Extraction and characterization of humic acid with high bio-activity by mechanical catalytic treatment

In order to extract humic acid (HA) with high quality from industrial waste weathered coal. The catalyst oxidation for preparation of HA is an environment-friendly and value-added strategy. A green catalyst of α-MnO2/kaolinite (α-MnO2/Kln) was prepared for oxidizing weathered coal for conversion to HA. The effects of ball-milling and catalysis for HA were studied. The catalysts contain oxygen vacancies and lower average oxidation state (3.55), which facilitates the oxidation reaction. Compared to untreated weathered coal HA (WHA), the yield of ball-milling and catalyst treated weathered coal HA (BC/WHA) increased by 18.67%. The catalyst treated weathered coal HA (C/WHA) and BC/WHA displayed better quality, including higher oxygen content (29.90% and 28.68%), increased O/C ratio (0.52 and 0.52), and higher total acidic groups (7.88 and 7.64 meq/g) than those of WHA (25.43%, 0.44, 6.46 meq/g, respectively). The small-molecule fatty acid (79.07%) of C/WHA was obviously higher than that of WHA (66.03%). The active substance of sterols content (19.95%) of BC/WHA increased significantly. These proved the bio-activity of C/WHA and BC/WHA was improved, and α-MnO2/Kln played an effective catalytic oxidation. Overall, BC/WHA has high extraction yield and enhanced bio-activity, making it highly HA output efficient and suitable for agricultural applications.