Aluminum shells are dissolved in alkali or nitric acid, and in the latter case, partial or complete dissolution of the metallic uranium core is possible.
The dissolution of aluminum in a solution of caustic soda proceeds according to the reaction:
Al+ NaOH+ H 2 0 NaAlO 2 + 1,5H 2 , (3.1)
flowing with the release of heat 7000 kcal / kg of dissolved aluminum. With an increase in the concentration of NaOH from 2 to 5 M, the rate of dissolution of aluminum increases by about seven times. Losses of uranium when using NaOH solutions with concentrations up to 30% are very small, but in a 50% solution, the rate of uranium dissolution becomes noticeable. The disadvantage of this process is the release of an explosive gas - hydrogen. To suppress the reaction of hydrogen evolution, oxidizing agents are introduced into the reaction mixture: nitrite or sodium nitrate. In this case, aluminum dissolution reactions proceed according to the equations:
Al + 0.5NaOH + 0.5NaNO 3 + 0.5H 2 O = NaAlO 2 + 0.5NH 2 (3.2)
Al + 0.625NaOH + 0.375NaNO 3 + 0.25H 2 O = NaAlO 2 + 0.375NH 3; (3.3)
Al + 0.85NaOH + 1.05NaNO 3 = NaAlO 2 + 0.9NaNO 2 + 0.15NH 3 + 0.2H 2 O (3.4)
The minimum release of hydrogen occurs at stoichiometric ratios of the last reaction. The dissolution rate of aluminum increases with increasing temperature and concentration of sodium hydroxide. For example, for a solution containing 10% NaOH and 20% NaNO 3 , as the temperature increases from 60 to 100°C, the linear dissolution rate of aluminum increases by about 3 times. Crystallization of sodium aluminate depends on the concentration of this salt in the alkali and can be prevented if the molar ratio of sodium hydroxide and aluminum in solution is 1.65:1.
HNO 3 passivates the surface of aluminum, and therefore, the dissolution is carried out in the presence of a catalyst - mercury nitrate. Possible reactions are:
Al + 6HNO 3 \u003d Al (NO 3) 3 + 3NO 2 + 3H 2 O; (3.5)
Al + 4HNO 3 \u003d Al (NO 3) 3 + NO + 2H 2 O; (3.6)
8Al + 30HNO 3 \u003d 8Al (NO 3) 3 + 3N 2 O + 15H 2 O 4 (3.7)
2Al + 6HNO 3 = 2Al(NO 3) 3 + 3H 2 (3.8)
As HNO3 is formed during the hydrolysis of aluminum nitrate and interacts with Al, acid-deficient solutions are obtained:
Al (NO 3) 3 + 3H 2 O \u003d Al (OH) (NO 3) 2 + HNO 3; (3.9)
HNO 3 + Al + H 2 O \u003d Al (OH) 2 (NO 3) 3 + nitrogen compounds. (3.10)
To describe the process of Al dissolution in 4 M HNO3, the following reaction is applied:
Al+3.75HNO3=Al(NO3)3+0.225NO+0.15N2O+0.1125N2+1.875H2O. (3.11)
However, some data do not confirm the presence of nitrogen in the reaction products. The hydrogen content in the exhaust gases after the condenser is 2–8% at an acid concentration of 1–2 M and rapidly increases for solutions with an acid deficiency, reaching a maximum of 23% at a deficiency of 2 M. This indicates that, as the process proceeds, the stoichiometry of the solution is that the reaction with the formation of nitrogen dioxide gradually decays in favor of other reactions. The consumption of acid for dissolving cast and stamped rods is the same. On average, it is 4 - 4.1 M HNO3 per 1 M of dissolved Al. The lowest acid consumption of 3.8M was obtained by dissolving the stamped rod with a 2M acid deficiency.
The solubility of A1 hydroxides in acidic media is directly proportional to the third power of the concentration of hydrogen ions, and in alkaline media it is inversely proportional to it. At the isoelectric point, aluminum hydroxide has minimal solubility. According to Kolthoff for A1(OH)3, this point lies within the range of pH 6.5-7.5. For the rate of hydrolysis of aluminum salts, there is also a certain optimum pH value, which for concentrations of A BO h from 400 to 100 mg/l ranges from 4.95 to 5.40, and the limiting pH values. at which hydrolysis is still proceeding, are 3 and 6.8.[ ...]
The relationship between solubility and chemical interaction is especially clearly manifested in systems with complex formation. Here we can recall the well-known fact of a sharp increase in the solubility of molecular iodine in water in the presence of potassium iodide due to the formation of polyiodide: N-K1 \u003d K13- Sodium chloride, for example, is practically insoluble in nitrobenzene, but in the presence of aluminum chloride its solubility increases sharply due to the formation of a complex salt Nyayuts, which dissolves perfectly in that solvent.[ ...]
The minimum solubility of aluminum hydroxide lies in the region of pH = 6.5+7.5. Precipitation of aluminum hydroxide begins at pH = 3.0 and reaches a maximum at pH = 7. With a further increase in pH, the precipitate begins to dissolve, which becomes noticeable at pH = 9.[ ...]
Aluminum sulphate is used to purify turbid and colored waters: purified - with high turbidity, unpurified or containing clay and silicate materials as ingredients - with low water turbidity. This coagulant is effective in the pH range of 5-7.5, and the higher the hardness of the water and the lower its color, the higher the optimal pH values of the medium. Relatively low cost, good solubility, lack of special requirements for the handling of dry and dissolved product made aluminum sulfate the most common coagulant.[ ...]
The solubility product of HgS in distilled water is 1.6XIu 52, which corresponds to a residual concentration of mercury ions in solution equal to 2.5X10-21 mg/l. In industrial wastewater, the solubility product of HgS is slightly larger, while the main part of mercury sulfide is in water in the form of finely dispersed colloidal particles, which can be precipitated by coagulating wastewater with aqueous aluminum sulfate Al2 (S04) 3-I8H2O, aqueous iron sulfate FeS04-7H20, CaO lime, a mixture of these coagulants, etc.[ ...]
Thus, the solubility of aluminum hydroxide in an alkaline medium is inversely proportional to the concentration of hydrogen ions to the first degree.[ ...]
When using soluble electrodes (usually iron or aluminum), anodic dissolution of the metal occurs at the anode, as a result of which iron or aluminum cations pass into the water, leading to the formation of hydroxide flakes. Simultaneous formation of coagulant flakes and gas bubbles in the cramped conditions of the interelectrode space creates the preconditions for reliable fixation of gas bubbles on flakes and intensive pollution agulation, which ensures the efficiency of the flotation process. Such installations are called electrocoagulation-flotation. At bandwidth up to 10-15 m3/h, the units can be single-chamber, and with a higher throughput - two-chamber horizontal or vertical type.[ ...]
Some hardly soluble dyes are dissolved together with soda and treated first with a solution of aluminum sulfate, and then with barium chloride.[ ...]
In addition to the listed soluble impurities, natural waters contain insoluble substances in suspension - from coarse suspensions to colloidally dissolved compounds. They are represented by particles of sand, loess, silt and carbonate rocks, aqueous oxides of aluminum, iron, manganese, as well as high-molecular humic substances.[ ...]
During hydrolysis, hydrated aluminum ions donate a proton from a coordinated water molecule, forming successively complex ions [A1 (H20) 5 (OH)] 2+ and [A1 (H20) 4 (OH) 2] +, remaining in solution. When the last neutral complex [A1(H20)3(OH)3] loses water, poorly soluble aluminum hydroxide is formed. Iron(III) salts are also stepwise hydrolyzed. But, unlike aluminum salts, in addition to iron hydroxides, sparingly soluble hydroxosalts can also form.[ ...]
| 2 |
In dilute acid, the solubility of Al2(SO4)3 is higher than in pure water, but with a further increase in the concentration of H2SO4, the solubility decreases sharply, reaching 1% in 60% sulfuric acid. In a stronger acid, the solubility of aluminum sulfate increases again.[ ...]
Freshly precipitated aluminum and iron phosphates can be assimilated by plants, but with aging of the sediments, they crystallize and become less soluble and hardly available to plants. Therefore, phosphoric acid in krasnozems and soddy-podzolic soils is fixed very firmly and much stronger than in serozems and chernozems.[ ...]
It can be seen from the above that the solubility of aluminum hydroxide in an acidic medium is directly proportional to the third power of the concentration of hydrogen ions [Н+]3, and in an alkaline medium it is inversely proportional to [Н+].[ ...]
In acidic solutions with excess aluminum, the most stable solid phase is basic aluminum phosphate. If the pH value is greater than the pH corresponding to the minimum phosphate solubility (pH = 6), then the basic salt is hydrolyzed to aluminum hydroxide, on the surface of which phosphate is sorbed. At a high concentration of phosphate, taranakite is precipitated, which turns into an average salt if the pH of the system increases.[ ...]
Polyacrylamide is a white amorphous, water-soluble substance containing ionogenic groups; upon hydrolysis, it forms acrylic acid and its salts. The mechanism of action of PAA is based on the adsorption of its molecules on particles of water impurities, aluminum or iron (III) hydroxides, formed during the hydrolysis of coagulant salts. Due to the elongated shape of the molecule, adsorption occurs in different places with several particles of hydroxide, as a result of which the latter are bound by polymer bridges into heavy, large and strong aggregates (globules).[ ...]
Only samples with limited water solubility (y=38) are retained by wood pulp in an amount of 60%. The addition of aluminum sulphate causes complete retention of α-CMC, which is independent of the stoichiometric ratio between the amount of A13+ required for complete retention of α-CMC and the amount of OCH2COO groups present in CMC. In other words, the retention of -CMC is determined not only by the production of an insoluble aluminum salt, but also by electrostatic adsorption between the positively charged A1-CMC and the negatively charged cellulose fibers.[ ...]
Developed new technology using soluble amounts of aluminum chloride in the high-temperature process of alkylation of benzene with propylene.[ ...]
This chapter discusses the interaction between aluminum (III) and phosphate over a wide range of concentrations and pH. In order to characterize reactions between dissolved particles and soluble phases, the solubility of aluminum phosphate precipitates was studied. In addition, soluble and insoluble reaction products between aluminum (III) and phosphate were identified, and their concentration distribution was determined over a wide range of pH and P and Al concentrations. These studies were carried out using pure solutions of aluminum phosphates of a certain composition. There were no other dispersed solid phases in the studied system, except for those that precipitated during the interaction between aluminum and phosphate or as a result of a change in pH.[ ...]
In a simplified form, it can be considered that the precipitation by iron and aluminum is very similar in many respects and that the determining factors in both cases are the solubility and the ratio of the concentrations of the added metal ion Me and the orthophosphate present. The process of precipitation by calcium ions is highly dependent on pH, therefore, when calculating the required amount of calcium salt, it is necessary to take into account the alkalinity of the waste water.[ ...]
Iron salts as coagulants have a number of advantages over aluminum salts: better action at low water temperatures; more wide area optimal pH values of the medium; high strength and hydraulic fineness of flakes; the ability to use for waters with a wider range of salt composition; the ability to eliminate harmful odors and tastes due to the presence of hydrogen sulfide. However, there are also disadvantages: the formation of strongly coloring soluble complexes during the reaction of iron cations with some organic compounds; strong acidic properties that increase the corrosion of equipment; less developed flake surface.[ ...]
With a significant content of exchange-absorbed hydrogen and aluminum ions in the soil (for example, in soddy-podzolic soils and krasnozems), many of its properties also deteriorate. Hydrogen ions do not disperse soil colloids, but, entering the absorbed state, cause a gradual destruction of the minerals that make up the soil absorbing complex. As a result, the soil is depleted of the colloidal fraction, its structure worsens, and the absorption capacity decreases. In addition, aluminum and hydrogen ions are displaced from the absorbed state into the solution in exchange for cations of soluble salts. A high concentration of hydrogen and aluminum ions in a solution has a harmful effect on the development of plants.[ ...]
In recent years, a method has begun to be used for obtaining coagulants in electrolyzers with soluble electrodes, called the electrocoagulation method. The essence of the method lies in the anodic dissolution of metals, mainly aluminum and iron, in aqueous media under the influence of electric current followed by the formation of hydroxides. This method allows for effective purification of water from suspensions of mineral, organic and biological origin, colloids and substances in the molecular or ionic state. Electrocoagulation has significant advantages over reagent methods: compactness of the installation, ease of maintenance and the possibility of full automation. This method is promising for use on small autonomous objects (on ships of the river fleet, for small settlements, etc.).[ ...]
The negative effect of high acidity is largely associated with an increase in the solubility of aluminum and manganese compounds in the soil. Their increased content in solution impairs the development of plants even more than an excess of hydrogen ions.[ ...]
Equation (4.17) was solved by trial and error for a pH value corresponding to the minimum solubility of phosphate, about 6. At pH [ ...]
In the study of hydrolysis in the Fe2(504)s-A1203-H20 system at 100 °C, it was found that with an increase in the amount of alumina in the system, the yield of iron in the precipitate of the basic salt increases, reaching 98% at a mass ratio of Al2O3/Fe2(504)3 = 0.111 and 90% HgO. In solution, aluminum oxide is converted into soluble basic aluminum sulfates as a result of chemical interaction. With an increase in the content of iron(III) sulfate in the system, the amount of reacted alumina increases and at a mass ratio of Al203/Fe2(804)3 = 3 and 40% H20 reaches 91%.[ ...]
The course of the coagulation process largely depends on the pH of the medium. When aluminum sulfate coagulant solution is added to water, hydrolysis occurs with the formation of colloidal aluminum hydroxide. The optimal value for wastewater from this catalyst production is pH=7.5-8.5. Figure 1 shows the dependence of the degree of wastewater treatment with a suspended solids content of 1200 mg/l on pH.[ ...]
With an increase in the dose of 50% sulfuric acid within 80-100% of the stoichiometric amount at a temperature of 120°C and a process duration of 1.5 hours, the degree of decomposition of aluminum hydroxide increases. So, for an acid dose of 83.3% (mol. ratio 503/A1203 = lo = 2.5), the degree of decomposition of aluminum hydroxide is 92.4%, while for a dose of 90% (zo = 2.7) in the indicated conditions, the hydroxide completely decomposed. The decomposition of aluminum hydroxide at an incomplete dose of sulfuric acid can be explained by the interaction of hydroxide with aluminum sulfate to form soluble basic aluminum salts, which is discussed in more detail below.[ ...]
The electrochemical method has the following advantages over the reagent method: reducing the load on desalination plants, since when using it, soluble salts do not enter the water, and dosed aluminum is completely removed from the water during its preliminary purification. The method of water desiliconization in electrolyzers with an aluminum anode can be recommended for pre-training water in water treatment schemes at thermal power plants and other industrial enterprises.[ ...]
For activation, 1.5% (calculated as Sig) solutions of sodium silicate are usually used with a degree of neutralization of alkalinity of 80-85%. In the case of using active chlorine, the degree of neutralization of soluble glass is increased to 100% and even some excess of it is introduced. After mixing the reagents, the sol "ripens" for some time, and then it is diluted with water to a SiO2 content of less than 1%. The most promising way to prepare active silicic acid is to treat liquid glass with chlorine and aluminum sulfate, commonly used in water purification processes.[ ...]
When interacting with the soil cover, the processes of leaching of biogens intensify. At pH [ ...]
Blast-furnace and open-hearth slags are obtained as wastes during the smelting of iron and steel and have a different composition: CaO - 30-50%; Si02-12-37; A1203-U-15; MgO-2-10; MnO -0.4-5.6; P205 - 0.1-3.5; S - 0.1 - 4.5%. In most cases, they require pre-grinding. Most of the calcium in the slag is in the form of less soluble silicic compounds (CaSiO3 and Ca2Si04), so the fineness of their grinding should be finer than that of lime flour. In terms of neutralizing ability, basic slags (with CaO + MgO content over 40%) are close to carbonic lime. Their effectiveness is often higher than lime. This is due to the presence of magnesium, phosphorus, manganese, sulfur and other plant nutrients in the slag. In addition, the silicic acid contained in them can reduce the amount of mobile aluminum in soils and contribute to better absorption of phosphorus by plants. For soddy-podzolic soils in areas close to metallurgical plants, blast-furnace slag, rich in lime, is a valuable fertilizer.[ ...]
Fluorine compounds are another group of specific substances, the presence of which has been established in the atmospheric air of a number of populated areas and which can have a significant impact on human health. In the atmospheric air, various fluorine compounds have been found - from relatively well soluble in liquid media of the body to completely insoluble; from highly irritating and corrosive hydrogen fluoride to relatively inert compounds. The main industrial processes that are accompanied by the emission of fluorine compounds into the atmosphere are the production of artificial fertilizers, the production of aluminum and some methods of steel production.[ ...]
The increase in yield from lime and mineral fertilizers when they are applied together in most cases is much higher than the sum of the increases from the separate use of these fertilizers. The effectiveness of physiologically acidic ammonia and potash fertilizers increases especially sharply during liming. These fertilizers, when systematically applied on low-buffer, acidic soddy-podzolic soils, cause their further fertilization. Therefore, with the systematic application of such fertilizers on unlimed soil, the increase in yield gradually decreases, and in subsequent years, as a result of strong acidification of the soil, the yield may be lower than in the control. The positive effect of lime on the effectiveness of physiologically acidic forms of mineral fertilizers is more pronounced when they are applied under crops sensitive to high acidity (beet, corn, wheat), and less or not at all when; application under cultures resistant to acid reaction. The effect of liming on the effectiveness of phosphate fertilizers depends on the properties of the soil and the forms of these fertilizers. The effectiveness of soluble phosphorus fertilizers [for example, Ca(H2PO4)2 superphosphate] on strongly acidic soils with a significant content of mobile aluminum and iron compounds is noticeably increased by liming. When lime is applied in a normal dose, the mobile compounds of aluminum and iron pass into insoluble forms, therefore, the chemical fixation of superphosphate phosphorus by them decreases and its use by plants increases.
When determining the concentration of impurities in drinking and natural water, attention is paid to the volume of nitrates, sulfates, nitrites, chlorides, forgetting about aluminum, the most common metal in nature. Under normal conditions, aluminum dissolves in water with the formation of various compounds that actively react with other impurities. As a result, the substance is saturated with aluminum hydrochloride, salts and other compounds. And this leads to a change in water quality - a deterioration in the chemical composition, organoleptic properties, microbiological, bacterial indicators. 
The official MPC for aluminum in drinking water and natural water bodies is calculated by WHO and environmental organizations. But this parameter does not take into account the numerous ways in which metal enters natural sources and the human body. Therefore, the exact determination of aluminum in water is important.
Aluminum in natural waters
The natural saturation of water with metal occurs due to the ingress of aluminosilicates and some types of clay into it. After their dissolution, the interaction of aluminum with water begins, which directly depends on its pH. Dissolution under natural conditions is slow, but always with the release of hydroxide, bauxite, hydrochloride and other compounds. Substances and aluminum itself are contained both in sea water and in river water. But this is under normal conditions.
Metal enters natural waters from:
- drains of technical and domestic waters;
- effluents of chemical industries (any production increases the concentration of aluminum in waste water 2-5 times);
- building drains and emissions.
Every year, such emissions in environment becomes more and more, and the control over the degree of their contamination is ever lower. In dirty effluents with a high content of impurities and suspensions, aluminum solubility in water passes faster. It enters water bodies in the form of suspended forms, ions and colloids. It is ions and oxides that have increased toxicity. They have a detrimental effect on most living organisms living in natural sources. According to the standards, the concentration of aluminum in natural waters should not exceed 0.5 mg/dm3.
Aluminum in drinking water
The most common metal on the planet will certainly be contained in drinking water. According to the standards and requirements of GOST, aluminum in water must contain in volume:
- no more than 0.5 mg/l in a water substance;
- within 0.2-0.3 mg/l in bottled water;
- within 0.1-0.2 mg/l in filtered water.
Every day, no more than 90 mg of metal should enter the human body. But after the reaction of aluminum with water is completed, toxic impurities also appear in it. Therefore, plumbing, as well as well, borehole substance, should be checked for the concentration of unsafe impurities and components. Below is a table of MACs for aluminum in drinking water and other substances important to human health. 
Why should you drink water with a minimum concentration of aluminum?
Having found out where aluminum appears in the water, it is worth dwelling on the other ways it enters the body. This will help control the daily rate of the metal. The bulk of the chemical element comes from food. 
The metal is also found in:
- cosmetic preparations;
- dishes from the metal of the same name;
- medicines;
- deodorants, etc.
With the standard content of aluminum in water, there will be no effect on the body. With excessive concentration, the nervous system suffers, memory decreases, depression and irritability appear. The consequences do not come immediately. This is due to the fact that not the entire volume of the metal is absorbed by the body. Scientists have also proven that a high content of aluminum in water leads to neurological diseases and disruption of calcium-phosphorus metabolism, which inhibits the production of hemoglobin. Therefore, it is recommended to use a drinking substance with a metal volume of not more than 0.3 mg / l. With such a content of dissolved aluminum in water, the daily intake will not exceed 50 mg/l. For cleaning, household filter systems are used.
Water purification by coagulation
In order for liquid suitable for drinking or technical needs to flow from the taps, it must first be cleaned. This procedure must go through both groundwater and surface water before any use. The above describes what happens when aluminum interacts with water - an unpleasant odor is formed, unwanted impurities, the substance becomes cloudy, and a precipitate appears. Deteriorating the organoleptic qualities of the liquid, some metal compounds can act as excellent coagulants - elements that bind dangerous and unnecessary particles in the substance. They are effectively used to improve the quality of fluid in water treatment systems.
Aluminum sulfate is most often used to purify water for any need. The coagulate is most active in an environment with an acidity of 4.4-6.1 pH. But they are also applied to substances with a pH of 7 to 8. The water treatment procedure is as follows:
- adding aluminum sulfate to the liquid;
- mixing media - complete mixing occurs within 1-3 minutes;
- coagulation, in which the medium passes from one reservoir to another (the process lasts from 30 minutes to 1 hour);
- settling of bound sediment;
- filtration of the purified medium.
At the moment, water purification with aluminum is affordable and effective method removal of suspended particles from liquids. In the course of coagulation, the removal of bicarbonates and carbonates of sodium and calcium is also observed. Upon completion of the water treatment procedure, the consumer receives clean and pleasantly smelling water.
For the first time, aluminum was obtained only at the beginning of the 19th century. This was done by the physicist Hans Oersted. He conducted his experiment with potassium amalgam, aluminum chloride and.
By the way, the name of this silvery material comes from the Latin word "alum", because this element is extracted from them.
AlumAlum is a natural metal-based mineral that combines salts of sulfuric acid in its composition.
Previously, it was considered a precious metal and cost an order of magnitude more expensive than gold. This was explained by the fact that the metal was quite difficult to separate from impurities. So only rich and influential people could afford aluminum jewelry.
japanese aluminum decoration
But in 1886, Charles Hall came up with a method for mining aluminum on an industrial scale, which dramatically reduced the cost of this metal and allowed it to be used in metallurgical production. The industrial method consisted in the electrolysis of a cryolite melt in which aluminum oxide was dissolved.
Aluminum is a very popular metal, because many things that a person uses in everyday life are made from it.
Application of aluminum
Due to its malleability and lightness, as well as its resistance to corrosion, aluminum is a valuable metal in modern industry. Aluminum is used not only for kitchen utensils - it is widely used in auto and aircraft construction.
Also, aluminum is one of the most inexpensive and economical materials, as it can be used indefinitely by melting down unnecessary aluminum items, such as cans.
aluminum cans
Metallic aluminum is safe, but its compounds can be toxic to humans and animals (especially aluminum chloride, acetate, and aluminum sulfate).
Physical properties of aluminum
Aluminum is a fairly light, silvery metal that can form alloys with most metals, especially copper, and silicon. It is also very plastic, it can easily be turned into a thin plate or foil. The melting point of aluminum = 660 °C and the boiling point is 2470 °C.
Chemical properties of aluminum
At room temperature, the metal is coated with a strong Al₂O₃ aluminum oxide film, which protects it from corrosion.
Aluminum practically does not react with oxidizing agents due to the oxide film protecting it. However, it can be easily destroyed so that the metal exhibits active reducing properties. destroy oxide film aluminum can be a solution or melt of alkalis, acids, or with the help of mercury chloride.
Due to its reducing properties, aluminum has found application in industry - for the production of other metals. This process is called aluminothermy. This feature of aluminum is in the interaction with oxides of other metals.
Aluminothermic reaction involving iron oxide (III)
For example, consider the reaction with chromium oxide:
Cr₂O₃ + Al = Al₂O₃ + Cr.
Aluminum reacts well with simple substances. For example, with halogens (with the exception of fluorine), aluminum can form aluminum iodide, chloride, or aluminum bromide:
2Al + 3Cl₂ → 2AlCl₃
With other non-metals such as fluorine, sulfur, nitrogen, carbon, etc. aluminum can only react when heated.
Silver metal also reacts with complex chemicals. For example, with alkalis, it forms aluminates, that is, complex compounds that are actively used in paper and textile industry. Moreover, it reacts as aluminum hydroxide
Al(OH)₃ + NaOH = Na),
and metallic aluminum or aluminum oxide:
2Al + 2NaOH + 6Н₂О = 2Na + ЗН₂.
Al₂O₃ + 2NaOH + 3H₂O = 2Na
With aggressive acids (for example, with sulfuric and hydrochloric), aluminum reacts quite calmly, without ignition.
If you lower a piece of metal into hydrochloric acid, then a slow reaction will begin - at first the oxide film will dissolve - but then it will accelerate. Aluminum dissolves in hydrochloric acid with the release of mercury for two minutes, and then rinse it well. The result is an amalgam, an alloy of mercury and aluminum:
3HgCI₂ + 2Al = 2AlCI₃ + 3Hg
Moreover, it is not held on the surface of the metal. Now, by lowering the purified metal into water, one can observe a slow reaction, which is accompanied by the evolution of hydrogen and the formation of aluminum hydroxide:
2Al + 6H₂O = 2Al(OH)₃ + 3H₂.
Aluminum - destruction of metal under the influence of the environment.
For the reaction Al 3+ + 3e → Al, the standard electrode potential of aluminum is -1.66 V.
The melting point of aluminum is 660 °C.
The density of aluminum is 2.6989 g / cm 3 (under normal conditions).
Aluminum, although it is an active metal, has quite good corrosive properties. This can be explained by the ability to be passivated in many aggressive environments.
The corrosion resistance of aluminum depends on many factors: the purity of the metal, the corrosive environment, the concentration of aggressive impurities in the environment, temperature, etc. The pH of solutions has a strong influence. Aluminum oxide on the metal surface is formed only in the pH range from 3 to 9!
Its purity greatly affects the corrosion resistance of Al. For the manufacture of chemical aggregates, the equipment uses only high purity metal (without impurities), such as aluminum grade AB1 and AB2.
Corrosion of aluminum is not observed only in those environments where a protective oxide film is formed on the metal surface.
When heated, aluminum can react with some non-metals:
2Al + N 2 → 2AlN - interaction of aluminum and nitrogen with the formation of aluminum nitride;
4Al + 3С → Al 4 С 3 - reaction of interaction of aluminum with carbon with the formation of aluminum carbide;
2Al + 3S → Al 2 S 3 - the interaction of aluminum and sulfur with the formation of aluminum sulfide.
Corrosion of aluminum in air (atmospheric corrosion of aluminum)
Aluminum, when interacting with air, passes into a passive state. When pure metal comes into contact with air, a thin protective film of aluminum oxide instantly appears on the aluminum surface. Further, the growth of the film slows down. The formula of aluminum oxide is Al 2 O 3 or Al 2 O 3 H 2 O.
The reaction of interaction of aluminum with oxygen:
4Al + 3O 2 → 2Al 2 O 3 .
The thickness of this oxide film is between 5 and 100 nm (depending on operating conditions). Aluminum oxide has good adhesion to the surface, satisfies the condition of the continuity of oxide films. When stored in a warehouse, the thickness of aluminum oxide on the metal surface is about 0.01 - 0.02 microns. When interacting with dry oxygen - 0.02 - 0.04 microns. During heat treatment of aluminum, the thickness of the oxide film can reach 0.1 µm.
Aluminum is quite resistant both in clean rural air and in an industrial atmosphere (containing sulfur vapor, hydrogen sulfide, gaseous ammonia, dry hydrogen chloride, etc.). Because aluminum corrosion in gaseous media is not affected by sulfur compounds - it is used for the manufacture of sour oil processing plants, rubber vulcanization devices.
Corrosion of aluminum in water
Corrosion of aluminum is almost not observed when interacting with clean fresh, distilled water. Increasing the temperature to 180 °C has no particular effect. Hot water vapor also has no effect on aluminum corrosion. If a little alkali is added to water, even at room temperature, the rate of aluminum corrosion in such an environment will slightly increase.
The interaction of pure aluminum (not coated with an oxide film) with water can be described using the reaction equation:
2Al + 6H 2 O \u003d 2Al (OH) 3 + 3H 2.
When interacting with sea water, pure aluminum begins to corrode, because. sensitive to dissolved salts. To exploit aluminum in sea water, a small amount of magnesium and silicon is introduced into its composition. The corrosion resistance of aluminum and its alloys, when exposed to sea water, is significantly reduced if copper is included in the composition of the metal.
Corrosion of aluminum in acids
As the purity of aluminum increases, its resistance to acids increases.
Corrosion of aluminum in sulfuric acid
For aluminum and its alloys is very dangerous sulphuric acid(possesses oxidizing properties) medium concentrations. The reaction with dilute sulfuric acid is described by the equation:
2Al + 3H 2 SO 4 (razb) → Al 2 (SO 4) 3 + 3H 2.
Concentrated cold sulfuric acid has no effect. And when heated, aluminum corrodes:
2Al + 6H 2 SO 4 (conc) → Al 2 (SO 4) 3 + 3SO 2 + 6H 2 O.
This forms a soluble salt - aluminum sulfate.
Al is stable in oleum (fuming sulfuric acid) at temperatures up to 200 °C. Due to this, it is used for the production of chlorosulfonic acid (HSO 3 Cl) and oleum.
Corrosion of aluminum in hydrochloric acid
In hydrochloric acid, aluminum or its alloys quickly dissolve (especially with increasing temperature). Corrosion equation:
2Al + 6HCl → 2AlCl 3 + 3H 2 .
Solutions of hydrobromic (HBr), hydrofluoric (HF) acids act similarly.
Corrosion of aluminum in nitric acid
A concentrated solution of nitric acid has high oxidizing properties. Aluminum in nitric acid at normal temperature is exceptionally stable (higher resistance than stainless steel 12X18H9). It is even used to produce concentrated nitric acid by direct synthesis.
When heated, the corrosion of aluminum in nitric acid proceeds according to the reaction:
Al + 6HNO 3 (conc) → Al(NO 3) 3 + 3NO 2 + 3H 2 O.
Corrosion of aluminum in acetic acid
Aluminum has a fairly high resistance to impact acetic acid any concentration, but only if the temperature does not exceed 65 °C. It is used for the production of formaldehyde and acetic acid. At higher temperatures, aluminum dissolves (with the exception of acid concentrations of 98 - 99.8%).
In bromine, weak solutions of chromic (up to 10%), phosphoric (up to 1%) acids at room temperature, aluminum is stable.
Citric, butyric, malic, tartaric, propionic acids, wine, fruit juices have a weak effect on aluminum and its alloys.
Oxalic, formic, organochlorine acids destroy the metal.
The corrosion resistance of aluminum is greatly affected by vaporous and droplet-liquid mercury. After a short contact, the metal and its alloys corrode intensively, forming amalgams.
Corrosion of aluminum in alkalis
Alkalis easily dissolve the protective oxide film on the surface of aluminum, it begins to react with water, as a result of which the metal dissolves with the release of hydrogen (corrosion of aluminum with hydrogen depolarization).
2Al + 2NaOH + 6H 2 O → 2Na + 3H 2;
2(NaOH H 2 O) + 2Al → 2NaAlO 2 + 3H 2.
aluminates are formed.
Also, the oxide film is destroyed by salts of mercury, copper and chloride ions.
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