Activated alumina products have stable performance and wide range of uses

A Application of activated alumina in environmental science   Li Guodong/Books   (Class 02 (2), Environmental Science, School of Chemistry and Environment, South China Normal University, 022424429, Guangzhou, 510006)   Abstract: The properties and preparation of activated alumina are introduced, and its application in environmental science is described, especially the treatment of fluorine-containing wastewater is introduced in detail.

  A Application of activated alumina in environmental science
  Li Guodong/Books
  (Class 02 (2), Environmental Science, School of Chemistry and Environment, South China Normal University, 022424429, Guangzhou, 510006)
  Abstract: The properties and preparation of activated alumina are introduced, and its application in environmental science is described, especially the treatment of fluorine-containing wastewater is introduced in detail.
  Key words: activated alumina, fluorine-containing wastewater, application
  In polluted wastewater treatment technology, adsorption method has the advantages of simple operation, high selectivity and high purification. There are many kinds of solid adsorbents, including activated carbon, diatomaceous earth, adsorption resin, etc. They all have their own characteristics and uses. This paper mainly introduces the application of activated alumina in the environment.
  1 Introduction Activated Aluminum Oxide
  1.1 Types and characteristics of activated alumina
  Alumina is a porous, highly dispersed solid material with a large specific surface area and a microporous surface with adsorption capacity.
  Activated alumina is white or reddish spherical, insoluble in water and organic solvents, but soluble in strong acids, strong alkalis, odorless, tasteless, and non-toxic. It absorbs moisture in the air, and does not expand, crack, and remain in its original state after absorbing water. It is a porous and highly dispersed solid material with a large specific surface, and its microporous surface has an adsorption function. As far as the molecular formula Al2O3 is concerned, it seems to be a simple oxide, but when spatial factors are considered, it is found to be a substance with complex morphological changes. So far, it has been found that more than 8 forms such as χ、η、γ、δ、κ、θ、ρ and α-Al2O3, not only between different forms, but even if the macroscopic structural properties (density, porosity, pore size distribution, specific surface area, etc.) of the same form also depend on their source. Very different. Regarding the adsorption properties of activated alumina, powdered activated alumina are γ-A1203 with a pore volume of 300-800 mm3/g and a surface area of 100-300 m2/g. The pore size is mainly in the range of mesopores, and when in contact with aqueous solutions It is mainly covered by groups, and weak organic acids are mainly bound to it through the coordination matrix exchange mechanism.
  1.2 Preparation method of activated alumina
  Activated alumina is used as adsorbent for adsorption and filtration Activated alumina is made by burning the hydrate of alumina at 400 ° C to 600 ° C, or burning it into a white granular porous adsorbent at 400 ° C to 500 ° C with ordinary alumina adding alkaline metal ions. The mechanism of this method is that fluorine is adsorbed on the surface of the adsorbent to form insoluble fluoride, and at the same time, SO42-on the adsorbent can exchange other anions such as F- and HCO3 in water. The adsorbent can be placed in the filter, the thickness is generally 700~ 1000mm, the particle size is 0.5~ 2.5mm, the filtration speed is 1.5~ 2.5m/n, the supporting layer is pebbles, the thickness is 400~ 700mm, and the pH of the raw water is adjusted to 5.5~ 6.5 by adding acid. The use of small particles of activated aluminum oxide (large specific surface area) can improve the defluorination effect and reduce the cost of water production. When the fluoride removal ability of the adsorbent does not reach the standard, aluminum sulfate can be formulated into a solution of 1% to 2%, passed through the filter column for 6 to 8 minutes at a flow rate of 0.6m/n (the required dosage is about 60 times the amount of fluoride removal) to regenerate, and then repeated use. This method has strong fluoride removal ability and is the best technology for removing various inorganic ions such as fluoride. [1]
  2 Application of activated alumina in the treatment of fluorinated water
  2.1 Toxicity of high fluoride water
  According to statistics, there are currently more than 77 million people in my country who drink high-fluoride water for a long time. Medical research has shown that drinking high-fluoride water for a long time will lead to fluorosis, and patients with severe fluorosis will lose their ability to work, causing a heavy burden on families and society. [2]
  Fluoride is one of the important trace elements in the human body. Fluoride is closely related to human life activities and the metabolism of teeth and bone tissue. Domestic and foreign scholars have reported that long-term excessive intake of fluoride can cause fluorosis. In my country, the epidemic areas of bone fluorosis are quite widespread, and there are reports of bone fluorosis epidemics in cities or villages, mountains or plains, coasts or inland. In addition, with the rapid development of social industrialization, environmental pollution has become one of the causes of bone fluorosis epidemics.
  Fluoride widely exists in nature, and fluoride dissolved in drinking water is more related to fluorosis. High fluoride concentration in water in high fluoride areas can easily cause the epidemic of fluorosis. It is generally believed that the main sources of fluoride causing fluorosis are: fluoride in drinking water and the environment, especially water and air in polluted environments; high fluoride food, etc. Therefore, the hygienic standard for fluoride content in drinking water stipulated by the United Nations Health Organization is 0.5-1.0 × 10-6, and the upper limit is 1.5-1.7 × 10-4. The sanitary standard for fluoride in drinking water proposed by my country is 0.5-1.0-6. Higher than 1.0 × 10-6 may cause disease damage caused by high fluoride.
  2.2 Principle of fluoride removal
  As a conventional fluoride remover, activated alumina has strong removal ability and selectivity for fluorine. In the model of Peri et al., it is pointed out that the surface of the dried alumina surface is divided into two layers containing oxygen ions and aluminum ions. The oxygen ions of the first layer are connected to the aluminum ions of the second layer, and the content is half of it. Therefore, half of the aluminum ions are exposed on the surface; and the number of oxygen ions in the second layer conforms to the Al/O ratio of Al2O3. During dehydration, the adjacent hydroxide ions attached to the second layer remove a molecule of water. After 2/3 of the OH- is removed, one OH- and one exposed aluminum ion remain. The aluminum ion is connected to three oxygen ions and can adsorb multielectronic compounds such as water, ammonia, and hydrocarbons. Therefore, the use of activated alumina as an adsorbent can be used to adsorb fluoride ions present in water. [3]
  The reaction formula is:
  [AlxOy (OH) z] (OH) (3x-2y-z) + (3x-2y-z) F- → [AlxOy (OH) z] F (3x-2y-z) φ + (3x-2y-z) OH-
  That is, F- migrates from the water body to the boundary layer through dispersion, turbulence and molecular diffusion, and then diffuses from the molecules into the particle surface and pores, and reacts with the polyaluminum in the activated alumina to precipitate, and at the same time releases the same amount of OH- The pH value of the water rises. Also due to the difference between the properties of aluminum and fluorine compounds and the properties of the activated alumina itself, the precipitate and the particle itself are not tightly bound enough, so it is easy to fall off and enter the water body under strong dynamic conditions. In the fluoride remover, it appears that part of the fall-off is intercepted by the filtration effect of the filter bed, so that most of it remains in the filter bed. [4]
  2.3 Factors affecting the adsorption effect
  2.3.1 Adsorption time and adsorption effect
  The adsorption capacity of various adsorbents increased with the extension of adsorption time, but after a certain period of time, the adsorption increment of adsorbents tended to be slow.
  2.3.2 Adsorbent dosage and fluoride removal effect
  Adsorbent, the less its dosage, the more sufficient the adsorption, and the better the adsorption effect. Therefore, when using adsorbent to remove fluorine, the minimum amount of adsorbent should be selected based on the floor area, adsorption time, treatment scale, and regeneration method and frequency under the premise of ensuring that the effluent is qualified.
  2.3.3 Solution pH value and fluoride removal effect
  Activated alumina has the worst adsorption effect on F-at about pH 7.0; under acidic or alkaline conditions, its adsorption capacity is significantly improved. [5]
  2.4 Regeneration of activated alumina
  Soak the activated alumina saturated with adsorption in a 100 g/L aluminum sulfate solution for 30 h, discard the solution, and wash it with water for 3 to 5 times, with 2 L of water each time. The surface of activated alumina after long-term use is yellowish-brown, and the fluoride removal effect is reduced. This is caused by the adsorption of impurities. It can be treated with 3% hydrochloric acid once, and then regenerated by the above method. The following problems should be paid attention to when regenerating activated alumina or processing:
  (1) The first regeneration of the filter material is more thorough;
  (2) The adsorption capacity of the regenerated filter material for fluorine is significantly reduced;
  (3) Running the fluoride removal tank without adjusting the pH value of the incoming water for a long time not only saturates the filter material in advance, but also affects the adsorption capacity after regeneration.
  (4) Prolonging the contact time between the activated alumina filter material and the strong alkali regeneration solution can increase the elution rate of fluorine;
  (5) Prolong the soaking time of the filter material in the acid solution, which can neutralize the residual lye of the filter material more thoroughly.
  (6) Adjusting the pH value of the influent within the specified range (6.5-7.0) can not only improve the quality of the effluent, but also prolong the service cycle of the activated alumina filter material, and better exert the fluoride removal function of the filter material.
  (7) The cost of active alumina filter material regenerated by strong alkali is high, and a large amount of wastewater containing strong alkali and strong acid is discharged to seriously pollute the surrounding environment; and the operation cycle of the filter material after regeneration is significantly shortened. This regeneration method is not suitable for the actual operation of the water plant. [6]
  2.5 Application
  A new type of carbon nanotube-supported alumina defluorination material was prepared by using carbon nanotubes and aluminum nitrate. X-ray diffraction detection found that when the calcination temperature was lower than 850 ° C, the alumina was amorphous, and when the calcination temperature was 1 050 ° C, the alumina was A form, and scanning electron microscope observed that carbon nanotubes and alumina were uniformly doped. At the same time, the carbon nanotube-supported alumina composite was used to study the adsorption of fluoride ions in water. The results show that the composite has excellent fluoride removal efficiency. The adsorption and defluorination ability of carbon nanotube-supported alumina composites prepared under the conditions of 30% alumina load and calcination temperature of 450 ° C is 2.0 to 3.5 times that of C2 alumina, which is comparable to the adsorption and defluorination ability of IRA 2410 polymeric resin. The suitable pH range is 5.0~ 9.0. [7]
  Activated alumina is a porous adsorbent with mechanical strength, physicochemical stability, high temperature resistance and corrosion resistance. It has a good effect on the treatment of fluorine-containing wastewater. Activated alumina will play a certain role in other fields.
  The principle of defluorination of B activated alumina
  Fluorine is one of the essential trace elements for the human body. An appropriate amount of fluorine is beneficial to human health, but too low or too much content will endanger health, especially too much will cause fluorosis. The fluoride content of people's daily drinking water is generally controlled at 0.4-0.6mg/L, and long-term drinking of fluoride ion concentration greater than 1mg/L water is not good for the human body. Seriously, it will cause fluorosis, skeletal fluorosis and other diseases, and even induce tumors, which seriously threaten human health.   
  With the development of modern industry, a large number of high-concentration fluoride-containing industrial wastewater has been discharged, and these wastewater generally contains fluorine in the form of fluoride ions (F-). And many enterprises do not have perfect treatment facilities to treat these wastewater. The fluorine content in the discharged wastewater exceeds the national discharge standard, and the fluoride ion concentration should exceed 10mg/L, which seriously pollutes the environment on which human beings depend and poses many threats to human health. Therefore, the research on the treatment of high-concentration fluorine-containing wastewater has become an important research topic in the field of environmental protection and sanitation.
  At present, there are several treatment methods for high-concentration fluorine-containing wastewater at home and abroad, the common ones are adsorption method and precipitation method. Among them, the precipitation method is mainly used in the treatment of industrial fluorine-containing wastewater, and the adsorption method is mainly used for the treatment of dry drinking water. In addition, there are freezing method, ion exchange method, ultrafiltration fluoride removal method, electrocoagulation method, electrodialysis, reverse osmosis technology and other methods.
  The adsorption method is to put equipment containing adsorbents such as activated alumina, polymeric aluminum salt, lignite adsorbent, functional fiber adsorbent, activated carbon, etc. into industrial wastewater, so that fluoride ions can be exchanged with solid media through special or conventional ion exchange or chemical reaction, and finally adsorbed on the adsorbent to be removed, and the adsorbent can also restore the exchange capacity through regeneration. In order to ensure the treatment effect, the pH value of the wastewater should not be too high, generally controlled at about 5, and the adsorption temperature of the adsorbent should be controlled, not too high. This method is generally used for the treatment of low-concentration fluorine-containing wastewater, and the effect is very significant. Because of its low cost and good fluoride removal effect, it is an important method for fluorine-containing wastewater treatment. 2.3 Other methods In addition to the above two more commonly used methods, there are some methods that have not been widely used, but have become the object of research by industry professionals and have achieved good results in some special fluorine-containing wastewater treatment. These include ion exchange, electrodialysis, reverse osmosis membrane method and other methods. Reverse osmosis technology uses a higher pressure than the osmotic pressure to change the natural osmosis direction of water molecules in high-fluoride water, and is separated through a reverse osmosis membrane. It is mainly used in water desalination and ultrapure water manufacturing processes. The current reverse osmosis membranes mainly include low-pressure composite membranes, seawater membranes and cellulose acetate membranes. Electrodialysis is an external direct current field that uses the selective permeability of ion exchange membranes to enable directional migration of ions in water. Ion exchange method is a method of using ion exchange resin or ion exchange fiber to remove fluoride ions. Ion exchange resin needs to be pretreated and regenerated with aluminum salts, so the cost will be relatively high. Compared with ion exchange resin, ion exchange fiber is less expensive, has a larger specific surface area, strong adsorption capacity, fast exchange speed and regeneration speed, has good radiation resistance, and will not cause any pollution to the water body after treatment, but has a cleaning effect. It is an ideal method for deep removal of fluoride ions in water.
  In the process of fluorine-containing wastewater treatment, the actual situation should be selected when choosing the treatment method, and it should be determined according to the water quality situation and the standards required to be met, especially attention should be paid to waste treatment and comprehensive utilization. Therefore, the principle of combining resource utilization and harmlessness should be followed in the treatment of fluorine-containing wastewater to obtain better economic benefits.  
  Preparation Technology of C Series Special Activated Alumina
  1. Technical overview
  Activated alumina generally refers to g-Al2O3, which is usually obtained by heating and dehydrating the corresponding hydrated alumina-pseudoboehmite under high temperature conditions. Determined by the particularity of the catalytic industry, commercial activated alumina is generally hydrated pseudoboehmite. Studies have confirmed that the structural properties of pseudoboehmite determine the performance and use of the final product. Pseudoboehmite produced by different routes and methods has different water content, giving the product ever-changing properties.
  After 20 years of research and development, Shanxi Institute of Coalification, Chinese Academy of Sciences has carried out several industrial scale-up tests to form a complete set of industrial production technologies with independent intellectual property rights. This series of technologies has the following characteristics:
  1. The special synthesis process is used to effectively solve the problem of unstable production.
  2. The produced alumina is mainly used as a petrochemical catalyst carrier and can also be used as special materials.
  3. The reaction system is universal, and different varieties of products can be produced by only changing the raw materials or operating process conditions, including small-hole alumina, medium-hole alumina and macroporous alumina.
  4. Quasi-boehmite can be prepared from a variety of raw materials, such as sodium aluminate solution, aluminum sulfate, aluminum hydroxide, an intermediate for the production of aluminum hydroxide from bauxite/coal gangue.
  2. Main raw materials and sources
  The raw materials that can be used in this technical process include: various cheap aluminum salts, sodium aluminate, carbon dioxide and inorganic acids. The source of raw materials is wide, and cheap waste resources such as coal gangue can also be used as the starting material, and sodium aluminate and aluminum salts can be obtained by alkali or acid dissolution first.
  3. Product use and market
  Activated alumina belongs to special alumina, and its added value is much higher than that of ordinary metallurgical alumina. Activated alumina is mainly used as a catalyst and catalyst carrier in the fields of petroleum, chemical industry, medicine, and fertilizers. According to alumina