Pyrrhotite Ash Waste for Capacitive Adsorption and Fixed-Bed Column Studies: Application for Reactive Red 141 Dye

The purpose of this research was to use pyrrhotite ash, a residue from the phosphate industry, as an adsorbent material for the removal of reactive red 141 (RR141) dye from aqueous solution. The collected pyrrhotite ash was characterized by X-ray diffraction (XRD), scanning electron microscopy combined with energy-dispersive X-ray analysis (SEM-EDAX), Fourier transform-infrared spectroscopy (FTIR), and pHpzc. In batch assays, diverse operating parameters impacting the dye removal were scrutinized such as pH, contact time, initial RR141 concentration, temperature, and pyrrhotite ash dose. The equilibrium of adsorption was obtained after 60 min contact time, and 97% of RR141 dye was adsorbed at ambient temperature. The isotherm of Langmuir and the pseudo-second-order kinetic model yield a suitable fit for the obtained batch experimental data; thermodynamic parameter analysis reveals the spontaneous, exothermic aspect of adsorption. Fixed bed column experiments were also tested to probe the effectiveness of pyrrhotite ash for applications in continuous mode. The breakthrough curve was described by the models of Yoon–Nelson and Thomas.