Premium
Boron Adsorption Mechanisms on Oxides, Clay Minerals, and Soils Inferred from Ionic Strength Effects
Author(s) -
Goldberg Sabine,
Forster H. S.,
Heick E. L.
Publication year - 1993
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/sssaj1993.03615995005700030013x
Subject(s) - gibbsite , kaolinite , goethite , adsorption , ionic strength , montmorillonite , inorganic chemistry , chemistry , point of zero charge , clay minerals , oxide minerals , halloysite , surface charge , chemical engineering , mineralogy , aqueous solution , organic chemistry , engineering , chemical reaction
Prediction of anion adsorption behavior is enhanced by understanding the adsorption mechanism. This study was conducted to evaluate ionic strength effects on B adsorption and to infer B adsorption mechanisms on various surfaces. Boron adsorption on the Fe oxide goethite, the Al oxide gibbsite, the clay minerals kaolinite and montmorillonite, and two arid‐zone soils was investigated as a function of solution pH (3–11) and ionic strength of the background electrolyte (0.01–1.0 M NaCl). Boron adsorption on the oxides and kaolinite increased from pH 3 to 6, exhibited a peak at pH 6 to 8.5, and decreased from pH 8.5 to 11. For B adsorption on montmorillonite and the soils, the adsorption maximum was located near pH 9. Ionic strength dependence, measured as the increase of the B adsorption maximum in 1.0 M NaCl solutions compared with 0.01 M NaCl solutions increased in the order: goethite (3%) < kaolinite (15%) < gibbsite (−30%) < montmorillonite (109%) = montmorillonitic soil (116%) = kaolinitic soil (129%). Shifts in zero point of charge were observed on goethite, gibbsite, and kaolinite following B adsorption. Ionic strength effect results suggest an inner‐sphere adsorption mechanism for goethite, gibbsite, and kaolinite and an outer‐sphere adsorption mechanism for montmorillonite and the soils. These mechanisms are also indicated by zero point of charge determinations, microelectrophoresis measurements, or both. The constant capacitance model, containing an inner‐sphere adsorption mechanism, was able to describe B adsorption on goethite, gibbsite, kaolinite, and kaolinitic soil. The model was unable to describe B adsorption on montmorillonite and montmorillonitic soil because the computer optimizations diverged.