Synthesis of Iron-containing Nanoparticles from Iron-Steel Industrial Waste for Adsorption of Malachite Green

Abstract

For the synthesis of iron-containing nanoparticles (FeNPs), the iron ions were recovered from iron-steel industrial waste by leaching method followed by the chemical precipitation of ferric hydroxide with NH3. The ferric hydroxide was reduced pyrometallurgical to iron-containing nanoparticles by the reducing agent of CO generated from charcoal. FeNPs were characterized by XRD and SEM analysis. XRD results showed that FeNPs had predominantly face-centered cubic Fe3O4 structure, besides, the peaks of Fe2O3 and Fe0 structures were also observed. The particle size of FeNPs was calculated as 57.75 nm using Williamson–Hall equation. According to SEM images, FeNPs had homogeneous and spherical-like structures; also, the structures partially decomposed and the particle size increased due to the agglomeration of the particles after adsorption. FeNPs were used as an adsorbent for the removal of Malachite Green (MG). The experimental design and the optimization of experimental conditions were investigated by using response surface methodology (RSM) according to central composite design (CCD). The optimum experimental conditions were determined as 180 min contact time, 75 °C temperature, and 300 mg/L initial MG concentration. The agreement between the adsorbed MG concentrations at the equilibrium (qe) calculated from the model (148.43 mg/g) and determined experimentally (146.63 mg/g) under the optimum conditions showed that the selected model was suitable for MG adsorption by FeNPs. Langmuir isotherm model had higher R2 and lower ARE values than Freundlich isotherm model, showing that the equilibrium data of MG adsorption with FeNPs was the best agreement to Langmuir isotherm model with the maximum monolayer coverage capacity of 175.44 mg dye/g FeNPs. The thermodynamic studies suggested that the adsorption process was endothermic, spontaneous at the optimum conditions, and the positive ΔS value indicated the increased disorder at the solid-solution interface during the adsorption.