Article Info Received : 15.05.2014 Accepted : 14.10.2014 The parameters of adsorption of Cu 2+ , Pb 2+ , and Zn 2+ cations by southern chernozem and their particle-size fractions were studied. The adsorption of metals by soils and the strength of their fixation on the surface of soil particles under both mono-and poly-element contamination decreased with the decreasing proportion of fine fractions in the soil. The aim of this work was to study the effect of the particle-size distribution and the silt and physical clay fractions on the adsorption of copper, lead, and zinc by chernozems. The objects of study included the upper humus horizons of different southern chernozems of the Rostov oblast. To study the ionexchange adsorption of the Cu 2+ , Pb 2+ , and Zn 2+ cations, the soil in the natural ionic form was disaggregated using a pestle with a rubber head and sieved through a 1mm sieve. The soil samples were treated with solutions of Cu 2+ , Pb 2+ , and Zn 2+ nitrates and acetates at the separate and simultaneous presence of heavy metals (HMs). In the solutions with the simultaneous presence of HMs, their molar concentrations were similar. The concentrations of the initial solutions varied in the range from 0.05 to 1 mM/l. The soil: solution ratio was 1:10. The contents of HMs in the filtrates were determined by atomic absorption spectrophotometry. The contents of adsorbed HM cations were calculated from the difference between the metal concentrations in the initial and equilibrium solutions. The increase in the degree of dispersion of the particle-size fractions in similar soils resulted not only in an increase in the content of adsorbed HMs but also in an enhancement of their fixation on the surface of the fine particles. Therefore, the adsorption capacity of the Lower Don soils for Cu 2+ , Pb 2+ , and Zn 2+ decreased in the following sequence: clay loamy southern chernozem > loamy southern chernozem > loamy sandy southern chernozem. This was related to the qualitative differences in the mineralogy and chemistry of the separated fractions and the significant effect of their composition and properties on the parameters of the HMs adsorption.

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The influence of the composition and properties of the mineral matrix in soils on the humification of corn residues was studied. The substrate (silica sand, loam, silica sand + 10% bentonite, or silica sand + 30% kaolinite) was mixed with 10% corn residues (milled to 3-5 mm) and incubated under stationary conditions for 6-19 months. Sampling for the analysis was performed every month, and a few times in the first month. The dynamics of mineralization and humification of plant residues was studied by applying elemental and bulk analyses of neogenic organic matter (OM), densitometric fractionation of substrates, FTIR spectroscopy, solid-phase 13 C-NMR spectroscopy, and scanning electron microscopy with an electron microprobe. It was shown that the humification processes had a wavelike character for loam and sand substrates, which could be explained by the transformation of the microorganism populations together with the change in the amount and quality of OM in the system. The main mechanism for the stabilization of neogenic OM was adsorption on a mineral matrix with formation of relatively resistant compounds. This adsorption can be selective, depending on the composition and properties of the mineral matrix. The FTIR and 13 C-NMR analyses of OM distribution in different substrates and densitometric fractions showed that sand and heavy fractions (HF >2.2 g/cm 3) were enriched with compounds of an aromatic nature and polypeptides. Light fractions (LF-2, 1.4-2.2 g/cm 3) accumulated compounds that also contained alkyl and carboxyl groups. The sandy substrate and HF have higher aromaticity indices than LF-2. Higher aromaticity index values of humus substances in the sandy substrate and HF in the loamy substrate, compared to LF-2, evidenced the formation of steady aromatic compounds, in which there may be kernels of humic acids (HA). We do not exclude the possibility of the matrix synthesis of the HA-like substances.

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