Magnetite Recovery by Magnetic Separation in Coal Preparation
In the process of coal mining and washing, magnetite powder, as a key medium in the dense medium coal preparation process, its efficient recovery and recycling are not only related to the control of coal washing costs, but also directly affect the separation efficiency of coal resources and the economic benefits of enterprises. As the core equipment for magnetite powder recovery, the magnetic separator realizes the precise separation of magnetite powder from coal slime and water through the specific adsorption of magnetic minerals by magnetic field force, and has become an important technical support for resource recycling in the coal washing process.
Principle of Magnetite Recovery by Magnetic Separation
The core principle of magnetite recovery by magnetic separation is based on magnetism technology. In the coal washing process, magnetite powder has strong magnetism (specific magnetization coefficient > 38×10⁻⁶cm³/g), forming an obvious magnetic difference with non-magnetic impurities such as coal slime and gangue. When the coal slurry containing magnetite powder (i.e., dense medium suspension) enters the magnetic field area of the magnetic separator, the magnetic particles (magnetite powder) will be adsorbed on the surface of the drum by the magnetic force generated by the magnetic field, rotated with the drum to the non-magnetic field area, and separated from the drum under the action of gravity or flushing water to form magnetite powder concentrate; while the non-magnetic particles are discharged from the tailings outlet with the slurry flow, thus completing the recovery and purification of magnetite powder.
Please refer to the details of Wet Drum Separator
Magnetite Recovery Process Based on Magnetic Separator (Analysis Combined with Flow Chart)
1. Coal Slurry Pretreatment Link
The coal slurry generated after coal washing (containing magnetite powder, coal slime, fine gangue, etc.) first enters the thickener for preliminary sedimentation. The addition of flocculant accelerates particle sedimentation, reduces the amount of water and fine mud entering the magnetic separation system, and improves the magnetic separation efficiency. The thickened underflow (concentration about 30%-40%) is used as the feed of the magnetic separator, and the overflow returns to the coal washing water circulation system.
2. Core Link of Magnetic Separator Separation
The pretreated coal slurry enters the permanent magnetic drum separator (commonly used models in coal mines, such as CTN and CTB series). The permanent magnetic system inside the equipment generates a strong magnetic field. When the slurry flows through the surface of the drum, the magnetite powder is adsorbed on the surface of the drum, and non-magnetic impurities such as coal slime are discharged from the tailings tank below with the slurry. In this process, by adjusting the drum speed (usually 15-30r/min), feed concentration (25%-35%) and magnetic field strength (adjusted according to the particle size of magnetite powder, generally 1000-2000Gs) of the magnetic separator, the separation effect can be optimized to ensure that the recovery rate of magnetite powder reaches more than 90%.
3. Concentrate Purification and Circulation Link
The magnetite powder concentrate (concentration about 50%-60%) discharged from the magnetic separator enters the filter (such as disc filter) for dehydration treatment, so that the moisture content is reduced to below 10%, forming a directly reusable magnetite powder product. The purified magnetite powder is transported to the dense medium preparation system and reconfigured into a qualified dense medium suspension (density 1.2-1.8g/cm³) for recycling in the coal washing process, realizing the closed-loop utilization of resources.
Advantages of Magnetite Recovery by Magnetic Separator
High Recovery Rate and Low Loss: With efficient permanent magnet system design, the recovery rate of magnetite powder can reach 90%-95%, significantly reducing the consumption of magnetite powder per ton of coal washing (from 2-3kg/t in traditional processes to 0.5-1kg/t), with significant annual cost savings.
Strong Adaptability: It can handle magnetite powder of different particle sizes (0.05-0.5mm), and has a good recovery effect on fine-grained magnetite powder generated due to wear during coal washing, adapting to the complex characteristics of coal slurry in coal mines.
Stable Operation and Low Energy Consumption: The equipment has a simple structure, no vulnerable parts, the single-machine power is usually only 1.5-5.5kW, the operation failure rate is low, and the maintenance cost is only 30%-50% of that of traditional recovery equipment.
Environmental Protection and Resource Recycling: It reduces environmental pollution caused by magnetite powder discharge, and realizes medium recycling at the same time, which meets the requirements of green and low-carbon development of coal mines and helps enterprises meet environmental protection discharge standards.
Practical Application Effects and Case Reference
After a large coking coal enterprise introduced 3 sets of CTB-1230 magnetic separators to form a magnetite powder recovery system in the coal washing plant, the unit consumption of magnetite powder decreased from 2.1kg/t to 0.8kg/t, with an annual coal washing capacity of 1.5 million tons, saving about 2.8 million yuan in magnetite powder costs annually; at the same time, the coal slurry discharge decreased by 40%, and the sewage treatment cost decreased by 15%, with significant comprehensive economic and environmental benefits. This case shows that magnetic separators can effectively improve resource utilization in magnetite powder recovery in coal mines and create considerable economic value for enterprises.
Development Trend and Optimization Direction
With the intelligent upgrading of coal washing processes, magnetic separators will develop towards automatic control in the future. Through online monitoring of slurry concentration, magnetic field strength and concentrate grade, parameter automatic optimization will be realized; at the same time, the application of new high-gradient magnetic separation technology will further improve the recovery rate of fine-grained magnetite powder (<0.074mm). Combined with the magnetic separation-flotation combined process, the collaborative recovery of magnetite powder and associated rare metals can be realized, providing a new path for the comprehensive utilization of coal mine resources.