Zn adsorption by different fractions of Galician soils

To evaluate the contribution of organic matter, oxides, and clay fraction to Zn adsorption in six soils from Galicia (Spain), after soil characterization, adsorption isotherms were obtained by adding nine solutions containing between 20 and 500 mg L(-1) concentrations of Zn(NO(3))(2). Distribution coefficients were obtained from the data of adsorption isotherms. Zn adsorption isotherms corresponding to untreated soil and to the organic matter removed samples and organic matter and oxides removed samples were compared with curves pattern and adjusted to Langmuir and Freundlich empirical models. Untreated soils described L-curves whereas when soils were deprived of any component, the curves described were S-type. Distribution coefficients allowed knowing the Zn adsorption capacity of the untreated soil, and of the organic matter, oxides, and clay fraction. Soil organic matter is the main component that affects Zn adsorption as long as soil pH is near neutrality. At acid pH, the oxides are the main component that affects Zn adsorption, although to a much smaller extent than the organic matter near neutral conditions. So soil pH is the main soil factor that determines Zn adsorption, before any other soil property.