Effect of Chemical State of Dispersed Phase on Magnetic Filtration Efficiency

• Published in: Separation science and technology 2004-09, Vol.39 (12), p.2827-2838
• Main Authors: Sato, Soichi, Mitsuhashi, Kazunari, Ohara, Takeshi
• Format: Article
• Language: English
• Subjects: Chemical state; High-gradient magnetic field; Salt concentration; Zeta potential
• ISSN: 0149-6395; 1520-5754
• DOI: 10.1081/SS-200028783

Magnetic filtration is a technology that uses magnetic forces to remove particles from a suspension of dispersed particles. The magnetic force occurs either because of the difference of magnetic susceptibility between the medium and the dispersed particles, and/or the difference of magnetic susceptibilities between particles composed of different materials. There is a small effect of the chemical state of the medium on magnetic filtration efficiency for filtrating ferromagnetic and/or strongly magnetizable paramagnetic materials, such as Fe 3 O 4 . In contrast, however, we showed that the chemical state affects the magnetic filtration efficiency when separating paramagnetic materials from each other, and that controlling the chemical state is important for controlling magnetic filtration processes. We demonstrated this by measuring the magnetic filtration efficiency for a weakly magnetizable paramagnetic Eu 2 O 3 powder dispersed into solutions with varying salt concentration and pH, both of which affect the zeta potential of dispersed particles. We measured the filtration efficiency for a 0.8 Tesla magnetic field applied to a magnetic filter. Our experimental results indicate that the filtration efficiency increased for decreasing zeta potential. When zeta potentials of Eu 2 O 3 powder are 30 and 0 mV, the collection efficiency was 30% and 38%, respectively. This occurs because the repulsion force decreases for decreasing zeta potential, and at low zeta potentials the electrical repulsion forces are sufficiently weak so that particles can approach each other without hindrance by the electric force. Lower zeta potential also allows particles to agglomerate and grow. Larger particles are more easily removed by the filter, thereby increasing the filtration efficiency.