Low-intensity separators are used to treat ferromagnetic materials and some highly paramagnetic minerals.Minerals with ferromagnetic properties have high susceptibility at low applied field strengths and can therefore be concentrated in low intensity (<~0.3T) magnetic separators. For low-intensity drum separators used in the iron ore industry, the standard field, for a separator with ferrite-based magnets, is 0.12 T at a distance of 50 mm from the drum surface. Work has also shown that such separators have maximum field strengths on the drum surface of less than 0.3 T. The principal ferromagnetic mineral concentrated in mineral processing is magnetite (Fe3O4). although hematite (Fe2O3) and siderite Fe2CO3 can be roasted to produce magnetite and hence give good separation in low-intensity machines.
Permanent magnetic drum separators combine the attributes of a high-strength permanent magnetic field and a self-cleaning feature. These separators are effective in treating process streams containing a high percentage of magnetics and can produce a clean magnetic or non-magnetic product. The magnetic drum separator consists of a stationary, shaft-mounted magnetic circuit completely enclosed by a rotating drum. The magnetic circuit is typically comprised of several magnetic poles that span an arc of 120 degrees. When material is introduced to the revolving drum shell (concurrent at the 12 oclock position), the non-magnetic material discharges in a natural trajectory. The magnetic material is attracted to the drum shell by the magnetic circuit and is rotated out of the non-magnetic particle stream. The magnetic material discharges from the drum shell when it is rotated out of the magnetic field.
Permanent magnetic drum separators have undergone significant technological advancements in recent years. The magnetic circuit may consist of one of several designs depending on the application. Circuit design variations include:
The standard magnetic drum configuration consists of series of axial poles configured with an alternating polarity. This type of drum is simple in design and can be effective for low-intensity applications such as the recovery of ferrous metals and magnetite. This configuration typically does not provide a sufficient field strength or gradient for the recovery of paramagnetic minerals at high capacities. A typical axial circuit is shown in Figure 3.
The high-gradient element, as the name implies, is designed to produce a very high field gradient and subsequently a high attractive force. Several identical agitating magnetic poles comprise the element. The poles are placed together minimizing the intervening air gap to produce the high surface gradient. Due to the high gradient, the attractive force is strongest closer to the drum making it most effective when utilized with a relatively low material burden depth on the drum surface and, thus, a lower unit capacity. A high-gradient magnetic circuit is shown in Figure 4.
The interpole-style element utilizes a true bucking magnetic pole or interpole between each main pole. The magnetic field of the bucking element is configured to oppose both of the adjacent main poles resulting in a greater projection of the magnetic field. As a result, the interpole circuit allows for a relatively high material burden depth on the drum surface and thus higher unit capacity or improved separation efficiency. An interpole magnetic circuit configuration is shown in Figure 5.
A second interpole configuration consists of steel pole pieces placed between the magnetic poles. This is commonly termed a salient-pole element. The steel interpoles concentrate the magnetic flux providing a very high magnetic gradient at the drum surface. The magnetic field configuration is similar to the high- gradient type element but with an intensified surface gradient. This configuration offers the strongest field projection of any of the previously described circuits. The salient-pole circuit design is shown in Figure 6.
The magnetic elements described above are axial elements. The magnetic poles run across the width of the drum and are of alternating polarity. Magnetic elements are typically assembled with a minimum of five magnetic poles that span an arc of 110 degrees. (For all practical purposes, an arc of only 80 degrees is required to impart a separation. Non-magnetic particles usually leave the drum surface with a natural trajectory at a point of 60 to 70 degrees from top dead center dependent on the drum speed, particle size, and specific gravity.) The poles have alternating polarity to provide agitation to the magnetic components as they are transferred out of the stream of the non-magnetics. A magnetic particle will tend to rotate 180 degrees as it moves across each pole. This agitation is functional in releasing physically entrapped non-magnetics from the bed of magnetics. Agitating magnetic drums are most effective in collecting fine particles or where the feed contains a high magnetics content.
Dense-medium circuits have been installed in many mineral treatment plants since its original development about thirty years ago. In the intervening period the process has been thoroughly evaluated and many innovations have been introduced. The Heavy Density Cyclone is one of the newer systems which has extended the operating range of this process to 65 mesh size.
Medium recovery is obviously important since any loss is a direct cost against production. In coarse coal dense-medium plants a loss of 1 pound of magnetite per ton is usually acceptable but reduction to pound per ton as has been obtained in some plants.
Efficient cleaning maintains fluidity in the bath and increases sharpness of the coal-waste separation. Most dense-medium systems will tolerate some non-magnetic dilution of the bath but the magnetic separator must be capable of keeping this within workable limits, particularly on difficult coals. In some plants a partial bleed of the operating dense-medium bath is maintained through the magnetic separator to keep it clean.
Operating gravities of dense-medium coal plants are usually low enough so that a straight magnetite bath can be used. The return of a magnetic separator concentrate having 50% or more solids will maintain gravity without need for a thickening device. The use of a drum wiper has permitted the return of a 70% solids concentrate back to the separatory vessel. Operation at a high solids concentrate discharge is recommended since medium cleaning is improved. The colloidal slimes carried over with water are more completely rejected at high solids discharge.
Several types of magnetic separators have been used in magnetic medium recovery.The first magnetic drum separators were electro magnetic types but the development of efficient wet permanent drum separators has resulted in nearly universal acceptance of permanent drums in new plants.
The basic construction of each drum is the same. It consists of a stationary magnet assembly held in a fixed operating position by clamp bearings mounted on the separator support frame. An outer rotating cylinder driven through a sprocket bolted to one of the drum heads carries the magnetic material to the magnetic discharge point.
Normally, extreme cleanliness of the magnetic concentrate is not of prime importance in dense-medium plants but this can be a factor in some coals that separate with difficulty. The concurrent tank, reduced separator loading and in some instances dilution of the feed pulp will improve magnetic cleaning. Recleaning of a primary concentrate would improve cleaning but has not been used in commercial plants.
Hematite processis a common solution for hematite ore which is an important raw material for the metallurgy departments of steel production, due to Hematite has a certain magnetism, so hematite flotation and separation is commonly used in hematite processand enrichment.Magnetic separationin anhydrous media participation can be divided into dry magnetic separation and wet magnetic separation when process and separate hematite, hematite ore process dry magnetic separation equipment mainly is a magnetic roller, the layout of eccentric rotating magnetic field dry separation machine etc. Hematite ore wet process equipment mainly are downstream type permanent magnetic drum magnetic separator, counter flow type permanent magnetic cylinder type magnetic sorting machine, semi counter current type permanent magnetic drum magnetic separator, vertical ring pulsating high gradient magnetic separator etc., and the vertical ring pulsating high gradient magnetic separator has characteristics like stable operation, high enrichment ratio, and high recovery rate. Here is a brief introduction.
The vertical ring pulsating high gradient magnetic separation device is widely used in thehematite separation process. At present, it is a kind of advanced equipment for hematite process. The magnetic separation equipment swivel adopts vertical arrangement and swivels mounted inside the stainless steel bar, and during the hematite process, swivel does clockwise direction select along the counter. The internal magnetic medium in the swivel occurs magnetization under the action of a magnetic field and on its surface can produce the large gradient magnetic field. Magnetic particles in slurry adsorbents on the surface of the magnetic medium and alone with the swivel magnetic mineral will rotary to the top field where there is no magnetic, then goes into concentrate hopper under the wash water effect. While weak magnetic or non-magnetic mineral through the gap of the hematite yoke goes into the tailings and eventually discharged.
Because strong magnetic separator has to produce a strong magnetic field when process hematite, in order to reduce the magnetic flux leakage problem, strong magnetic separator magnetic system spacing is generally smaller, and this also brings the separator a problem of easy blockage. Vertical ring pulsating high gradient magnetic separator of hematite process solves the problem of conventional strong magnetic separator blockage. Through its working process, we can see its prospecting and exploration direction are just opposite, unloading ore in the hematite process of reverse flushing can effectively wash out coarse mineral, avoid iron yoke slot of the plug. Also the lower part of the magnetic separation equipment is also equipped with a pulsating device, pulp continued to move up and down makes the internal particles remain in suspension which is conducive to the recovery of magnetic particles in the process of hematite, on the other hand when pulp does the moving magnetic particles can be adsorbed on the surface of the magnetic medium which increases the magnetic minerals in magnetic surface adsorption area and improves the utilization rate of the magnetic system when separation the hematite.
As one of the common mineral processing technologies, magnetic separation method is widely used in the separation of magnetite, manganese, ilmenite and other magnetic minerals by virtue of the advantages of simple equipment and good separation effect. But do you know how many factors affecting the magnetic separation process? And How does each factor affect the effect of the magnetic separation process?
According to the working principle of the magnetic separation process, we can know that the magnetic separation process mainly uses the magnetic differences among various minerals to realize mineral separation in the uneven magnetic field of various magnetic separation equipment. Thus, we can find two key factors that affect the magnetic separation process: one is the magnetic difference of minerals, another is the magnetic field distribution of magnetic separation equipment.
According to the magnetic differences, the minerals can be classified into strong magnetic minerals, weak magnetic minerals and non-magnetic minerals. It is because of the magnetism of the minerals that we can use the magnetic separation method to separate the different minerals. In other words, the magnetic differences in minerals are the basis of magnetic separation technology.
For strong magnetic minerals, such as magnetite, pyrrhotite, magnetite hematite, etc., the specific susceptibility is more than 3.810-5m3/kg. The low-intensity magnetic separator (magnetic field intensity is 0.1-0.3T) is usually applied;
For weak magnetic minerals, such as chromite, ilmenite, manganese ore, etc., the specific susceptibility is between 7.510-6 to 1.2610-7m3/kg. The strong intensity magnetic separator (magnetic field intensity is 1-2T) is usually applied.
There are many factors that affect the magnetic properties of minerals, and the magnetic properties of minerals in different regions and deposits are not the same, and some of them are quite different. Therefore, when conducting the magnetic separation for the specific minerals in a certain region, we should judge the magnetic properties by the magnetic determination results of minerals, and then select the strong magnetic separation process or the weak magnetic separation process.
In order to enlarge the magnetic difference of minerals in the actual production, some magnetic separation plants usually change the magnetic properties of minerals with the help of some methods, such as magnetization roasting, alkali dipping magnetization, magnetization of magnetic species, etc., so as to change the magnetic properties of minerals and facilitate the magnetic separation.
The magnetic field is a special state in the space around a magnet. The magnet placed in a magnetic field is subjected to the magnetic force. The magnetic field intensity, gradient and direction (that is, whether the magnetic field is evenly distributed) in the separation space of the magnetic separation equipment often affect the effect of the magnetic separation process.
In the uniform magnetic field, the mineral particles are only affected by the steering force, the diversion of the mineral particle sizes is parallel to the field direction. In the heterogeneous magnetic field, the mineral particles are subject to the steering force and magnetic force. The minerals rotate and move towards the increasing magnetic gradients, which forms the rollover phenomenon, so the magnetically different grains are separated.
Magnetic separation equipment can be divided into weak magnetic field separator (magnetic field intensity is 0.1t-0.2t), medium magnetic field separator (magnetic field intensity is 0.2t-0.5t) and strong magnetic field separator (magnetic field intensity is 0.5t-2.0t).
The common strong magnetic field separators include dry magnetic separator, continuous high gradient magnetic separator, electromagnetic pulsating high gradient magnetic separator, etc. Most of them have a more complex magnetic field design.
Take dry magnetic separator as an example, the magnetic separator has few types, such as single row single roll type, double row double roll type, double row multiple roll type. After the coil is energized, the magnetic field is generated between the induction roller and the magnetic pole. The material is separated by the magnetic field that passes.
In summary, it is not difficult to find that although the magnetic separation process is a kind of relatively simple mineral processing technology, it is not simple in the process design and selection. It is very necessary to understand the mineral properties, magnetic separation process and magnetic separation equipment in advance.
It is suggested to entrust the mineral processing equipment suppliers with qualification of mineral processing test to seek technical support, and choose the scientific and reasonable magnetic separation process and equipment according to the recommended results of ore dressing test, so as to ensure the perfect matching of technological process and ore properties, and the win-win situation of production indexes and economic benefit.
The selected grade was 23.15%, the concentrate grade was 65.95% and the tailings grade was 10.05%, which greatly improved the technical index of mineral processing. At the same time, the new mineral processing equipment and high-efficient mineral processing agents played a very good role, greatly promoting the progress of hematite ore processing technology, which was highly praised by the project customer.
Multotec supplies a complete range of magnetic separation equipment for separating ferromagnetic and paramagnetic particles from dry solids or slurries, or for removing tramp metal. Multotec Dry and Wet Drum Separators, WHIMS, Demagnetising Coils and Overbelt Magnets are used in mineral processing plants across the world. We can engineer customised magnetic separation solutions for your process, helping you improve the efficiency of downstream processing and lower your overall costs of production.
Multotec provides a wide range of magnetic separators including: Permanent magnet Low Intensity Magnetic Separators (LIMS) or Medium Intensity Magnetic Separators (MIMS) and electromagnetic High Intensity Magnetic Separators (HIMS). Multotec provides unmatched global metallurgical expertise through a worldwide network of branches, which support your processing operation with turnkey magnetic separation solutions, from plant audits and field service to strategic spares for your magnetic separation equipment.
Whether you need to recover fast moving tramp metal, recover valuable metals in waste streams or enhance the beneficiation of ferrous metals, Multotec has the magnetic separator you require. Dry drum cobber magnetic separators provide an initial upgrade of feed material as well as a gangue material rejection stage. By improving the material fed to downstream plant processes, our magnetic separation solutions reduce the mechanical requirements of grinding, ultimately lowering overall costs. Our heavy media drum separators are ideally suited for dense media separation plants. Our ferromagnetic wet drum separators can be used in iron ore separation plants in both rougher or cleaner beneficiation applications. We also provide demagnetising solutions that reverse the residual effects that magnetic separation has on the magnetic viscosity of ferrous slurries, to return the mineral stream to an acceptable viscosity for downstream processing. These demagnetising coils generate a magnetic field that alters magnetic orientation at 200 Hz.
The trend towards larger and faster travelling conveyors in the African mining industry has highlighted the vital role of overbelt magnets. Solutions need to be optimised to such factors as belt speed and width, the belt troughing angle, the burden depth, the material density and bulk density, the expected tramp metal specifications, ambient operating temperatures and suspension height to provide maximum plant and cost efficiency. Multotec can supply complete overbelt magnet systems, from equipment supply to a turnkey service by means of its strategic partners, including even the gantry work.