Preparation of an Iron–Carbon Microelectrolysis Filler Based on Red Mud/Coal Gangue and Its Application for the Treatment of Electroplating Wastewater

Abstract Microelectrolysis fillers experience caking during operation, posing challenges such as reduced activity and increased treatment costs during long-term use. Concurrently, solid waste generation continues to escalate alongside rapid industrial expansion. The accumulation of substantial solid waste not only consumes valuable land resources but also poses severe threats to the ecological environment. Against this backdrop, this study employs solid wastes (red mud and coal gangue) alongside activated carbon powder as raw materials. Through a process of mixing, granulation, and high-temperature sintering, a novel iron–carbon filler is developed for removing chemical oxygen demand (COD), Ni2+, and Zn2+ from simulated electroplating wastewater. Results indicate that under the specified preparation conditions (calcination temperature 1100 °C, calcination time of 45 min, 40% gangue content, and a red mud-to-carbon powder ratio of 3:1), and under treatment conditions (500 g/L filler dosage, 8 h reaction time, 150 rpm oscillation speed, and initial pH of 3), the filler achieved optimal treatment performance through multiple mechanisms including redox reactions, adsorption-flocculation, coprecipitation, and Fenton-like reactions. Under these conditions, the removal efficiencies for COD, Ni2+, and Zn2+ in simulated electroplating wastewater reached 70.58%, 98.38%, and 97.43%, respectively. Elemental composition and chemical state analysis revealed the filler primarily comprised five elements: Fe, O, C, Si, and Al, with Fe present as Fe(III), Fe(II), and Fe(0). Microscopic morphology and elemental analysis reveal a uniform microstructure with rational elemental distribution, demonstrating excellent resistance to caking. Cyclic experiments indicate that after being reused for 10 times, the removal rates of COD, Ni2+, and Zn2+ still remain at 60.51%, 94.28%, and 93.51%, exhibiting favorable reusability and stability. After regeneration with 1 mol/L sulfuric acid combined with ultrasonic cleaning, the treatment performance of the filler is almost restored with only a slight decrease, which demonstrates outstanding regeneration capacity and applicability for continuous wastewater treatment. Long-term service causes the consumption of Fe(0) and gradual activity decay of the filler, and timely supplementation or replacement of the filler is required in practical application. This study presents a novel process for preparing iron–carbon microelectrolysis fillers using solid waste, exhibiting treatment efficacy slightly superior to commercial fillers. It achieves the objective of treating waste with waste, possessing considerable economic value.