Mica often exists in the parent rock of marble, granite and other sand and stone raw materials, while the content of mica in sand and stone aggregate is strictly regulated, and the content of free mica in finished sand is required to be ≤ 2%. The beneficiation method of mica is mainly determined by the composition, distribution characteristics and occurrence state of minerals in the ore. at present, gravity separation, flotation or the combined process of various methods are generally used for separation. Fodamon Engineer explained the following five methods:
- Crushing, screening and sorting
In the crushing process, mica and other symbiotic minerals have obvious selective crushing. Mica minerals are still flake after crushing machine and grinding machine, while other minerals are irregular granular. Screening is carried out with the help of the shape difference of crushing products to realize the mechanical separation of mica and other minerals.
The screening machinery generally includes cylindrical screen and vibrating screen. This method mainly adopts vibrating screens with more than two layers of different screen holes. After the raw ore enters the screen surface, small pieces of flake mica and gangue can leak from the screen seam of the first layer to the screen surface of the second layer through vibration or rolling. Gangue falls under the screen, while flake mica remains on the screen surface to realize separation.
Features: this method has the advantages of simple process flow, less equipment, high production efficiency and strong sorting ability. The required sorting equipment is basically the same as the main processing equipment of the sand and gravel processing system, and can be applied to the sand and gravel processing system. Mica separation can be realized by targeted mica removal transformation of the ordinary crushing and screening process.
- Shaking table reselection
According to the ore properties, there is little difference in the density between mica and its associated minerals, but mica is in obvious flake shape, while other minerals are basically granular. After grinding the raw ore to a certain mesh number, it is placed on the shaking table. Due to the thin flake diameter, mica can be enriched and layered in the light mineral belt, while other minerals are enriched in the heavy mineral belt, so as to realize the separation of mica.
Features: simple process, good sorting capacity, but additional equipment such as shaking table is required, with high energy consumption, large water consumption and large site occupation. Before considering the shaker equipment, the shaker separation test shall be carried out for the crushed ore in the sand and gravel processing system, and the advantages and disadvantages shall be weighed according to the separation effect.
Biotite, iron lepidolite and other mica minerals contain iron and are weakly magnetic minerals. Such mica minerals can be separated by magnetic separation. Tests have shown that after magnetic separation and mica removal, the mica content in the finished sand is greatly reduced and can be controlled within 2%, which meets the sand standard, and the concrete produced by mica free machine-made sand has good mixing performance.
Features: iron bearing mica can be removed. Before considering magnetic separation, the sand and stone processing system needs to conduct chemical analysis on the properties of sand and stone raw ore and the mica minerals contained to judge whether it contains iron, and conduct magnetic separation test according to the iron content. At present, there are successful examples of applying magnetic separation in sand and gravel processing system in China.
- Air separation
The air separation method is a gravity separation method with air as the separation medium. It has a wide application range and can separate ores with different density, particle size, shape, type and properties in the moving air flow. After the raw ore is crushed, the ore morphology changes, and mica has a certain elasticity. When it is crushed together with other minerals, mica is easy to realize extrusion stripping, while other minerals with brittleness are crushed into fine particles. When the minerals in the same particle size fall naturally by gravity, the wind resistance of flaky mica is greater than that of granular gangue minerals, and the decline speed is slow, so as to realize the separation from gangue minerals.
Common air separation methods include vibrating air separation, chamber separation, Kipp Kelly air separation, etc.
Features: this method needs to be combined with screening and other methods to achieve mica separation effect. The principle of air separation is similar to that of dust collector of sand and gravel system, which requires raw ore to be kept dry, so it is only suitable for sand and gravel processing system of dry production. Some data show that when the moisture content of raw ore exceeds 2%, fine sand is easy to adhere to the mica surface, resulting in the blockage of each vibrating screen and affecting the mica removal effect.
- Flotation method
As a widely used beneficiation method, flotation method mainly uses the difference of physical and chemical properties on the mineral surface to selectively enrich one or more target materials at the “solid, liquid and gas” three-phase interface, so as to realize the phase separation from waste materials.
Due to the different pH environment of pulp, the types of collectors used in flotation are also different:
a. When pulp pH < 6.0, cationic collector is generally used;
b. When pulp pH > 9.0, cation and anion mixed collectors are generally used.
Mica flotation includes acid pulp cation flotation and alkaline pulp Cation Anion mixed flotation.
Features: flotation method is mainly used for the recovery of crushed mica and fine mica in gravel industry, especially the mica resources in tailings. Flotation method has strict requirements on the pH value of pulp, and a large number of chemical reagents such as pH regulator and dispersant, collector and inhibitor need to be added. Flotation method has large water consumption, high cost and difficult wastewater treatment, and the added chemical reagents have an unpredictable impact on the quality of concrete.
According to the differences between mica and sand properties, the separation methods are concentrated in physical separation and flotation. Due to the particularity of sand processing system, the physical separation method is a more reasonable choice. The separation principle of air separation mica is simple and the production cost is moderate. It is more practical for the sand and gravel processing system produced by dry method. Mica separation can be carried out by selecting appropriate air separation equipment and air separation process.