Pankratov D.A., Sorkina T.A., Karelina E.E., Anuchina M.M. The interaction of the metal iron with humic substances. /Abstracts of Second International Conference of CIS IHSS on Humic Innovative Technologies Natural and engineered nanoparticles in clean water and soil technologies, Moscow, Russia, 2012, p. 40
The humic substances (HS) are considered to be one of the most complex and diverse natural organic compounds in terms of structure and composition. HS contain aromatic skeleton, highly substituted with various functional groups. It is believed that their presence determines the ability of HS to form stable complexes, compounds and soluble composites with metal ions or their compounds. In addition, these functional groups can themselves be involved in the interaction of HS with dissolved metal compounds. In this work we studied the reaction products of HS concentrated solutions with metallic iron.
HS compounds with iron are one of the most interesting, because of their prevalence in nature. Besides iron-containing HS are widely used – starting from regulators of iron deficiency in plants and up to the base of nanocomposites for biomedical applications. Due to the fact that these kind of iron-containing compounds are generally amorphous, heterogeneous, multiphase and nanoscale the only possible method of investigation is Mossbauer spectroscopy.
Mossbauer spectroscopy of frozen aqueous solutions showed that in the presence of air there is a transition of iron into humic solutions of alkali metals, with stabilization in the form of finely dispersed hydrated oxides of iron(III) (δ=0.45 mm/s, Δ=0.73 mm/s, 85 K). On the other hand, under anaerobic conditions, up to 60% of the iron in the solution is in the form of stabilized hydroxocompounds of iron(II) – (δ=1.28 mm/s, Δ=2.74 mm/s, 85 K). To model (simulate) the interconversion of compounds of iron(II)-iron(III) in HS solutions we conducted a similar study for EDTA aqueous solutions. It is shown that under anaerobic conditions in the model solutions of chelating ligands with metallic iron it was observed the formation of compounds of iron (II), easily and reversibly oxidized in air to form compounds of iron (III).
Evolution of the Mossbauer spectra of frozen (85 K) solution of the product of interaction of metallic iron and HS from oxidation in air.