Effects of Organic Matter and Ionic Strength of Supporting Electrolyte on Zinc Adsorption in Benchmark Soils of Punjab in Northwest India

Organic matter is one of the most important components of soil and influences the physical and chemical properties of the soil. Its presence increases the adsorption of zinc (Zn). Zinc adsorption by soils and soil components is highly influenced by ionic composition, species, and concentration of supporting electrolyte solution. The present investigation was carried out to study adsorption behavior of Zn in the presence of supporting electrolytes and aqueous media for eight benchmark soils of Punjab, varying in physical and chemical characteristics. The effect of ionic strength on the adsorption of Zn was studied in the presence and absence of organic matter using three different concentrations (viz., 0.001, 0.01, and 0.1 M) of sodium sulfate (Na2SO4) as an electrolyte. The results revealed that Zn adsorption was greater in the presence of organic matter (untreated soils) than in the absence of organic matter (treated soils). The adsorption decreased after the removal of organic matter both in the presence of 0.01 M Na2SO4 and in aqueous medium. Zinc adsorption data conformed to Langmuir and Freundlich adsorption equations for both organic matter and ionic strength factors. The Langmuir constants, Freundlich constants, and distribution coefficient K-d were determined. Partial molar free energy change () decreased after the removal of organic matter both in the presence of 0.01 M Na2SO4 and in aqueous medium.