Pollution Research Paper

MECHANISMS OF HEAVY METALS IMMOBILIZATION BY HUMIC SUBSTANCES OF ORGANOGENIC SOILS

I. KUZNETSOVA, S. SELYANINA, I. ZUBOV, N. LARIONOV AND T. PONOMAREVA

Abstract

Humic substances of organogenic soils (primarily peat) are interesting for solving problems of protecting the environment from various pollutants. They are capable both to immobilize heavy metals, and to increase their migratory ability. This is determined by the peculiarities of metal binding. Immobilization of heavy metals, in particular lead and cadmium, in organogenic soils is largely provided by the ion exchange and chelate complexation processes realized by carboxyl and hydroxyl functional groups of humic acids. Therefore, the subject of current research is to study the main regularities of interaction of heavy metals with humic acids (HA). Humic substances were isolated from samples of the high-moor peat from bog massif, typical for the White Sea seaside province that was not subjected to anthropogenic impact. Analysis of the composition and polymolecular characteristics of peat humic acids (HA) indicates a lower condensation of peat HA than that of coal. Carboxyl (pK 4.4) and phenolic hydroxyl groups (pK 9.2), whose content is respectively 8.4 ± 0.7 and 4.8 ± 0.4% are capable to provide the immobilization of heavy metals in the HA macromolecules are. The high content of aliphatic structures in HA macromolecules is confirmed by the atomic ratio H/C (1.09) and viscosimetry data. The fact of formation of chelate complexes is confirmed by measurements of the particle sizes of HA-Cd, which are 5-10 times higher than the size of the molecularly dispersed macromolecules of peat HA, while the polyelectrolyte effect is suppressing. The amphiphilic character of the structure and the presence of oxygen-containing groups provide high sorption capacity of HA relative to heavy metals (up to 0.90 mmol/g for Pb2 + and 0.95 mmol/g for Cd2 +). The high degree of binding of cadmium (II) and lead (II) ions to HA of low-decomposed peat indicates their highly pronounced sorption properties, due to which they have a high potential for use as industrial sorbents.