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Monovalent Ion Adsorption by an Oxisol
Author(s) -
Charlet Laurent,
Sposito Garrison
Publication year - 1987
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1987.03615995005100050011x
Subject(s) - oxisol , ionic strength , electrolyte , chemistry , surface charge , adsorption , titration , charge density , analytical chemistry (journal) , point of zero charge , inorganic chemistry , soil water , aqueous solution , chromatography , physics , electrode , soil science , environmental science , quantum mechanics
An experimental method was developed to measure simultaneously the net proton surface charge density (σ H ) and surface excesses of metal ( n M ) and ligand ( n L ) on an Oxisol suspended in a ML electrolyte solution. The soil sample was first saturated with a LiClO 4 solution whose pH and ionic strength were equal to the maximum values to be used in the adsorption experiments. The ionic strength then was decreased, LiClO 4 was exchanged for ML (ML = NaCl or KNO 3 ), and a soil paste was prepared to allow reproducible sampling of small quantities of the whole soil. A discontinuous titration followed in which the soil paste was equilibrated with a series of ML electrolyte solutions of specific pH and ionic strength. Values of n M and n L were measured at 25°C, and it was shown that the point of zero net charge (PZNC) ≈ 4.2, independent of the electrolyte and its ionic strength in the range 4 to 500 mol m −3 . Given a negligible permanent surface charge, typical of Oxisols, PZNC = PZNPC (point of zero net proton charge). The net proton surface charge density then could be calculated from titration data renormalized to the PZNC. The net proton surface charge of the Ha‐plustox used in this study vanished at pH 4.2 and showed very little dependence on ionic strength, indicating the dominant role of kaolinitic and organic matter constituents in determining its surface properties. Surface complexation reactions between the soil and a 1:1 electrolyte solution were characterized quantitatively by intrinsic equilibrium constants calculated according to the triple layer model. The average values found were similar to those that have been obtained previously for specimen hydrous oxides suspended in 1:1 electrolyte solutions.