Valorization of Cow Bone Waste into HCl-Activated Biochar for the Removal of Congo Red Dye and Heavy Metals from Wastewater

Abstract

The work investigated the potential of biochar derived from cow bones as a low-cost and effective adsorbent for the removal of Congo red dye and heavy metals (Pb²⁺ and Cd²⁺) from simulated wastewater. Cow bone biochar was prepared via pyrolysis at 400 to 700 °C under oxygen-free conditions and activated with hydrochloric acid to enhance its adsorption properties. Unactivated biochar exhibited very low adsorption efficiency (less than 4%) and removed negligible amounts of Congo red. In contrast, HCl-activated biochar achieved a removal efficiency of 88% at 20 mg/L and maintained approximately 50% removal at 100 mg/L, indicating effective adsorption even at high initial concentrations. Biochar adsorbed 59.6% of Pb²⁺ at 20mg/L and 32.2% at 80mg/L of simulated wastewater. It also adsorbed 94.45% of Cd²⁺ at 20mg/L and 55.26% at 80mg/L of wastewater. The reduced metal removal at higher concentrations was attributed to saturation of the adsorption location. These results indicated that biochar had a high affinity for Cd²⁺ and had a strong potential to remove dyes and heavy metals from aqueous solutions. This work highlights the utilization of cow bone waste as a precursor for high-performance biochar. Acid-activated cow bone biochar was found to be an effective and low-cost adsorbent for wastewater remediation, indicating its suitability for industrial wastewater remediation.