Ligand dissolved organic matter

The Chemical Speciation of Iron Dissolved Organic Matter as a Ligand... 

The kinetics of the oxidation of Cr(III) and Cu(I) have been discussed before. Cr(VI) is reduced by dissolved organic matter, the slow re-oxidation resulting in a large enough ti for an existence of Cr(III). Also the existence of Cu(I) in seawater is a steady state between the reduction- and back-oxidation reactions. The lifetime is dependent on pH, PC>2, complexing ligands and redox intermediates such as H2O2 (Moffet and Zika, 1983). 

DOM is the ligand used by MINTEQA2 to represent dissolved organic matter (dissolved humic substances). The units of mol dm-3 are based on a knowledge of DOC (mg dirT3) and a titratable acidity of 7 mol kg-1 for the humic substance. 

Afcharian, A., Levi, Y., Kiene, L. and Scribe, E (1997) Fractionation of dissolved organic matter from surface waters using macroporous resins. Water Res., 31, 2989-2996. Ahrland, S., Chatt, J. and Davies, N.R. (1958) The relative affinities of ligand atoms for acceptor molecules and ions. Quart. Rev. Chem. Soc., 12, 265-276. 

Fig. 4. Two alternative pathways for the redox cycles photocatalyzed by Fe(III) or Cu(II) complexes (a) and by chromium compounds (b) L, ligand D, external electron donor DOM, dissolved organic matter.

Chemical Speciation Models. Using the stability constants derived by us for copper complexes with hydroxo and carbonate ligands (Table I) and for natural organic ligands (Table II), the Newport and Neuse Rivers were modeled for copper speciation as a function of pH, total copper, carbonate alkalinity and total dissolved organic matter. Speciation models were calculated from the equation ... 

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