Removal of cadmium ions from aqueous solution by zero valent iron nanoparticles: Equilibrium and thermodynamic studies

Abstract

Nano zero valent iron particles (NZVI) were synthesized, via reduction method using sodium borohydride in presence of ultrasonication and used for the removal of cadmium ions in an aqueous solution. The removal process was studied thermodynamically to explore the suitable mechanism. Eyring equation, vant’ Hoff equation and Arrhenius equation were applied in this study using pseudo second order, chemical first order and chemical second order, the results showed that the removal of cadmium ions by NZVI was by two steps with probability of presence of three steps. The reacted (NZVI) were characterized by different characterization techniques; scanning electron microscope, transmission electron microscope and X-ray diffraction to support the predict mechanism, and the results showed creation of laminar residuals related to cadmium oxide indicating the chemical irreversible process. A new method in calculating of the equilibrium constant in heterogeneous system was explored and showed higher agreement with the applied equations in addition to the independence from variety in initial concentration and a simple comparing was performed with Langmuir constant after proving the agreement of that model on the adsorption process.