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[MIS31-03] Dissolution behavior of compacted smectite clay
Keywords:smectite, dissolution, compaction, AFM, VSI
Among many approaches for dissolution of smectite, AFM (atomic force microscopy) can directly measure dissolving nano-dispersed particles, but high-densiry random aggregates. In order to improve AFM, we developed in-situ VSI (vertical scanning interferometry) and auto-compaction cell. By this means, we conducted in-situ measurements of compacted smectite (Na-montmorillonite) immersed in 0.3M NaOH at 70 ℃. This method can realize real-time measurements of decreasing material volume of smectite under various densities. After measurements, recovered particles were measured by AFM to refine the step-edge surface area.
As the result of AFM-assisted VSI measurements, dissolution rates of compacted smectite vary from 2.9E-11 mol/m2/s (density 0.001, Sato et al., 2005) to 2.6E-13 mol/m2/s (density 1.64, compacted, Satoh et al., 2013). Most possible reason explaining this behavior is self-masking effect which nano-particulates mask step-edges each other (reduced dissolution). However, compaction on random aggregates induces edge-dislocation that newly produces dissolution centers. This was well-recognized especially in the early compaction stage (promoted dissolution).
Thus, high density clay as nano-stacked or aggregated particles always accompanies with dissolution, but it is not continued by self-masking effect as a kind of negative-feedback mechanism. To investigate and understand such a complex behavior of clay, computer simulation by Monte-Carlo calculation is needed.