Abstract
The role of lipid components in the aggregation of several humic acids isolated from different sources was investigated using surface tensiometry. A combination of aqueous alkaline and organic solvent extractions was used to isolate two humic-like fractions (HA 1 and HA 2) and one lipid-like fraction from each humic acid. Fraction HA 1 represents approximately two-thirds of the total organic carbon of the original humic acid and under alkaline conditions is a weak surfactant that lowers the surface tension of water by only a small amount. The HA 2 fraction represents up to one-third of the humic acid and significantly lowers the surface tension of water. It is also intimately associated with the lipid fraction. Unlike the original humic acid samples, HA 2 does not show micelle-like aggregation over the concentration range studied. Aggregate formation is discussed as an emergent characteristic that results from the interaction of the humic acid’s components with the lipid components serving a facilitative role.
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