KYANITE

 
Kyanite is a natural refractory raw material mineral with high refractoriness and high volume expansion. There are parallel stripes on the crystal face. The color is light blue or cyan, bright gray and so on. Belongs to high aluminum minerals.

Chemical composition: Al2O3 63.1%, SiO2 36.9%. A single crystal is often in the form of a long plate or blade parallel to (100). Naturally produced kyanite is often close to the ideal component. Its chemical resistance is strong, thermal shock mechanical strength is large, and thermal expansion is irreversible.

It is the main raw material for the production of amorphous materials, electric furnace top bricks, phosphate bricks, mullite bricks and low creep bricks. It is also a metamorphic mineral, mainly produced in regional metamorphic crystalline schist, whose metamorphic phase is from the green schist facies to the amphibolite facies. Also used as a gemstone ring, bracelet, necklace. Switzerland and Austria are well-known places of origin.

Mineral deposit

Kyanite, the English name for kyanite, is derived from the Greek kyanos and refers to the most common color of kyanite. It is an island-like silicate mineral with a composition of Al2[SIO4]O. It is similar to the andalusite and the scorpion line. It belongs to the triclinic system, and the crystal is in the form of a flat slab. It is often in the shape of a columnar crystal and can be seen as a twin crystal. Sometimes it is a radial aggregate.

The color is blue, white with blue, and cyan. There are two sets of cleaves with {100} complete and {010} medium. The hardness has obvious anisotropy, so it is also known as the hard stone. The Mohs hardness in the direction in which the parallel crystals are elongated is 4.5, the vertical direction is 6, and the specific gravity is 3.53 to 3.65. The 435 nm, 445 nm absorption band is visible. The product of regional metamorphism occurs in crystalline schist and gneiss. When heated to 1300 ° C, kyanite becomes mullite and is a high grade refractory. Aluminum can also be extracted.

Kyanite crystal clear crystal can be used as a gemstone, preferably dark blue. North Carolina, USA has dark blue and green gemstone kyanite. The crystal can be ground into a faceted gemstone or bead, but it is difficult to honed and polish.

The main component of kyanite mineral is kyanite and a small amount of sillimanite, the secondary mineral component is quartz, and the secondary mineral is biotite, phlogopite and chlorite.

The theoretical composition of kyanite is 62.93%, which is 37.07%. Since kyanite mineral crystals often contain a small amount of by-product minerals, the content is generally not up to the theoretical value. For concentrates of kyanite minerals, the content is the sum of kyanite and impurity minerals.

Kyanite is one of the typical regional metamorphic minerals, which is mostly metamorphosed by argillaceous rocks. It is mainly formed under conditions of high intermediate metamorphic pressure. It exists in regional metamorphic schist and gneiss and related crystalline granites and quartz veins. It is symbiotic with garnet, cross stone, mica and quartz.

Physical properties

Symmetrical features: point group 1, space group P1.

Hardness: The hardness is significantly different in all directions, and is 4 to 5 on the fully developed cleavage surface. In the direction in which the vertical crystal is elongated, it is 6 to 7, showing extremely remarkable anisotropy, so kyanite is also known as bismuth.
 
Specific gravity: 3.53~3.64.

Cleavage: (100) cleavage is complete, (010) cleavage is medium to complete.

Fracture: easy to break.

Color: Generally blue, sometimes due to spots on the spar, or uneven texture, resulting in a darker middle color.

Streak: Not obvious.

Transparency: transparent to translucent.

Gloss: Glass luster, the fracture can have a glass luster to pearl luster.

Chemical composition: Naturally produced kyanite, often close to the ideal composition. It may contain elements such as Cr, Fe, Ca, Mg, and Ti.
Crystalline state: crystalline body.

Crystal system: triclinic system.

Crystal habit: often in the form of a columnar crystal, common twin.

Common colors: light to dark blue, green, yellow, gray, brown, colorless.

C axis direction: 4-5

Vertical C axis direction: 6-7

Density: 3.68 (+0.01, -0.12)

Photographic characteristics: heterogeneous, biaxial crystal, negative light.

Refractive index: 1.716 -1.731 (± 0.004 ).

Birefringence: 0.012-0.017.

UV fluorescence: weak

Long wave: red

Short wave: no

Absorption spectrum: 435 nm, 445 nm absorption band.

Magnification check: solid mineral inclusions, cleavage, ribbon.

Special optical effects: cat eye effect (rare).

Optimization processing: unknown.

Cause

Kyanite is an island-shaped aluminosilicate, which belongs to the triclinic system and has a flat long column along the C axis. Sometimes the end of the crystal expands into a cap-like shape. The % crystal face has a streak. % is a metamorphic mineral. It is mainly produced in the regional metamorphic crystalline schist, and its metamorphic phase is from the green schist facies to the amphibolite facies.

There are three forms of kyanite:

(1) Needle-like and fibrous aggregates

(2) Kinematic kyanite aggregates rich in kyanite

(3) Kyanite combined with ore

Place of origin

California, Iowa, Georgia; Canada, Ireland, France, Italy, Switzerland, India, Brazil, North Korea, Australia, etc.

Since the investigation of kyanite minerals in China in the 1940s, especially in the late 1970s and early 1980s, a large number of census exploration work has been carried out, and more than 20 kyanite mines have been discovered, distributed in more than a dozen provinces. Distribution of main deposits: Hanshan in Jiangsu Xiangyang, Hidden Mountain in Henan, Xingtai in Hebei, Point Bus Temple in Inner Mongolia, Braga in Xinjiang, Fanshan in Shanxi, Yuexi and Huoshan in Anhui, Dayougou in Liaoning, Wenchuan in Sichuan, and Hot Water Pond in Yunnan Jilin meteorite, Shaanxi Yangxian Caohekou and so on.

use

Due to the characteristics of kyanite minerals, it is used to manufacture excellent advanced refractory materials, refractory mortar, cement, cast resistant products, plastic beaten mixes, technical ceramics, spark plugs for automobile engines, insulators, ball mill spheres, test vessels, and earthquake resistance. Items, etc. The silicon-aluminum alloy can be refining by electrothermal method and applied to components of airplanes, automobiles, trains and ships. With the development of the steel industry, such mines manufacture key parts such as hot blast stoves, hot air towers, reheat furnaces, soaking furnaces in the form of refractory bricks and profiles. Kiln facilities are also available for use in a variety of auxiliary casting and handling equipment.

They can be used to produce sprayed membranes, the front edge of crystalline fluorspar and supersonic aircraft, metal attachments for spacecraft, and some as gemstones. It can also be used as an abrasive, as a glaze component and as a non-slip flooring material.

(1) Using the permanent expansion characteristics of kyanite at a high temperature (directly added to the unshaped refractory material, such as castable, plastic, and cement as a high-temperature expansion agent), the addition of 5% to 15% can increase the load softening temperature of the product.

Compressive strength, improve the indicator of post-burning line change, eliminate shrinkage cracks, peeling and affecting service life of unshaped refractory materials during high temperature and cooling process, thus prolonging the life of the lining.

(2) Aluminate fiber # produced from kyanite high-alumina minerals can be used to make parts for automobiles, spacecraft and radar.

(3) The mullite formed by calcination of kyanite is used to make high-grade refractory materials, which can be used for high-temperature furnaces to extend the furnace age by 5 to 6 years and save energy.

(4) Adding 5% to 15% of kyanite # in high alumina cement can be made into kyanite cement, and the fire resistance temperature is up to 1650 °C, which can be applied to military buildings.

Minerals are mainly used for the production of refractory materials, alumina, silicon aluminum alloys and metal fibers.

Therefore, the world is paying more and more attention to the development and utilization of kyanite minerals, especially in several developed countries. For example, in Japan, kyanite is an important raw material for refractory concrete, plastic and high alumina cement. The United States and some countries have pre-fired kyanite into various grades of mullite clinker, which are widely used in ceramics and precision casting.

Lightweight brick made in the Soviet Union with kyanite-sillimanite concentrate. The trial of the amorphous refractory material prepared by using kyanite as the expansion agent on the heating furnace is successful, the surface crack is small, the running fire phenomenon is less in use, and the use effect is better. In short, kyanite is a good expansion agent for amorphous refractories.

Refractory

(1) The volume is stable at high temperatures and does not shrink.

(2) Lower than other high alumina refractories.

(3) Good performance. It has a lower pressure of 43% than the clay brick and a refractoriness of up to 1825 °C.

(4) Saving energy. The heat capacity is 12% higher than clay bricks, which can be used in Martin furnaces to shorten smelting time and consume less energy.

(5) Adding to the unshaped refractory material as a high-temperature expansion agent, so that the product does not shrink and peel off at high temperatures. Mainly used in metallurgy, building materials, machinery, chemicals, light industry, nuclear industry and other industries.

Silicon aluminum alloy and metal fiber

(1) The method is lower in cost and economical than the method of synthesizing (using smelting metal silicon and electrolytic aluminum) or using electrothermal reduction of kaolin.

(2) Metallurgical, mechanical, aerospace and other industrial sectors that meet the special technical requirements for the manufacture of automobiles, spacecraft and radar components.

feature

Black cloud pomegranate blue crystal gneiss type ore, the main minerals are kyanite, biotite, plagioclase. The secondary minerals are quartz, bismuth (white) mica, garnet, cross stone, and the like.

Kyanite green mud schist type ore, the main minerals are kyanite and chlorite. Secondary minerals are plagioclase, biotite, muscovite, quartz, graphite, and the like.

Topaz kyanite quartz schist type ore, the main minerals are kyanite, quartz and muscovite. Secondary minerals are topaz, rutile, pyrite and the like.
The eutectic kyanite ore, the main mineral is quartz, kyanite, and the secondary mineral is bismuth (white) mica.

The kyanite mineral is calcined at high temperature (1100-1650 ° C) and converted into mullite and molten free silica (cristobalite), while producing different degrees of volume expansion.

Mullite has a high degree of refractoriness (still stable at 1800 ° C), chemical inertness and good mechanical strength. Its mineral properties are as follows: density (3.16) Mohs hardness (6-7) refractoriness (still stable at 1800 ° C, decomposition of corundum and liquid phase at 1810°C).

Three types of metamorphosis

Kyanite is a metamorphic mineral mainly produced in regional metamorphic crystalline schist, whose metamorphic phase is from the green schist facies to the amphibolite facies. According to the morphological characteristics of kyanite, the kyanite ore is divided into the following three types of metamorphosis:
(1) Needle-like and fibrous aggregates (fibrous acicular ore).

(2) An imaginary kyanite aggregate (artificial ore) rich in blastite.

(3) Kyanite tuberculosis (tuberculous type ore). If the deposit contains the above three metamorphosis, the ore is a mixed type.

Mineral industry type

The industrial types of kyanite deposits are mainly: black cloud pomegranate kyanite gneiss type, kyanite green mud schist type, topaz kyanite quartz schist type, pegmatite kyanite type.

The black cloud pomegranate kyanite gneissic deposit is produced in the Archean metamorphic rock series, and the ore-bearing rocks are mainly kyanite, garnet and biotite slanting gneiss. The single crystal ore body is layered or large lentils. A single ore body is generally extended by several hundred meters and the kyanite content is 10-25%.

The kyanite green mud schist type ore is produced in Archean, and the kyanite is unevenly distributed in the green mud schist. The ore body is lenticular, with a kyanite content ranging from a few percent to more than twenty percent. The original rock contains high levels of magnesium and sometimes contains trace amounts of corundum.

The Huangyu kyanite quartz schist deposit is produced in the Proterozoic quartzite, and the ore is dominated by kyanite quartz schist. Sometimes there are bluestone mica quartz schist, kyanite content 10-30%, containing a small amount of topaz, and see the radioactive polycrystalline pyrophyllite distributed along the fracture.

The eutectic kyanite deposit is a discontinuous lentil body distributed in the Paleozoic biotite schist. The ore composition is simple, and the kyanite crystal is generally above 5 cm.

Pyrolysis

Kyanite is an unstable phase at high temperatures. When heated to a certain temperature, it is converted into mullite and a glass polymer.

That is, when kyanite is calcined at a high temperature, it starts to decompose at 1100, and the decomposition of 1300 kyanite is intensified, and a large amount of mullite is formed. At 1350, the decomposition speed increased and completely decomposed at 1450. When the temperature reached 1500, quartz glass and fibrous mullite crystals began to appear. The cristobalite is formed below 1450. That is to say, the SiO2 which is decomposed by the kyanite at a high temperature exists in the form of a cristobalite phase below the temperature at which the kyanite is completely decomposed.

With the increase of calcination temperature, kyanite decomposition has the following characteristics:

1. The starting temperature of kyanite begins to decompose around 1100.

2. The significant decomposition temperature of kyanite is 1300 or 1360. At this time, the generated mullite reaches 3/4 of the theoretical production amount, and the content is more than 60%. The temperature range for significant decomposition is 1300-1450 or 1350-1450.

3. The temperature at which kyanite is completely decomposed is greater than 1450.

The swelling of kyanite at different calcination temperatures is restricted by its mineralization. The expansion of kyanite is divided into three stages with the increase of temperature:

1. Expansion period:

The temperature is 1100-1300 (or 1350). At this stage, the volume expansion is not large, the kyanite is slowly decomposed, the Molybdenum is incomplete, and the crystal is minute.

2. Inflated drama:

The temperature is 1300-1450 (1350-1450). At this stage, the volume expansion is very large, the kyanite is rapidly decomposed, and the Molai petrochemical is gradually becoming complete.

3. Expansion period:

The temperature is higher than 1450. At this stage, the kyanite has completely decomposed, and the mullite is completely crystallized. The phase transition phase ends with a transition to sintering, and the material expands and even shrinks.

Industrial indicators

The main factors determining the industrial value of the kyanite deposit are the ore-bearing rate (ie, the mineral content of the kyanite deposit) and the mineral chemical composition and physical properties. The general industrial requirements for deposits are shown in the table below:

Raw ore content and mining technical conditions (kyanite)

Boundary grade (%): ≥5

Industrial grade (%): ≥10

Available thickness (m): ≥1-2

Stone removal thickness (m): ≥ 1-2

Note: When delineating ore bodies, the reserves should be calculated according to the kyanite mineral content of 5-10%, >10-15%, >15-20%, >20%.

Process characteristics

(1) Thermal expansion

The kyanite mineral is converted to a mixture of mullite and kyanite during heating. During this transformation, the mineral expands with volume and forms a good ashhole needle network with a volume expansion rate of 16-18%.

The kyanite is heated to 1000 ° C without change, and gradually changes to mullite and white silica at 1300 ° C or higher. In the process of conversion to mullite, kyanite will produce a certain volume expansion and volume expansion: gradual period, dramatic period, falling period, and gradual period.

When the temperature is between 1100 and 1300 °C, the volume expansion of the sample is not large, the decomposition of kyanite is slow, the mineralization of Molybdenum is incomplete, and the crystal is in a microscopic period. When the temperature reaches 1300~1450 °C, the kyanite decomposes rapidly.

The petrochemicals have gradually become complete, and the volume expansion is very large, reaching a maximum drop period at about 1450 °C. When the temperature exceeds 1450 ° C, the kyanite has completely decomposed, and the material developed by Moly Petrochemical basically does not expand or even shrink. The expansion of kyanite is an important basis for evaluating its quality.

The larger the kyanite particles, the larger the volume expansion. On the contrary, the small 'kyanite expansion' is not only related to the particles, but also related to the purity. The higher the purity, the larger the expansion, and the higher the Al2O3 content. Its line expansion also increases.

(2) Stability

Kyanite minerals produce refractory materials that are 1.5 times more stable than clay refractories. Kyanite refractory bricks have a 43% lower loss than clay bricks and 150-200 furnaces longer than clay bricks.

(3) High refractoriness

Typical clay refractories have a refractoriness of 1670-1770 ° C, while kyanite refractories are typically greater than 1790 ° C and up to greater than 1850°C.

(4) Irreversibility

Calcination of kyanite minerals into mullite is an irreversible transformation. It is stable below 1810 °C. Therefore, the mullite refractory material has the characteristics of stable volume at high temperature, low expansion ratio, strong chemical corrosion resistance, high mechanical strength and strong thermal shock resistance.

Mineral processing method

The beneficiation of kyanite minerals generally uses three methods of flotation, magnetic separation and re-election. There are also methods of electrification, but often re-election flotation. Magnetic separation is used as a means of removing impurities.

The specific beneficiation method, chemical system, and selection process shall be determined according to the characteristics of the deposit, the composition of the ore, the structural structure, and the nature of the surrounding rock. Fine-grained kyanite ore is mainly used in flotation.

Because the proportion of kyanite minerals and gangue minerals and gangue minerals is not large, re-election is generally not considered.

Mixed kyanite ore, including two types of ore of coarse-grained and fine-grained inlays, can be combined with a re-floating process.

Development trend

Development status

With the expansion of industrial use, the demand for kyanite concentrate will continue to increase, and its growth rate is generally 5-7% per year. In the steel industry, the growth rate is 10% per year. It is expected that the amount of kyanite required by China's metallurgical industry will reach 40,000 to 60,000 tons next year. In the electrical, radio, chemical porcelain, high-strength porcelain and other industries, the amount of kyanite needed to reach 14,000 tons. If the export capacity is strengthened, it is about 30,000 tons.

The development and utilization of kyanite is in a situation where the product and market demand are not right, and the supply of high quality kyanite is in short supply. Low-quality kyanite products have become saturated, resulting in a large market gap. Research on mineral processing technology should be strengthened to develop economically reasonable high-quality kyanite product production technology and change the contradiction between supply and demand.

trend

(1) The amount of kyanite concentrate in the steel industry, the preparation of floor and wall refractory bricks will increase significantly. The amount used in the glass and ceramic industry will be stable.

(2) The requirements for kyanite concentrates are mainly to the direction of high purity, and the products are developed in various aspects and high quality.

(3) The re-election and reverse flotation process for the production of ultra-purity kyanite concentrate is promising, and application technology research and production conversion should be strengthened.