Adsorption of hexavalent chromium onto activated carbon derived from Leucaena leucocephala waste sawdust: kinetics, equilibrium and thermodynamics

The adsorptive removal of Cr(VI) was studied using activated carbon derived from Leucaena leucocephala (ACLL). The physico-chemical properties of ACLL were determined using proximate analysis and N-2 BET surface area analysis. The N-2 BET surface area of ACLL was determined to be 1131 m(2) g(-1). The point of zero charge (pH(pzc)) of 5.42 indicated that ACLL surface was positively charged for pH below the pH(PZC), attracting anions. The effect of experimental operating parameters such as time of contact, ACLL dose, pH, initial concentration and temperature was investigated. The optimum values of parameters such as concentration of 100 mg L-1, 300 mg of ACLL dose, time of contact of 60 min, pH of 4 indicated the maximum Cr(VI) uptake of 13.85 mg g(-1). The pseudo-second-order kinetic model best fitted with the Cr(VI) adsorption data. Adsorptive removal of Cr(VI) onto ACLL satisfactorily fitted in the order of Redlich-Peterson > Freundlich > Langmuir > Temkin adsorption isotherm model. The thermodynamic parameters showed the adsorption of Cr(VI) onto ACLL was an endothermic and spontaneously occurred process.