What are the uses and social value of clay?

Kiln industry

Ceramic industry

The most common application of clay is in ceramics. The value of clay in this respect is due to its plasticity and its hardening properties after burning. Therefore, it is easy to be molded into various shapes and it will be fixed forever after burning. The finished product can resist pressure and heat.

Famous household ceramics include Chinese porcelain, German Dresden porcelain, Bohemian porcelain and French Sèvres porcelain.

It can make pottery and coarse earthenware (clay is burnt enough to melt some ingredients, so it is impermeable to water).

Kaolinite is fired at a higher temperature to obtain faiences and translucent porcelain for household and sanitary use.

Architecture and engineering

Architecture and engineering

Clay has been used in construction since ancient times. Clay can be mixed with sand or straw to form a puddle-like substance called daub.

Clay can be used to make bricks, tiles and cement (a mixture of limestone and 25% of clay).

When drilling oil wells, mud is often added as an aid. The continuous injection of mud can cool the drill bit and bring out cuttings.

Refractories

Refractories

The walls of high-temperature kilns can be coated with a layer of clay and sand as refractory materials. This coating is very important in brick kilns, glass kilns, bread ovens, and many metallurgical furnaces.

Daily life

Daily life

Clay minerals, especially montmorillonite, have an adsorption effect. In ancient times, the finest clay (ie, bleaching earth) was used to wash clothes and wool.

The lubricative clay minerals can form a stable colloidal suspension, which is very useful for the manufacture of brighteners, cosmetics, pesticides, etc.

Kaolin or argil can be used as the filler and coating for paper, which not only makes the surface of the paper particularly smooth, but also absorbs ink.

Agriculture

Agriculture

Clay minerals can easily absorb many free mineral ions in the soil and easily exchange with hydrogen ions in plant roots. Therefore, clay minerals are the source of mineral nutrients needed by plants.

The aqueduct and sink of the storage reservoir can be covered with a layer of clay, which can lead the water to the vegetable garden and rice fields without leakage.

Industry

Industry

Decolorization of mineral oils

Filtration of beer, wine and molasses

Clarification of water (being used as an ion exchanger)

Degreasing of wool

Model making or artwork modelling, etc.

Medicine

Medicine industry

Clay minerals have been used as active ingredients and excipients of many drugs due to their large specific surface area, rich porosity, good adsorption performance, high adsorption and ion exchange capacity.

They can be:

used for the treatment and protection of stomach and intestinal diseases.

used as pharmaceutical excipients.

used for skin disease treatment.

used as cosmetic accessories, such as clay facial mask.

What are the types of clay?

Because clay is formed from different sources, its composition and properties are also different.

Residual clay

By origin

Residual clay

Its rock is mainly the product of feldspar left in the parent rock area by weathering. Kaolin, quartz and soluble salts are generated after the weathering of the rock. Soluble salts are washed away by rainwater, leaving only kaolin and quartz sand. Due to the presence of quartz sand, this kind of soil is usually called kaolin with poor plasticity, which is the main raw material for preparing china clay.

Residual clay

By origin

Drift clay

It is a clay deposit that is transferred from primary clay to another place by the rainwater and river. It is the main raw material for preparing pottery clay. Its main features are:

A. During the drifting process, due to the heavier phase particles, the quartz sand is deposited first and removed, while the clay itself is thinned by friction, so its plasticity is better.

B. During the drifting process, other minerals or organic matter are mixed, which reduces the purity of clay minerals.

Kaolin

By mineralKaolin

Kaolinite, nacrite, dickite and halloysite are included in this category. Kaolinite is named because it was first discovered in the Kaolin area near Jingdezhen, Jiangxi Province, China. The clay that makes up kaolinite is called kaolin, which is mainly used in papermaking, ceramics and refractory materials.

Montmorillonite

By mineralMontmorillonite

Montmorillonite is widely used in high-temperature grease, rubber, plastic, paint and other industries. The clay mainly composed of them is called bentonite.

(Bentonite, commonly known as argil, has a series of special physical and chemical functions such as good water swelling, cohesiveness, adsorption, catalytic activity, thixotropy, suspension, plasticity, lubricity and cation exchange.)
Illite

By mineralIllite

Illite has a wide range of uses, especially in the three major industries of papermaking, cosmetics (facial mask, sunscreen, foundation make-up, etc.) and ceramics. It is named illite because it was first discovered in Lake Erie, the US. Water mica, sericite, etc. belong to this category. Little of these clays are only made of their own and most are contained in other clays.

Pyrophyllite

By mineralPyrophyllite

Pyrophyllite is suitable for making ceramics, refractory materials, fiberglass, carving stones, etc. It is not a clay mineral by nature, but is classified as the clay because some of its properties are close to those of clay.

Allophane

By mineralAllophane

It is a kind of uncommon clay mineral and is often contained in small amounts in other clays in an amorphous state. It can be used to make refractory clay and porous ceramics.

Classification by refractoriness

Classification by refractoriness

01

Fire clay: The refractoriness of fire clay is above 1580℃, containing no more than 3 ~ 4% of iron oxide and less than 6 ~ 8% of total impurities.

Refractory clay can be used to manufacture lining bricks for metallurgical furnaces, kilns in the silicate industry, coke ovens, etc.

02

Refractory clay: Its refractoriness is 1350-1580℃.

Refractory clay can be used to make ceramic tiles, pottery, stoneware, etc.

03

Fusible clay: Its refractoriness is below 1350℃, containing a lot of impurities and generally plenty of iron.

Fusible clay can be used to make bricks, tiles, coarse earthenware, etc.

Classification by habit

01Kaolin: It is the purest clay with poor plasticity. Its color is gray or white after burning.

02Cohesive soil: Generally, it is secondary clay, so its particles are finer with good plasticity and more impurities.

03Barren clay: It's relatively hard and will not come loose in the water. It is not easy to form a plastic mud ball due to its poor plasticity.

04Shale: Its properties are similar to barren clay, but it contains more impurities (K2O, Na2O, TiO2, CaCO3, Fe2O3, etc.), up to more than 25% at most. After burning, it shows red, brown, yellow, gray or other colors.

Classification by plasticity index

01High plasticity clay: Its plasticity index is greater than 15.

02Medium plasticity clay: Its plasticity index is between 7-15.

03Low plasticity clay: Its plasticity index is less than 7.

Classification by drying sensitivity

01High-sensitivity clay: The drying sensitivity coefficient is greater than 2.

02Medium sensitivity clay: The drying sensitivity coefficient is between 1-2.

03Low-sensitivity clay: The drying sensitivity coefficient is less than 1.

Classification by particle composition
Types Particle content
Clay fractions Dust particles and sand grains
Heavy clay >60 <40
Clay 30-60 40-70
Loam 10-30 70-90
Sandy soil 5-10 90-95
Sand 0-5 >95

What are the properties of clay?

Plasticity of clay

Plasticity is the basic property of clay. The clay mud mixed with moderate water can be formed into various required shapes and it can maintain its shape unchanged. This property of clay is called plasticity.

The plasticity of clay is affected by many factors:

  1. 1The particle size of clay. The smaller the particles are, the larger the surface area becomes, the more attachment points, and the better the plasticity.
  2. 2The particle shape of clay. For example, flaky clay particles tend to slide and bond relatively, so they have higher plasticity than angular ones.
  3. 3The chemical properties of the liquid. Soft sludge can be obtained only by mixing liquids containing hydroxyl groups, such as water. If the clay is mixed with hydrocarbons such as gasoline or kerosene, soft sludge cannot be generated.
The plasticity of clay is divided into the following four categories according to the plasticity index (PI):
Types of clay
(by plasticity)
Plasticity index (PI)
High plastic clay >15
Medium plastic clay 7-15
Low plastic clay 1-7
Non-plastic clay <1

Associativity of clay

The associativity of clay refers to the combination of clay and barren material, forming good plastic muds with a certain dry strength. Generally, the clay with strong plasticity has strong associativity.

Thixotropy of clay

Thixotropy refers to the performance of the clay mud that its viscosity will decrease and fluidity will increase when it is agitated or vibrated, and it will gradually return to its original state after standing.

In actual production, it is expected that the mud has certain thixotropy, but if the thixotropy is too strong, it will affect the flow of mud in the pipeline.

Thixotropy of clay can be expressed by consistency:
The consistency of the mud used for fine porcelain is generally between 1.8 ~ 2.2.
The consistency of refined pottery is generally between 1.6 ~ 2.6.

Drying performance of clay

The drying properties of clay include drying shrinkage, drying porosity and drying strength. After the mud is dried, the particles get close to each other and shrinkage due to the evaporation of water. After the moisture is removed, the voids between the particles are occupied by air, forming pores.

In the production of ceramics, the drying strength of clay or mud directly affects the damage rate of the green body during demoulding, transportation, glazing, trimming, gilding, setting, etc. Especially when adopting mechanization and automation forming, the dry strength of the mud is required to be higher.

Sinterability of clay

The sintering performance is mainly reflected by the firing shrinkage of the clay. During the firing process of clay, due to a series of physical and chemical changes, its length or volume shrinks, which is called firing shrinkage.

In order to facilitate production control, the sintering range of clay is expected to be as wide as possible. The sintering range of high-quality kaolin is up to 200 ℃, the impure clay is about 150 ℃ and the illite clay is only 50 ℃ ~ 80 ℃.

Clay refractoriness

The refractoriness of clay refers to the ability to resist high temperature without melting. In the daily-use ceramic industry, it is an important technical index for the manufacture of refractory materials such as saggers.

The fire resistance of clay depends mainly on its chemical composition. The refractoriness of pure kaolin is 1170℃ and it decreases with the increase of impurities.

Where do you find clay?

The best place to find clay

How to find clay
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Major countries producing clay

The main countries producing clay include the United States, China, Greece, Turkey, India, etc. The specific data are as follows:

Mine production
Bentonite Fuller's earth Kaolin
2018 2019e 2018 2019e 2018 2019e
United States 4,670 4,700 1,880 2,000 5,530 5,500
Brazil (beneficiated) 520 520 - - 1,800 1,800
China 5,600 5,600 - - 3,200 3,200
Czechia 277 280 - - 3,620 3,600
Germany 395 390 - - 4,300 4,300
Greece 1,360 1,400 53 60 - -
India 800 810 6 6 4,000 4,000
Iran 360 360 - - 790 790
Mexico 470 470 110 110 330 330
Senegal - - 178 180 - -
Spain 175 180 625 630 450 450
Turkey 1,500 1,500 20 - 1,400 1,400
Ukraine 110 110 - - 2,400 2,400
United Kingdom - - - - 1,000 1,000
Other countries 2,230 2,200 345 350 13,400 13,000
World total (rounded) 18,500 18,500 3,220 3,300 42,200 42,000

Source: https://pubs.usgs.gov/periodicals/mcs2020/mcs2020-clays.pdf

Drying of clay

Natural air drying

Natural air drying

Water-based air-dried clay is a natural modelling clay that hardens when dried. It does not need to be fired or baked because it only requires to place the clay block for several hours in a ventilated and dry environment.

Oven baking

Oven baking

An oven is needed for the solidification of polymer clay (or any heat source, if small enough, such as beads, you can easily use a hairdryer). Otherwise, it will not dry out.

Clay dryer drying

Clay dryer drying

Because the clay is buried deep in the ground for a long time, the clay contains few sand particles and water cannot easily pass through it, so it contains a lot of water. Therefore, it needs to be dried and dehydrated to ensure that the final moisture content is below 0.5-1% before it can be applied to industrial production on a large scale.

Features of Fote Clay Dryer:

Methods to improve the working efficiency of clay dryer:

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Grinding of clay

Clay ore is an important mineral that makes up clay rock. After processing, it can be used as the main raw material for ceramics and refractory materials. It can also be used in petroleum, textile, papermaking, construction, painting, catalyst, cement and many other fields.

Clay ball mill is a grinding equipment for grinding clay to the range of 0.173-0.044mm. The processed clay has greater application value and is widely used by people.

Firstly, after the raw ore of the clay mine is crushed in the jaw crusher, it is sent to the silo by a bucket elevator, and then it is evenly and quantitatively fed into the ball mill by the vibrating feeder for grinding.

The grinding of clay

The ground fine clay powder is effectively sorted in the analyzer under the airflow of the fan. The finished products that meet the fineness will be sent to the storage bin along with the airflow through the pipeline device, otherwise, it'll be sent back to the ball mill for further grinding. The finished product is finally produced.

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grinding

Calcination of clay

Clay is a common type of material calcined in rotary kiln equipment, but it is also the most troublesome processing material.

Clay is mainly composed of materials containing water-containing aluminium silicate. In the calcination process of rotary kiln, kaolin is the most common materials followed by montmorillonite.

Calcination of clay

Taking kaolin as an example, it is mainly composed of kaolinite. When it is heated to 100 degrees in the kiln, its kaolinite will lose the adsorbed water. When the temperature continues to rise to 400-600 degrees, it will lose the constitution water and becomes metakaolin, and then becomes highly active amorphous oxide alumina and silicon oxide. Because of the detachment of hydroxy radical in the metakaolin, it promotes another reaction with calcium oxide and produces other chemical products.

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