KINETICS AND THERMODYNAMICS OF NITRATE ADSORPTION BY BIOCHAR

Abstract

High concentration of nitrate in surface and ground water is a universal water pollution challenge for several. Four biochar samples were produced and subjected to batch sorption experiment. Data obtained were fitted into the linear forms of four adsorption isotherm and kinetics models. Least square regression analysis was used to test the best fitting isotherm and kinetic model using the coefficient of determination (R2). Results revealed that only maize cob biochar (MCB) and poultry litter biochar (PLB) had the ability to adsorb nitrate with maximum quantities of adsorbed nitrate (73.915 and 133.887 mgg-1). Similarly, adsorption kinetics indicated better fitting of the adsorption data onto the linear form of the pseudo second order kinetics (PSOK) model. Lower R2 values recorded by the intra particle diffusion and Elovich adsorption kinetic models suggest that the adsorption process was physical and intra- particle diffusion was not the rate controlling step. Similarly, 99% change in nitrate adsorption was accounted by the combined influence of biochar electrical conductivity (EC), zero point of charge (ZPC) and pH. Hence, modification of biochar EC, ZPC and pH are necessary for using biochar to successfully remove nitrate from polluted environments.

Keywords

• adsorption isotherms
• kinetics
• biochar
• nitrate
• thermodynamics