Biosorption of Cd2+ and Zn2+ from aqueous solution using tilapia fish scale (Oreochromis sp): Kinetics, isothermal and thermodynamic study

This work investigates the feasibility of removal of Cd 2+ and Zn 2+ from aqueous solution using a low cost biosorbent prepared from tilapia fish scale. Effects of some important parameters such as pH, initial metal concentrations, temperature and adsorbent dosage on adsorption process were investigated. The prepared biosorbent was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX), Fourier trans- form-infra red (FTIR), X-ray diffraction (XRD) and thermal gravimetry-differential thermal analysis (TG-DTA). Data from kinetic study were analyzed with pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models while equilibrium data were evaluated using Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models. The adsorption kinetics of the metals ions followed pseudo-first-order with average rate constants of 4.95 × 10 –2 and 3.89 × 10 –2 min –1 for Cd 2+ and Zn 2+ respectively. Langmuir adsorption isotherm fitted the isotherm study with R 2 > 0.9 while the maximum adsorption capacities of 112.57 and 95.69 mg/g were obtained for Cd 2+ and Zn 2+ respectively. Negative values of Δ G ° obtained from thermodynamic evaluations revealed that the adsorption process is spontaneous. The values Δ H ° and Δ S ° obtained for Cd 2+ and Zn 2+ respectively are 13.06 and 14.61 kJ mol –1 and 43.0 and 48.64 J mol –1 K –1 . The results indicated that fish scale could be utilized as cheap, eco-friendly and excellent biosorbent for the removal of Cd 2+ and Zn 2+ from aqueous solution.