whole_BakerWilliamErnest1978_thesis.pdf (7.39 MB)
The interaction of humic acids from Tasmanian Podzolic soils with minerals and the properties of their metal humates
thesisposted on 2023-05-27, 06:32 authored by Baker, William Ernest, 1932-
The humic acids from podzolic soils of north-western and western Tasmania have the general chemical and optical properties of the group as described in the literature. They do not correspond closely to the humic acids of the classical Northern Hemisphere podzol in that they have higher C : H ratios and lower optical densities. In addition they provide a far higher proportion of the total humic substances than do the humic acids of the classical podzol. All samples of humic acids extracted from the Tasmanian soils exhibit very strong solvent activity towards minerals, particularly those of economic deposits. For example, 50 ml of a 500 mg/ solution of the humic acids from soil developed under white topped stringybark (Eucalyptus delegatensis) and bracken fern (Pteridium aquilinum), extracted 2 500 pg of lead from 7.6 g of 0.3 to 0.6 mm diameter grains of galena in 24 hours. Even gold is soluble in solutions of humic acids and it is likely that the formation of gold humates is the important mechanism of transport of this metal in wet temperature climates. The aggressive action of humic acids towards minerals in the experimental studies, leaves no doubt as to their potential in weathering. Since the minerals of economic deposits are highly vulnerable, the rapid degradation of sulphides and secondary minerals may explain the poor development of gossans over mineralisation in Tasmania during the current erosional cycle. The activity of humic acids presents a problem in geochemical prospecting since secondary dispersion patterns may be weakened or obliterated. The mechanism of the interaction of humic acids with minerals and cations has been investigated by means of pH measurements, potentiometric titration, polarography, x-ray diffraction, electrophoresis and infra-red spectroscopy. All these indicate that complexation is an important mechanism of reaction. Polarographic studies also suggest that the most probable value for the standard reduction potential of humic acids is about 0.7V. Reaction kinetic studies of several of the rapid reactions between humic acids and minerals indicate that the reactions involved are of first order. The simple organic compounds of soils, such as amino acids for example, are no more active in mineral degradation than are humic acids. In view of the low concentration and rapid bacterial utilisation of these compounds their contribution to weathering must be limited. Waters enriched in CO2 also appear less efficient as solvents than humic acids, since on the basis of equivalent carbon contents the latter are far more effective. From an extremely conservative estimate, it appears that some 150 000 tonnes of humic substances flow to the sea from an aggregate catchment of about 20 000 km 2 in western Tasmania every year. Thus these substances have both the power and quantity to play an important role in the wet temperate weathering cycle.
Rights statementCopyright 1977 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (Ph.D.)--University of Tasmania, 1978. Bibliography: l. 110-121