Action characteristics and mechanism of Salix wood powder-based high-efficiency adsorption materials on Fe(II) and Mn(II) in coal mine wastewater

In response to the problem of acidic coal mine wastewater containing high concentrations of iron and manganese ions, Salix wood powder was used as the main raw material, following the principle of extraction and reuse of agricultural and forestry waste, the delignified wood powder (DWF) was obtained after the treatment with NaOH, Na₂SO₃ and other solutions. Through microwave assisted in-situ synthesis, an adsorbent (AA-DWF-PAM) for Fe(II) and Mn(II) in coal mine wastewater was prepared. The microstructure, reaction mechanism and thermal stability of the product were analyzed by scanning electron microscopy (SEM), N₂ adsorption desorption, Fourier transform infrared spectroscopy (FTIR) and infrared thermogravimetry (TG-FTIR). The optimal adsorption conditions, adsorption kinetics and adsorption isotherms of AA-DWF-PAM were discussed. The adsorption characteristics and adsorption mechanism of AA-DWF-PAM for Fe(II) and Mn(II) were studied. The characterization experiment results show that the AA-DWF-PAM has many holes and presents a network structure, and the BET specific surface area is 150.83 m²/g, indicating that the modified adsorbent has a large specific surface area, which can provide more sites and spaces for the adsorption of Fe(II) and Mn(II). In addition, the gaseous products of AA-DWF-PAM pyrolysis mainly include H₂O, CO₂ and a small amount of CO, with high pyrolysis temperature and strong structural stability. The experimental study on adsorption characteristics shows that the best adsorption conditions for the AA-DWF-PAM are determined as follows: the AA-DWF-PAM dosage is 4 g/L, solution pH=4, and adsorption time is 200 min. According to the calculation, the AA-DWF-PAM is closer to the pseudo second order kinetic hypothesis, the main control process of adsorption is a chemical process, and the adsorption process is more consistent with the single-layer molecular adsorption of Langmuir equation. The theoretical maximum adsorption capacities of Fe(II) and Mn(II) are 192.29 mg/g and 123.65 mg/g respectively. According to the molecular simulation and quantum chemical calculation of the modified adsorption process in Materials Studio, the —NH₂, —COOH and —OH functional groups play an electrostatic adsorption role in the adsorption process. Therefore, the rational utilization of agricultural and forestry waste provides a new approach for the treatment of acidic coal mine wastewater. The developed AA-DWF-PAM adsorbent can effectively treat iron and manganese ions in the acidic coal mine wastewater.