Kinetic and Isothermal Studies for Removal of Zn (II) Ions from Aqueous Solutions by Using Lawsonia inermis as a Novel Biosorbent

In this work, the use of a cost-effective biosorbent Lawsonia inermis was investigated for removal of Zn (II) ions from aqueous solutions. Different operational parameters such as the effect of pH, biomass dose, equilibrium time, temperature and initial metal ion concentrations were studied. Maximum adsorption of Zn (II) took place at optimum conditions of pH 5.0 and biomass dose of 0.2 g/L. It was found that the interactions between zinc ions and Lawsonia inermis were complicated, and the pH of solution was a key governing factor of such interactions. Biosorption equilibrium was achieved in 60 minutes. The adsorption kinetics followed Pseudo second order kinetic model and the value of rate constant was found to be 1.23 × 10-2 g mg-1min-1. Fourier transform infrared (FTIR) spectroscopy was used to characterize the surface functional groups of the biosorbent. FTIR analysis was used to reveal the involvement of hydroxyl and carboxyl groups in the removal of Zn (II) from aqueous streams. Linear Langmuir and Freundlich models were applied to describe the equilibrium isotherms, and both of the two models were synchronic. The Langmuir adsorption capacity (qm) was found to be 76.92 mg g-1. Desorption experiments indicated that 0.5 M HCl was efficient desorbent for the recovery of Zn (II) from biomass. All the experimental facts reveal the efficiency of Lawsonia inermis based Zn (II) removal technology.