The following is a brief introduction to the main methods, technologies and equipment of nonmetallic mineral processing in China.
I. Mineral processing and purification
After the 1990s, the mineral processing and purification technology of nonmetallic minerals in China has made great progress: ① the varieties of nonmetallic minerals purified by mineral processing have increased compared with before; ② Purification process of traditional nonmetallic minerals (such as graphite, asbestos, kaolin, mica and fluorite). ) has been improved; ③ Remarkable progress has been made in the high-purity processing technology of fine nonmetallic minerals. Thus, a large number of low-grade and fine-grained useful minerals are recovered, and the recovery rate of non-metallic mineral resources and the comprehensive utilization rate of other resources are significantly improved.
At present, the mineral processing methods and selected minerals commonly used in China are introduced as follows:
(1) flotation method
Used for graphite, fluorite, quartz, feldspar, nepheline syenite, bauxite, kyanite, cassiterite, andalusite, diamond, etc.
(2) Re-election method
1) is sorted according to particle size and used for clay minerals such as washed kaolin, bentonite, attapulgite clay, sepiolite and illite.
2) Sorted by relative density, used for andalusite, diamond, etc.
(3) magnetic separation
Used to remove iron from white minerals used as coatings and fillers, impurities from raw materials of refractories, iron from raw materials of electrical insulation materials, etc.
(4) Electrical separation
Used to purify tourmaline, rutile, zircon, garnet, actinolite and other minerals.
(5) chemical beneficiation
1) chemical bleaching, which removes iron oxide from clay minerals by reduction and pyrite by oxidation.
2) Chemical purification, that is, chemical methods are used to remove impurities from minerals, which are used for graphite, diamond, cassiterite, andalusite, diatomite, kyanite, etc.
3) Selective flocculation, that is, the polymer flocculant absorbs some mineral particles in the fine-grained pulp to form flocs, but does not absorb other mineral particles, and is still in a dispersed state. Polymer selective flocculation separation is mainly used for selective flocculation of kaolin and selective flocculation and purification of bauxite, which can effectively remove hematite, rutile and other impurity minerals.
(6) Friction selection
Used to separate fiber minerals such as asbestos, fibrous brucite and flaky mica.
(seven) the main problems existing in the purification and processing of non-metallic minerals.
1) The recovery rate of mineral processing is not high and the comprehensive utilization rate of resources is low.
2) Industrialized high-purity processing technology and equipment can't meet the needs.
3) The degree of mechanization and automation is not high, and some mines (such as talc, calcite, wollastonite, etc. ) or use manual selection.
Second, ultrafine grinding and classification
Use mechanical force or chemical mechanical force to make nonmetallic mineral products reach the required fineness.
(1) superfine grinding and classification process
There are three processes: dry process, wet process and dry-wet process.
1) The principle flow of dry ultrafine grinding process (Figure 1-2- 1) is as follows:
Figure 1-2- 1 Flow chart of dry superfine grinding principle
This process is used to process ultrafine powder with D97 > 5 microns. ..
2) There are many processes for wet ultrafine grinding, and the principle flow (Figure 1-2-2) is generally as follows:
Figure 1-2-2 Flow chart of wet ultrafine grinding principle
This process is generally used to process ultrafine powder with d97≤5μm and powder materials with special requirements on particle shape and surface properties.
3) Dry-wet combination process: it is mainly used to produce powder products with different specifications (or fineness), such as superfine grinding of coal-series calcined kaolin and heavy calcium carbonate production enterprises. Dry grinding is used to grind d97 (> 5) ~10μ m, and then wet ultrafine grinding is used to grind paper coatings and heavy calcium carbonate products to d90≤2μm m. The processing of ultra-fine coal-series calcined kaolin is also an example of this wet-dry ultrafine grinding process. For example, the main process flow of "Double 90" product (Figure 1-2-3) of ultra-fine coal-series calcined kaolin is as follows:
Figure 1-2-3 principle flow chart of superfine grinding with dry and wet combination
(2) Ultrafine crushing equipment
The research and development of ultrafine grinding equipment for non-metallic minerals in China began in the early 1980s. After importing a large number of foreign technologies and equipment and digesting and absorbing them, they developed rapidly and successively developed equipment suitable for China's national conditions. 10 years later, China entered the stage of independent development and manufacturing, supplemented by introduction. From the late 1990s to the present, the number of superfine grinding technologies and equipment with independent intellectual property rights or invention patents in China has greatly increased compared with the previous decade, and the comprehensive performance of equipment in terms of processing capacity, energy consumption per unit product, wear-resistant materials, process matching and automatic control has been significantly improved, and the gap with the comprehensive technical indicators of foreign advanced technologies and equipment has gradually narrowed.
1) jet mill superfine grinding equipment is still one of the best equipment for products with small fineness, high purity and large added value. On the basis of imitating and digesting foreign equipment, domestic jet mill has made some innovations, especially in target jet mill, fluidized bed jet mill and improving the wear resistance of flat jet mill. The disadvantage is the lack of several tons of large equipment and high energy consumption per unit product.
2) Mechanical impact superfine pulverizer is widely used in nonmetallic mineral industry in China, which is widely used in nonmetallic minerals with medium hardness such as kaolin, talc and calcite. The fineness of the product can generally reach d97 =10 μ m. If it is matched with a fine classifier, ultrafine powder products with D97 = 5 ~ 7μ m can be produced.
After digestion and absorption, the domestic ultra-fine pulverizers include: CM5 1 ultra-fine pulverizer, DTM900 ultra-fine pulverizer, CLM-2 multi-stage rotary pulverizer, LHJ ultra-fine pulverizer, JCF 1000 mechanical pulverizer, JZC-400 graded impact pulverizer, CZM impact pulverizer and so on.
3) Medium and ultra-fine mills include stirred ball mills, vibrating ball mills, drum ball mills and grinding strippers, tower mills, sand mills, planetary ball mills, etc. Domestic stirring mill has been widely used in kaolin, heavy calcium carbonate and other enterprises, and dry or wet grinding can be used. Wet-milled mineral products can reach about d97 = 2 microns, and the fineness of dry-milled mineral products can reach d97 = 6 microns ... The types of stirring mills are: JM vertical spiral stirring mill, which is used for superfine grinding of heavy calcium carbonate, kaolin, barite, zircon sand and other minerals; Domestic vibration mills include single cylinder, multi-cylinder (2-3) type, WGM-3 frequency conversion type and MGZ- 1 type high-amplitude vibration mills, which are widely used for fine grinding and ultra-fine grinding of graphite, talc, kaolin, barite and other minerals. Vibrating ball mill can be used for superfine grinding of materials with various hardness. The fineness of domestic equipment products can reach about D90 = 20μ m, and the fineness of wet grinding products can reach about D97 = 5μ m ... The particle size range of drum ball mill is very wide, and it often forms a closed-circuit process with classifier. When the feed particle size is less than or equal to 5 mm, the fineness of the product can reach D97 = 6 ~ 7 microns ... There are many kinds of domestic leather grinders, such as 20 L, 80 L, 300 L, 500 L, 800 L, etc. Wet grinding and multi-stage series continuous grinding are adopted, and the fineness of the product can reach about D95 = 2μ m, which has been applied to wet ultrafine grinding of coal-series kaolin and heavy calcium carbonate. The domestic CTM tower mill uses special natural pebbles as grinding medium and classifier, which can be used for ultrafine grinding of talc and bentonite. The fineness of the product can reach about d97 =10μ m. There are two types of sand mills: horizontal and vertical. Domestic sand mills are mainly used for grinding and dispersing pigments and fillers, and in recent years, they are also used for regrinding graphite concentrates. The fineness of the product can reach about d97 = 2μ m. The continuous planetary ball mill is one of the important advances in the field of superfine grinding technology in China, and the large-scale industrialization of the equipment has been realized. XQ600× 1500×3 continuous planetary ball mill is used for ultrafine grinding talc, calcite and other minerals, which can grind mineral raw materials with particle size ≤5mm into products with fineness ≤ d9710 μ m, and the output reaches 2000 ~ 3000 kg/h.
4) Cyclone mechanical mill (LHJ) is a new type of dry fine grinding and ultra-fine grinding equipment independently developed in China. It is used for grinding limestone, calcite, talc, wollastonite, kaolin, barite, feldspar and other materials. The feed particle size is less than or equal to ≤40mm, and the product fineness d97 = 40 ~15 μ m. If it is matched with a fine classifier, it can produce ultrafine powder products of about d976 ~ 7 μ m. ..
5) High-pressure jet mill (ultra-fine peeling homogenizer) has utility model patent. The equipment has been used for ultrafine grinding of mica and kaolin. According to the particle size of the feed, the product with D97 = 10 ~ 45μ m can be obtained by one-time crushing.
The main problems existing in ultrafine grinding of nonmetallic minerals are: the equipment is not large enough, and the output of some large-scale air mills and fine air classifiers abroad is ten times higher than that of China; Most production lines are basically controlled by manual operation, and the product quality is not stable enough; Wear and high energy consumption per unit product; Special superfine grinding equipment with special crystal form has not been developed.
(3) Fine classification equipment
1) At present, domestic dry classification equipment is mostly used around mechanical impact superfine pulverizer or air jet pulverizer, and the fineness of products classified by MS classifier can reach about D97 = 10μ m; The fineness of products classified by MSS and ATP classifier can reach about d97 = 6 microns. The product fineness of LHB dry fine classifier developed by our country can reach D97 = 5 ~ 7μ m, and the hourly processing capacity is 2 ~ 15t.
2) Domestic wet classifier. There are two types: one is a hydraulic classifier based on gravity settlement principle, and the other is a cyclone classifier based on centrifugal settlement principle. The latter includes settling centrifuges, such as WL-350A, D and WLDB-600; Horizontal spiral centrifugal separator (stage), small diameter hydrocyclone, LS centrifugal screen, GSDF superfine hydrocyclone, etc. These are the main equipment for wet classification of ultrafine powders such as kaolin in China at present. Among them, the fineness of overflow products of settling centrifuge (including horizontal spiral centrifugal classifier) can reach about d97 = 2 microns; The fineness of overflow products of GSDF superfine hydrocyclone classifier can reach about D90 = 2 microns; The fineness of overflow product of small-diameter hydrocyclone can reach D80 = 2 microns; The fineness of overflow product of LS cyclone can reach D60 = 2 microns. ..
Third, surface modification.
Many nonmetallic mineral products, as inorganic mineral fillers, play an important role in polymer material industries such as plastics, rubber, adhesives and polymer-based composite materials. Their functions can not only improve the hardness, stiffness, dimensional stability and mechanical properties of materials, but also give them some special physical and chemical properties (corrosion resistance, weather resistance, flame retardancy and insulation, etc.). ). In addition, it can also reduce the production cost of materials.
The commonly used surface modification methods of nonmetallic mineral materials include chemical coating method and precipitation reaction method, supplemented by mechanochemical method.
Surface chemical coating is a method to coat the surface of nonmetallic mineral filler by coupling treatment, chelating reaction and chemical adsorption to improve its surface hydrophobicity. The processing process is as follows: a certain amount of surface modifier (solid or liquid) is added to the powder filler, and at a certain temperature, the modifier reacts with the surface of inorganic filler particles and coats the surface of the filler particles by stirring or fluidization. Modifiers mainly include silane, titanate, aluminate, aluminum-titanium complex and other coupling agents; Surfactants such as stearic acid; Organic oligomer such as polyethylene wax and polyethylene glycol; Saturated organic acids such as polymethylsiloxane (silicone), acrylic acid, crotonic acid and vinyl acetate. The main manufacturers are: Zhangjiagang Guotai Huarong Chemical New Materials Co., Ltd., Chongqing Jiashitai Chemical Co., Ltd., Nanjing Shuguang Chemical No.1 Factory and dozens of others.
At present, SLG and PSC continuous powder surface modification machines are widely used for surface modification. SLG surface modifier has the advantages of automatic dosing, continuous production, controllable temperature, less consumption per unit product, low energy consumption, highly dispersed particles, high degree of automation and simple operation. The main models are SLG-3/300 and SLG-3/600; PSC machine is also a kind of powder surface modification equipment with good comprehensive performance. Heat transfer oil is used for heating, continuous production, less modifier consumption, high surface coating rate and non-adhesion of particles.
Precipitation reaction modifier uses chemical precipitation to form one or more coating layers on the surface of mineral particles. For example, TiO _ 2, ZrO2 _ 2 and FeO are used to coat the surfaces of mica, kaolin and other powders, while TiO _ 2 is used to coat the surfaces of SiO _ 2 and Al _ 2O _ 3 particles. Modification by precipitation reaction is realized by using inorganic surface modifier.
The surface modification technology of nonmetallic minerals in China is still backward, and the continuous modification technology and equipment need to be further promoted. There are few kinds of coupling agents, and the quality is not stable enough; The production technology of colored mica and pearlescent mica is backward, with low output, few color varieties and unstable quality, which need to be strengthened in the future.
Fourth, thermal processing.
Heat treatment can remove external water, zeolite water and hydroxyl water from minerals, thus improving the properties of minerals. Calcination can also remove organic matter and whiten some minerals, especially coal-series kaolin (including minerals such as black talc). Some minerals (such as vermiculite) can expand several times or dozens of times under the action of heat and have new functions.
Calcination is an important method to improve the characteristics of nonmetallic mineral materials, and it is also one of the important processes for deep processing of kaolin, magnesite, gypsum and other mineral products. These products are mainly used in papermaking, plastics, coatings, rubber, petrochemical and other industries. For example, calcined kaolin has excellent light scattering ability and special ink absorption. As a paper coating material, compared with ordinary washed kaolin, it can greatly improve the gloss, smoothness, opacity and base paper coverage, which is why it can improve the paper coating quality and replace the expensive titanium dioxide. As a filler in plastics and rubber, it has better strength, shrinkage, flame retardancy, hygroscopicity and resistivity than ordinary kaolin. In paints and other coatings, adding calcined kaolin can make the products have better opacity, film integrity and scrub resistance.
Calcined coal-series kaolin is a unique processing technology in China, including the integration of processing technologies such as wet superfine, calcination whitening, drying, dispersion, depolymerization and classification, and corresponding special equipment, which can produce calcined kaolin series products used in many industries. The above technology and equipment have been applied in many coal-series kaolin enterprises in Xinzhou, Datong, Meng Xi, Inner Mongolia and Huaibei, Anhui, and achieved remarkable economic and social benefits. The scale of the enterprise has also increased from the initial annual output of several thousand tons to the annual output of 30 thousand to 50 thousand tons.
Calcination process: Take the calcination of coal-series kaolin as an example (Figure 1-2-4).
Figure 1-2-4 Flowchart of Calcination Principle of Kaolin in Coal Measures
Calcination equipment: tunnel kiln, rotary kiln (including direct calcination and flame-proof calcination), vertical kiln, inverted flame kiln and shuttle kiln are mainly used for nonmetallic minerals. The flame-proof rotary kiln introduced and imitated in 1990s has developed into a direct-fired rotary calcining kiln in recent years, which improves the energy utilization rate and significantly reduces the energy consumption and production investment. At present, due to the large-scale equipment, the direct-fired rotary kiln calcination technology and depolymerization classification technology are adopted, which not only ensures the product quality (product whiteness ≥95%, product granularity -2μm≥92%), but also reduces the investment of 10,000 tons of capacity from about 50 million yuan to about 20 million yuan.