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Charge Characteristics of Soils with Variable and Permanent Charge Minerals: I. Theory
Author(s) -
Uehara G.,
Gillman G. P.
Publication year - 1980
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/sssaj1980.03615995004400020008x
Subject(s) - point of zero charge , surface charge , charge (physics) , chemistry , electrolyte , ion , potentiometric titration , charge density , analytical chemistry (journal) , adsorption , effective nuclear charge , titration , inorganic chemistry , physics , chromatography , organic chemistry , electrode , quantum mechanics
The net surface charge density of soil colloids consisting of mixtures of variable and permanent charge minerals is treated as the sum of the two types of surface charge. The permanent charge is assumed to be constant in magnitude, and negative, zero, or positive in sign, and the variable charge is permitted to vary in magnitude and sign with pH and electrolyte concentration. Based on these assumptions, relations are developed which show that there are two zero points of charge. The zero point of charge of the mixture as a whole is designated ZPNC and the zero point of charge of the variable charge component is designated pH 0 . The ZPNC can be determined by ion adsorption measurements, and pH 0 by potentiometric titration. In mixtures, ZPNC is lower than pH 0 when permanent charge is negative and higher than pH 0 when the permanent charge is positive. The magnitude of the permanent charge can be determined by measuring cation and anion retention at the pH corresponding to pH 0 . Specific surface of mixed systems can be estimated by measuring negative ion adsorption at pH values sufficiently different from pH 0 .