Rock alteration in alkaline cement waters over 15 years and its relevance to the geological disposal of nuclear waste

Elizabeth B.A. Moyce, Christopher Rochelle, Katherine Morris, Antoni E. Milodowski, Xiaohui Chen, Steve Thornton, Joe S. Small, Samuel Shaw

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Abstract

The interaction of groundwater with cement in a geological disposal facility (GDF) for intermediate level radioactive waste will produce a high pH leachate plume. Such a plume may alter the physical and chemical properties of the GDF host rock. However, the geochemical and mineralogical processes which may occur in such systems over timescales relevant for geological disposal remain unclear. This study has extended the timescale for laboratory experiments and shown that, after 15 years two distinct phases of reaction may occur during alteration of a dolomite-rich rock at high pH. In these experiments the dissolution of primary silicate minerals and the formation of secondary calcium silicate hydrate (C–S–H) phases containing varying amounts of aluminium and potassium (C–(A)–(K)–S–H) during the early stages of reaction (up to 15 months) have been superseded as the systems have evolved. After 15 years significant dedolomitisation (MgCa(CO3)2 + 2OH− → Mg(OH)2 + CaCO3 + CO32−(aq)) has led to the formation of magnesium silicates, such as saponite and talc, containing variable amounts of aluminium and potassium (Mg–(Al)–(K)–silicates), and calcite at the expense of the early-formed C–(A)–(K)–S–H phases. This occured in high pH solutions representative of two different periods of cement leachate evolution with little difference in the alteration processes in either a KOH and NaOH or a Ca(OH)2 dominated solution but a greater extent of alteration in the higher pH KOH/NaOH leachate. The high pH alteration of the rock over 15 years also increased the rock’s sorption capacity for U(VI). The results of this study provide a detailed insight into the longer term reactions occurring during the interaction of cement leachate and dolomite-rich rock in the geosphere. These processes have the potential to impact on radionuclide transport from a geodisposal facility and are therefore important in underpinning any safety case for geological disposal.
Original languageEnglish
Pages (from-to)91-105
Number of pages15
JournalApplied Geochemistry
Volume50
DOIs
Publication statusPublished - Nov 2014
Externally publishedYes

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Radioactive Waste
Radioactive wastes
Waste disposal
radioactive waste
leachate
Cements
cement
Rocks
silicate
Water
rock
dolomite
Aluminum
Magnesium Silicates
potassium
plume
aluminum
Silicates
Potassium
timescale

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Moyce, E. B. A., Rochelle, C., Morris, K., Milodowski, A. E., Chen, X., Thornton, S., ... Shaw, S. (2014). Rock alteration in alkaline cement waters over 15 years and its relevance to the geological disposal of nuclear waste. Applied Geochemistry, 50, 91-105. https://doi.org/10.1016/j.apgeochem.2014.08.003
Moyce, Elizabeth B.A. ; Rochelle, Christopher ; Morris, Katherine ; Milodowski, Antoni E. ; Chen, Xiaohui ; Thornton, Steve ; Small, Joe S. ; Shaw, Samuel. / Rock alteration in alkaline cement waters over 15 years and its relevance to the geological disposal of nuclear waste. In: Applied Geochemistry. 2014 ; Vol. 50. pp. 91-105.
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Moyce, EBA, Rochelle, C, Morris, K, Milodowski, AE, Chen, X, Thornton, S, Small, JS & Shaw, S 2014, 'Rock alteration in alkaline cement waters over 15 years and its relevance to the geological disposal of nuclear waste', Applied Geochemistry, vol. 50, pp. 91-105. https://doi.org/10.1016/j.apgeochem.2014.08.003

Rock alteration in alkaline cement waters over 15 years and its relevance to the geological disposal of nuclear waste. / Moyce, Elizabeth B.A.; Rochelle, Christopher; Morris, Katherine; Milodowski, Antoni E.; Chen, Xiaohui; Thornton, Steve; Small, Joe S.; Shaw, Samuel.

In: Applied Geochemistry, Vol. 50, 11.2014, p. 91-105.

Research output: Contribution to journalArticle

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T1 - Rock alteration in alkaline cement waters over 15 years and its relevance to the geological disposal of nuclear waste

AU - Moyce, Elizabeth B.A.

AU - Rochelle, Christopher

AU - Morris, Katherine

AU - Milodowski, Antoni E.

AU - Chen, Xiaohui

AU - Thornton, Steve

AU - Small, Joe S.

AU - Shaw, Samuel

PY - 2014/11

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AB - The interaction of groundwater with cement in a geological disposal facility (GDF) for intermediate level radioactive waste will produce a high pH leachate plume. Such a plume may alter the physical and chemical properties of the GDF host rock. However, the geochemical and mineralogical processes which may occur in such systems over timescales relevant for geological disposal remain unclear. This study has extended the timescale for laboratory experiments and shown that, after 15 years two distinct phases of reaction may occur during alteration of a dolomite-rich rock at high pH. In these experiments the dissolution of primary silicate minerals and the formation of secondary calcium silicate hydrate (C–S–H) phases containing varying amounts of aluminium and potassium (C–(A)–(K)–S–H) during the early stages of reaction (up to 15 months) have been superseded as the systems have evolved. After 15 years significant dedolomitisation (MgCa(CO3)2 + 2OH− → Mg(OH)2 + CaCO3 + CO32−(aq)) has led to the formation of magnesium silicates, such as saponite and talc, containing variable amounts of aluminium and potassium (Mg–(Al)–(K)–silicates), and calcite at the expense of the early-formed C–(A)–(K)–S–H phases. This occured in high pH solutions representative of two different periods of cement leachate evolution with little difference in the alteration processes in either a KOH and NaOH or a Ca(OH)2 dominated solution but a greater extent of alteration in the higher pH KOH/NaOH leachate. The high pH alteration of the rock over 15 years also increased the rock’s sorption capacity for U(VI). The results of this study provide a detailed insight into the longer term reactions occurring during the interaction of cement leachate and dolomite-rich rock in the geosphere. These processes have the potential to impact on radionuclide transport from a geodisposal facility and are therefore important in underpinning any safety case for geological disposal.

U2 - 10.1016/j.apgeochem.2014.08.003

DO - 10.1016/j.apgeochem.2014.08.003

M3 - Article

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JF - Applied Geochemistry

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