Other
Scientific paper
Nov 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997gecoa..61.4599o&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 61, Issue 21, pp.4599-4604
Other
2
Scientific paper
Humic acids in solution behave as a kinetic system that is characterized by steady-states rather than by equilibria. This is shown by redox measurements at 0.1 M NaCl and 24°C under carefully controlled anaerobic conditions. When the humic acids were titrated with HCl from pH 6.4 to 3, the redox potential, after relaxation to a steady-state, showed a linear pH dependence with a slope of -42 mV/pH unit. (A supplementary study in a 0.1 M NaClO 4 medium, using humic acids prepared from another source, agrees within the limits of experimental errors of ±1 mV giving a slope of -44 mV/pH unit). In each titration point there was an initial, relatively fast relaxation with a tau-value within the range 150-400 s, followed by further slow relaxation (tau > 2.5 h) and/or oscillations, followed by arrival at a steady-state. This nonequilibrium behaviour implies the presence of polyphenolic residues, such as resorcinol, within the humic acid particles and their free radicals. In a redox diagram, the pH dependence of the apparent redox potential of humic acids is compared with the redox potential of various other redox pairs present in soil.
Österberg Ragnar
Shirshova L.
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