Complexation of Humic Acids with Trace Elements: Methods and Approaches

The review analyzes research over the past 20−25 years in the field of physical chemistry of complexation of humic acids with cations, including radionuclides, in aqueous solutions. Problems have been identified in describing the reactivity of humate complexes with consideration for the objective complexity of the chemical nature of humic acids as one of the main classes of natural organic matter. The main methods of modeling complexation with humic acids, experimental methods for separating humate complexes and unbound cations (ultrafiltration, dialysis, etc.), and direct instrumental (electrochemical and spectroscopic) methods for detecting complexes were considered. Attention was also paid to the practical aspect of using humic acids for the treatment of natural water and wastewater to remove pollutants—heavy metals and radionuclides. Published data on the sorption capacity of humic acids of various origins in relation to heavy metal cations and quantitative data characterizing the stability of humate complexes were analyzed.