engleski

Effect of oxalic and citric acid on adsorption of cooper and cadmium onto vermiculite, kaolinite and goethite.

Mineral cations from soil solution can adsorb to the negatively charged colloidal fraction of soil matrix. Once adsorbed, these minerals provide a source of nutrients available for plant roots and can be replaced by other cations. The capacity of soil to store and exchange cations depends on the factors like soil texture, types of present minerals, organic matter content, soil pH and the composition of soil solution. In general, exchange capacity of most soils increases with the increase of soil pH. Simple organic acid, mostly produced by the microorganisms and plants, strongly influence the release of these elements from exchange complex. The aim of this study was to investigate the adsorption of cooper and cadmium by vermiculite, kaolinite and synthetic goethite at different pH values, in presence and absence of oxalic and citric acid which are among the most abundant low molecular-weight organic acids in soil solution. To evaluate the adsorption of Cu and Cd under different conditions we conducted batch experiments in centrifuge tubes at an ionic strength of 0.02 M KNO3. In the absence of an acid, the amount of adsorbed metals on onto vermiculite, kaolinite and goethite increased with the increasing pH. Organic ligands, generally, decreased the amount of Cu and Cd adsorbed on these three sorbents. Oxalic acid had only minor effect on adsorption of cadmium on goethite. The observed tendencies were attributed to the processes of complexation between cations and organic ligands. The study confirmed the significant role that organic acids, as abundant plant and microorganisms’ exudates, can play in enhancing the mobilization of adsorbed heavy metals in environment and in the similar geochemical processes.

Soil minerals; Exchange complex; Heavy metals; Organic acids

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