Measurement of pH of the compacted bentonite under the reducing condition

Syeda Afsarun Nessa, Kazuya Idemitsu, Yosuke Yamasaki, Yaohiro Inagaki, Tatsumi Arima

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


Compacted bentonite and carbon steel have been considered as the good buffer and over-pack materials in the repositories of high-level radioactive waste disposal. Sodium bentonite, Kunipia-F contains approximately 95wt% of montmorillonite. It has a high cation-exchange capacity and a high specific surface area, and its properties determine the behavior of bentonite. The pH of the pore water in compacted bentonite is an extremely important parameter because of its influence on radionuclide solubility, migration and Sorption, and as well as repository safety studies. In this study, the pH of pore water in compacted bentonite was measured with a paper pH indicator wrapped with semi-permeable membrane of fresh egg under reducing conditions. On 30 days, the paper of pH indicator in the experimental apparatus indicated that the pH of pore water in compacted bentonite had been around 9-10 before electromigration. During electromigration the pH of bentonite was decreased and it reached 6-7 on 7 days. The concentration of iron and sodium showed nearly complementary distribution in the bentonite specimen after electromigartion. It is expected that iron ion could migrate as ferrous ion through the interlayer of montmorillonite replacing exchangeable sodium ions in the interlayer. Egg shell membrane does not affect the color of pH test paper during the experiment.

Original languageEnglish
Pages (from-to)25-31
Number of pages7
JournalMemoirs of the Faculty of Engineering, Kyushu University
Issue number1
Publication statusPublished - Mar 22 2007

All Science Journal Classification (ASJC) codes

  • General Energy
  • Atmospheric Science
  • General Earth and Planetary Sciences
  • Management of Technology and Innovation


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