Samples of materials, collected at different stages of vermicompostaging, were submitted to extraction procedures of humic acids. Titration, termogravimetry (DTG), X-ray diffraction, spectrophotometry in the uv/visible and infrared techniques, were used in the study of these materials. The data from the potentiometry titration analysis were submitted to adjustment by non-linear regression, determining thus five values of pKa's characteristic of five classes of titrable groups. In the DTG curves two stages can be observed, being the first one characteristic of the separation of aliphatic and/or alycyclic structures and the second of decomposition of aromatic structures. The X-ray diffraction technique exhibed marked differences in the results, mainly in the first three peaks, were a structural reorganization and a polymerization along the vermicompostaging process. The infrared spectra practically no differentiation between the samples. The values for the ratio E4/E6 found are in accordance with the characteristic values for humic acids, but do not supply information that can contribute to the elucidation of the structure and formation of these acids.
titration; termogravimetry; diffraction; spectrophotometry; non-linear regression
