Recent progress in magnet technology has enabled the realization of economically and operationally favorable superconducting magnets. Consequently, this has made it possible to utilize high-intensity magnetic fields occupying a large volume with very small electric power consumption in much broader areas of science and technology than in the past. Magnetic separation is a promising application because it can separate (or purify) a large quantity of dilute suspension at high speed; it is repeatedly usable, and is recognized as a secondary-waste-free technology that will contribute significantly to the preservation of global environment. This introductory article discusses some of the fundamental characteristics of magnetic separation and the recent R & D activities from the viewpoint of an industrial application of superconducting magnets.
Magnetic seeding processes were reviewed and classified from the viewpoint of interface chemistry and colloid chemistry. The description of the fundamental chemical processes of magnetic seeding was made to relate the modern seeding processes to traditional ones, such as ferrite, coprecipitation and flocculation. The processes developed in 1970s were found to provide a clue to develop a new method of magnetic seeding processes.
Magnetic separation is a method to separate and capture fine magnetic particles by the magnetic force acting on the particles in a gradient magnetic field. For the practical use of the magnetic separation, it is necessary to remove the captured particles from the separation area where the magnetic force is active. High gradient magnetic separation utilizes the high spatial magnetic field gradient generated in the matrix of fine ferromagnetic wires (filter matrix) magnetized by an applied magnetic field. In batch-type magnetic separation, the filter matrix is washed by water flushing and by reducing the applied magnetic field to remove the captured particles in the filter matrix. When the particle content in the slurry is large, the short cycle of the water flushing of the filter matrix results in a decrease in separation efficiency. The frequent interruption of the separation process for the flushing is a problem for the practical magnetic separator. Therefore, from the viewpoint of the practical application of magnetic separation, a continuous separation process without interruption for the flushing is useful. In this paper, recently developed magnetic separators for continuous process are reviewed, and their mechanism is explained.