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 molecules of humic substances of peats sorbed on hydrophilic mica in the absence and presence of heavy metal ions was studied by atomic-force microscopy in semi-contact mode in an aqueous medium. A model of the lignin-carbon complex is proposed, which ensures the conformation of the three-dimensional ring structure of humic substances depending on pH and allows accurate description of the surface structure of humic substances. The sizes of single globular molecules of humic substances were determined: 140-320 nm in diameter and 5-25 nm in height. Possible ways of the interaction of humic substances of peats with metal cations (Pb^{2 +} and Zn^{2 +)} with account of conformational changes of humic substances have been established. It has been proven that lead cations are sorbed mainly on the surface of humic molecules, and sorption of zinc cations proceeds with reorientation of humic substances around zinc ions.