Treatment of Acid Mine Wastewater Using Sludge Based Biochar Particles Pyrolyzed at Different Temperatures

<p indent="0mm"> Sewage sludge biochar particles (SBP) were prepared by pyrolysis at 350 °C and 500 °C under anoxic conditions, resulting in SBP350 and SBP500. The differences in physicochemical properties between SBP350 and SBP500 were characterized using infrared spectroscopy, X-ray diffraction, specific surface area and pore size analysis, elemental analysis, and scanning electron microscopy . Dynamic adsorption experiments were performed to investigate the purification effects of SBP prepared at different pyrolysis temperatures on simulated acid mine drainage. The results show that after SBP treatment, the acidic wastewater pH increased to between 5.5 and 8.5. Due to competitive adsorption among metals, the removal efficiency of heavy metals from the acidic wastewater by SBP followed the order of Fe&gt;Cu&gt;Zn&gt;Cd&gt;Ni. The average removal rates of Fe, Cu, Zn, and Cd were all above 90%, reflecting good performance, while the average removal rates of Ni and SO₄^2– were below 50%. The trend of Cu, Zn, Cd and Ni removal with effluent time was similar to pH,whereas SO₄^2– showed an opposite trend to pH. Accordingly, pyrolysis temperature affects the physicochemical properties of SBPs. Compared to SBP350, SBP500 exhibited stronger alkalinity and aromaticity, higher ash content and zero potential, larger pore size and specific surface area, as well as more complex pore structure. Consequently, SBP500 demonstrated better purification performance for simulated acid mine drainage than SBP350.