The research of the influence of heavy metal ions on the aggregation of humic substances on the mica by atomic force microscopy

Abstract

The conformation of the molecules of humic substances of peats sorbed on the hydrophilic mica in the absence and the presence of heavy metal ions was studied by atomic-force microscopy in a semi-contact mode in an aqueous medium. A model of the lignin-carbon complex providing the conformation of the three-dimensional ring structure of humic substances as a function of pH is proposed and allows to accurately describe the surface structure of the molecules of humic substances. The sizes of single globular molecules of humic substances are determined; there are (140 ÷ 320) × (5 ÷ 25) nm. Possible ways of the interaction of humic substances of peats with metal cations (Pb2+ and Zn2+) with allowance for conformational changes of humic substances are established. It has been proved that lead cations are sorbed mainly on the surface of the molecules of humic substances, and the sorption of zinc cations passed with a reorientation of humic substances around zinc ions.