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Abstract

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.

Item Type:	Thesis - PhD
Authors/Creators:	Baker, William Ernest,1932-
Keywords:	Humic acid, Podzol, Soils
Copyright Holders:	The Author
Copyright Information:	Copyright 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).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 1978. Bibliography: l. 110-121
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