THE EFFECT OF pH ON THE CATALYTIC SYNTHESIS OF HUMIC SUBSTANCES BY ILLITE

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Abstract
This work elucidates the effect of pH on the catalytic synthesis of humic substances by illite. Several portions of the sieved, peroxidized calcium illite (Morris, Illinois) were adjusted to pHs 4.0, 5.7, 6.9, and 8.5, respectively. A separate portion, of pH 8.5, was mixed with calcite powder (97:3). Each of the treated portions of illite was allowed to react with an adequate amount of a solution of phenolic compounds and urea on glass plates. Then all the plates were placed in a closed, sterilized glass cabinet. The rate of chemical change of the phenolic compounds increased with the pH of the illite, due to enhanced formation of free radicals and more intensified autooxidation. The neutral and alkaline illite favored the formation of humic and fulvic acids, particularly humic acids, whereas the alkaline illite containing CaCO3 gave the lowest yield. At pH 4.0 and 8.5 + CaCO3, the formation of fulvic acids predominated that of humic acids. Elemental composition, functional groups, and infrared absorption spectra of the organic polymers were also presented.

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