Agro waste material as ecofriendly adsorbent for the removal of Zn(II): isotherm, kinetic, thermodynamic and optimization studies

Contamination of environment by heavy metals posed significant threat to human, animals and plants health due their accumulation in the living tissues and their non-degradability. Excess of zinc in living system is detrimental to health adverse effects therefore; this work investigates the feasibility of removal of Zn2+ from aqueous solution using agricultural biowaste adsorbent prepared from groundnut shell. Effects of some important parameters such as pH, initial metal concentrations, temperature and adsorbent dosage on adsorption process were investigated. These factors were optimized by Box-Behnken experimental design using Design Expert 6.0. The prepared biosorbent was characterized using Scanning electron microscopy (SEM), Fourier Transform Infrared (FT-IR) and X-ray dispersion (XRD). Data from kinetic study was analyzed with pseudo-first-order and pseudo-second-order kinetic models while equilibrium data were evaluated using Langmuir and Freundlich isotherm models. The surface morphology of groundnut shell revealed porous pores indicatives of available sites for sorption of metal ion on the surface of the groundnut shell. The adsorption kinetics of the metals ions followed pseudo-first-order with average rate constants of 5.63 x 10-2. Langmuir adsorption isotherm fitted the isotherm study with R2 > 0.9 while the maximum adsorption capacities of 23.46 mg g-1. Negative values of.G degrees obtained from thermodynamic evaluations revealed that the adsorption process is spontaneous. The values.H degrees and.S degrees obtained respectively are 29.90 and 105 J mol-1 K-1. Prediction of regression models was in good agreement with experimental result. This study showed that groundnut shell to be a good adsorbent for the removal of Zn(II) from aqueous solution.