Equilibrium isotherm analysis of the biosorption of Zn2+ ions by acid treated Zea Mays leaf powder

Abstract

The potential of Zea Mays leaf powder for the removal of Zn2+ ions from waste waters was investigated using the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) adsorption isotherms. Batch biosorption studies were carried out in stopper Erlenmeyer flasks to optimize pH, contact time and biomass dosage at a solution temperature of 27 ± 2 oC, a flask agitation rate of 200 rpm and initial concentration of Zn2+ ions of 100 mg/L. Adsorption isotherm experiments were contacted by varying metal ion initial concentration in the range from 10 to 100 mg/L under optimum conditions of pH 5, 120 minute contact time, a dosage of 1g/L at constant temperature and agitation rate of 27 ± 2 oC and 200 rpm respectively. The equilibrium data showed good fit to all the adsorption isotherms with R2 ≥ 0.98. High maximum sorption capacities were obtained from Langmuir (74.0741 mg/g) and D-R (13.2779 mg/g) isotherms. The Langmuir dimensionless separation factor (RL) depicted sorption favorability with all its values falling between 0 and 1 for all initial concentrations investigated. The Freundlich adsorption intensity parameter fell in the range 1 < n < 10 showing asyseparation beneficial biosorption. The magnitude and sign of the mean biosorption energy (ED = 22.9419 kJ/mol) suggested the sorption process to be physisorption and endothermic in nature. The equilibrium sorption study showed that Zea Mays leaf powder can be effectively used for the biosorption of Zn2+ ions from waste waters.