Abstract
In this study, to resolve the formation of manganese ions (Mn2+) and radical products of the 1-napthol removal reaction via birnessite, humin was oxidized in a potassium permanganate solution to synthesize humin–manganese oxides (Ox–Hu/δ-MnO2). Experiments were performed to compare the radical products and 1-napthol removal efficiencies of Ox–Hu/δ-MnO2 with different humin ratios (250–1000 mg), Ox–Hu, and δ-MnO2. In the 12.5 mg loading/batch experiment, the 1-napthol reaction rate constant (k1 = 0.12) was over three times higher for Ox–Hu/δ-MnO2 (250 mg) than for Ox–Hu/δ-MnO2 (500–1000 mg) and the absorbed Mn2+ was effectively eluted in the reacted solution (Mn2+ < 0.025 mg/L). High-performance liquid chromatography results of extracted mediator reaction products revealed that most of the 1-napthol and polymer reaction products (e.g, 1,4-napthoquinon) were recovered from Ox–Hu and δ-MnO2 but not from Ox–Hu/δ-MnO2, confirming that the residues were strongly bound in Ox–Hu/δ-MnO2. Therefore, Ox–Hu/δ-MnO2 enhanced the 1-napthol removal efficiency via the δ-MnO2 mediated oxidation coupling reaction and by irreversible sorption to humin. In this study, the stability of bound residues contributes significantly to the proposed method by disposing mediators after the treatment.
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