Iron ore magnetic separation innovative technology innovative technology—mineral magnetism

Magnetism is one of the fundamental characteristics of matter. Among more than one hundred known elements, three elements, iron (Fe), nickel (Ni), and cobalt (Co), are ferromagnetic. Compounds containing one or two of these elements can be strongly ferromagnetic or weakly ferromagnetic; they can also be paramagnetic. 55 elements are paramagnetic, including scandium (Sc), titanium (Ti), vanadium (V), chromium (er), manganese (Mn), yttrium (Y), molybdenum (Mo), technetium (Te), nail ( Ru), rhodium (Rh), palladium. (Pd), Tantalum (Ta), Tungsten (w), Rhenium (Re), Osmium (Os), Iridium (Ir), Platinum (Pt), Cerium (Ce), Error (Pr), Neodymium (Nd), Samarium (sin), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tin), ytterbium (Yb), uranium (U), plutonium Compounds of 32 elements (Pu), americium (Am) are paramagnetic (gadolinium, dysprosium, and chin are ferromagnetic); lithium (Li, oxygen (O), sodium (Na), magnesium (Mg), aluminum (Al) ), calcium (Ca), gallium (Ga), (Sr), zirconium (Zr), niobium (Nb), tin (Sn), (Ba), lanthanum (La), lutetium (Lu), hafnium (Hf), Several elements of thorium (Th) are paramagnetic in the pure state and diamagnetic when they form compounds. Among them, nitrogen (N), potassium (K), copper (Cu), (Rb), (Gs), gold ( Among the seven elements Au) and (Tl), compounds containing one or more of these elements (although N and Cu are slightly diamagnetic in pure state) are paramagnetic. The other 46 elements are all diamagnetic. . In the field of mineral processing technology, natural mineral deposits are generally divided into three categories: strong magnetic mineral deposits, weak magnetic mineral deposits and non-magnetic mineral deposits. (1) Strong magnetic mineral deposits Strong magnetic mineral deposits refer to mineral deposits in a weak magnetic field (field strength 120 kA/m ) Mineral deposits that can be recovered in a magnetic separator. The specific magnetic susceptibility Hematite), titanomagnetite and pyrrhotite (some are weakly magnetic). A Magnetite (FeO·Fe2O3) The magnetic properties of magnetite are: Curie point θ=578℃; full magnetization, Strength Ms=451~454 kA/m; coercivity Hc=1.6 kA/m; starting specific magnetic susceptibility When magnetized in a kiloampere/meter magnetic field, the initial magnetization is full. The initial magnetization, hysteresis curve and specific magnetic susceptibility of magnetite are shown in Figure 1. From Figure 2, it can be seen that the coercive force of magnetite changes with the particle size. It decreases and increases, while the specific magnetic susceptibility is opposite.

[next] The specific magnetic susceptibility of magnetite and weakly magnetic mineral deposits or non-magnetic mineral deposits is only related to the magnetite content between them. Within the range of magnetizing field intensity of 60 to 120 kA/m, the specific magnetic susceptibility Ore specific magnetic susceptibility; m3/kg; δm and δl——density of magnetite and conjoined body, kg/m3; a——iron content % in the form of magnetite in conjoined body; 72.4———— Iron content of chemical formula of pure magnetite, %. When the conjoined body is magnetized in a magnetic field of 10~20 kA/m, the specific magnetic susceptibility can be calculated by the following formula ;b′=27;c′=1.36×103 The coercive force of artificial magnetite and magnetic hematite is larger than that of natural magnetite (HC≈10 kA/m). During magnetic separation, these mineral deposits form strong agglomerates, with more non-magnetic inclusions than natural magnetite agglomerates. ​ Magnetite concentrate containing a lot of divalent titanium also has high coercive force (HC=5~10 kA/m) and a slight decrease in specific magnetic susceptibility (Xs=0.38×-3 m3/kg). B Pyrrhotite (FeS1+x;0＜x≤1) Pyrrhotite exists in different anomalies in nature. According to its magnetic properties, it can be classified as a weak magnetic mineral deposit or a strongly magnetic mineral deposit. Hexagonal pyrite (FeS) is weakly magnetic; anomalous pyrrhotite at 0<X≤0.1 is also weakly magnetic; and pyrrhotite at 0.1<X≤1/7 is strongly magnetic. Figure 3 shows the magnetic properties of strongly magnetic pyrite.

(2) Weakly magnetic mineral deposits Weakly magnetic mineral deposits are a large type of mineral deposits in nature. They are all paramagnetic, as long as individual mineral deposits (such as hematite) are classified as antiferromagnetic. The magnetic characteristic of weakly magnetic mineral deposits is that the specific magnetic susceptibility is a constant, which has nothing to do with factors such as magnetizing field intensity, particle shape and particle size; there is no magnetic saturation and hysteresis phenomena, and its magnetization intensity has a linear relationship with the magnetizing field intensity. Sometimes it is observed that the specific magnetic susceptibility of some weakly magnetic mineral deposits is related to the intensity of the magnetizing field. This phenomenon is interpreted as the presence of strong magnetic material inclusions. The specific magnetic susceptibility of weakly magnetic mineral deposits and strongly magnetic mineral deposits can be calculated according to equations (1) and (2). The specific magnetic susceptibility of weakly magnetic mineral deposits and non-magnetic mineral deposits can be calculated as follows:

In the formula, ai——the content of i weakly magnetic or non-magnetic mineral deposits (Σai=1) [next] (3) The impact of mineral magnetism on the magnetic separation process The magnetism of the mineral deposit is the decisive factor in determining the magnetic separation process. A weak magnetic field magnetic separator is used to recover strong magnetic mineral deposits; a strong magnetic field magnetic separator is used to recover weak magnetic mineral deposits. When magnetic separation of highly magnetic mineral deposits, in addition to the particle magnetic susceptibility, the coercive force and residual magnetic induction intensity of the mineral deposit also play an important role. These factors cause the particles to form agglomerates in the magnetic separator or magnetizing equipment, and after it leaves the magnetic field, some of the agglomerations remain, accelerating the sedimentation of the particles. ​ The phenomenon of magnetic aggregation will affect the classification power in the classification operation of the grinding circuit, especially in the mechanical classifier. Therefore, demagnetization equipment must be used to demagnetize the magnetic separation products before regrinding to destroy the magnetic agglomeration. The fine-grained magnetite concentrate must be demagnetized before filtering, which can reduce the moisture content of the filter cake and improve the production capacity of the filter. The magnetite particles form agglomerates when passing through the magnetic field of the magnetic separator, which helps to obtain tailings with lower iron content. This is due to the fact that the demagnetization coefficient of the agglomerate is smaller and the magnetic susceptibility is higher, and its resistance to movement in water is smaller than that of individual particles. Regarding concentrate quality, the formation of magnetic agglomerates is unfavorable because non-magnetic particles can also be mixed in the agglomerates. The formation of agglomerates prevents conjoined bodies from being separated from individual mineral grains. In order to magnetically separate two mineral deposits with equal magnetic susceptibility but different Curie points, magnetic separation can be carried out at an intermediate temperature. At this temperature, the magnetism of one mineral deposit has significantly decreased, while the other mineral deposit remains unchanged. (4) Selectivity of magnetic separation The ratio of the specific magnetic susceptibility of the separated mineral deposits X″s/X′s is called the selectivity of magnetic separation. Here X′s and The specific magnetic susceptibility. The magnetic field of the magnetic separator is uneven regardless of the magnetic field strength (H) and the relative magnetic force (μoHgradH). In this case, the particle size has an impact on the uniform magnetic force value acting on the particles, so particles with different magnetic susceptibilities and different sizes may experience the same magnetic force. Here we introduce the concept of “specific attraction coefficient” of particles during magnetic separation. The ratio of equal-attraction particle sizes d′/d″ depends on many factors, the most important of which are the change range of the specific magnetic susceptibility of magnetic particles, the degree of magnetic field inhomogeneity (μoHgrad-H), the resistance of the medium to particle movement and the ore feeding method (upper or Lower feeding). This ratio varies with different ores and is also related to the type of magnetic separator. When sorting wide-grained ores, they should be screened in advance. The relative magnetic force is constant in an equal magnetic field, so before magnetic separation Materials do not need to be classified, because the specific magnetic force encountered by particles of any size in any direction of the magnetic field is the same. For the upper single-layer ore feeding cylinder magnetic separator, magnetic separation must be between the upper limit d′ and the lower limit d″ of the selected ore particle size. The particle size difference can be calculated as follows: Δd=d′-d″=lgK″/Clge=2.311lgK″/π=0.731lgK′ (4) In the formula, k′=X′bs/X″bs; /ι——Magnetic system magnetic uniformity, m-1;        Pole distance, m. It can be seen from Equation 4 that the necessary difference between the upper and lower limits of the selected ore particle size changes with the magnetic field unevenness C decreases (or the polar distance increases) and increases. The magnetic separation power is calculated according to the following formula:                                                                                                                                                              ——The selected particles have relatively poor specific magnetic susceptibility: n′=(X′bs/X″bs) bs=constant, that is, n′=constant), the magnetic separation power is determined by m′; and when the structure of the magnetic separator and the separation conditions are fixed (m′=constant), the magnetic separation power is calculated based on the required selectivity. The coefficient n′ resolution.