A Complex Compound of Mechanochemically Modified Humic Acids and Fe(III) as a Base of a Geochemical Barrier

A complex of mechanochemically modified humic acids with Fe(ІІІ) was prepared by coprecipitation at pH varied from 12 to 2. Fe(ІІІ) interacts with humic acids via ionized groups. The ionized phenolic and carboxyl groups of humic acids at рН 8–12 bind Fe³⁺. At рН < 7.5, carboxyl groups of aromatic fragments of humic acids enter into the ion exchange with positively charged iron species {[Fe(OH)₂]aq}⁺ and {[Fe(OH)]aq}²⁺. The sorption exchange capacity of the modified humic acids is preserved to up to 50% and depends on the fraction of the humic component in the complex. The active sites of the organomineral complex are negatively charged oxygen-containing functional groups of macromolecules of the modified humic components and positively charged micellar Fe(ІІІ) forms. The humic complex with Fe(III) can be used as a base of a geochemical barrier to reduce the concentration of polluting chemical elements and organic ecotoxicants in soil.