Abstract
The electrical charges in soil particles are divided into structural or permanent charges and variable charges. Permanent charges develop on the soil particle surface by isomorphic substitution. Variable charges arise from dissociation and association of protons (H+), protonation or deprotonation, and specific adsorption of cations and anions. The aim of this study was to quantify the permanent charges and variable charges of Reference Soils of the State of Pernambuco, Brazil. To do so, 24 subsurface profiles from different regions (nine in the Zona da Mata, eight in the Agreste, and seven in the Sertão) were sampled, representing approximately 80 % of the total area of the state. Measurements were performed using cesium chloride solution. Determination was made of the permanent charges and the charges in regard to the hydroxyl functional groups through selective ion exchange of Cs+ by Li+ and Cs+ by NH4+, respectively. All the soils analyzed exhibited variable cation exchange capacity, with proportions from 0.16 to 0.60 and an average of 0.40 when related to total cation exchange capacity.
Highlights
The study of electric charges in clays is important for an understanding of various physicochemical phenomena in the soil because most electrochemical reactions take place at the surface of these clay particles
Permanent charges develop on the soil particle surface through isomorphic substitution
Mineralogical analysis was performed through X-ray diffraction of the clay fraction, which was separated from the samples after particle-size analyses and mounted on an oriented glass slide through the smear technique
Summary
The study of electric charges in clays is important for an understanding of various physicochemical phenomena in the soil because most electrochemical reactions take place at the surface of these clay particles. This analysis is important for interpreting the results of soil dispersion in response to the use of different sodic solutions in soil particlesize analysis. Permanent charges originate from isomorphic ionic substitution in the mineral structure and are manifested at any soil pH (Sposito, 2008). This charge is inherent to the mineral and can be called a structural charge. Isomorphic ionic substitutions, referred to as isomorphic substitutions, occur in primary minerals, in their magmatic differentiation, and in secondary minerals in their formation in the soil or through inheritance from primary minerals
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