Wollastonite is a triclinic system, thin plate-like crystals, and the aggregates are radial or fibrous. The color is white, sometimes with light gray, light red tones. Vitreous luster and pearl luster on the cleavage surface. The hardness is 4.5~5.5, and the density is 2.75~3.10g/cm3. Completely soluble in concentrated hydrochloric acid. Under normal circumstances, it is resistant to acid, alkali and chemical corrosion. Hygroscopicity is less than 4%. Low oil absorption, low conductivity and good insulation. Wollastonite is a typical metamorphic mineral, mainly produced in the contact zone between acid rock and limestone, and coexists with fushan stone and garnet. Also found in deep metamorphic calcareous crystalline schist, volcanic eruptions and some alkaline rocks. Wollastonite is an inorganic acicular mineral, which is characterized by non-toxicity, chemical corrosion resistance, good thermal stability and dimensional stability, glass and pearl luster, low water absorption and oil absorption value, excellent mechanical and electrical properties, and certain properties. Reinforcing effect. Wollastonite products with long fibers and easy separation, low iron content and high whiteness. This product is mainly used as a reinforcing filler for polymer matrix composites. Such as plastics, rubber, ceramics, coatings, building materials and other industries.
Wollastonite belongs to a chain metasilicate, and is also a fibrous and needle-like silicate. Because of its special crystal morphology and crystal structure, wollastonite has good insulation, high whiteness, good dielectric properties and high heat and weather resistance. Because wollastonite is widely used in ceramics, chemical industry, metallurgy, papermaking, plastics, coatings and other fields.
The chemical molecular formula of wollastonite is CaSiO3, the structural formula is Ca3[Si3O9], the theoretical chemical composition: CaO 48.25%, SiO251.75%, transparent brittle crystal with glass texture or pearl texture. Pure wollastonite is rare in nature. In the process of its formation, Ca is sometimes partially replaced by Fe, Mn, Ti, Sr and other ions to form a homogeneous body, and is mixed with a small amount of Al and a small amount of K, Na, so it has a white color. , gray-white, light green, pink, brown, red, yellow and other colors, mixed with white stripes. Due to the different conditions such as temperature and pressure during the formation of wollastonite, three homogeneous polymorphs may appear:
①Tc-type wollastonite with triclinic chain structure, commonly known as low-temperature triclinic wollastonite (α-CaSiO3);
②ZM-type para-wollastonite with monoclinic chain structure, commonly known as para-wollastonite (α′-CaSiO3);
③ Pseudo wollastonite with triclinic ternary ring structure, commonly known as pseudo wollastonite (β-CaSiO3).
Low-temperature triclinic wollastonite is widely used as an industrial mineral raw material.
Low-temperature triclinic wollastonite is a triclinic crystal system, most of which are needle-like, fibrous or flake-like, often clustered in fan-shaped, radial aggregates, and some are in the form of fine particles. White microstrip gray, red, vitreous luster, the cleavage plane is pearl luster, the cleavage plane is parallel and medium, and the intersection angle of the two groups of cleavage planes is 74°. The density is 2.78～2.91 g/cm3, the hardness is 4.5～5, and the melting point is 1540℃. The thermal expansion coefficient is low, the thermal expansion coefficient is 6.5×10-6 mm/(mm·℃) at 25～800℃, the PH value is 9.9, and it has excellent heat resistance, corrosion resistance and weather resistance. ; It can be converted into pseudo wollastonite at about 1125 ℃, the thermal expansion coefficient increases at this time, and the color changes from white to cream, red or brown due to the release of impurities such as Fe and Sr. The natural types of wollastonite ore usually have two types: skarn type ore and wollastonite-quartz-calcite type ore. The former is mainly produced in skarn deposits, with complex mineral components, often associated with skarn minerals such as quartz, calcite, diopside, and garnet; the latter is mainly produced in contact metamorphic and regional metamorphic deposits, with mineral groups. The points are simple and can be divided into 3 subtypes: wollastonite-quartz, wollastonite-calcite and wollastonite-quartz-calcite. There are usually two kinds of structures of wollastonite ore: dense massive ore with fine-grained granite or fibrous crystal structure, dense massive structure, wollastonite is a fine granular, columnar or fibrous aggregate, and individual extremely Fine-grained and dense ones are jade-like; coarse-crystalline wollastonite ore has a fibrous crystalline structure, massive, breccia-like, giant spot-like or strip-like structure, wollastonite crystals are coarse, plate-columnar, bundle-like or radial (Chrysanthemum-shaped).
Wollastonite also has unique technological properties, such as the use of wollastonite raw materials, which can effectively reduce the shrinkage of the green body. Moreover, the hygroscopic expansion of the green body can be reduced, and the later dry cracking of the ceramic green body can be prevented. The wollastonite-containing body also has higher mechanical strength and lower dielectric loss. The green body of wollastonite is introduced into the sintering process, and the maturity speed is accelerated, and the green body can be matured within ten minutes to several tens of minutes, which greatly reduces the heat loss per unit product. , down to just 50 minutes. Wollastonite was first introduced into the formulation of glazed tile blanks, which reduced the thermal energy loss of the tile from 3600 kcal/kg to 1850 kcal/kg product. In addition to glazed tiles, wollastonite raw material has expanded its application range. The effect of its energy saving and consumption reduction has been obvious to all people in the ceramic industry.
The purification task of wollastonite is to select harmful iron minerals and reduce the content of limited minerals such as calcite, tremolite, garnet, and quartz. The purification methods include hand selection, screening, magnetoelectric separation, flotation and combined selection.
Wollastonite as an emerging raw material of industrial concern comes from its special needle-like structure. In addition to being fine-grained and surface-activated like other mineral powders, the aspect ratio should also be maintained as much as possible. Natural wollastonite products can be divided into five categories according to particle size: block, ordinary powder, fine powder, ultrafine powder and needle powder. The preparation method of powder is mainly mechanical pulverization. The equipment used for wollastonite plagiarism processing includes gravel mill, jet mill, high-speed mechanical impact magic machine, etc. Mechanical pulverization can be divided into dry method and wet method, wet method saves energy and protects the fiber aspect ratio; mechanical pulverization based on shear force can obtain wollastonite ultrafine powder with high aspect ratio.
The papermaking-grade wollastonite powder can still maintain its unique needle-like structure after special processing technology, so that the white board paper added with wollastonite powder can improve its whiteness, opacity (surface covering degree), flatness, smoothness , Adaptability, reduce quantitative transverse difference and wet deformation of cardboard, improve printing adaptability, and can greatly reduce the use of various other raw materials, and reduce the cost of paper products in general.
Adding appropriate amount of wollastonite powder to the ceramic raw materials can greatly reduce the firing temperature, shorten the firing time, and achieve low-temperature and rapid one-time firing. It saves a lot of fuel and significantly reduces the cost of the product; at the same time, it improves the mechanical properties of the product, reduces the crack and warpage of the product, increases the luster of the glaze, and improves the strength of the embryo body, thereby improving the qualification rate of the product.
Wollastonite can be used to make brake pads, ceramic glaze, etc., and is widely used in automotive, metallurgy, ceramics, plastics and other industrial production. Among them, the most promising field of wollastonite consumption in the world is the engineering plastics industry. As a filler and reinforcing agent in the plastics and rubber industry, wollastonite is increasingly replacing metal parts in industrial finished products. Demand is growing rapidly.
Due to the improvement of processing methods and the acquisition of ultra-fine particles, potential new uses are being discovered one after another, making wollastonite more and more widely used. According to the forecast of foreign experts, the proportion of wollastonite applications in the future is as follows: 6% in the ceramic industry and related departments; 22% in coatings, plastics and decorative materials; 5% in asbestos substitutes; 12% in insulating ceramic foams for daily insulating items; Insulating ceramic foam for construction 6%; ceramic foam for refractory insulating layer 2%; ceramic foam for foundry production 4%; slag concrete block surface coating 3%; paper production 40%.
It has a good reinforcement, which can not only improve the toughness and durability of the coating, but also keep the coating surface smooth and good gloss. Moreover, it improves the resistance to scrubbing and weathering, reduces the oil absorption of coatings and inks, maintains alkalinity, and has anti-corrosion capabilities. Can get high-quality bright color paint, and has good leveling and anti-aging properties. The coating can get better mechanical strength, increase durability, enhance adhesion and corrosion resistance. There is also good coverage and adhesion.
With unique needle-like fibers, it has good insulation, wear resistance, and high refractive index. It is a good filling material for plastic and rubber products. Features and performance: Wollastonite powder can improve impact strength, enhance fluidity and improve tensile strength, impact strength, linear tensile and mold shrinkage.
It is a special needle-like structure with unique physical and mechanical properties of wollastonite. Greatly enhances the friction resistance and heat resistance of the finished product. When the product is filled into it, it can improve the characteristics of friction flexibility and stability.
After special processing technology, it can still maintain its unique needle-like structure, so that the white board paper added with wollastonite powder can improve its whiteness, opacity (surface layer coverage), flatness, smoothness, adaptability, reduce Quantitative transverse difference and wet deformation of cardboard, improve printing adaptability, and can greatly reduce the use of various other raw materials, and reduce the cost of paper products in general.
It is a kind of non-toxic, odorless, non-radioactive and other advantages that gradually replace asbestos which is harmful to human health, and become a new raw material for environmental protection building materials in the new century. After special processing technology, it can still maintain its unique needle-like structure, which greatly improves the impact resistance, bending strength and wear resistance of materials such as silicon calcium board and fireproof board with wollastonite acicular powder. In the field of building materials, wollastonite will be more widely used.
An appropriate amount of wollastonite powder is added to the ceramic raw material to improve the qualified rate of the product.
The world's wollastonite resources are abundant, and the total resources are estimated to be more than 800 million tons, but the distribution is very uneven. Only more than 20 countries have found wollastonite deposits, mainly distributed in China, India, Kazakhstan, Uzbekistan, Tajikistan, America, Mexico, the United States and other countries in Asia, with proven reserves of 300 million tons; in addition, Finland, Turkey , Namibia, South Africa, Sudan, Canada and Yugoslavia have also found wollastonite deposits.
China and India are the countries with the most abundant wollastonite resources in the world. Although China's wollastonite geological prospecting started relatively late, since 1975, great progress has been made in more than 20 years. More than 100 mineral deposits have been discovered in 17 provinces and autonomous regions, with an estimated resource of nearly 200 million tons. As of the end of 1996, there were 31 mining fields with proven reserves in 14 provinces and autonomous regions, with ore reserves of 132.65 million tons, ranking among the top in the world. Huojiadian, Lishu County, Jilin Province has the largest retained ore reserves, accounting for 40% of the national total retained ore reserves; the rest are Yunnan, Jiangxi, Qinghai, and Liaoning provinces, accounting for 49% of the national retained ore reserves; Zhejiang and Hunan 5 provinces, Anhui, Inner Mongolia and Guangdong, account for 10% of the country's reserves; Jiangsu, Guangxi, Hubei, and Heilongjiang account for 1% of the country's reserves.
Among the 31 mineral fields with reserved reserves in my country, after the reserved ore reserves are converted into mineral reserves according to their grades, the scale of wollastonite deposits in the National Mineral Reserves Committee's "Wollastonite Geological Exploration Specifications" (trial) belongs to the extra-large scale. There are 6 mines, 12 large mines, 5 medium-sized mines, and 8 small mines. Among them: 18 mining sites have been exploited, including 4 extra-large mines, 8 large-scale mines, 2 medium-sized mines, and 4 small-scale mines, occupying a total of 76.61 million tons of retained ore reserves, accounting for 58% of the national retained ore reserves ; 10 mines are available, including 2 extra-large mines, 3 large mines, 1 medium-sized mine, and 4 small mines, with a total retained ore reserves of 48.16 million tons, accounting for 36% of the national retained ore reserves; Due to coexistence with other minerals, it is difficult to mine and select and due to poor mining conditions, there are 3 mining areas that are difficult to use, including 1 large mine and 2 medium-sized mines, with a total retained ore reserves of 7.88 million tons, accounting for 6% of the national retained ore reserves. %.
Production, storage and transportation:
The main production methods of wollastonite are as follows:
First, it is formed by calcining and melting calcium oxide and silicon dioxide at high temperature;
Second, in 150-200 mg of a mixture of calcium hydroxide and silica gel with a molar ratio of 1:1, add 5 mL of conductive water, use a silver-lined autoclave, and treat at 200 ° C for 10 days or at 180 ° C for 14 days. In the future, it is filtered, washed with acetone, and air-dried to obtain tombstone (CaO·SiO2·16H2O). If this compound is heated to above 800°C, it will be dehydrated and converted into β-CaSiO3;
Thirdly, using the cooling of α-CaSiO3 for the preparation, the transfer of α-CaSiO3 to β-CaSiO3 is difficult in pure solid state, and even with relatively slow cooling, it is difficult to make the conversion proceed. Therefore, add calcium metavanadate Ca(VO3)2 which is about a fraction of its weight in α-CaSiO3 as flux, heat for several days at 800-900°C, extract with water and dilute hydrochloric acid to remove vanadate, namely β-CaSiO3 can be obtained;
Fourth, pure quartz and calcium carbonate are mixed at a ratio of 1:1 (molar ratio) of CaO/SiO2, put into a platinum crucible and fully melted at a temperature above 1500°C.
The storage conditions of wollastonite are mainly: to ensure that the storage container is sealed, the workshop has good ventilation or exhaust device, and it is placed in a cool and dry place.
my country's wollastonite output and export volume ranks first in the world. my country's wollastonite industry has an annual output of 550,000 tons. The products are exported to Asian countries such as Japan, South Korea and Southeast Asia, and European countries such as Germany and Spain. The export volume reaches 200,000 tons, accounting for 70% of the international market. The main market for my country's wollastonite exports is Europe, with an export volume of about 150,000 tons per year. The products exported to Japan and South Korea are mainly ultra-fine needle powder. The wollastonite industry has achieved overall profits, but the profits are still very low. In particular, the appreciation of the RMB and the reduction of the export tax rebate rate from 8% to 0 have compressed the profit margins of enterprises. The increase in processing costs has brought a lot of pressure to corporate profits.
From the perspective of import volume, the data shows that from January to September 2016, my country's wollastonite import volume reached 1,645.12 tons, an increase of 18.53% compared with the same period of the previous year. From the perspective of export volume, the data shows that from January to September 2016, my country's wollastonite export volume reached 151,200 tons, an increase of 2.86% compared with the same period of the previous year. Due to the continuous growth of domestic and foreign wollastonite market demand and the gradual increase in price, some large international companies pay close attention to my country's market and resource advantages, and try to seize my country's high-quality wollastonite resources through joint ventures, mergers and acquisitions, and then monopolize the market. Domestic enterprises and the policy departments of the regions where the resources belong should be cautious about the intervention of foreign capital, make rational and proper use of resources, and ensure the healthy development of the industry and enterprises.