubility-limit of Ni at the pH of NRVB, and trace Ni in the NRVB itself.
Precipitation of Ni-based hydroxides and layered double-hydroxides dominate the
sequestration mechanisms over any surface adsorption.
investigated. Significant quantities of Pb occur in intermediate-level radioactive wastes (ILW)
that will be held in a UK geological disposal facility (GDF). Pb is chemotoxic and a priority for
risk assessments as part of the GDF safety-case. Ni will occur in nuclear waste as radioactive isotopes 59Ni and 63Ni. Therefore, it is important to understand their migration and
retardation behaviour within the engineered barriers of a GDF. Specifically, in the
cementitious material which might be used to backfill the ILW vaults. One such material is the
Nirex Reference Vault Backfill (NRVB).
In this work, three aspects of NRVB behaviour were investigated: the amount of Pb and Ni
ions adsorbed by NRVB, whether that adsorption is reversible, and the phases in NRVB that
primarily control the uptake. To reflect the GDF scenario, batch sorption analysis was
performed of Pb and Ni uptake onto hydrated NRVB. Pb batch sorption experiments were
also carried out on constituent components (CEM-1, Ca(OH)2, CaCO3) and calcium silicate
hydrate (C-S-H) gels. The results indicate Langmuir-type sorption onto the NRVB. Desorption
experiments suggested that, on these experimental timescales, Pb sorption is reversible, in
contrast to previous studies where Pb was introduced during cement curing. Surface analysis
techniques found that Pb is homogeneously distributed on the NRVB surface, suggesting that
the dominant sorbent phase is C-S-H gel; a hypothesis consistent with the batch sorption
measurements. X-ray absorption spectroscopy (results suggest that Pb is linked to the C-S-H
gel through Si–O–Pb bonds. In contrast, Ni sorption investigations were complicated by the
extremely low solubility-limit of Ni at the pH of NRVB, and trace Ni in the NRVB itself.
Precipitation of Ni-based hydroxides and layered double-hydroxides dominate the
sequestration mechanisms over any surface adsorption.
Version
Open Access
Date Issued
2020-08
Date Awarded
2021-02
Copyright Statement
Creative Commons Attribution NonCommercial Licence
Advisor
Ryan, Mary
Vandeperre, Luc
Sponsor
Amec Foster Wheeler
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)