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Journal Articles

Na-montmorillonite dissolution rate determined by varying the Gibbs free energy of reaction in a dispersed system and its application to a coagulated system in 0.3M NaOH solution at 70$$^{circ}$$C

Oda, Chie; Walker, C.; Chino, Daisuke*; Ichige, Satoru; Honda, Akira; Sato, Tsutomu*; Yoneda, Tetsuro*

Applied Clay Science, 93-94, p.62 - 71, 2014/05

 Times Cited Count:7 Percentile:24.7(Chemistry, Physical)

Na-montmorillonite dissolution in a 0.3M NaOH solution has been investigated at pH12 and 70$$^{circ}$$C. The flow-through dissolution experiments were conducted in a dispersed system with varying concentrations of Si and Al to derive a Na-montmorillonite dissolution rate, as a non-linear function of the Gibbs free energy of reaction, dGr. This rate equation was used to simulate the batch-type Na-montmorillonite reaction experiments conducted in a coagulated system. The model simulation of the batch-type experiment adopting the empirical rate equations of Na-montmorillonite dissolution and secondary mineral analcime precipitation were able to reproduce the measured changes in the amount of dissolved Na-montmorillonite and concentrations of Si and Al in solution. The results showed that the empirical rate equation of Na-montmorillonite dissolution determined in the dispersed system was applicable to the coagulated system over a higher dGr range and that the concentrations of Si and Al in the batch experiment were controlled by the precipitation of analcime.

Oral presentation

Effect of compaction on dissolution rate of smectite under hyperalkaline condition

Sato, Tsutomu*; Takayama, Hideki*; Chino, Daisuke*; Nakabayashi, Ryo*; Oda, Chie; Yoneda, Tetsuro*

no journal, , 

The dissolution experiments for the compacted smectite with different dry densities were performed to understand the effect of compaction on dissolution rate of smectite. From the experimental results, it is clearly showed that the more compacted smectite has the less dissolution rate. According to the results of caesium adsorption test, variable charge density was decreased with increasing of dry density. This decreasing indicates that active edge surface area was decreased. According to the previous studies such as Yokoyama, et al. (2005), smectite particles are predominantly dissolved from the edge of the particle. However, the difference in dissolution rate between lower and higher compacted smectites can not be fully explained by considering of the decreasing in the reactive surface area. According to the results of reactive transport modeling, delta-Gr effect obtained by Sato, et al. (2007) should be took into account for filling the gap in dissolution rate.

Oral presentation

Effect of aqueous aluminium and silica concentrations on smectite dissolution kinetics at hyperalkaline conditions

Chino, Daisuke*; Sato, Tsutomu*; Otani, Yusuke*; Nakabayashi, Ryo*; Oda, Chie; Yoneda, Tetsuro*

no journal, , 

Steady-state dissolution rates of smectite were determined as function of aqueous Al and Si concentrations using a stirred-flow-through reactor at 70 degrees in 0.3M-NaOH solution to obtain the reliable dissolution rates of smectite at hyperalkaline condition and to formulate the effect of deviation from equilibrium on smectite dissolution rate. The dissolution rates were calculated based from the dissolved Si or Al concentrations of the output solutions or from ex situ AFM observations. Results of the flow-through dissolution experiments and ex situ AFM observations suggest that the dissolved Si and Al concentrations in the solutions appear to be retarding the dissolution rate of smectite. If we assume the decrease is attributed by the effect of deviation from equilibrium on dissolution rate, the dissolution rate of smectite can be expressed in a non-linear function of the Gibbs free energy. This non-liner relationship is nearly same as that obtained by Cama, et al. (2000).

Oral presentation

Observation of the interaction between bentonite and hyperalkaline fluid by X-ray computed tomography and geochamical modeling of the interaction

Nakabayashi, Ryo*; Elakneswaran, Y.*; Chino, Daisuke*; Sato, Tsutomu*; Yoneda, Tetsuro*; Oda, Chie; Kaneko, Katsuhiko*

no journal, , 

Flow-through dissolution experiment was carried out using compacted bentonite with hyperalkaline solutions. In-situ observation of bentonite during the experiment was concocted by using X-CT analysis. Time-dependence of secondary minerals formation inside the compacted bentonite during the experiment was analysed and quantified based on the observation. Geochemical modeling using a 1D reactive transport code was able to reproduct time-dependence of space-distribution of minerals in the bentonite and Si, Al concentrations in the output solutions.

Oral presentation

An Evaluation study on the interaction of bentonite with highly alkaline porewater by using X-ray CT method; Dissolution rate of montmorillonite in compacted bentonite

Nakabayashi, Ryo*; Elakneswaran, Y.*; Chino, Daisuke*; Sato, Tsutomu*; Yoneda, Tetsuro*; Oda, Chie; Kaneko, Katsuhiko*

no journal, , 

Flow-through dissolution experiment of compacted purified bentonite with highly alkaline solution was carried out in order to quantitatively understand the bentonite-cement interaction. A combined analysis with XRD and in situ-observation by using X-ray CT method were applied. A geochemical model simulation of the experiment considering kinetics of montmorillonite (the main component of bentonite) dissolution was carried out. From output of the simulation, it was found that (1) dissolution rate of montmorillonite in compacted system were slower than that in suspension system, (2) slowering rate resulted in invisible change in dry density of montmorillonite in the simulation, which was consistent with the experimental result, and (3) the reason for slowring rate could likely to be attributed to the constraint of reactive surface area of montmorillonite and the effect of saturation degree of powewater.

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