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Description of titration curves of mixed materials with variable and permanent surface charge by amathematical model. 1. Theory. 2. Application to mixtures of lepidocrocite and montmorillonite
Author(s) -
MADRID L.,
DIAZBARRIENTOS E.
Publication year - 1988
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1988.tb01208.x
Subject(s) - montmorillonite , surface charge , adsorption , oxide , titration , lepidocrocite , ion , mixed oxide , titration curve , chemistry , charge (physics) , charge density , inorganic chemistry , materials science , thermodynamics , mineralogy , physics , organic chemistry , quantum mechanics , goethite
SUMMARY A model to describe titration curves of mixed materials with variable and permanent charge surfaces is based upon published proposals, but includes the adsorption of potential‐determining ions on both kinds of surface, and the influence of the permanent charge. It also considers the interface formed by a system of capacitors in parallel and series. Some typical outputs of the model are given. The model was tested for mixtures of an iron oxyhydroxide and montmorillonite. The best fit of the model to titration data of the pure materials gave a set of values for the parameters that were used to predict the behaviour of the mixtures. It was concluded that most of the parameters estimated in this way reproduced the behaviour of the mixtures. However, the maximum density of sites on the oxide decreased when the latter was mixed with montmorillonite, and the binding constants of the clay mineral for the p‐d ions reached values, intermediate, between those of both minerals when the oxide was present in low proportion. These results suggested that some kind of association occurs between the solid surfaces, which would block part of the oxide surface. However, there is insufficient evidence to confirm this hypothesis.