Magnetism can be seen as the result of the movement of charged particles in a substance and is one of the basic properties of matter. All kinds of substances in nature have different degrees of magnetism, most of them have weak magnetic properties, and only a few substances have strong magnetic properties. Speaking on the magnetic substance can be divided into three categories: paramagnetic, ferromagnetic and diamagnetic material substance.
The paramagnetic material exhibits weak magnetic properties in the magnetization field, and the additional magnetic field generated after magnetization is in the same direction as the magnetization field. Many substances belonging to the paramagnetic, have Na, K, Cr, Mn, and many rare earth metals, salts of iron group elements and the like.
The diamagnetic material exhibits weak magnetic properties in the magnetization field, and the additional magnetic field generated after magnetization is opposite to the direction of the magnetization field. However, the reverse magnetism is only exhibited when the magnetization field does not exist and the atomic magnetic moment of the atom is equal to zero. Under the remaining conditions, the reverse magnetism is masked by the paramagnetic and ferromagnetic effects. There are many substances belonging to the reverse magnetism, such as metal Cu, Zn, Ag, Sb, etc., non-metal Si, P, S, etc., inert gases and many organic compounds.
The magnetization of the ferromagnetic material produces a strong magnetic field in the magnetization field that is strong and in the same direction as the magnetization field, exhibiting strong magnetic properties. Ferromagnetic is the result of the exchange of a large number of paramagnetic atoms distributed on the lattice nodes of the material, causing the magnetic moments of the atoms to be arranged in parallel.
In addition, antiferromagnetic materials and ferrimagnetic materials are also present. The atomic magnetic moments of the antiferromagnetic material are arranged in antiparallel, exactly offsetting each other. The ferrimagnetic material has an ionic magnetic moment that is arranged in anti-parallel, but since the ionic magnetic moments are not equal, they cannot be completely canceled, and a part remains. Ferromagnetic materials, ferrimagnetic materials, and antiferromagnetic materials exhibit paramagnetism above a certain temperature. This temperature becomes the Neel temperature. Since the temperature of the inner surface of the antiferromagnetic material is very low, the antiferromagnetic substance can be included in the paramagnetic substance at normal temperature. The macroscopic magnetic properties of ferrimagnetic materials are generally similar to ferromagnetic materials, and they are included in ferromagnetic materials from the application point of view.
The relationship between the magnetization of a typical paramagnetic, reverse magnetic, ferromagnetic material and the strength of the magnetic field is shown in Figure 4-5-2.
The above relationship of paramagnetic substances is a linear relationship with a positive slope; the reverse magnetic material is a linear relationship with a negative slope; the ferromagnetic material is an asymptotic curve, and as the magnetic field strength increases, the magnetization of the material begins to change rapidly, and then tends to be gentle. And finally reach saturation. It is worth noting that when the magnetic field strength is relatively small, the magnetization tends to be saturated.
(2) Classification of magnetic properties of magnetically selected minerals
The classification of magnetic properties of magnetically selected minerals is different from the physical classification of magnetic properties. Generally, all minerals are classified into ferromagnetic minerals, weak magnetic minerals and non-magnetic minerals according to the specific magnetic susceptibility.
The ferromagnetic mineral material has a specific magnetic susceptibility of X>4.0×10-5 m3/kg, and can be recovered in a weak magnetic field magnetic separator with a magnetic field strength of 80 to 136, kA/m. Such minerals are mainly magnetite, maghemite, magnetite, titanium, pyrrhotite and zinc ferrite, etc., these minerals are mostly ferrimagnetic substance.
The magnetic permeability of the weak magnetic mineral material is X=1.26×10-7~ 7.5×10-6m3/kg, which can be selected in the magnetic separator with magnetic field strength H=480~1840 and kA/m. More minerals such as iron, manganese and most minerals: hematite, hematite, siderite, goethite, manganite, psilomelane pyrolusite and rhodochrosite and the like; number containing titanium, chromium, tungsten Minerals: ilmenite, rutile, chromite, wolframite , etc.; some rock-forming minerals: biotite , hornbeam, chlorite, epidote, garnet, olivine, pyroxene, etc. Most of these ores are paramagnetic and some are antiferromagnetic.
Non-magnetic mineral material specific magnetic susceptibility; X <1.26 X10-7 m3/kg, is a mineral that cannot be recovered by magnetic separation. Many of these minerals, such as partially metallic minerals: molybdenite, sphalerite, galena, stibnite, scheelite, cassiterite, niccolite, and gold; most non-metallic minerals: coal, natural Sulfur , diamond , kaolin , gypsum , fluorite, etc.; most rock-forming minerals: quartz , feldspar , calcite, etc. Some of these minerals are paramagnetic, and some are retromagnetic, such as galena, gold, stibnite and natural sulfur.
It should be pointed out that the above classification is based on the current level of magnetic separation technology. There are certain discrepancies in the specific classification indicators of various countries, especially the boundaries between weak magnetic minerals and non-magnetic minerals. This boundary will follow the development of magnetic separation technology. The magnetic field force of the machine is gradually weakened, so this is only a rough classification. In addition, the magnetic properties of minerals are also affected by the size and shape. Therefore, for a specific mineral, it is necessary to actually measure the magnetic size of the mineral.
(3) Magnetic properties of ferromagnetic minerals and their influencing factors
Strong magnetic minerals such as magnetite, maghemite, titanomagnetite, and pyrrhotite have common properties. Magnetite is a typical ferromagnetic mineral and the main ore processed by magnetic separation.
Magnetite is a ferrimagnetic substance and is a typical ferrite. There are three main crystal structures of ferrite: spinel type, magnetoplumbite type and garnet type. The chemical formula of spinel ferrite is XFe204, wherein X represents a divalent metal ion, common are Fe2+, Ca, Zn2+, Cd2+, Mn2+, etc., the molecular formula of magnetite is Fe304, and can also be combined with Fe2: Fe204, which is a ferrite of the spinel type.
The magnetic characteristics of magnetite are:
1 The magnetism of magnetite is not from the rotation of the atomic magnetic moment, but from the magnetic domain rotation, and the movement of the magnetic domain wall plays a major role. Therefore, magnetite has a large magnetization and magnetic susceptibility, and there is magnetic saturation, and saturation can be achieved at a low magnetic field strength.
2 Magnetite has a curvilinear relationship between magnetization, magnetic susceptibility and magnetic field strength. The magnetic susceptibility is not constant, but varies with the strength of the magnetic field. The magnetization of magnetite is related to the nature of the ore and the history of the change in the strength of the magnetic field.
3 Magnetite has hysteresis, and when it leaves the magnetization field, it still retains a certain remanence.
4 The magnetism of magnetite is related to the shape and particle size of the ore.
Magnetization process of magnetite
Figure 4-5-3 shows the relationship between specific magnetization, specific magnetic susceptibility and magnetic field strength of a mine magnetite in China. It can be seen that when the magnetic field strength H=0, the specific magnetization of the magnetite is J=0. As the magnetic field strength increases, the specific magnetization of magnetite begins to increase slowly [0~1 segment], then rapidly increases [1~2 segments], and then slowly increases [2~3 segments] to a specific After the value does not change, this particular point (3) is called the magnetic saturation point. Indicates [Jmax=135A/(m.kg)]. Lowering the magnetic field strength H, the specific magnetization J decreases, but not along the original curve (0~1~2~3), but decreases along the upper curve [3 ~4]. When the magnetic field strength When it is reduced to 0, the specific magnetization J does not fall to 0, but a certain value is retained. This value is called remanence and is expressed by [about 5A/(m.kg)]. This phenomenon is called hysteresis. Phenomenon. If you want to eliminate the remanent magnet, you need to apply a reverse magnetic field to the magnetite. As the demagnetizing field gradually increases, the specific magnetization J decreases along the curve (4~5) until J=0. The strength of the demagnetizing field applied by the remanence is called the coercive force. It is shown from the specific magnetic susceptibility curve that the specific magnetic susceptibility of magnetite is not a constant, but varies with the magnetic field strength H. At the beginning, the magnetic field The increase in strength is faster than the magnetic susceptibility, reaching a maximum at a magnetic field strength of about 8 k/m, 2.5 X 10 -3 m 3 /kg. After that, the magnetic field strength H is increased, and the specific magnetic susceptibility is decreased. Different minerals have different specific magnetic susceptitivity. The magnetic field strength required to reach the maximum is also different, and they have different remanence and coercivity. Even the same kind
2. Magnetization essence of magnetite
The magnetization nature of magnetite can be explained by magnetic domain theory.
Magnetite belongs to the ferrimagnetic substance, and there are many magnetic domains inside, and adjacent magnetic domains are separated by magnetic domain walls. When the applied magnetic field strength H =0, the magnetic domains are randomly arranged [Fig. 4-5-4(a)], and the total magnetic moment is 0. At this time, the specific magnetization J = 0, the mineral does not show magnetism (Fig. 4) 0 point of 5-3] When there is a small magnetic field, the magnetic domain whose spontaneous magnetization direction is close to the direction of the applied magnetic field is enlarged by the action of the magnetic field, and the magnetic domain whose spontaneous magnetization direction is greatly different from the direction of the applied magnetic field is reduced. Figure 4-5-4 (b)], this process is achieved by the movement of the magnetic domain wall, when the total magnetic moment of the mineral is not equal to 0, J≠0, the mineral begins to show magnetism, J slowly increases, X Increase rapidly (equivalent to 0~1 in Figure 4-5-3). When the magnetic field strength increases to a certain value, the magnetic domain wall jumps at a fairly fast speed until the spontaneous magnetization direction is very different from the magnetic field direction. Large magnetic domains are annexed, producing a mutation [Fig. 4 - 5 -4(c)], which corresponds to the 1~2 segment in Fig. 4-5-3), J increases rapidly, and X increases rapidly from one to the maximum. The value drops, starts to fall fast, and then falls slowly. At this stage, the increase of J is composed of many jumping mutations, which is discontinuous, so it is a Reversible process. Increase the magnetic field strength, the direction of the magnetic domain gradually turns to the direction of the magnetic field until the direction of all magnetic domains is the same as the direction of the magnetic field [Fig. 3-14 [d]. At this time, the magnetization reaches saturation and J reaches the maximum value [equivalent In paragraphs 2~3 of Figure 4-5-3], when the magnetic field strength is reduced, the magnetic domain wall movement is hindered due to the irreversible jump movement of the magnetic domain wall and the presence of impurities and compositional inhomogeneities inside it. The magnetic domain wall cannot be restored to its original position, thus causing hysteresis.
From the change law of the magnetic domain in the magnetization process, in the early stage of magnetization, the magnetic domain wall is mainly moved, and the magnetic domain is mainly rotated in the later stage. The energy required to move the magnetic domain wall is small, and the energy required to rotate the magnetic domain is large.
3. The effect of particle properties on magnetism
In addition to the influence of the magnetic field strength on the mineral magnetic properties, the shape of the particles, the particle size of the particles, the content of the ferromagnetic minerals, and the degree of oxidation of the minerals also have an effect on the magnetic properties.
(1) Effect of particle shape
Figure 4-5-5 shows the relationship between specific magnetization, specific magnetic susceptibility and magnetic field strength of magnetite with the same composition, the same content and different shapes.
It can be seen from Fig. 4-5-5 that different shapes of ore particles exhibit different magnetic properties when magnetized in the same magnetic field. The specific magnetization and specific magnetic susceptibility of the long strips are larger than those of the spherical ore. Table 4-5-2 provides the relationship between the specific magnetization and the specific magnetic field strength of the cylindrical magnetite under the same magnetic field strength and its length: the larger the length of the ore, the specific magnetization and the ratio The magnetic susceptibility is also greater. It can be seen that the shape or relative size of the ore particles has a certain influence on the magnetic properties of the ore particles, and this effect is closely related to the demagnetizing field generated by the ore particles during magnetization.
It is known from Table 4-5-3 that as the size ratio m increases, the demagnetization factor gradually decreases. When the size ratio is small, the geometry of the object has a great influence on the demagnetization factor, and when the size ratio m is greater than 10, the influence of the geometry of the object on the demagnetization factor is substantially absent. The small size ratio leads to an increase in the strength of the demagnetizing field in the ore particles, which reduces the strength of the magnetic field actually acting in the ore particles, and objectively causes a decrease in the specific magnetization and specific magnetic susceptibility of the ore particles. When the size ratio is above 10, the demagnetization factor of the ore particles is very small. At this time, the strength of the demagnetizing field inside the ore particles can be neglected. It can be approximated that the magnetic field strength inside the ore particles is the intensity of the external magnetic field. In the SI unit system, 0 < N < 1.
In fact, the shape of the ore is irregular, and the magnetic field in the magnetic separator is also non-uniform. The magnet is magnetized by the uneven magnetic field differently than the uniform magnetic field. Therefore, the data listed in the table can only be used to approximate The demagnetization factor N of the ore particles. In practice, the ore particles or nuggets are generally slightly longer in a certain direction, their size ratio m is approximately equal to 2, and the demagnetization factor can be averaged 0.16.
The magnetic field strength actually acting on the ore particles is not the applied magnetic field strength but the effective magnetic field strength minus the demagnetizing field strength. Corresponding to the applied magnetic field strength and the effective magnetic field strength, the volume magnetic susceptibility and the specific magnetic susceptibility are divided into two categories: objects and substances. The effect of the applied magnetic field strength, which does not take into account the shape size, varies with the shape of the ore particle, and is called the volume susceptibility or specific magnetic susceptibility of the object. The effective magnetic field strength is used to eliminate the influence of the shape size. When magnetized in a magnetic field of a large size, the same value is obtained, which is called a volumetric magnetic susceptibility or a specific magnetic susceptibility.
However, the effective magnetic field strength is not easy to know. Generally, the mineral sample is made into a long rod shape when the mineral magnetic susceptibility is measured, and the size ratio is large to eliminate the influence of the demagnetization factor and the demagnetizing field, so that the total magnetic field acting on the mineral H is the applied magnetic field H. Basically the same, the volume magnetic susceptibility or specific magnetic susceptibility measured by the applied magnetic field at this time can be regarded as the volume magnetic susceptibility or the specific magnetic susceptibility.
Knowing the volume magnetic susceptibility or specific magnetic susceptibility of minerals, the volume magnetic susceptibility or ratio of minerals of different shapes or sizes can be calculated
Figure 4-5-7 shows the relationship between the specific magnetic susceptibility and coercivity of magnetite and its particle size. It can be seen from the figure that the size of the ferromagnetic ore particles has a significant influence on the magnetic properties of the ore particles. As the particle size decreases, the specific magnetic susceptibility of the ore particles also decreases, and the coercive force increases. That is, the smaller the particle size of the ore particles, the less magnetized, and the magnetization is not easy to demagnetize, especially when the particle size is less than 20~30μm.
The above relationship can be explained by magnetic domain theory. It is believed that the magnetic properties of large-grained ore particles are caused by the movement of magnetic domain walls and the rotation of magnetic domains, with magnetic domain wall movement as the main. As the particle size decreases, the number of magnetic domains contained in each of the ore particles decreases. When magnetized, the movement of the magnetic domain walls is relatively reduced, and the magnetic domain rotation gradually plays a leading role. When the particle size is reduced to the single magnetic domain state, no magnetic domain wall is moved, and the magnetic properties of the ore particles are completely generated by the magnetic domain rotation. The energy required for the rotation of the magnetic domain is much larger than the magnetic domain wall movement. Therefore, as the particle size decreases, the specific magnetic susceptibility of magnetite decreases and the coercive force increases.
The finer the ore particle size, the weaker the magnetic properties, and the more likely it is to cause loss during magnetic separation, so it cannot be overgrinded during grinding. As long as the target mineral monomer is high, it will do. On the other hand, the fine grain size and large coercive force make the fine ore relatively firmly formed into a magnetic group or a magnetic chain, and the flux linkage is much larger than the single ore particle, and the overall magnetic property is also enlarged, and the sorting process is also performed. In the middle, the fine particle loss is correspondingly reduced.
When magnetite is magnetically selected, it rarely appears as a single ore, and most of it exists in a magnetic or magnetic chain state. The existence of magnetic agglomeration can reduce metal loss. However, the magnetic clusters cause a part of the gangue to be wrapped in a magnetic group or a magnetic chain, thereby causing contamination of the magnetic concentrate. In addition, when the process of sorting in the stage grinding stage is adopted, some magnetic groups or flux Chains will be used as grit to re-grind; and some magnetic groups or flux chains will enter the classifier to overflow, so that the classification granularity becomes thicker. This affects the process effect of the following grinding and grading operations. Therefore, the material needs to be demagnetized by demagnetization equipment before the grading operation.
(3) Influence of mineral oxidation degree
After long-term oxidation of the magnetite in the deposit, it partially or completely becomes pseudo-hematite; the crystal shape is magnetite, and the chemical composition has become hematite. As the degree of oxidation of magnetite increases, the magnetic properties decrease and the specific magnetic susceptibility decreases significantly. The maximum value of the specific magnetic susceptibility is less and less obvious, and the curve is getting closer to a horizontal line.
The composition of ore is relatively simple. The content of iron silicate, iron sulfide and iron dolomite in iron ore is less than 3%. The main iron minerals are magnetite, hematite and limonite. That is, the percentage of FeO content in the ore and the total iron Fet content reflect the magnetic properties of the iron ore. The magnetic permeability of pure magnetite is one (56 10 16) / (56X3) X 100% - 42.8%. The magnetic permeability of iron ore is low, indicating that it has a high degree of oxidation and weak magnetic properties. Industrially, iron ore with a magnetic rate of >37% is classified as magnetite ore; iron ore with a magnetic rate of 28^~37% is classified as a semi-artificial hematite ore; iron ore with a magnetic rate of <28% For the illusion of hematite ore.
The composition of the ore is complicated, and the content of iron silicate, iron sulfide and iron dolomite in the iron ore is relatively high, and the magnetic properties of the iron ore cannot be reflected by the magnetic rate method. For example, some iron ore contains more iron silicate minerals, and its magnetic rate is sometimes higher than that of pure magnetite ore, but the actual magnetic separation effect is very poor; More pyrrhotite, its magnetic rate is not high, but the actual magnetic separation effect is very good; as in some iron ore, the semi-artificial hematite can also be selected in the weak magnetic separation, magnetic separation The effect is still good, so it can be classified as a magnetite type. In this case, it is best to use iron ore in the ore to divide the iron ore type. The ratio can be referred to as the magnet ratio. The standard is: Fem/Fet> 85% for magnetite ore, Fem /Fet = 15%~ 85% is mixed ore, and Fem/Fet <15% is hematite.
(4) Influence of ferromagnetic mineral content
The continuous body of magnetite and gangue minerals is easily mixed into the magnetic concentrate during the production process, affecting the quality of the concentrate. The magnetic properties of the continuum and the structure, magnetic domain strength and sorting medium of the continuum.
The relationship between the specific magnetic susceptibility of the continuum and the magnetite content is shown in Figure 4-5-8.
It is seen from FIG 4-5-8, with the living body than the magnetic susceptibility increases with increasing magnetic magnetite content of α. At the beginning, the specific magnetic susceptibility increases slowly, when α magnetic > 50%, the increase is faster. When alpha magnetic = 10% with the living body than the magnetic susceptibility of 37.5 × 10 6 a m 3 /kg when α magnetic = 50% when compared with the living body magnetic susceptibility was 185.5 X 10 6 a m 3 /kg, it can be seen that the lean magnetic body of ferromagnetic minerals has a larger specific magnetic susceptibility than that of weak magnetic gangue minerals, while the specific magnetic susceptibility of rich Liansheng is larger. Therefore, when sorting by a magnetic separator using a constant magnetic field, the possibility that the living body enters the magnetic concentrate is large. Analysis of the composition of the concentrate found that the content of monomeric gangue is very small, but there are many gangues in the form of continuous organisms, so the continuous body is an important factor affecting the quality of concentrate.
In the range of magnetic field strength of 60 ~ 1 20 kA / m , the specific magnetic susceptibility of the continuum can be calculated according to the empirical formula:
If a mixture of ferromagnetic minerals and non-magnetic minerals is sorted in the medium, the situation is similar to that of the continuum. At this time, the magnetic susceptibility of the entire dispersion system depends not only on the volume concentration of the ferromagnetic mineral but also on the type of the sorting medium. The curve of Figure 4-5-9 shows the relationship between the specific magnetic susceptibility of the magnetite and quartz mixture and the magnetite volume content. It is known from Fig. 4-5-9 that when the mixture is magnetically selected by air, the relationship between the specific magnetic susceptibility of the mixture and the magnetite content is similar to that of the magnetite orthosilicate, and the water is wet. When the mixture is magnetically selected, the relationship between the specific magnetic susceptibility of the mixture and the magnetite content is proportional to a linear relationship.
(4) Magnetic properties of weak magnetic minerals and their influencing factors
Compared to ferromagnetic minerals, the magnetic properties of weak magnetic minerals are significantly different:
1 The magnetic susceptibility of weak magnetic minerals is much smaller than that of ferromagnetic minerals;
2 The specific magnetic susceptibility of weak magnetic minerals is only related to the mineral composition, which is a constant, independent of the magnetic field strength and the shape and particle size of the mineral itself;
3 weak magnetic minerals have no magnetic saturation phenomenon and hysteresis, and its magnetization and magnetic field strength are linear;
4 If a weak magnetic mineral is mixed with a ferromagnetic mineral, even a small amount will have a certain or even greater influence on its magnetic properties.
The ratio of the magnetic susceptibility of the symbiotic body composed of the weak magnetic mineral to the non-magnetic mineral is approximately proportional to the content of the weak magnetic mineral. The specific magnetic susceptibility of the continuum is equal to the weighted average of the magnetic susceptibility of each mineral.
As for the magnetic properties of weak magnetic minerals, weak magnetic iron minerals and weak magnetic manganese minerals are studied. For weak magnetic iron minerals: hematite, root iron ore, siderite, pyrite, they can be artificially increased by magnetization roasting, so that they become artificial magnetic minerals Fe304 or γ- Fe203 can be sorted by a weak magnetic field magnetic separator.
The magnetic properties of artificial ferromagnetic minerals are basically the same as those of natural ferromagnetic minerals, but the remanence and coercive force of artificial magnetite are larger than natural ones, and the magnetic susceptibility is smaller. Therefore, the magnetic agglomeration phenomenon is serious in the beneficiation , and the quality and recovery rate of the concentrate are lower than the natural one.
Outoutdoors harnesses & Climbing Harnesses are specially made for outdoor activities.
They can be the best co-worker you got when you are doing outdoors activities like mountaineering.
Sometimes we might get confused between Hunting Harnesses and outdoors harnesses,but remember,they are the very similar thing,just with different functions.
Alse these harnesses are of stronger water-absord ability,stronger pulling & tugging resistance,more tend to be invisible at night,etc.
If you are doing this business,come and contact us for more!
Outdoor Harnesses & Climbing Harnesses
Rock Climbing Harnesses,Cheap Climbing Gear,Climbing Rope,Outdoor Harnesses
WINNERLIFTING(H.K.)INT'L TRADING LIMITED. , https://www.massagebeds.nl