Magnetic separation and recovery of powder particles from water using Fe3O4@CTS-BDAT

A novel magnetic separation method has been developed to efficiently separate and recover powder particles used in water or wastewater treatment processes. The magnetic composites were prepared through the grafting of 2,4-bis(dimethylamino)-6-chloro-(1,3,5)-triazine (BDAT), chitosan (CTS), and SiO₂ onto the Fe₃O₄ surface, obtaining Fe₃O₄@BDAT, Fe₃O₄@CTS, Fe₃O₄@CTS-BDAT, Fe₃O₄@SiO₂@BDAT, and Fe₃O₄@SiO₂@CTS-BDAT. g-C₃N₄, Ni/Fe-PAC, and La/Al-BTC were chosen as the target particles. Results showed that Fe₃O₄@CTS-BDAT exhibited the best separation performance, achieving efficiencies of 98.3 %, 97.2 %, and 99.1 % for the three target particles, respectively. These high efficiencies were maintained over a broad pH range (3.0–11.0) and initial target particle concentrations (50–5000 mg/L). The target particles could be detached from the magnetic aggregates using an electromagnetic field, with efficiencies exceeding 75.3 %. Characterization using SEM, XPS, and FTIR revealed that Fe₃O₄@CTS-BDAT possessed a microsphere cluster structure, with a saturation magnetization of 64.02 emu/g, a point of zero charge (pH_PZC) of 7.7, and a d₅₀ value of 3.56 μm. Microscopic image analysis displayed that fluid kinetic energy and magnetic dipole force facilitated the formation of magnetic aggregates during the stirring stage. The size of these aggregates increased from 2–10 to 15–30 μm during stirring and further expanded to 18–37 μm during the separation stage. Particle image velocimetry (PIV) analysis indicated that the magnetic aggregates migrated towards the magnet via eddy currents, with maximum velocity from 0.532 to 1.412 m/s. DLVO and MDLVO models revealed that the magnetic interaction energy of Fe₃O₄@CTS-BDAT was sufficient to surpass electrostatic repulsion, thereby enabling efficient capture and separation of target particles.