New Technology of Magnetic Separation of Iron Ore---Mineral Magnetics

Magnetic is one of the basic properties of matter. Among the more than one hundred elements known, iron (Fe), nickel (Ni), and cobalt (Co) are ferromagnetic. The compound containing one or both of the elements may be strongly ferromagnetic or weakly ferromagnetic; it may also be paramagnetic. 55 elements have paramagnetism, of which strontium (Sc), titanium (Ti), vanadium (V), chromium (er), manganese (Mn), yttrium (Y), molybdenum (Mo), cerium (Te), nail ( Ru), rhodium (Rh), palladium . (Pd), 钽 (Ta), tungsten (w), 铼 (Re), 锇 (Os), 铱 (Ir), platinum (Pt), 铈 (Ce), er(Pr), 钕 (Nd), 钐 (sin), 铕 (Eu), 钆 (Gd), 铽 (Tb), 镝 (Dy), 钬 (Ho), 铒 (Er), 铥 (Tin), 镱 (Yb), uranium (U), 钚(Pu), 镅 (Am) 32 elements of compounds have paramagnetic properties (where 钆, 镝, 钦 have ferromagnetism); lithium (Li, oxygen (O) sodium (Na), magnesium (Mg), aluminum (Al ), calcium (Ca), gallium (Ga), strontium (Sr), zirconium (Zr), niobium (Nb), tin (Sn), barium (Ba), lanthanum (La), lanthanum (Lu), lanthanum (Hf) ), 钍 (Th) several elements are paramagnetic in the pure state, and diamagnetic in the case of compounds, in nitrogen (N), potassium (K), copper (Cu), strontium (Rb), strontium (Gs) Among the seven elements of gold (Au) and strontium (Tl), compounds containing one or more of these elements (although .N and Cu are slightly diamagnetic in the pure state) are paramagnetic. The elements are all diamagnetic.
In the field of mineral processing technology , natural minerals are generally divided into three categories: ferromagnetic minerals, weak magnetic minerals and non-magnetic minerals.
(1) Strong magnetic minerals Strong magnetic minerals are minerals that can be recovered in a weak magnetic field (field strength 120 kA/m) magnetic separator. The specific magnetic susceptibility of such minerals is X _s > 4 × 10 ⁵ m ³ /kg. Among these minerals are magnetite (natural and man-made), magnetic hematite (or gamma-hematite), titanomagnetite and pyrrhotite (some are weakly magnetic).
A magnetite (FeO · Fe ₂ O ₃ )
The magnetic properties of magnetite are: Curie point θ = 578 ° C; saturation magnetization, strength M _s = 451 ~ 454 kA / m; coercivity H _c = 1.6 kA / m; initial specific magnetic susceptibility X _s = (0.18 ~ 1.28) × 10 ^{- 2} m ³ / kg. Magnetite begins to magnetically saturate when magnetized in a magnetic field with a magnetic field strength of approximately 320 kA/m. The initial magnetization and hysteresis curve and specific magnetic susceptibility of magnetite are shown in Fig. 1. It can be seen from Fig. 2 that the coercive force of magnetite increases as the particle size decreases, and the specific magnetic susceptibility is opposite.

[next]

The specific magnetic susceptibility of magnetite and weak magnetic minerals or non-magnetic minerals is only related to the magnetite content. In the range of magnetization field strength 60-120 kA/m, the specific magnetic susceptibility X _{sl of the} continuum can be calculated according to the empirical formula X _sl =(δ _m /δ _l )(a/72.4) ² Xsm (1)
Where X _sm ———magnetization ratio magnetic susceptibility; m ³ /kg;
δ _m and δ _l — the density of magnetite and continuum, kg/m ³ ;
a———% of the iron content in the form of magnetite in the living body;
72.4———The iron content of pure magnetite chemical formula, %.
When the continuous body is magnetized in a magnetic field of 10 to 20 kA/m, the specific magnetic susceptibility can be calculated by the following formula: X _sl =[(a _m +b ′ )/c ′ ] ³ (2)
Where a _m ———the content of magnet in the continuous body; b ′ =27; c′=1.36 ×10 ³
The coercive force of artificial magnetite and magnetic hematite is larger than that of natural magnetite (H _C ≈ 10 kA/m). These minerals form a strong agglomerate during magnetic separation, in which non-magnetic inclusions are more concentrated than natural magnetite.
Magnetite concentrates containing a large amount of divalent titanium also have a high coercive force (H _C = 5 to 10 kA/m) and a slight decrease in specific magnetic susceptibility (X _s = 0.38 × ^-3 m ³ /kg).
B pyrrhotite (FeS _1+x ; 0<x≤1)
In nature, pyrrhotite exists in different metamorphosis. It may belong to weak magnetic minerals according to its magnetic properties, and may also belong to ferromagnetic minerals. Hexagonal pyrite (FeS) is weakly magnetic; metamorphic pyrrhotite with 0<X≤0.1 is also weakly magnetic; and pyrrhotite with 0.1<X≤1/7 is ferromagnetic. Figure 3 shows the magnetic properties of ferromagnetic pyrite.

(2) Weak magnetic minerals Weak magnetic minerals are a large class of minerals in nature. They are all paramagnetic, and only a few minerals (such as hematite) are antiferromagnetic. The magnetic characteristics of weak magnetic minerals are a constant ratio of magnetic susceptibility, independent of magnetization field strength, particle shape and particle size. Without magnetic saturation and hysteresis, the magnetization is linear with the magnetization field strength. It is sometimes observed that the specific magnetic susceptibility of some weakly magnetic minerals is related to the strength of the magnetization field, which is explained by the presence of inclusions of ferromagnetic substances.
The specific magnetic susceptibility of weak magnetic minerals and ferromagnetic minerals can be calculated according to formulas (1) and (2). The specific magnetic susceptibility of weak magnetic minerals and non-magnetic minerals can be calculated as follows

Where a _i ———i content of weak magnetic or non-magnetic minerals (Σa _i =1)[next]
(III) Influence of mineral magnetism on magnetic separation process Mineral magnetism is the decisive factor in determining the magnetic separation process. A weak magnetic field magnetic separator is used for recovering ferromagnetic minerals; a strong magnetic field magnetic separator is used for recovering weak magnetic minerals.
In the magnetic separation of ferromagnetic minerals, in addition to the magnetic susceptibility of the particles, the coercivity and residual magnetic strength of the mineral also play an important role. These factors cause the particles to form agglomerates in the magnetic separator or magnetizing device, and after it leaves the magnetic field, some of the agglomerates remain, causing the particles to settle faster.
The phenomenon of magnetic agglomeration affects the classification efficiency in the classification operation of the grinding circuit, especially in the mechanical classifier. Therefore, the demagnetization device is demagnetized before the magnetic separation product is reground to destroy the magnetic agglomeration.
Fine-grained magnetite concentrates are demagnetized prior to filtration, which reduces the moisture content of the filter cake and increases the productivity of the filter.
The formation of agglomerates of magnetite particles through the magnetic field of the magnetic separator helps to obtain tailings with lower iron content. This is because the agglomeration has a small demagnetization coefficient and a high magnetic susceptibility, and its resistance to movement in water is smaller than that of a single particle. For concentrate quality, the formation of magnetic agglomerates is disadvantageous because non-magnetic particles are also entrained in the agglomerates. The formation of agglomerates prevents the continuum from separating from the individual mineral particles.
In order to achieve magnetic separation of minerals with different magnetic susceptibility and different Curie points, magnetic separation can be carried out at an intermediate temperature at which the magnetic properties of one mineral have been significantly reduced while the other remains unchanged.
(4) The selectivity of magnetic separation is the ratio of the magnetic ratio of separated minerals X′′s/X ′ s is called the selectivity of magnetic separation. Here X ′ s and X′′ s are magnetic and weak magnetic minerals, respectively. Specific magnetic susceptibility.
The magnetic field of the magnetic separator is not uniform regardless of the magnetic field strength (H) and the relative magnetic force (μoHgradH). In this case, the particle size has an effect on the average magnetic force value acting on the particles, and therefore particles having different magnetic susceptibility and different sizes may be subjected to an equal magnetic force. Here, the concept of "a ratio of equal suction coefficient" of a particle during magnetic separation is introduced. Other suction particle size ratio d '/ d "depends on many factors, the most important is the magnetic susceptibility than the particles range, the degree of magnetic field inhomogeneity (μ _o Hgrad-H), and media resistance to movement of the ore particles methods ( Upper or lower feed.) This ratio varies from ore to mine and is also related to the type of magnetic separator.
When sorting wide-grain grade ore, it should be pre-screened. The relative magnetic force is constant in an equal magnetic field, so the material before magnetic separation does not need to be graded because any particle size at any position in the magnetic field is subjected to a specific magnetic force equal.
Ore to the upper cylindrical separator monolayer is between d 'and a lower limit d "have a particle size of magnetic mineral crystal size limit difference may be calculated as follows:
Δd=d'-d"==lgK"/Clge=2.311lgK"/π=0.731lgK' (4)
Where k'=X' _bs /X′′ _bs ;
C≈π/ι———magnetic system magnetic uniformity, m ^-1 ;
ι———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 increases as the magnetic field unevenness C decreases (or the pole pitch increases).
The magnetic separation efficiency is calculated as follows:
η=1-em'n' (5)
Where m'--the coefficient related to the magnetic separator structure and sorting conditions (according to experimental data m' ≤ 4);
n'————The selected particles have a relatively poor magnetic susceptibility:
n'=(X' _bs /X" _bs )X' _bs (6)
From the formula 5, it is concluded that when the selectivity is given (X′′ _bs /X′ _bs = constant, ie n′=constant, the magnetic separation efficiency is determined by m′; and when the magnetic separator structure and sorting conditions are fixed (m' = constant), the magnetic separation efficiency is determined by the coefficient n' calculated according to the required selectivity.

Silicone Bibs

About baby bib:

The mothers have common perplex that they worry the baby get dirt on clothes when they have meal.What can we do to avoid that? Many mothers will buy baby bib! However, the baby bib which is made of cloth is easy to get dirty and difficult to clean! Can we solve this problem ? Absolutely yes! Silicone baby bibs are not only can help you avoid dirty problems when they have meal, but also easy to clean! Why? Because the silicone material is smooth and waterproof, more important , it can dry quickly which save you a lot of time. So, when mothers choose to buy a baby bib, most of them choose the silicone one!