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Proton Adsorption on an Aluminum Oxide in the Presence of Bicarbonate
Author(s) -
Schulthess C. P.,
Wijnja H.,
Swanson K.
Publication year - 1998
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/sssaj1998.03615995006200010018x
Subject(s) - adsorption , bicarbonate , chemistry , aqueous solution , inorganic chemistry , ionic strength , titration , proton , oxide , stoichiometry , organic chemistry , physics , quantum mechanics
The aqueous species of CO 2 [CO 2 (aq), H 2 CO 3 , HCO − 3 and CO 2− 3 ] are often ignored in adsorption studies despite the fact that CO 2 in soil air can be hundreds of times greater than in the atmosphere. Adsorption studies that do not account for CO 2 species may be under‐estimating proton adsorption in natural environments. The objective of this study was to discern the effect CO 2 species have on proton adsorption to an Al oxide. The backtitration method was used to produce proton adsorption curves as a function of pH for samples of Al oxide with and without aqueous bicarbonate. Sodium chloride was used to vary the ionic strength. Proton adsorption increased in the presence of the bicarbonate below pH 9.7. The greater the concentration of bicarbonate, the greater the proton adsorption. The point of zero salt effect (PZSE = 8.30) was unaffected by the bicarbonate. The data presented show an approximate 1:1 stoichiometry for proton removal with inorganic‐C (HCO 3 plus all other species) adsorption data. That is, this research directly quantified that every inorganic C adsorbed (expressed as HCO 3 adsorbed) is accompanied by the removal of one proton (more precisely, 1.10 ± 0.28) from the aqueous phase by the Al oxide. Thus, the net removed from the liquid phase is equivalent to one H 2 CO 3 in mass‐balanced terms. The use of traditional titration methods, rather than the backtitration method, resulted in a questionable pH‐dependent pattern that reflects the impact of Al dissolution on these measurements.