Acidification has become recently an important environmental problem in many countries. Despite huge amount of papers published in this topic, there exist many knowledge gaps, particularly in the area of surface properties of soils and minerals and their alteration after acidic degradation of soils. Alkalization of soils, being a problem of arid zone countries, has been studied mainly from the point of view of soil amelioration and no results of the detailed studies on surface reaction with alkali are available as well. The aim of the studies performed in the present paper was to observe the changes of the surface properties of soils and clay minerals under acid and alkaline conditions in more details. Particular attention was directed upon surface inhomogeneity. Samples of most abundant clay minerals and soiJs of various mineralógica) composition were acidified and alkalized with extreme concentrations of HCL and NaOH, and studied via water vapor adsorption-desorption, mercury intrusion porosimetry and back-titration experiments. Adsorption, porous and variable surface charge properties were studied by estimations of surface areas, average adsorption energies, adsorption energy distribution functions, micro and mesopores radii and volumes, pore size distributions, fractal dimensions, amount of variable charge and apparent surface dissociation constants distributions. The general changes of the selected materials were registered also, using XRD patterns, solubility, CEC, Mossbauer spectra, magnetic susceptibility, clay and organic matter content measurements. Marked changes of the studied surface characteristics were observed in most of the materials investigated. The general tendencies of these changes for all of the samples were difficult to establish due to the great variability of natural materials, however, a few of the surface characteristics (e.g. surface areas, fractal dimension of micropores, amount of variable charge, average value of apparent surface dissociation constant) changed in a given direction with pH of acidification and/or alkalization. These characteristics may possibly be used for monitoring of environmental processes accompanied with changes of soil reaction.
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