Magnetic separation methods

Before sulphide flotation, magnetite was removed using a low-intensity magnetic separation method. 

Chemical composition Chemical composition of the liquid phase affects separability of the particles. Electrical conductivity may determine suitability of electrically assisted separation processes. Paramagnetism may prevent use of high intensity magnetic separation methods. 

The treatments used to recover nickel from its sulfide and lateritic ores differ considerably because of the differing physical characteristics of the two ore types. The sulfide ores, in which the nickel, iron, and copper occur in a physical mixture as distinct minerals, are amenable to initial concentration by mechanical methods, eg, flotation (qv) and magnetic separation (see SEPARATION,MAGNETIC). The lateritic ores are not susceptible to these physical processes of beneficiation, and chemical means must be used to extract the nickel. The nickel concentration processes that have been developed are not as effective for the lateritic ores as for the sulfide ores (see also Metallurgy, extractive Minerals recovery and processing). 

Scrap from municipal refuse may be in the form of source-separated steel cans, a mixed ferrous fraction, metal magnetically separated from mixed waste or incinerator ash, and C D debris. An ASTM specification (E1134-86) was developed in 1991 for source-separated steel cans. The Steel Recycling Institute has a descriptive steel can specification entitled "Steel Can Scrap Specifications". PubHshed standards for municipal ferrous scrap also include ASTM E701-80, which defines chemical and physical test methods, and ASTM E702-85 which covers the chemical and physical requirements of ferrous scrap for several scrap-consurning industries. 

Solids separation based on density loses its effectiveness as the particle size decreases. For particles below 100 microns, separation methods make use of differences in the magnetic susceptibility (magnetic separation), elec trical conductivity (electrostatic separation), and in the surface wettability (flotation and selec tive flocculation). Treatment of ultrafine solids, say smaller than 10 microns can also be achieved by utilizing differences in dielectric and electrophoretic properties of the particles. 

Solenoid magnetic separators are designed for batch-type, cyclic, and continuous operation. Devices which can use matrices of expanded metal, grooved plates, steel balls, or filamentaiy metals have been designed. Continuous separators with capacities to 600 t/h for iron ores (similar to the Brazilian hematite) are commercially available (Sala International Inc.). Selection of the method of operation is apphcation-dependent, being based on variables such as temperature, pressure, volume of magnetics in the feed, etc. 

If the ore consists of separate grains containing the desired material, it can be separated from undesired minerals by physical methods such as flotation, sedimentation, or magnetic separation. For metals this step can lead to 80 to 95 percent concentration of the value of the ore. Ceramic raw materials such as sand and clay can often be found pure enough in nature so that no concentration is needed. 

Other purification methods include a liquid phase chromatography, electrophoretic separation by mass spectroscopy, separation using magnetic properties, and so on. These separation methods are limited only for the metal nanoparticles having a special property useful for these purification methods. 

All minerals in some way or the other are influenced by an external magnetic field although the degree of this response varies widely. Based on different response of different minerals in external magnetic field minerals have been classified into different groups that have essentially to development of an important physical separation method called magnetic separation which has been described quite in detail in the next chapter on mineral processing. Present topic is, therefore, not pursued any further. 

The combination of physical and chemical characteristics of nodules make impossible the application of methods of physical beneficiation such as flotation and magnetic separation to produce concentrates of valuable metals, and so chemical processing must be used. Their processing also tends to be much more energy-intensive, vis-a-vis that of conventional land-based ores. Deep-sea manganese nodules are quite unlike any terrestrial ores, both with respect to their physical characteristics and to their mineralogical and chemical compositions new processes are, therefore, required. 

When ores are mineralized in such a way that discrete grains of valuable minerals are contained in a matrix of gangue minerals, physical concentration methods such as flotation, gravity separation, and magnetic separation can yield valuable mineral concentrates with recoveries in the range of 80 to 95% of the value in the ore. However, there are important ore types in which the nature of mineralization is not amenable to physical concentration, and so primary processing by chemical means is necessary. 

Rikers, R.A., Rem, P. and Dalmijn, W.L., Improved method for prediction of heavy metal recoveries from soil using high intensity magnetic separation (HIMS), Int. J. Miner. Process., 54, 165-182,... 

The methods developed by EBC and others in the late 1990s using hydrocyclones and phase-inversion techniques may be sufficient for separation of the treated oil from the aqueous phase and biocatalyst. However, a cost analysis of such methods may be necessary to determine the economic feasibility. Recent work using hydrophobic membranes, magnetically separable immobilized biocatalysts and other techniques may provide alternate methods for separation of oil and recycling biocatalyst. A comparison of these techniques with each other and the previously investigated hydrocyclone techniques is needed to demonstrate improvements in the separation efficiency. 

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