The role of soil's particle-size fractions in the adsorption of heavy metals

摘要

The parameters of adsorption of Cu 2+ , Pb 2+ , and Zn 2+ cations by southern chernozem an d 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 i n 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 differe nt southern chernozems of the Rostov oblast. To study the ion - exchange 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 w ere 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 dif ference 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 enhan cement 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 so uthern 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.