EXTRACTION OF HUMIC ACID BY ALKALI AND CHELATING RESIN

Abstract

Humic acid was extracted from the A1 horizon of a Dark Chestnut soil (pH = 6.9) with 0.5 N NaOH after decalcification and with Na-Dowex A-1 resin without decalcification. The two humic acids were characterized by chemical and spectroscopic methods and by permanganate oxidation after methylation. Whereas ultimate, functional group, and infrared analyses showed the two humic acids to be very similar, permanganate oxidation indicated a number of differences between the two preparations. The yield of oxidation products from the resin-extracted humic acid was twice as high as that from the alkali-extracted material. In addition, the resin-extracted humic acid produced appreciably larger amounts of high-molecular weight phenolic and benzenecarboxylic acids than did the alkali-extracted humic acid. These findings, in conjunction with E4/E6 ratios, indicated that the chelating resin-extracted humic acid was more condensed or less degraded than that removed by alkali. Permanganate oxidation of methylated humic substances appears to be a more sensitive technique for uncovering structural changes in such materials than are functional group analysis and spectroscopic methods.