Modelling of multi-minerals kinetic evolution in hyper-alkaline leachate for a 15-year experiment
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RESEARCH ARTICLE
Modelling of multi-minerals kinetic evolution in hyper-alkaline leachate for a 15-year experiment Yousef Baqer 1 & XiaoHui Chen 1
&
Christopher Rochelle 2 & Steven Thornton 3
Received: 25 March 2020 / Accepted: 23 June 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Cement has been widely used for low- to intermediate-level radioactive waste management; however, the long-term modelling of multiple mineral transfer between the cement leachate and the host rock of a geological disposal facility remains a challenge due to the strong physical-chemical interactions within the chemically disturbed zone. This paper presents a modelling study for a 15year experiment simulating the reaction of crystalline basement rock with evolved near-field groundwater (pH = 10.8). A mixed kinetic equilibrium (MKE) modelling approach was employed to study the dolomite-rich fracture-filling assemblage reacting with intermediate cement leachate. The study found that the mineralogical and geochemical transformation of the system was driven by the kinetically controlled dissolution of the primary minerals (dolomite, calcite, quartz, k-feldspar and muscovite). The initial high concentration of calcium ions appeared to be the main driving force initiating the dedolomitization process, which played a significant role in the precipitation of secondary talc, brucite and Mg-aluminosilicate minerals. The modelling study also showed that most of the initially precipitated calcium silicon hydrate phases redissolved and formed more stable calcium silicon aluminium hydrate phases. The findings highlight the importance of a deep and insightful understanding of the geochemical transformations based on the type and characteristics of the host rock, where the system is under out of equilibrium conditions, and the rates of mineral reactions. Keywords Cement . Radioactive waste disposal . Mineral evolution . Modelling . Cement leachate . Alkaline fluids . PHREEQC
Introduction Underground geological facilities are the most secure places to store/dispose of radioactive wastes generated during the civil/military programmes, and also generated through scientific, engineering and medical usage. One concept for lowand intermediate-level radioactive waste involves constructing an underground facility in a host rock at a depth of several hundred metres, then backfilling with a cementitious material. Such a facility is designed to achieve two main safety Responsible editor: Marcus Schulz * XiaoHui Chen [email protected] 1
School of Civil Engineering, University of Leeds, Leeds LS2 9JT, UK
2
British Geological Survey, Nottingham, UK
3
Groundwater Protection and Restoration Group, Dept of Civil and Structural Engineering, The University of Sheffield, Sheffield, UK
objectives: (1) to isolate the radioactive waste from the biosphere and (2) to provide multiple barriers (including a high pH environment) to minimise radionuclide mobility over long timescales. The containment system involves multiple barriers in which
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