Batch reactor experiments were performed at 150°C, 175°C, and 200°C to determine the effect of high pH NaOH solutions on the mineralogy of the Opalinus shale. In these experiments, the change in solution quench pH at 25°C, solution composition, and mineralogy were monitored as a function of time for up to ≈40 days. Runs were performed in 50 ml titanium hydrothermal reactor vessels. Each reactor was charged with 0.5–5.0 g of the 80–200 mesh size fraction of Opalinus shale, and 25 ml of solution (0.1 and 0.01 M NaOH). The general sequence of reaction products observed under these high pH conditions include first the formation of analcime, followed by vermiculite, and finally Na-rectorite formation.

Batch reactor experiments were performed at 150°C, 175°C, and 200°C to determine the effect of high pH KOH solutions on the mineralogy of the Opalinus shale. In these experiments, the change in solution quench pH at 25°C, solution composition, and mineralogy were monitored as a function of time for up to ≈ 50 days. Runs were performed in 50 ml titanium hydrothermal reactor vessels. Each reactor was charged with 0.5–5.0 grams of the 80–200 mesh size fraction of Opalinus shale, and 25 ml of solution (0.08 and 0.008 m KOH). Under these high pH conditions, the general sequence of reaction products observed is the formation of phillipsite, followed by K-feldspar ± K-rectorite. Phillipsite is a metastable intermediate that eventually transforms to K-feldspar. This sequence of mineral reaction products is very different from that found in the NaOH system.

The impact of alkaline solutions (pH = 13.2) on the clay mineralogy of the Callovo-Oxfordian formation hosting the French underground laboratory for nuclear waste disposal investigation (Meuse-Haute Marne site) has been studied experimentally. Initially, each of the four samples selected as representative of the mineralogical transition in this Callovo-Oxfordian formation consists of a mixture of three main clay phases: discrete illite, discrete smectite and a randomly interstratified mixed-layered mineral (MLM) containing ∼65% of non-expandable layers. Clay separates were altered in batch reactors at 60°C using high solution:solid ratios. The mineralogy of this clay fraction and solution chemistry were monitored as a function of reaction time. In addition, the interactions between organic matter and clay particles were investigated using scanning transmission X-ray microscopy (STXM).

The clay mineralogy is little affected even though the pH is still high after 1 y reaction time. The only significant mineralogical evolution is the partial dissolution of the discrete smectite component leading to the formation of a new randomly interstratified illite-expandable MLM. Additional mineralogical transformations lead, for one sample, to the dissolution of micro-crystalline quartz and, for another sample, to the crystallization of a tobermorite-like phase. The low reactivity of clay minerals may be attributed to the presence of organic matter in the samples. In their initial state, all outer surfaces of clay particles are indeed covered with organic matter. After 1 y reaction time, STXM studies showed the basal surfaces of clay particles to be devoid of organic matter, but their edges, which are the most reactive sites, were still protected.

The reaction of a Wyoming-type bentonite with pH 13.5 solutions was investigated experimentally at 35 and 60°C for periods of 1 to 730 days. Some crystal properties of the starting montmorillonitic clay remain unchanged, i.e. stability of the octahedral sheet, total cation exchange capacity (CEC) and CEC after neutralization of the octahedral charge, full expandability in the Casaturated state, and size distribution. Other properties are changed, e.g. there is an increase in the expandability after octahedral charge neutralization; a slight increase in the average layer charge; a decrease of the total surface area; and a particle morphological change from flakes to hexagonal shape.

The composition and the structure of the smectite layers did not change significantly during the reaction. The increasing number of expandable layers after octahedral charge neutralization is attributed to modifications in the stacking sequence. The number of interlayers surrounded by two charged tetrahedral sheets increases with reaction time.

We revise the data fitting in our original paper [The dissolution rates of simulated UK Magnox - ThORP blend nuclear waste glass as a function of pH, temperature and waste loading, Miner. Mag.79 (2015) 1529–1542]. The intrinsic rate constant data were calculated incorrectly, the corrected data are presented herein. To support the corrected analysis we have also taken the opportunity to report some additional 90°C data. The conclusions of the original paper remain sound.