This article reviews the current status and recent progress of magnetic separation technologies using superconducting magnets and conventional magnets. In this article, firstly, the research and development history of magnetic separation technologies is reviewed. Secondly, the main component technologies for magnetic separation, such as options for magnetic separation methods, magnet devices as magnetic-field generators, magnetic seeding methods, magnetic filters and magnetic separation methods utilizing the Magneto-Archimedes effect, are summarized. Thirdly, the contents of presentations at the CSJ and CSSJ conferences held from 2006-2018 are summarized. Based on this summary, the status quo of the research and development of magnetic separation technologies in Japan is analyzed. It is confirmed that the component technologies for magnetic separation have advanced well and many new applications of magnetic separation using superconducting magnets have been developing. It is worth noting that the magnetic separation method removing radioactive Cs from contaminated soil using a superconducting magnet has been developed. In China and Korea, the research and development of magnetic separation technologies have continued as well. Particularly in China, there is much interest in magnetic separation since the environmental pollution that has become apparent with economic development has become serious. Through the technical review in this article, it is found that recent magnetic separation technologies have advanced to the level where social implementation is possible. Sustainable Development Goals (SDGs) and promotion of sustainable economies are the tailwinds for spreading magnetic separation with superconducting technology because of contributions to the environment, materials recycling, CO2 emission reduction, cost reduction and innovation.
To improve a biological wastewater process, magnetic separation was applied to a biological wastewater treatment process. An aerobic biological wastewater treatment process utilizing magnetic activated sludge (MAS) was introduced to simplify process operations, as well as to enable excess sludge production to be controlled. Standard bench-scale experimental equipment and a few mobile pilot plants for the MAS process have been developed in the past few years. After developing a full-scale magnetic separator with a typical MAS suspension separation capacity of 200 m3d-1, it became possible to design a full-scale plant and estimate the initial cost. It has been estimated that the total cost of the process (i.e., initial setup and operation) will result in savings, being less than that required for the conventional activated sludge process. It is possible that a new field of superconductive magnet applications can be developed if the MAS process is applied for large-scale wastewater treatment processes such as municipal sewage treatment.
Three kinds of magnetic separation technique utilized to recycle nickel from the waste fluid of electroless plating processes are introduced in the article, with reference made to HTS bulk magnet systems activated by pulsed-field magnetization and field cooling methods. Actual magnetic separation experiments were conducted using Ni-based coprecipitated slurry, thermally-docomposed Ni-P metallic particles, and coarse NiSO4 crystals in the regenerated fluid from Nickel phosphite slurry, which were all processed from the Ni-plating waste. Through the investigations, the author refers to the feasibility of practical recycling of Ni as a rare metal with the use of HTS bulk magnets generating intense magnetic fields of 2-4 T.
An investigation as to whether or not superconducting high-gradient magnetic separation is capable of reducing the volume of cesium in contaminated soil is reviewed. This unique physical method can selectively remove paramagnetic 2:1-type clay minerals that strongly trap cesium inside the interlaminar site from soil suspensions. However, there are technical issues, such as wide particle size distribution and particle aggregation. To solve these problems, advanced pretreatments of advanced classification and alkaline dispersion treatments were performed, and the radioactivity concentration reduction rate was successfully increased. Based on the results, issues for practical application were discussed.
The development of magnetic separation systems for thermal power plants, including our recent studies, are reviewed. The magnetic separation systems reduce the scale in boiler feed water in thermal power plants and maintain energy conversion efficiency at a high level, reducing the amount of carbon dioxide discharged from thermal power plants.
The magneto-Archimedes effect is a technique to enhance the effect of the magnetic force acting on materials by considering the influence of the surrounding medium. Application of this technique as a way of materials separation is known as the magneto-Archimedes separation. The magneto-Archimedes separation enables the separation of many different materials into each component based on the differences in their magnetic susceptibilities and densities irrespective of the particle size. In this topical review, the principle of the magneto-Archimedes effect and its application as a way to separate materials are described and some other examples applying the magneto-Archimedes effect are introduced.
In order to efficiently collect used phosphors containing rare earths, an attempt was made to concentrate the phosphors. The technique used was a combination of high-gradient magnetic separation and the magneto-Archimedes’ method. Each phosphor was fractionated and concentrated from waste phosphors. LAP that emits green light is fractionated using highgradient magnetic separation and YOX that emits red light was fractionated using the magneto-Archimedes' method. Concentrations of 5.5 and 1.9 times were achieved, respectively.
A physico-chemical process combined with electrocoagulation using iron electrodes, high gradient magnetic separation and electrochemical oxidation was investigated for human wastewater treatment using a bench scale system. Magnetically-seeded suspended solids and phosphorus in human wastewater were removed effectively at a flow rate of 100 L/h applying magnetic separation using a magnetic filter at 10 T. The electrochemical oxidation process reduced ammonium nitrogen (NH4-N) and chemical oxygen demand (COD) in effluent from the magnetic filter at a flow rate of 15 L/h. The results indicate that this physico-chemical process is effective treating human wastewater.