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

Abstract

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 5.5T, respectively. The TP removal rate increased by 21.9% when the magnetic gradient increased from 6×103 to 15×103 at 5.5T. The magnetic susceptibility of flocs in 1.0-T HGMS effluents was 1.5emu/g, and saturation magnetization was not observed at 5.0T. 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 1.0T to 5.5T captured more ferric precipitates, which subsequently improved the TP removal efficiency.