Green and sustainable synthesis of magnetite from copper slag via citrate complexation for methylene blue dye removal from water

Abstract This study proposes a novel, green, and sustainable method for synthesizing magnetic iron oxides from metallurgical copper slag (CS), leveraging its iron content as a valuable resource. Iron was extracted via acid leaching using edible citric acid (ECA), forming a citrate–iron complex (CSL), which was subsequently thermally decomposed at 300°C to yield CSL300. Characterization revealed that approximately 58% of the iron was successfully recovered. Fourier transform infrared spectrophotometry (FT‐IR) and X‐ray diffraction (XRD) analyses confirmed the formation of low‐crystallinity magnetite (Fe 3 O 4 ), with a notably high surface area of 123.3 m 2 /g. The CSL300 material was evaluated for methylene blue (MB) dye removal under various conditions—as an adsorbent, catalyst, and photocatalyst. Kinetic studies indicated that MB removal followed a pseudo‐second‐order model, with adsorption on the magnetite surface as the dominant mechanism (50% removal efficiency) at 120 min of contact time. Under optimal conditions, the Cl‐CSL300‐UV system achieved 95% MB removal, outperforming all other tested configurations. CSL300 exhibited comparable performance to magnetite synthesized from analytical‐grade reagents, but at significantly lower cost, offering a sustainable and economically viable solution aligned with circular economy principles for wastewater treatment.