In addition to the main component MgCO3, magnesite ore often contains impurities such as CaCO3, FeCO3, MnCO3, Al2O3 and SiO2. In order to remove harmful impurities and improve the grade of ore, the current industrial beneficiation methods of magnesite mainly include flotation, roasting and chemical treatment.
Flotation
Flotation is a method that uses the differences in physical and chemical properties on the surface of the target mineral and gangue minerals to sort. This method is most commonly used in my country and has become one of the main processes for processing magnesite ore.
Impurities in magnesite can be divided into two categories: silicates (including talc, quartz, serpentine, etc.) and carbonates (dolomite, calcite, etc.). The flotation separation of magnesite generally uses reverse flotation and forward flotation alternately, that is, amine collectors are first used to reverse flotation siliceous minerals, and then fatty acid collectors are used to flotate magnesite. The positive flotation of magnesite should be carried out under alkaline conditions. Adding water glass, sodium hexametaphosphate or Aspergillus can selectively partially inhibit dolomite and other calcium-containing minerals.
Magnetic separation
The application of magnetic separation in magnesite mineral processing is mainly to remove iron impurities in the ore. The presence of impurity iron in magnesite is very harmful to the refractory performance. Fe2CO3 and Al2O3 react with CaO to generate low melting point minerals C2F (1436°C) and C4AF (1415°C); iron oxide is reduced to metallic iron. It will also cause molten holes to form in refractory products. Therefore, it is necessary to remove iron impurities in magnesite.
Magnesite ore contains iron in different forms. Iron in magnesite ore with MgO ≥ 47wt% usually contains about 0.07wt%, and it exists in the form of homogeneous isomorphism in magnesite crystals; in magnesite dolomite crystals, iron is present in the form of homogeneous isomorphism. It exists in the form of images or in the form of FeCO3 microscopic inclusions. The iron that exists in magnesite as isomorphic admixtures is difficult to remove, while the FeCO3 in magnetite, limonite, and chlorite embedded in magnesite as particles cannot be removed after grinding to a certain level. The mesh can be basically separated.
Reselection
The gravity separation method can be used to replace hand separation to improve the recovery rate of magnesite. This method is only suitable for processing lump ore with lower raw ore grade and coarser particle size. The gravity separation method generally uses a heavy medium mineral separation method. The heavy medium used is generally ferrosilicon or a mixture of ferrosilicon and magnetite. The addition of magnetite can reduce the amount of more expensive ferrosilicon by 20% to 25%. The gravity separation equipment used is usually a conical resuspension separator, a drum resuspension separator and a heavy medium cyclone.
Roasting method
Roasting method is a method that uses the thermodynamic properties of different minerals in ores to sort. When magnesite is roasted to 800~1000℃, CO2 will decompose and escape. The resulting light-burnt magnesium is brittle, soft and brittle, while the gangue mineral talc will become hard as the temperature increases, so it can By utilizing this hardness difference between the two to selectively crush the burned ore and then screen it, the two minerals can be separated.
In January 2020, Dai Shujuan and others from Liaoning University of Science and Technology publicly invented a patent: a thermal separation process for low-grade hydromagnesite ore. First, low-grade hydromagnesite with a particle size of -2mm is used as raw material, and the hydromagnesite is roasted at a temperature of 850-950°C and kept for 160-200 minutes to basically decompose the hydromagnesite; then the hydromagnesite is The product after roasting magnesite is put into a 60-mesh or 65-mesh sieve, and wet sieving is performed using liquid fuel without water as the medium. Useful minerals with differences in particle size after roasting are separated from impurity-containing minerals, and SiO2, CaO, Al2O3 and Fe2O3 impurities improve the purity of hydromagnesite light-burned magnesium oxide. The advantages are: the thermal separation process of low-grade hydromagnesite ore uses anhydrous ethanol as the wet screening medium. The MgO content of the obtained light-burned magnesium oxide is more than 97%, and the thermal separation concentrate yield is more than 70%.
Overall, the roasting method is low-cost and simple. However, it also has certain limitations. Especially when processing ores with complex mineral composition or high calcium type, its effect is relatively poor. Therefore, this method is generally only used as a pretreatment or pre-enrichment operation for other sorting processes.
chemical treatment
For magnesite ores whose minerals are embedded in fine particles and whose impurities are homogeneous, it is difficult to obtain satisfactory sorting indicators using conventional mineral processing methods. When processing such ores, it is generally Use chemical methods.
The chemical treatment method of magnesite ore is to first calcine the ore at high temperature to improve its surface activity and increase its solubility, and then leaching with hydrochloric acid or nitric acid, sulfuric acid, ammonium salt, bicarbonate, etc. Depending on the leaching degree of magnesium and impurities, different methods are used to precipitate and separate the impurities, and finally obtain high-purity MgO products. The chemical treatment method to extract basic magnesium carbonate from magnesite can be divided into hydrochloric acid method, ammonia method and carbonization method.
In addition to the above methods, methods such as electric separation can also be used to sort magnesite. For example, photoelectric separation uses mineral surface color differences to sort minerals, which is one of the main processes that replaces manual selection in the mineral processing process. Electrostatic beneficiation is a process that utilizes the rectification properties and critical potential differences of minerals to achieve mineral separation in a high-voltage electric field. Japan uses the difference in critical potential of magnesite, calcite and talc to achieve effective separation of magnesite from talc and calcite by adjusting the high-voltage positive potential of the electrostatic concentrator. Overall, the magnesite beneficiation method is mainly determined by the origin of the ore, the composition of associated minerals, etc., so a large number of beneficiation tests are needed to determine the best beneficiation plan.