Experimental and modeling studies on sorption and diffusion of radium in bentonite

Y. Tachi, T. Shibutani, H. Sato, M. Yui

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

The sorption and desorption behavior of radium on bentonite and purified smectite was investigated as a function of pH, ionic strength and liquid to solid ratio by batch experiments. The distribution coefficients (Kd) were in the range of 102 to 104 ml g-1 and depended on ionic strength and pH. Most of sorbed Ra was desorbed by 1 M KCl. The results for purified smectite indicated that Ra sorption is dominated by ion exchange at layer sites of smectite, and surface complexation at edge sites may increase Ra sorption at higher pH region. Reaction parameters between Ra and smectite were determined based on an interaction model between smectite and groundwater. The reaction parameters were then used to explain the results of bentonite by considering dissolution and precipitation of minerals and soluble impurities. The dependencies of experimental Kd values on pH, ionic strength and liquid to solid ratio were qualitatively explained by the model. The modeling result for bentonite indicated that sorption of Ra on bentonite is dominated by ion exchange with smectite. The observed pH dependency was caused by changes of Ca concentration arising from dissolution and precipitation of calcite. Diffusion behavior of Ra in bentonite was also investigated as a function of dry density and ionic strength. The apparent diffusion coefficients (Da) obtained in compacted bentonite were in the range of 1.1×10-11 to 2.2×10-12 m2 s-1 and decreased with increasing in dry density and ionic strength. The Kd values obtained by measured effective diffusion coefficient (De) and modeled De were consistent with those by the sorption model in a deviation within one order of magnitude.

Original languageEnglish
Pages (from-to)171-186
Number of pages16
JournalJournal of Contaminant Hydrology
Volume47
Issue number2-4
DOIs
Publication statusPublished - Feb 21 2001
Externally publishedYes

Keywords

  • Bentonite
  • Diffusion
  • Models
  • Radium
  • Smectite
  • Sorption

ASJC Scopus subject areas

  • Environmental Chemistry
  • Water Science and Technology

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