Stability of Cl, NO3, ClO4, and S04 surface complexes at synthetic goethite/aqueous electrolyte interfaces

Somsak Maneepong, Shin-Ichiro Wada

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We carried out potentiometric titrations of a synthetic goethite in solutions of NaCl, NaNO3, NaC1O4, and Na2SO4 to determine the intrinsic acidity constant Kintaj and intrinsic complexation constants of Cl, NO3, ClO4, and S04 surface complexes formed at the goethite/aqueous electrolyte interfaces *Kintaj. The determined Kintaj values for the four electrolytes were in a narrow range of 5.9-6.2. The values of Kintaj were found to be 6.7, 6.5, and 6.2 for Cl, NO3, ClO4, and S04, respectively, and Kintaj took the value of 16.0 under the assumption that one SO42− occupies two charged sites. The values of point of zero salt effect (PZSE), which is defined as the pH value at which titration-curves in an electrolyte intersect, were 8.5, 8.6, 8.2, and 8.9 for NaCl, NaNO3, NaC1O4, and Na2SO4, respectively. There was a highly positive correlation between the PZSE and Kintaj. Selectivity coefficients for stoichiometric Cl-NO3 and NO3-SO4 exchange reactions on goethite were calculated from the Kintaj values and exchange isotherms were drawn.

Original languageEnglish
Pages (from-to)141-150
Number of pages10
JournalSoil Science and Plant Nutrition
Issue number1
Publication statusPublished - Jan 1 1991

All Science Journal Classification (ASJC) codes

  • Soil Science
  • Plant Science


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