Hydrothermal Conversion of Sn-Bearing Sludge into Fe/S Rods for Efficient Heavy Metal Removal in Wastewater

Hydrothermal conversion is an effective strategy to transform heavy metals in electroplating sludge into catalytic materials and use them to treat electroplating wastewater. This study presents a one-step hydrothermal method for converting Sn-bearing sludge, containing 23.41% Sn, 52.12% Fe, and other impurities, into Fe/S rods using a NaOH/Na2S solution. The resulting Fe/S rods, with a diameter of 50–100 nm and length of 0.5–2.5 μm, showed excellent performance in wastewater treatment. In the presence of 50 mg/L EDTA, the Fe/S rods removed 22.9% of Ni, 30.2% of Cu, and 41.5% of Zn. When activated with PMS, the removal efficiencies increased significantly to 68.9%, 90.9%, and 91.6% for Ni, Cu, and Zn, respectively. The optimal rod dosage (1 g/L) achieved removal efficiencies of 94.2%, 78.5%, and 99.7% for Cu, Ni, and Zn, while increasing PMS dosage led to nearly 100% removal within 60 min. Additionally, the process allowed for the complete recycling of the alkaline solution, with regenerated rods showing similar performance to the original ones in wastewater treatment. This method offers an efficient and sustainable approach to sludge resource utilization and heavy metal removal from wastewater.