A long-term experimental study of the reactivity of basement rock with highly alkaline cement waters: Reactions over the first 15 months

Abstract

A series of long-term laboratory experiments was started in 1995 to investigate longer-term dissolution/precipitation reactions that may occur in the alkaline disturbed zone surrounding a cementitious repository for radioactive waste. They consist of samples of UK basement rock reacting with either Na-K-Ca-OH water ('young' cement porewater) or Ca-OH water ('evolved' cement porewater) at 70°C. This paper summarises results of reactions occurring over the first 15 months. Experiments of both fluid types showed many similar features, though primary mineral dissolution and secondary mineral precipitation were more extensive in the experiments involving Na-K-Ca (younger) cement porefluids compared to more evolved (Ca-rich) cement porefluids. Dissolution of dolomite, and to a lesser extent silicates (most probably K-feldspar, but possibly also mica) occurred relatively rapidly at 70 °C. Dolomite dissolution may have been a key factor in reducing pH values, and may be a key mineral in controlling the extent of alkaline disturbed zones. Dissolution was followed by precipitation of brucite close to dolomite grains, at least two generations of CSH phases

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“…This highlights the duality of such fluids, enhancing reservoirs through increased through reactor after 36, 37, 42, 27, 38, and 48 minutes, respectively (absence of data points reflects concentrations below the limits of detection). 16 Geofluids permeability but potentially also leading to issues with precipitation in surface infrastructure. Total concentrations of "at risk elements" are approximately 50 ppb in the case of reaction with deionised water, 830 ppb in the case of reaction with acetic acid, and 8500 ppb when mineral acid was used.…”

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“…Acetone with 10% corundum ( 2 3 ) was then applied as an ionized agent. A diffractometer device (PANalytical X'Pert Pro) with PANalytical X'Pert Highscore Plus software was then used to carry out the final mineralogical analysis (Moyce et al 2014;Rochelle et al 2016).…”