Analyzing the Dynamics of Interaction between Humic Coal Substances and Metallic Iron

Abstract

The dynamics of interaction between metallic iron and aqueous solutions of three preparations of humic coal substances from different manufacturers is analyzed. Humic substances are characterized via elemental analysis, NMR spectroscopy, size-exclusion chromatography, electronic absorption spectroscopy, and chemical analysis. Distinctions are observed between the investigated humic substances in the content of aromatic moieties, the degree of their substitution, the content of carboxylic groups, and the degree of oxidation. It is shown that regardless of the background of humic substances, the interaction between their solutions and iron is based on the same set of consecutive reactions, which can be divided into three basic stages of interaction using data on the changes in easily controllable parameters (redox potential, pH, and solution absorbance). These stages of interaction are qualitatively described in Pourbaix diagram coordinates. Features of the structural and group composition of humic substances result in different times of the corresponding stages of interaction. Based on an analysis of the main components, a way of describing the complicated sequence of reactions between humic substances and iron in the coordinates of a two-factor plane is proposed to allow the clear attribution of experimentally measured parameters of the reaction medium to a certain stage of interaction between metallic iron and aqueous solutions of humic substances, regardless of the specific properties of the latter.