• journal_title：Clay Minerals
• Contributor：H. Satoh ; T. Ishii ; H. Owada
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2013-05-01
• Format：text/html
• Language：en
• Identifier：10.1180/claymin.2013.048.2.10
• journal_abbrev：Clay Minerals
• issn：0009-8558
• volume：48
• issue：2
• firstpage：285
• section：Alteration processes in bentonite buffer systems

In situ measurements were carried out to quantify montmorillonite dissolution rates at a compaction pressure ranging from 0.04 to 10.00 MPa and temperature of 70°C in 0.3 m NaOH solution (pH 12.1 at 70°C) using vertical scanning interferometry (VSI) and an auto-compaction cell. Ex situ measurements of the reacted samples using atomic force microscopy (AFM) were performed to quantify the ratio of edge surface area (ESA) to total surface area (TSA) (X_ESA = ESA/TSA). Accordingly, the actual ESA for the montmorillonite examined by in situ VSI could be estimated. The X_ESA value increases as a function of run duration or compaction pressure. At atmospheric pressure, X_ESA is approximately 0.0054 and converges to ∼0.0107 at 10 MPa, An expression that relates reactive surface area and montmorillonite compaction (X_ESA/X_{ESA initial} = kX_ESA, k: variable factor) is kX_ESA = 1.0 + 0.64628P^0.1527 where P is in MPa. Using the calculated X_ESA, dissolution rates from the in situ VSI measurements are obtained. The early dissolution (<1500 min) at less compaction pressure tends to show faster rates (>1.0 × 10^–11 mol/m²/s) than that at higher compaction pressure. The rates after >1500 min are slower, with values of less than 3 × 10^–12 mol/m²/s, but there is no significant dependency on the density in the range from 1.0 to 1.7 Mg/m³. These observed rates for compacted montmorillonite are two-orders of magnitude slower (2.63 × 10^–13 mol/m²/s) than dissolution rates in the suspended state.