Although there are many uses of bentonite, the four fields with the largest amount are drilling mud materials, iron ore pellet binders, sand binders for casting, petroleum products and edible oil decolorants. The amount of bentonite used for these three purposes accounts for more than 3/4 of the total bentonite, followed by civil engineering, animal feed, waterproof sealing materials and pesticide carriers. The consumption of bentonite for other purposes accounts for a small proportion.
1. Iron ore pellet binder
Iron ore pellet binder is the most important use of bentonite at present. In general, 5 ~ 10 kg sodium-based soil should be added to each ton of iron concentrate powder (previously hydrated lime was used as binder). The dried pellets are hard and resistant to beating, which can avoid the loss caused by crushing during transportation, storage and smelting to the maximum extent. At the same time, the pellet has uniform particle size, good reduction performance and uniform chemical composition, which can improve the production capacity of blast furnace and save economy. Bentonite is an ideal bonding material for pellets, and sodium bentonite with pure texture, good viscosity and large expansion is needed to produce pellets.
Quality requirements: The quality requirements of the first-grade sodium bentonite for metallurgical pelletizing in China are: water absorption (2h)≥400%, blue absorption ≥30g/ 100g, swelling index ≥ 15mL/2g, sieving rate (75μm, dry sieving ≥98%) and moisture (65438).
Table 6-3 Main Uses of Bentonite
2. Casting sand binder
Molding sand used in foundry industry is generally composed of standard sand, such as quartz sand, olivine sand and binder, and some additives are added. At present, clay is the most widely used binder for molding sand in foundry industry. Besides clay, water glass, cement, tung oil and synthetic resin are also used.
Bentonite has a long history as a binder and regulator of molding sand in mechanical industry. Bentonite is often added to the silica sand of green sand for casting steel. Generally, about 7.5% bentonite and 3% ~ 5% water are added to 100 part foundry sand. After such adjustment, the surface area of bentonite particles becomes larger, and the contact surface with silica sand becomes wider, which is easy to cover sand particles, thus improving the bonding efficiency of sand mold. This kind of casting sand has good formability, stability and proper air permeability, which can make the casting not honeycomb, and because of its good sand falling performance, it can process a smooth casting surface. At present, the largest amount of bentonite in China is the foundry industry. It accounts for more than 1/4 of the total output.
The requirement of bentonite as binder for sand casting is not very strict. Both kinds of bentonite can be used, but the comprehensive performance of sodium bentonite is better. Different types of metal castings need different technical indexes of sand casting binder. Low-cost calcareous bentonite can be used in iron castings and some non-ferrous metal castings, while some precision castings, high die castings and steel castings need sodium-based bentonite with high melting point and good durability. Sodium bentonite as binder can improve product quality. With the improvement of performance requirements of molding sand binder, the dosage of sodium bentonite for casting will also increase year by year.
See Table 6-4 for the industrial indexes of bentonite for casting, mainly including montmorillonite content, wet compressive strength and wet-heat tensile strength.
Table 6-4 Industrial Index of Bentonite for Foundry (GB/T 20973-2007)
Note: There is no requirement for the wet-heat tensile strength of calcium-based bentonite for casting.
3. Raw materials of drilling mud
Bentonite was used as drilling mud from the late 1920s to the early 1930s, and it is still the most effective mud material for drilling salt-free rocks. Because bentonite has great swelling property, the viscosity of suspension increases and it has better colloidal properties. Especially for high-quality sodium bentonite, the use of synergist can greatly improve the pulping ability, thus improving drilling efficiency and preventing drilling accidents.
Bentonite, as a drilling mud material, is mainly used for drilling in non-salt formations. Because the colloidal stability of bentonite mud in saturated brine is poor, sodium bentonite is mostly used. Because sodium bentonite swells violently into a stable suspension after absorbing water, it can form an impermeable hole wall around the borehole to prevent water leakage such as formation collapse.
The quality standard requirements of bentonite for drilling mud in China are: viscometer reading (600r/min)≥30, yield value ≤3 plastic viscosity, filtration loss ≤ 15.0cm3, and 75μm sieve allowance ≤4.0%. See GB/T 20973-2007 Mud with Viscosity Requirements for the quality requirements of untreated bentonite and OCMA bentonite for drilling mud. To prepare common mud, the concentration of sodium bentonite mud is 6% ~ 8%, and the concentration of low solid mud is 2%.
Bentonite used as drilling mud is measured by mud-making rate, that is, how much m3 mud can be produced by 1t clay in fresh water or salt water that meets viscosity requirements. China's former Ministry of Geology stipulates: the first-class pulping rate >; 16m3/t, grade b pulping rate 10 ~ 16m3/t, grade c pulping rate 6 ~10m3/t; The apparent viscosity is1.5 pa s s; Dynamic shear force < 1.5× plastic viscosity (10-5n/cm2); Water loss (ml/30min): Grade I; 16 m3/t； The apparent viscosity is1.0 ~ 2.51pa s; Water loss (ml/30min): Grade I.
4. Decolorization of petroleum refining
Petroleum crude oil is cracked (thermal cracking or catalytic cracking) to produce a series of petroleum products: gasoline, kerosene, diesel oil and lubricating oil. In addition, waste engine oil, waste transformer oil and liquid paraffin have different colors, so it is unsafe to store and transport. At present, one of the important methods of refining petrochemical products in petrochemical industry is to use activated clay for decoloration and purification. To remove asphaltenes and other impurities. It can also be treated by hydrogenation reaction.
Bleached soil can absorb a large number of impurities such as pigments and mucilage, so it is often used as decoloring agent or bleaching agent when refining petroleum products and various animal and vegetable oils. Generally, activated clay activated by acid is used.
According to foreign patent reports, bentonite can be used as a new catalyst to produce efficient fuel and other petrochemical products from petroleum tailings (such as asphalt and heavy oil). Activated clay is widely used in petrochemical industry.
The quality standards of bentonite for adsorption decoloration are as follows:
The decoloring power meets the inspection standard D> 1 10, and the export activated clay D >；; 150, activity 180 ~ 220, free acid (calculated as H2SO4) < 0.2%, 200 mesh sieve residue < 5%, moisture.
5. Application in civil buildings
Bentonite mixed with cement can be made into various grouting materials for engineering, which can strengthen and prevent seepage in rock mass, gravel layer and soft foundation. Bentonite is of great significance in the production of cement, especially special cement. According to foreign patents, the cement produced by bentonite at present includes impervious cement, water storage cement and thixotropic cement. For example, water storage cement is made of a molding mixture containing a binder and bentonite; The underground foundation is produced with thixotropic cement (formula: bentonite, fly ash, cement, formaldehyde resin plasticizer and water); Anti-seepage mixture for building (formula: bentonite, attapulgite, clay, water), etc. ; Geotechnical material-waterproof blanket.
Using bentonite in waterproof coatings can reduce the dosage of other additives, reduce the production cost of coatings, and improve the quality and waterproof effect of coatings. Example: Used as emulsifier for emulsified asphalt waterproof coating.
Bentonite emulsified asphalt waterproof coating is a thick waterproof material with good stability, which uses bentonite as emulsifier and water as dispersion medium to disperse asphalt under the action of mechanical force. Because of the great polarity difference between asphalt and water, there is a great interfacial tension difference between them, and they are immiscible. If molten asphalt is broken into fine particles by mechanical force and dispersed in water, hot asphalt-water dispersion can be formed. Once the mechanical action is cancelled, asphalt will gather. This phenomenon is because when asphalt is broken into single fine particles, the total surface area increases, while the residual bonding on the surface tends to decrease its total surface area. In order to form a highly dispersed and stable emulsion of asphalt in water, it is necessary to reduce the residual bond energy at the interface between asphalt and water molecules, so this goal can be achieved by adding emulsifiers and stabilizers. Emulsifiers are mostly polar substances, and there are groups of polar substances at one end of the molecule, which tend to be compatible with water; At the other end, nonpolar atomic groups tend to be close to their oil, while emulsifier molecules are oriented at the interface between asphalt and water, making it difficult for asphalt particles to aggregate. So that asphalt forms a uniform dispersion system in water.
Bentonite as an emulsifier is an inorganic emulsifier. Because it is easy to absorb water and swell in water, it has good dispersibility, adhesiveness, suspension and thixotropy, and its particles are fine and the surface residual adhesive force is large. It can be adsorbed on the interface between asphalt and water, reducing the free capacity of the interface and forming a solid particle protective film, which plays a role in stable dispersion.
At present, there are no specific industrial requirements for bentonite used for the above purposes. Calcareous bentonite or low-grade sodium bentonite (often containing more iron and organic matter) is generally used in construction industry.
6. Food processing
Refining of animal and vegetable oils: decolorization, purification and stabilization. Vegetable oil: Rapeseed, cottonseed, soybean, peanut, sesame, palm, etc. will be mildewed to varying degrees due to moisture during storage. The extracted vegetable oil contains a certain amount of Aflatxin (AFT), which is a macromolecular organic substance that will emit strong fluorescence under ultraviolet irradiation. AFT is a super toxic substance, which can cause liver cancer and parasitic aspergillus after human consumption. Especially in the south of China, the climate is warm and humid, and rape, peanuts and corn are the most vulnerable to aflatoxin pollution. Some edible oils extracted from these polluted oilseeds have a content as high as hundreds or even thousands of micrograms per kilogram, and the allowable limit stipulated by the state is
Activated clay can remove toxins and pigments (chlorophyll, lutein, etc. ), the odor and impurities of edible oil. After decoloration, toxins and impurities are removed from the oil, which increases the beauty of the oil color and the safety of storage. Generally speaking, the natural pigment in vegetable oil is harmless to human body, but under the irradiation of sunlight, the pigment easily absorbs the energy of sunlight, oxidizes oil molecules and produces fatty acids.
When the soil content is 1% ~ 3% (oil weight), the crude oil with AFT of 450μg/kg is heated and stirred at 100℃ for 30 ~ 60 min, and the residual AFT content after filtration is
When the amount of soil is 4%, the decoloration rate is as high as 98%. Due to the poor lipophilicity of activated clay, the oil absorption rate is low, which is generally 80% of the soil weight.
Food industry: Biscuits, instant noodles and cakes are all refined oil after decoloration, namely salad oil.
Clarification and purification of beverages, such as decoloration, clarification and purification of wine, sugar juice and beverages. During the fermentation of raw materials for producing wine, sugar juice and beverage, some protein residues and pigments will be produced, which must be removed. Otherwise, precipitation will occur after a long storage time, and the pigment will affect the whiteness and brightness of the final product.
Decolorizer for producing glucose (bright white powder) from corn starch: corn flour is converted into sugar solution under the action of glucoamylase, and then the bright white glucose powder is produced by decoloration, concentration and drying. The fermented sugar solution must be decolorized. At present, some manufacturers use activated carbon as decoloring agent to produce white sugar and rock sugar from sugarcane and beet, and the squeezed sugar solution must also be decolored and purified. Therefore, activated clay has a broad application prospect in this industry, and now some manufacturers are using activated clay to decolorize and purify sugar solution. However, activated clay is hydrophilic and difficult to filter, so it needs further treatment to improve its hydrophobicity. If 10% activated carbon is added to activated clay as filter aid and decoloring agent, the decoloring effect will be better.
7. Agriculture
In agriculture, bentonite is mainly used for soil improvement, water and fertilizer retention agent, carrier of pesticides and fertilizers, diluent, adhesive, seed treatment and animal feed.
Spraying a proper amount of bentonite on dry sandy soil can absorb and store water, prevent the loss of chemical fertilizers and pesticides, and improve crop yield. At present, some foreign countries have gained many successful experiences. According to foreign patent reports, a fatty improver made of bentonite and polyethylene glycol has a good improvement effect on sandy soil. Mixing calcium superphosphate and bentonite can stabilize fertilizers containing nitrogen, phosphorus and potassium and avoid loss.
During the period of 1985 ~ 1996 and 12, the total nitrogen input in China was about 220 million tons, and the nitrogen lost or escaped into the atmosphere was about 100 billion tons. If the nitrogen is calculated at $250 /t, the agricultural nitrogen loss in 12 is as high as $25 billion. According to research, about 1/3 of chemical nitrogen fertilizer applied to soil enters the atmosphere, and N2O in it destroys the ozone layer and produces greenhouse effect. About 1/3 of the fertilizer is leached into the hydrosphere by the soil, resulting in eutrophication of water resources. As a result, the content of NO-3-N in food (especially vegetables) in most areas of China is seriously exceeding the standard, and nitrosamines are easily formed in human and livestock. FAO estimates that 40% ~ 70% of nitrogen fertilizer is lost in the environment, which poses a serious threat to the environment.
The annual consumption of chemical fertilizer in China ranks first in the world, but the utilization rate is low, with 30% ~ 35% of nitrogen fertilizer, 65,438+00% ~ 20% of phosphate fertilizer and 75% ~ 85% of potash fertilizer. During the period of 65,438+0984 ~ 65,438+0994, the amount of chemical fertilizer increased by 90.7%. Kunming Institute of Diatomite Application has successfully developed a mineral nitrogen-fixing agent and applied it to the production of ammonium bicarbonate, which has increased the utilization rate of nitrogen to 59%. 1t ammonium carbonate plus mineral nitrogen-fixing agent, the fertilizer efficiency is 1.66 ~ 1.86t of ordinary ammonium carbonate.
Huainan Institute of Mining and Technology conducted an experimental study on montmorillonite as urea carrier. Experiments show that montmorillonite is also a good carrier of urea, which can adsorb 20% of urea, and the molecular state is mainly located between montmorillonite layers, followed by surface adsorption, thus improving the effective utilization rate of N.
In order to solve the problem of low utilization rate and easy loss of nitrogen fertilizer, a low-cost and excellent slow-release fertilizer was prepared by using the ion exchange ability and adsorption ability of natural porous minerals.
Composite super absorbent resin material (SAR) is a kind of polymer composite material which contains a large number of strong hydrophilic groups such as -OH and-COOH, and has a * * poly cross-linking structure. It can absorb hundreds to thousands of times its own weight, and the hydrogel after water absorption is difficult to dehydrate even under pressure. As a water-absorbing and water-retaining material, it is widely used in agriculture, industry, daily necessities, building materials and other fields.
Bentonite can be used as carrier and diluent of pesticides and fertilizers, which can increase its specific surface area, uniformly disperse pesticide toxicity, save fertilizers and pesticides and improve efficiency.
Using bentonite as animal feed additive can provide a variety of trace elements beneficial to animal growth: calcium, potassium, sodium, magnesium, copper, zinc and so on. It is conducive to the full digestion and absorption of organic nutrients such as opal and minerals, and accelerates the growth of livestock and poultry. Because bentonite has strong adsorption, adding 3% ~ 4% bentonite powder to compound feed can adsorb a large number of nutrients, prolong the residence time of feed nutrients in the stomach of livestock and poultry, reduce the consumption of grain and obtain obvious economic benefits. Reduce livestock and poultry diseases and reduce mortality. Because bentonite has certain adsorption capacity for viruses and bacteria, adding bentonite powder to feed can reduce the occurrence of diseases and mortality of livestock and poultry. 1979 The bentonite used as feed additive in the United States was162,000 tons, accounting for about 4% of the total bentonite production in China that year.
Generally, calcareous bentonite is used as agricultural bentonite, and its characteristics of moderate water absorption and poor cohesiveness meet the needs of agriculture. However, the bentonite used to concentrate urea to produce binder must be high-grade sodium bentonite with expansion coefficient ≥ 10.
8. Medicine and daily-use industries
In medicine, bentonite can detoxify morphine, cocaine, nicotine and nux vomica, improve the suspension performance of barium sulfate used for radioactive inspection and improve the stability of antibiotics.
According to foreign patent reports, medical high purity water can be obtained by treating distilled water with bentonite; Montmorillonite can be used to prepare medicines for treating tinea dampness. High-quality bentonite aqueous suspension can be used as skin cleanser; Adding bentonite to silver sulfide depilatory can prevent skin from being corroded by drugs.
Bentonite can be used as a filler in toothpaste, skin cream and other products in daily use and cosmetics. For example, surfactants used as drugs and lanolin, and surfactants containing cosmetics that are not irritating to the skin.
In the production of soap and soap, replacing some fatty acids with purified bentonite can improve the washing effect, because the adsorption of bentonite can adsorb bacteria and fungi in clothes and washing wastewater.
Sodium tripolyphosphate (STPP) in synthetic detergent is the builder of traditional synthetic detergent, and NaA zeolite produced by bentonite is an ideal substitute for it. STPP has the functions of synthesizing calcium ions and magnesium ions, softening water quality, decontamination and buffering the pH value of washing liquid, and is an ideal builder in common use. However, STPP has a fatal weakness, that is, washing wastewater contains a large amount of residual phosphorus, which will lead to excessive growth of algae and aquatic plants when discharged into the water area, resulting in so-called "eutrophication", leading to hypoxia in the water area, the death of fish or aquatic animals, and the death and decay of excess algae will seriously pollute the water quality. Therefore, many countries in the world are taking measures to ban or limit phosphorus in detergents. They have been looking for a substitute for STPP since 1970s. NaA synthetic zeolite, also known as 4A molecular sieve, has an effective pore size of 0.4nm, and its performance index and safety are ideal, so it is an ideal substitute for STPP. On the premise of ensuring the quality, it can also reduce the cost and has no pollution.
9. Environmental protection
Because bentonite is dispersive and suspended, it plays the role of a collector in sewage purification, and can absorb a large number of suspended solids, with good treatment effect.
Add 10% 200-mesh bentonite powder into the first pulping wastewater of paper mill, fully stir and stand for 24 hours. The wastewater turns from dark black to light yellow, and the pH value becomes 7. If a little aluminum sulfate is added, the effect will be better. And the purified sediment contains a lot of organic matter, which is a good long-term fertilizer after recovery.
The composite adsorbent made of bentonite and aluminum sulfate has certain demulsification, flocculation and adsorption effects on wastewater, and the purification effect is good.
In terms of gas purification, cobalt compounds and bentonite can be roasted at high temperature above 800℃ to make exhaust gas purifier of internal combustion engine; The mixture of chlorate, calcium hydroxide and bentonite containing alkali or alkali metal can be used to remove nitrogen compounds in the air, and the molding mixture of potassium permanganate, bentonite and zeolite can remove atmospheric pollutants.
In addition, bentonite can also be used to purify beverages, sulfuric acid waste gas and distilled water. Adsorption of waste gas: surface modification should be carried out according to the nature of gas (acid gas). Acid gases: SO2, H2S, etc. It should be modified by adding alkaline additives. Acidic additives such as phosphoric acid and sulfuric acid should be added to basic gases: NH3 and organic amine.
10 paper industry
Bentonite can be used as a filler for paper. Adding 1% bentonite to paper pulp can prevent fine particle resin, wax burning, asphalt and other substances from caking, thus ensuring the smoothness of paper, improving the ability of paper to retain pigments, and making the whole paper uniform in color, soft and white, and easy to store.
According to foreign patent reports, bentonite can be made into carbon-free carbon copy paper materials, and can also be made into pens for writing on blackboards and cardboard.
As a color developer for carbonless copy paper. Bentonite used as color developer needs to be modified into lithium-based bentonite, that is, lithium ions are exchanged with other cations between montmorillonite layers. Lithium-based bentonite has the best color effect on leuco dye crystal violet lactone CVL, followed by zinc-based, potassium-based and sodium-based soils. Complete sets of equipment and technology have been introduced to produce carbonless copy paper in China, but almost all raw materials are imported, and the price of color developer is 1200 USD /t, which limits the production and development of carbonless copy paper in China.
1 1. Textile printing and dyeing industry
Because bentonite has high dispersibility and expansibility, it can obtain stable suspension, which can replace a large number of grain starch to make paste.
20 grams of flour is mixed with 100 ml of water and stirred into paste, then 80 grams of bentonite powder wetted with water is added, stirred evenly and cooled. Features: There is no big difference between the performance and starch paste, and the cohesiveness is better than that of pure starch paste; Exposure to the sun for a few days, no dry knot, no mildew; 80% grain saving, low cost. Mainly engaged in cultural office paste, cotton yarn sizing and printing paste in textile industry.
In the early 1960s, China developed bentonite slurry for printing and sizing. While saving a lot of grain, the warp yarn is smooth, lint-free, clean and moldy, which improves the product quality. It can also be used as printing paste instead of starch in printing and dyeing. At present, bentonite is used as printing paste for silk pressing and rayon.
12. Plasticizer for ceramic raw materials
In the ceramic industry, bentonite, as a plasticizer of clay, can greatly simplify the process and be fired once, which can improve the quality and reduce the cost at the same time, and has good economic benefits. In addition, bentonite can also be used to make glaze suspending agent.
The quality requirements of bentonite for ceramics are as follows: Al2O3 >; 15%，fe2o 3+TiO 2 & lt； 1.5%。
13. Other uses
Bentonite can be used as raw materials for lubricating grease, rubber, plastic, ink, paint and other modifiers, as well as for producing desiccants. Its industrial requirements are: cation exchange capacity 60 ~100 mmol/100 g; Montmorillonite content >; 85%; More than 50% are particles with a particle size less than 2μm; It is easily dispersed in water to form a stable colloid. In addition, bentonite can also be used to make fast ionic conductors and pencil lead adhesives.