Adsorption performance and mechanism of lake sludge-derived ball milling biochar loaded with Fe3O4 on Cd(II) in aqueous solution

In this paper, air-dried lake sludge was pretreated by ball milling, and then pyrolysed at 600°C to prepare lake sludge-derived ball milling biochar, and Fe3O4 was loaded on lake sludge-derived ball milling biochar by chemical precipitation. Scanning electron microscopy-energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction were used to investigate and characterize the adsorbents. The results demonstrated that ball mill pretreatment and Fe3O4-loaded can effectively increase the content of O-containing groups in the adsorbent. The batch adsorption experiments revealed that Cd(II) removal followed the pseudo-second- order kinetic model and the Langmuir model. Additionally, the Cd(II) maximum adsorption by biochar (BC), MBBC and Fe3O4@MBBC was 31.33, 47.36 and 92.42 mg/g, respectively. The Cd(II) removal mechanisms were complexation, ion exchange, co-precipitation and electrostatic interaction. The Cd(II) removal efficiency on Fe3O4@MBBC was maintained at 91.35% after 5 adsorption– desorption experiments, indicating that Fe3O4@MBBC had the ability to be better applied for the removal of Cd(II)-containing wastewater.