Deposition behavior of supersaturated silicic acid in the condition of relatively high Ca or Na concentration

Taiji Chida, Yuichi Niibori, Hayata Shinmura, Hitoshi Mimura

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Around the radioactive waste repository, the pH of the groundwater greatly changes from 8 to 13 and the groundwater contains a relatively large quantity of calcium (Ca) and sodium (Na) ions due to cementitious materials used for the construction of the geological disposal system. Under such conditions, the deposition behavior of silicic acid is one of the key factors for the migration assessment of radionuclides. The deposition and precipitation of silicic acid with the change of pH and coexisting ions may contribute to the clogging in flow paths, which is expected as the retardation effect of radionuclides. Thus, this study focused on the deposition behavior of silicic acid under the condition of relatively high Ca or Na concentration. In the experiments, Na2SiO3 solution (250 ml, 14 mM, pH>10, 298 K) was prepared in a polyethylene vessel containing amorphous silica powder (0.5 g) as the solid phase. Then, a buffer solution (to adjust to 8 in pH), HNO3, and Ca(NO3)2 as Ca ions or NaCI as Na ions were sequentially added. Such a silicic acid solution becomes supersaturated, gradually forming colloidal silicic-acid and/or the deposit on the solid surface. In this study, the both concentrations of soluble and colloidal silicic-acid were monitored over a 40-day period. As a result, the deposition rate of silicic acid decreased with up to 5 mM in Ca ions. Besides, Na ions with up to 0.1 M slightly increased the deposition rate. Under the conditions of [Na+]>0.1 M or [Ca2+]>5 mM, the supersaturated silicic acid immediately deposited. These suggest that Na or Ca ions strongly affect the deposition behavior of supersaturated silicic-acid, depending on the surface alteration of solid phase, the change of zeta potential and the decrease of water-activity due to the addition of electrolytes (coexisting ions).

Original languageEnglish
Title of host publicationScientific Basis for Nuclear Waste Management XXXVII
EditorsLara Duro, Ignasi Casas, Joan de Pablo, Javier Gimenez
PublisherMaterials Research Society
Pages55-60
Number of pages6
ISBN (Electronic)9781605116426
DOIs
Publication statusPublished - 2014
Event37th International Symposium on the Scientific Basis for Nuclear Waste Management - Barcelona, Spain
Duration: 2013 Sep 292013 Oct 3

Publication series

NameMaterials Research Society Symposium Proceedings
Volume1665
ISSN (Print)0272-9172

Other

Other37th International Symposium on the Scientific Basis for Nuclear Waste Management
CountrySpain
CityBarcelona
Period13/9/2913/10/3

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Fingerprint Dive into the research topics of 'Deposition behavior of supersaturated silicic acid in the condition of relatively high Ca or Na concentration'. Together they form a unique fingerprint.

Cite this