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.
In the 21st century, an environmentally benign system is necessary for the environmental treatment and material resources that will ensure human survival. This paper describes a new water treatment system with electrolysis and magnetic separation. The system is composed of two different types of electrolysis reactors and a superconducting magnetic separation apparatus. The first iron electrolysis reactor produces iron phosphate and the paramagnetic iron hydroxide particles that absorb some organic compounds. These products are collected by the magnetic filter because of high-gradient magnetic separation. The second PbO2 electrolysis reactor treats the nitrogen and resultant organic compounds by electrochemical oxidation. This system has the following advantages in comparison with the conventional water treatment system that is a result of microbiology-and physical and chemical treatments: -no medicine, no secondary products, fast treatment, requires but small space, is easy to operate and is maintenance-free. This system was applied to on-site test for treating landfill water in the Tokyo Bay area for four months in 2001, from September to December. The flow rate of tested water is 100 liter per hour. The landfill water contains about 200 kinds of species; nitrogen, phospherous, organic compounds, bisphenol A, and others. The total removal efficiencies of this system are as follows; 88% for total phosphate, 77% for total nitrogen, and 62% for COD (chemical oxygen demand). These removal efficiencies are the same as or greater than those of the conventional landfill water treatment system. The results show the possibility of new water treatment system for treating landfill water.
We are developing a water processing system for the removal of arsenic from geothermal water. We adopt the coprecipitation method of Fe (III) hydroxide, in which As is adsorpted to the flocks of Fe (III) hydroxide, and the High Intensity and High Gradient Magnetic Separation (HIHGMS) by superconducting magnets to extract the flocks. We demonstrated that the method reduce arsenic to 0.015mg/L that closed to the environmental standard in Japan, from 3.4mg/L and we purified a large amount of water at high speed. We also describe an estimate of a feasible plant for removal of arsenic in the geothermal water for public use.
The abrasives have been recovered from the slurry wasted by the factory where the silicon wafers for solar batteries are processed. The separator has been designed and developed for a practical application of superconducting magnetic separation. The SiC abrasives to which iron fragments of the wire adhere were separated. The iron particles from the wire sawing machine were also separated. The abrasives were successfully separated, and the wasted slurry could be recovered.
A new method of oil separation from oil-contaminated seawater based on electromagnetic forces, the so-called MHD method was designed and performed. In comparison with a conventional method that uses magnetic powders, the MHD method has the advantages of making the treatment separated oil easy and of having little effect on the environment. An experimental apparatus, which consists of a 10-T class superconducting magnet, a separation cell, a seawater tank, and flowing systems was constructed. When high polymer particles were used instead of oil, the separation ratio (the mass of simulation particles separated/the total mass of simulation particles) for the sample fluid was measured as a function of electric current, magnetic field, and seawater velocity. The agreement between experimental values and calculated values based on a simple model was qualitatively satisfactory.