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Molybdate Adsorption on Kaolinite, Montmorillonite, and Illite: Constant Capacitance Modeling
Author(s) -
Motta M. Manuela,
Miranda C. F.
Publication year - 1989
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/sssaj1989.03615995005300020011x
Subject(s) - molybdate , adsorption , illite , montmorillonite , chemistry , inorganic chemistry , sodium molybdate , kaolinite , protonation , potentiometric titration , deprotonation , analytical chemistry (journal) , clay minerals , ion , mineralogy , organic chemistry
The adsorption of molybdate by kaolinite, montmorillonite, and illite was investigated at 25 and 40 °C, in a 0.01 M NaCl background medium, for equilibrium Mo concentrations ranging from 0.1 to 100 mg L −1 . The constant capacitance model was shown to be able to describe molybdate adsorption on the three minerals and for the two temperatures used. The model comprises five adjustable parameters for each mineral: two surface protonation‐deprotonation constants, two molybdate surface complexation constants, and a capacitance density parameter. However, for montmorillonite and illite the number of adjustable parameters was reduced to four since adsorption data could be fitted using only one molybdate complexation constant. The protonation‐deprotonation constants were obtained from potentiometric titration data and the molybdate complexation constants from adsorption data. The capacitance density was chosen on the basis of a literature compilation of values used in previous applications of the constant capacitance model to the adsorption of several ions on oxide minerals. Tentative estimations of thermodynamic functions of molybdate adsorption are presented.