UBC Theses and Dissertations

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UBC Theses and Dissertations

The relationship of metals and soil organic components with particular reference to copper Cross, Christine Hazel

Abstract

An ap horizon of a soil collected from a highly mineralized area was fractionated into five organic and mineral components and the distribution of cu, zn, pb, ca and mg within these components was determined. Zn and ca were removed to a considerable degree in the 0.1n hcl extract. Of the five metals, cu and pb were the only ones present which combined with organic matter to any considerable degree. Of the five organic and mineral components, fulvic acid was shown to display the greatest complexing activity. Although gel filtration has been used extensively in the field of biochemistry, it was shown that the metal retaining properties of the various sephadex and agar gels used caused the technique to be unsuitable for the separation of naturally occurring metal-organic complexes. In addition the distribution of fe, cu and zn within the profiles of two soils from less mineralized areas was determined but the low levels of metal found did not permit a direct investigation of their metal-organic complexes. In order to study in detail metal-0rganic matter reactions, humic acids were extracted from several of the above soils. Functional group analysis coupled with elemental analysis for c, h, N and 0 in these humic acids revealed that a large percentage of the oxygen was unaccounted for in carboxylic acid and phenolic Hydoxylic groups, thus indicating the presence of other oxygen containing groups. Infrared spectra showed decreases in the amount of aliphatic material present with increasing maturity of the humic acids and also gave supporting evidence of complex formation upon the addition of cu. The humic acids were used in a series of incremental potentio- Metric titration experiments which monitored the pattern of proton release in response to copper additions at a series of ph levels. The resultant curves for humic acids of various origins were alike in their general shapes but displayed differences in detail which were especially marked between the juvenile and the more mature acids. Whereas in all cases of humic acids derived from mineral soils the proton release increased with ph, the peat humic acid displayed a greater proton release at ph 5.0 than at ph 6.0. The shapes of the curves obtained with humic acids were compared with those obtained in similar experiments from a series of model compounds of known chemical composition and were found to approximate most closely the patterns derived from salicylic acid and phthalic acid. This provides additional evidence for the hypothesis that salicylic and phthalic acid-like functional groups play a significant role in the formation of metal-organic complexes in soils.

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