Eco-friendly activated carbon developed from rice hulls for chromium and iron ion removal

Rice hulls, a harmful biowaste, were used to produce nanosized activated carbon (RHAC) by combustion and phosphoric acid treatment. The developed RHAC was characterised using various structural and morphological techniques (scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and nitrogen (N₂) adsorption). The prepared RHAC was used to remove heavy metal ions (iron (III) (Fe³⁺) and chromium (VI) (Cr⁶⁺)) by using the adsorption mechanism. Adsorption parameters, such as contact time, dose and initial concentration of the heavy metal ions, were investigated. Five adsorption models (two and three parameters) were studied. Also, the adsorption kinetics through the intraparticle diffusion model was applied. RHAC showed adsorption capacities of 47.00 and 45.00 mg/g for iron (III) and chromium (VI), respectively. The findings recommend using RHAC as a low-cost and eco-friendly adsorbent for metal ion removal and water-treatment applications.