No abstract

Evaluation of the effect of soil properties on metals' sorption in soils is a highly complicated task due to the large heterogeneity of factors affecting this process. To lower this heterogeneity, Cd, Cu, Pb and Zn sorption properties of three acidic and three alkaline smectitic soils were studied in single element and competitive batch sorption experiments, and the sorption capacities of the soils were related to their major properties. Higher sorption of Pb and Cu than Cd and Zn was found also in smectitic soils, and this difference was increased by competition. In acidic soils, organic matter and smectites provides the sorption sites for Pb and Cu primarily, whereas precipitation of Pb as carbonate and sorption of Cu on soil organic matter is characteristic at alkaline conditions. Contrarily, Cd and Zn showed the highest affinity to smectites primarily if they are accumulated together with iron-oxyhydroxides. Processes affecting the shape of the sorption cure may result to misleading sorption capacity values, so an additional parameter describing the sorption of a given metal directly should be involved in the data evaluation. Cadmium and Zn may pose a higher risk to the environment than Pb and Cu in case of their release to the soil. However, accumulation of smectites together with iron may significantly decrease this risk. Elimination of one single variable was not enough to get a much deeper insight into soil-metal interaction, although several advantageous characteristics of smectites could be confirmed regarding metal sorption in soils.

Purpose. Heterogeneity of soil mineral particles may lead to the misinterpretation of bulk sorption data on their role in metal sorption, which may be resolved through the direct observation of metal distribution among the soil particles after the sorption. Materials and methods. Analytical transmission electron microscopy was used to study metal (Cd, Cu, Pb, Zn) sorption characteristics of clay minerals, Fe-oxyhydroxides and their natural assemblages in soils with contrasting pH under single element and competitive situations. Results and discussion. Iron-oxyhydroxides sorbed higher metal amounts than clay mineral particles mostly, and the sorption capacity of the latter phases were more affected by competition. Iron-oxyhydroxide particles acted as effective metal sorbents in soils not only as individual particles but also as coatings on other mineral particles, and the structural Fe in clay minerals may also resulted in higher metal sorption in some cases. Besides the direct observation of metal sorption onto soil mineral particles, metal precipitates could be identified directly, and the role of organic surfaces in metal sorption could be inferred indirectly in certain cases. Conclusions. Comparison of metal affinity sequences and their partition characteristics between the bulk soil and different mineral particles were found to be an effective tool to specify the most active mineral components in metal sorption at given soil and sorption condition.