Sustainable Synthesis and Immobilization of Mg/Fe‐LDH‐Functionalized Biochar Derived From Spinach Waste in Sodium Alginate for the Effective Elimination of Tetracycline and Cadmium

This study investigates a sustainable synthesis loop to produce a functionalized sorbent for groundwater remediation using permeable reactive barriers (PRBs). In the first stage, iron was extracted from spinach waste (SW) by acid treatment, which simultaneously enhanced its surface activity. The acid‐washed material was then pyrolyzed at 500°C to produce biochar, which served as a substrate for co‐precipitating magnesium and iron to form Mg/Fe‐layered double hydroxide (LDH) on its surface. In the second stage, an Mg/Fe‐LDH‐coated biochar was encapsulated in sodium alginate, forming a stable, reusable composite termed SA@LDH–Biochar. Batch experiments with laboratory‐prepared samples showed over 90% removal efficiency, with a maximum adsorption capacity ( q max ) of 21.4 and 15.2 mg/g for cadmium (Cd 2+ ) and tetracycline (TC), which fit the Langmuir and pseudo‐second‐order models. The composite was then evaluated for treating groundwater collected from a site in Baghdad, Iraq with naturally occurring ions in which Cd 2+ and TC were added to simulate contaminated groundwater. In column mode simulating PRB conditions, SA@LDH–Biochar showed breakthrough at 7 and 4 h, respectively. The application of the Bohart‐Adams and Thomas models showed high predictive performance, thus pointing to the potential use of the material in continuous‐flow groundwater remediation systems.