Fe[sub.3]O[sub.4]@Granite: A Novel Magnetic Adsorbent for Dye Adsorption

Magnetic granite (MG), a new and low-cost adsorbent, was prepared by the chemical co-precipitation of Fe[sup.2+] and Fe[sup.3+] using granite (G), which is a magmatic rock type. The adsorption of the Reactive Black 5 (RB5) dye from aqueous solutions on Fe[sub.3]O[sub.4]-modified granite was examined in a batch system. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray fluorescence spectrometry (XRF), X-ray diffractometry (XRD), N[sub.2] adsorption–desorption, vibrating-sample magnetometry (VSM), and point-of-zero charge (pH[sub.pzc]) analysis were used to characterize the prepared MG. Magnetic granite displayed significant magnetization and could be easily separated using external magnets. The maximum adsorption capacity was 29.85 mg/g at 298 K. According to kinetic and isothermal examinations, the pseudo-second-order model and Langmuir isothermal adsorption were the best fit for adsorption. It was found that the enthalpy change ΔH (kJ/mol) was −31.76, and the entropy change ΔS (kJ/mol) was 0.096 for a temperature change of 298–330 K. The ΔG° (kJ/mol) value was negative at all temperatures (298 K, −2.86 kJ/mol; 303 K, −2.85 kJ/mol and 313 K, −1.50 kJ/mol), indicating that the adsorption of RB5 on MG was spontaneous.