Adsorption of Zn(II) in Oxisols as affected by selective removal of soil fractions

The relative contribution of organic matter, amorphous and crystalline Fe oxides and Al oxides to soil Zn adsorption was evaluated in contaminated and uncontaminated Brazilian soils. Soil samples were equilibrated with Zn solutions and Zn adsorption was determined using the Langmuir adsorption isotherm. The Fe and Al oxides (non‐silicated clays) and the organic matter contents of the soils were the main contributors to the variation in Zn adsorption. The Zn maximum adsorption capacity in the soil with the greatest sand and organic carbon contents was higher than in the higher clay content soil, which was second in organic carbon content. Related to the whole soil samples, as the soil organic matter was removed, the Zn maximum adsorption capacity decreased in most of the observations. The removal of Fe and Al oxides decreased the soil Zn maximum adsorption capacity in some cases and increased it in others, with no clear variation in the pathway. For both whole soil and soil fractions, the isotherms for Zn adsorption to soil, fitted to the Langmuir equation, showed two linear portions or pathways (Part I and Part II). The bonding energy coefficient was higher in Part I (related to specific chemical adsorption) than in Part II (related to electrostatic interactions), which suggests a higher affinity between Zn and soil particles in Part I as compared with Part II.