Sustainable Valorization of Recycled Coffee Grounds Into High‐Performance Bio‐Adsorbents for Efficient Cr(VI) Removal From

ABSTRACT This study investigates the feasibility of valorizing spent coffee grounds (SCG) as a sustainable bio‐adsorbent for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions through a simple Ca(OH) 2 ‐assisted modification. Unlike conventional adsorbents that often require high‐temperature carbonization or aggressive chemical activation, the proposed approach employs a low‐cost, low‐temperature, and environmentally benign treatment to enhance the adsorption performance of SCG. The modified materials were prepared via washing, drying, sieving, and Ca(OH) 2 treatment at different concentrations, followed by systematic adsorption experiments under various conditions of contact time, pH, adsorbent dosage, temperature, and initial Cr(VI) concentration. The results indicate that Ca(OH) 2 treatment effectively improves the physicochemical properties of SCG by increasing surface reactivity and the availability of active adsorption sites. Under optimal conditions (contact time 180 min, pH 3, adsorbent dosage 1 g, and temperature of 313K), the modified SCG achieved a maximum adsorption capacity of 19.84 mg g −1 . Regeneration studies showed that HNO 3 was the most effective desorbing agent, with a desorption efficiency of 91.60%, although a gradual decline in adsorption efficiency was observed over successive reuse cycles. Overall, this work demonstrates a practical and sustainable strategy for converting waste coffee grounds into functional adsorbents, highlighting the potential of Ca(OH) 2 ‐assisted modification as a scalable and eco‐friendly route for Cr(VI) removal and wastewater remediation.