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Geochemical evidence for the application of nanoparticulate colloidal silica gel for in-situ containment of legacy nuclear wastes

DOI: 10.1039/D0EN00046A DOI Help

Authors: Pieter Bots (University of Strathclyde) , Joanna C. Renshaw (University of Strathclyde) , Timothy Payne (Australian Nuclear Science and Technology Organisation) , M. Josick Comarmond (Australian Nuclear Science and Technology Organisation) , Alexandra E. P. Schellenger (University of Strathclyde) , Matteo Pedrotti (University of Strathclyde) , Eleonora Cali' (Imperial College London) , Rebecca J. Lunn (University of Strathclyde)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Environmental Science: Nano

State: Published (Approved)
Published: March 2020
Diamond Proposal Number(s): 17114

Abstract: Colloidal silica is a nanoparticulate material that could have a transformative effect on environmental risk management at nuclear legacy sites through their use in in-situ installation of injectable hydraulic barriers. In order to utilize such nanoparticulate material as a barrier, we require detailed understanding of its impact on the geochemistry of radionuclides in the environment (e.g. fission products such as Sr and Cs). Here we show, through combining leaching experiments with XAS analyses, that colloidal silica induces several competing effects on the mobility of Sr and Cs. First, cations within the colloidal silica gel compete with Sr and Cs for surface complexation sites. Second, an increased number of surface complexation sites is provided by the silica nanoparticles and finally, the elevated pH within the colloidal silica increases the surface complexation to clay minerals and the silica nanoparticles. XAS analyses show that Sr and Cs complex predominantly with the clay mineral phases in the soil through inner-sphere surface complexes (Sr) and through complexation on the clay basal surfaces at Si vacancy sites (Cs). For binary soil – colloidal silica gel systems, a fraction of the Sr and Cs complexes with the amorphous silica-like surfaces through the formation of outer-sphere surface complexes. Importantly, the net effect of nanoparticulate colloidal silica gel is to increase the retention of Sr and Cs, when compared to untreated soil and waste materials. Our research opens the door to applications of colloidal silica gel to form barriers within risk management strategies at legacy nuclear sites.

Subject Areas: Environment, Chemistry, Earth Science

Instruments: B18-Core EXAFS

Added On: 31/03/2020 10:16

Discipline Tags:

Desertification & Pollution Earth Sciences & Environment Radioactive Materials Materials Science Engineering & Technology Nuclear Waste Geology Nanoscience/Nanotechnology Geochemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS)