In this study, the reaction between humus acids (humic acid and β-humus fulvic acid fraction) and bentonite and illite was studied at a variety of pH values. The degree of reaction was determined from the specific surface area and molar energy of adsorption. Characteristic parameters of adsorption isotherms for the formation of a mono-layer of the adsorbent, such as the constant C from the BET equation, mono-layer capacity (Nm), and standard error square (R2), were also included in the study. After the addition of humus acids, the specific surface area of illite and bentonite decreased at all pH values, reaching a minimum at pH 4. This indicates different degrees of reaction of humus acids with the clays and, probably, partial hydrophobization of the materials. The degree of reaction of humus acids with the minerals depended on the pH and, for certain combinations, it was highest at pH 4. This value is relatively close to that at which the humus acid fractions in question precipitate from solution.

The mechanism of the formation of organomineral complexes in soils is very complex and still little known. Examination of the complexes in unaltered form, as isolated from the soil, is very difficult due to the dispersing effect of all extraction agents which break the complexes up, destroying their natural properties. It is much easier to perform most of the tests on preparations of organomineral complexes obtained under laboratory conditions. This paper is concerned with model research on the formation of synthetic complexes of humic acids with minerals: Na-montmorillonite, mica, kaolinite at various pH values (3-7) and in the presence of aluminum ions. The aim of the research was to develop an optimum reaction of suspension for the synthesis of organomineral complexes, to study the role of aluminum ions, and to attempt to determine the degree of their complexity on the basis of the electrolytic conductivity (EC). An important influence of the suspension pH value on the value of EC was observed. The greatest correlation was found in the organomineral preparations with kaolinite and with aluminum (r = 0.93 *** ). Generally, it can be stated that the degree of reaction of humic acids with minerals depended most of all on the type of mineral, on the pH value, and on the presence of aluminum.

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