Biosorption of Ni(II) by Fig Male: Optimization and Modeling Using a Full Factorial Design.

The fig male (FM) is successfully used as biosorbent for Ni(2+) removal. The maximum removal efficiency (96.6%) is obtained at pH ~ 5 for a concentration of 1.70 mmol L(-1) and catalyst dose of 5 g L(-1) in less than 10 minutes. The Ni(2+) uptake follows a pseudo-second-order kinetic, the rate constants increase with increasing temperature, and an activation energy of 55.48 kJ mol(-1) is found. The thermodynamic parameters indicate a spontaneous endothermic bisorption. The isotherm data are fitted by the Langmuir and Dubinin-Radushkevich models. The former indicates a maximum Ni(2+) uptake of 0.459 mmol g(-1), which is higher than that of most biosorbents investigated to date. The FTIR spectra reveal the biosorption mechanism between Ni(2+) and FM functional groups. An empirical modeling is performed by using a 2(3) full factorial design, and a regression equation for Ni(2+) biosorption is determined. The biosorbent mass and pH are the most significant parameters affecting the Ni(2+) biosorption.