Synthesis of magnetic nZVI@biochar catalyst from acid precipitated black liquor and Fenton sludge and its application for Fenton-like removal of rhodamine B dye

Black liquor and Fenton sludge are common industrial wastes that come from the conventional kraft pulping process and the Fenton wastewater treatment process, respectively. In this study, the biochar-supported iron-based catalysts were synthesized through a simple one-step pyrolysis method using acid-precipitated black liquor (APBL) as carbon source and Fenton sludge as iron source, and were then applied for Fenton-like removal of rhodamine B (RhB) dyes. The optimized catalyst ([email protected]FAK), pyrolyzed at 900 ºC with KOH as the activator, was mesoporous biochar-supported nanoscale zero-valent iron (nZVI). Under the optimal conditions (50 mg L−1 RhB, initial pH 3, 2 mM H2O2 concentration, catalyst dosage of 0.2 g L−1), the [email protected]FAK/H2O2 system achieved almost 100% RhB dye removal within 10 min. Moreover, the [email protected]FAK/H2O2 system also exhibited excellent removal efficiencies for malachite green, crystal violet, and methylene blue. The [email protected]FAK had a good magnetic separation ability (146.4 emu g−1) and maintained a high removal efficiency of RhB (83.8%) in the presence of H2O2 after five times of recycling/reuse. The degradation of RhB dye was mainly attributed to •OH, including surface-bound •OH and free •OH. Besides the excellent catalytic ability and Fe(III) reduction ability of nZVI itself, the biochar supports with high specific surface area and mesoporous structure also played important roles in the removal of RhB dye, such as adsorbing RhB dyes, alleviating nZVI aggregation, and accelerating the reduction of Fe(III) to Fe(II).