Iron-biochar production from oily sludge pyrolysis and its application for organic dyes removal

In this study, a single-step pyrolysis approach was developed to directly convert oily sludge (OS) with high iron content into a magnetic iron-char catalyst for organic dyes removal. Magnetic iron-char catalysts were employed to degrade crystal violet (CV), methylene blue (MB), and sunset yellow (SY). The OC800 iron-char catalyst prepared from OS was not only rich in iron (mainly stable Fe₃O₄), but also showed favorable pore structures. Effects of operation parameters like temperature, H₂O₂ dosage, and pH on dye removal based on Fenton degradation were examined. In OC800 Fenton system (0.5 mL H₂O₂, 500 mg/L dye concentration, and pH = 2 in 50 mL solution), the maximum dye removal capacities of SY, CV, and MB were 83.61, 639.19, and 414.25 mg/g, respectively. In dyes degradation experiments, the prepared catalyst could be reused (more than 3 successive cycles) due to higher stability and less leaching of iron. One-step pyrolysis of OS with high iron content thereby represents a promising approach to transform sludge waste to functional biochar that removes hazardous dyes.