Bentonite, biotite, illite, kaolin, vermiculite and zeolite were acidified or alkalized with hydrochloric acid or sodium hydroxide at concentrations of 0.1, 1.0 and 5.0 mole dm−3 at room temperature for two weeks. In acid treatments, dissolution of Al prevailed over Si and the opposite was observed in alkali treatments. The XRD patterns showed severe alteration of the crystal structure after acid treatments, whereas sharpening of the XRD peaks after alkali treatments was observed. Illite and kaolin were most resistant to acid attack. with a few exceptions, the surface areas of the minerals computed from both water and nitrogen adsorption isotherms increased with acid and alkali treatments. with increasing reagent concentration, the nitrogen surface area increased faster than the water surface area. well-defined trends were not noted in either changes of average water or nitrogen adsorption energies or in relative amounts of adsorption sites, indicating that the effects of acid and alkali attack are controlled by the individual character of the minerals.

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Fractal parameters of soils become increasingly important in understanding and quantifying transport and adsorption phenomena in soils. It is not known yet how soil degradation affects fractal characteristics of soil pores. We estimated pore surface area fractal parameters from Hg porosimetry data on samples of a Udic Argiboroll, a Typic Haploboroll, and a Ustolic Orthid before and after simulated soil degradation. Three or four distinct intervals with different fractal dimensions were found in the range of pore radii from 4 nm to 5 µm. This was attributed to differences in composition of soil particles of different sizes. The simulated degradation caused an increase in fractal dimensions in one or more fractal intervals, thus manifesting the increased roughness and irregularity of the pore surfaces. The interval of the smallest radii had the highest average fractal dimension, close to 3; some estimated values were >3, probably due to the compressibility of bulk material and air entrapment. Values of the fractal dimension in this interval increased after cyclic wetting‐drying but were not affected by organic matter oxidation. Smaller fractal dimensions were found in the next interval of radii. Here average fractal dimension increased markedly after organic matter oxidation and grew slightly after cyclic wetting‐drying, reflecting the loss of bonds between particles. The range of largest radii included two fractal intervals after cyclic wetting‐drying and one fractal interval for all other samples. Neither organic matter oxidation nor cyclic wetting‐drying significantly affected the boundaries between the fractal intervals.

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