The advantages of a superconducting magnetic intensity greater than 1 T for phosphate-ferric flocs separation in HGMS

High-gradient magnetic separation (HGMS) is widely used for water treatment. However, the effects of high magnetic intensities on removing magnetized flocs are unclear. In this study, separating phosphate-ferric flocs via HGMS at different magnetic intensities and gradients were evaluated. The TP removal efficiencies in the 5% #1 steel wool matrix were 65.1%, 82.1%, 89.1%, and 97.5% when the magnetic intensity was 0, 1.0, 3.5 and 5.5 T, respectively. The TP removal rate increased by 21.9% when the magnetic gradient increased from 6 × 10³ to 15 × 10³ at 5.5 T. The magnetic susceptibility of flocs in 1.0-T HGMS effluents was 1.5 emu/g, and saturation magnetization was not observed at 5.0 T. The volume mean particle size D(4, 3) of the phosphate-ferric flocs decreased as the magnetic intensity increased. Magnetite was the primary mineral phase in the 0-T HGMS effluents, whereas no mature crystals were detected in the 1.0-T HGMS effluents. Microanalysis showed that magnetite particles in phosphate-ferric flocs were captured by the steel wool matrix by the magnetic force. It is expected that some of the phosphate-ferric flocs will break into magnetite and ferric precipitates. Increasing the magnetic intensity from 1.0 T to 5.5 T captured more ferric precipitates, which subsequently improved the TP removal efficiency.