Efficiency of Fe and Zn metal adsorption in post-tin mining water using Fe 3 O 4 /activated carbon composite coffee grounds waste

Abstract This study examined the adsorption efficiency of Fe and Zn metals from tin pond water using Fe 3 O 4 /activated carbon composites produced from used coffee grounds. The composite was synthesized through a coprecipitation method using two mass ratios of Fe 3 O 4 to activated carbon (M:AC = 1:1 and 1:2) and analyzed using FTIR, XRD, and SEM. FTIR confirmed the presence of Fe–O functional groups, whereas XRD showed characteristic magnetite diffraction peaks with sharper peaks at a 1:1 ratio, indicating better crystallinity. SEM analysis showed Fe 3 O 4 particles scattered on the surface of activated carbon with macro pores (0.1 µm). Adsorption tests showed that the 1:1 composite achieved a higher efficiency (Fe 3+ 80.7% and Zn 2+ 71.6%) than the 1:2 composite (Fe 3+ 75.8% and Zn 2+ 62%) at an optimal contact time of 60 min. When applied to real tin pond water, both composites reduced the Fe and Zn concentrations to below the ICP-OES detection limit, resulting in adsorption efficiencies of approximately 100%. These results highlight the potential of Fe 3 O 4 /activated carbon composites derived from waste as low-cost and effective adsorbents for heavy metals in mining waste.