Langmuir, Freundlich, Temkin and Dubinin–Radushkevich Isotherms Studies of Equilibrium Sorption of Zn 2+ Unto Phosphoric Acid Modified Rice Husk

Equlibrium sorption of the phosphoric acid modified rice husk was studied. The Physico-chemical properties of the modified rice husk were determined. The equilibrium sorption data were fitted into Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (DRK) isotherms. Of the four adsorption isotherm, the R 2 value of Langmuir isotherm model was the highest. The maximum monolayer coverage (Q o ) from Langmuir isotherm model was determined to be 101.01mg/g, the separation factor indicating a favourable sorption experiment is 0.133. Also from Freundlich Isotherm model, the sorption intensity (n) which indicates favourable sorption and the correlation value are 1.6 and 0,89 respectively. The heat of sorption process was estimated from Temkin Isotherm model to be 25.34J/mol and the mean free energy was estimated from DRK isotherm model to be 0.7KJ/mol which vividly proved that the adsorption experiment followed a physical process.