Technical Guidelines for Magnetic Separation Method
2019-08-08 18:31:24xinhai
Magnetic separation is a common method of separation. Magnetic separation is the use of magnetic differences in various minerals to achieve separation in the non-uniform magnetic field of magnetic separation equipment.
Although magnetic separation is a relatively simple separation process, it is not simple in the design and selection of the process. It is not necessary to blindly select the magnetic separation process and equipment according to the mineral type. It is necessary to understand the mineral properties and the magnetic separation process and equipment. It is recommended to seek technical support from the mineral processing equipment manufacturers who have the overall design qualification and experience of the mineral beneficiation to ensure that the process of the magnetic separation plant matches the minerals and the production indicators are not affected.
As different types of minerals have different permeability, they have different performances when they pass through the magnetic field.
The minerals with high magnetic permeability are sucked up by the disk and collected by the aggregate funnel,on the contrary, the minerals with low magnetic permeability are taken out as tailings to be separated.
Magnetic separation method just takes advantage of this property of minerals.
In general, the magnitude of the magnetic force that a magnetic-particle receives in a magnetic field is proportional to the strength and gradient of the magnetic field.
Generally, the minerals to be processed are classified into four categories according to the specific magnetic susceptibility:
1. Strong magnetic mineral, which the susceptibility x>3000×10 m /kg. Such as magnetite, titanomagnetite and pyrrhotite;
2. Medium magnetic minerals, which the susceptibility x = (600 ~ 3000) × 10 m / kg. Such as ilmenite, artifacts and semi-artificial hematite;
3. Weak magnetic minerals, which the susceptibility x = (15 ~ 600) × 10 m / kg. Such as hematite, mirror iron ore,siderite, limonite, pyrolusite, hard manganese ore and wolframite;
4. Non-magnetic minerals, which the susceptibility x<15×10 m /kg. Such as scheelite, quartz, long stone, galena,gold and fluorite.
There are many types of magnetic separators, which are usually classified and named according to the strength of the magnetic field, the type of magnetic media, the working medium and the structural characteristics.
The basic classification method of magnetic separators is divided into three categories according to the strength of magnetic field:
1. Low intensity magnetic separator, which magnetic field strength of the working gap is (0.6 ~ 1.6) × 10 A / m, process strong magnetic minerals;
2. Medium intensity magnetic separator, which magnetic field strength of the working gap is (1.6 ~ 4.8) × 10 A / m, process medium magnetic minerals;
3. High intensity magnetic separator, which magnetic field strength of the working gap is (4.8 ~ 20.8) × 10 A / m, process weak magnetic minerals;
4. Super-conducting Separators, which magnetic field strength can reach (28 ~ 40) × 10 A / m,process weaker magnetic minerals.
According to the working medium, the magnetic separator can be divided into dry magnetic separator and wet magnetic separator. The structure of magnetic separator is affected by the magnetic strength and particle size of selected minerals. In addition to magnetic pulley for selecting the bulk material, the general size of the material can be processed from mm to micron.
As one of common mineral processing technologies, magnetic separation has simple equipment, better mineral processing effect. It is the common beneficiation method of magnetite, manganese, ilmenite and other magnetic. For magnetic technology, what is the factors influencing magnetic technology? We will discuss this problem in the following paragraphs.
The key points in the principle of magnetic separation mainly include magnetic field of magnetic separator and magnetic difference of minerals. Next, let's look at these two aspects respectively.
A magnetic field is a special state in the space around a magnet. A magnet placed in a magnetic field will receive magnetic force. Magnetic fields are not only strong or weak, but also have directions. The magnetic field intensity and gradient size and direction of the separation space of the magnetic separator will affect the magnetic separation effect.
When the mineral particle is in the uniform magnetic field, it is only affected by the steering force. In an uneven magnetic field, mineral particles are subjected to not only steering force, but also magnetic force. The mineral not only rotates, but also moves towards the direction of increasing magnetic field gradient, so that mineral particles with different magnetic characteristics can be separated. Therefore, the distribution of uneven magnetic field will affect the magnetic separation process.
Different magnetic separators have different magnetic field distribution designs. From the strength of the magnetic field, magnetic separator can be divided into weak magnetic field separator (magnetic field strength 0.1t ~ 0.2t), medium magnetic field separator (0.2t ~ 0.5t), and strong magnetic field separator (0.5t ~ 2.0t). According to the type of magnetic field, magnetic separator can be divided into constant magnetic field separator, rotating magnetic field separator, alternating magnetic field separator, and pulsating magnetic field separator.
The common weak magnetic separator includes magnetic drum, wet permanent magnet drum, magnetic sieve and so on. Take the magnetic drum as an example, its magnetic field is arranged alternately along the circumference of N and S polarity, and the magnetic field design is relatively simple. Common magnetic separators with high magnetic field includedry electromagnetic induction roller separators, continuous high gradient separators and pulsating high gradient separators. Most of the magnetic separators with strong magnetic field design is more complex, take dry electromagnetic induction roller type strong magnetic separators as an example,this kind of magnetic separators have single row single roll, double row double roll, double row multi-roll, etc., when the coil is energized, the magnetic field is generated between the induction roll and the magnetic pole, so that the material passing through is separated by the magnetic field.
According to the magnetic difference, the minerals can be divided into strong magnetic minerals, weak magnetic minerals and non-magnetic minerals. Because of the magnetic nature of the minerals, we can use magnetic separation method to separate different minerals, that is to say,the magnetic nature of minerals is the basis of magnetic separation method.
For the strong magnetic minerals, such as magnetite, pyrrhotite, magnetite hematite, etc., the specific susceptibility is more than 3.8*10-5m3/kg, usually using the weak magnetic separator (magnetic field intensity is 0.1~ 0.3t) to separate.
For the weak magnetic minerals, such as chromite, ilmenite, manganese ore, etc., the specific susceptibility is from 7.5*10-6 to 1.26*10-7m3/kg, usually using the weak magnetic separator(magnetic field intensity is 1~2T) to separate.
The magnetic properties of minerals are affected by many factors, and the magnetic properties of minerals in different deposits are different in different areas, and some of them even differ greatly.Therefore, when separating the specific minerals in a certain area, the magnetic magnitude should be determined by the magnetic properties of minerals,and then choose the strong magnetic separation or weak magnetic separation.
In order to enlarge the magnetic differences of the selected minerals, there are still some ways to change the magnetic properties of minerals, such as magnetization roasting, alkali dipping magnetization, magnetic species magnetization, which can change the magnetism of minerals and facilitate the magnetic separation.