Aluminum has properties that are applicable in many industries: military, construction, food, transportation, etc. It is plastic, lightweight and widespread in nature. Many people do not even suspect how widely aluminum can be used.
Many sites and books describe this wonderful metal and its properties. Information is freely available.
In the laboratory, you can produce any aluminum compounds, but in small quantities and at high prices.
Element Production History
Until the mid-nineteenth century, neither aluminum nor the reduction of its oxide was discussed. The first attempt to obtain aluminum was undertaken by chemist H.K. Oersted and ended successfully. To restore the metal from its oxide, he used amalgamated potassium. But no one understood what happened in the end.
Several years passed, and aluminum was again obtained by the chemist Weller, who heated anhydrous aluminum chloride with potassium. The scientist worked hard for 20 years and, finally, managed to create granular metal. It resembled silver in color, but was several times lighter than it. For a long time before the beginning of the twentieth century, aluminum was valued more than gold and exhibited in museums as an exhibit.
Somewhere in the beginning of the XIX century, an English chemist Davy electrolyzed aluminum oxide and obtained a metal called "aluminum" or "aluminum", which can be translated as "alum".
Aluminum is very difficult to separate from other substances - this is one of the reasons for its high cost at that time. The scientific assembly and industrialists quickly learned about the amazing properties of the new metal and continued attempts to mine it.
In large quantities, aluminum began to be obtained at the end of the same nineteenth century. The scientist C. M. Hall proposed dissolving alumina in the cryolite melt and passing this mixture through an electric current. After some time, pure aluminum appeared in the vessel. In industry, metal is now produced by this method, but more on that later
For production, strength is needed, which, as it turned out a little later, aluminum did not have. Then the metal began to be fused with other elements: magnesium, silicon, etc. The alloys were much stronger than ordinary aluminum - it was from them that planes and military equipment began to be smelted. And they came up with the idea of ββmerging aluminum and other metals into a single whole in Germany. There, in Duren, an alloy called duralumin was put into production.
How to get aluminum from alumina
As part of the chemistry school curriculum, the theme is "How to Get Pure Metal from Metal Oxide."
We can also relate to this method our question of how to obtain aluminum from aluminum oxide.
To form a metal from its oxide, you need to add a reducing agent - hydrogen. A substitution reaction will take place with the formation of water and a metal: MeO + H 2 = Me + H 2 O (where Me is metal and H 2 is hydrogen).
Example with aluminum: Al 2 O 3 + 3H 2 = 2Al + 3H 2 O
In practice, this technique allows you to get pure active metals that are not reduced by carbon monoxide. The method is suitable for cleaning a small amount of aluminum and is quite expensive.
How to get aluminum from aluminum oxide by adding more electronegative metal
To get aluminum in this way, you need to select a more electronegative metal and add it to the oxide - it will displace our element from the oxygen compound. A more electronegative metal is one that is to the left in the electrochemical row (in the photo to the subtitle - higher).
Examples: 3Mg + Al 2 O 3 = 2Al + 3MgO
6K + Al 2 O 3 = 2Al + 3K 2 O
6Li + Al 2 O 3 = 2Al + 3Li 2 O
But how to get aluminum from aluminum oxide in a wide industry?
Industrial way
Most industries use ores called bauxites to mine the element. First, oxide is extracted from them, then it is dissolved in cryolite melt, and then pure aluminum is obtained by electrochemical reaction.
This is the cheapest and does not require additional operations.
In addition, it is possible to obtain aluminum chloride from alumina. How to do it?
Obtaining aluminum chloride
Aluminum chloride is the average (normal) salt of hydrochloric acid and aluminum. Formula: AlCl3.
To get you need to add acid.
The reaction equation is as follows - Al 2 O 3 + 6HCl = 2AlCl 3 + 3H 2 O.
How to get aluminum chloride from alumina without adding acids?
To do this, it is necessary to calcine a compressed mixture of aluminum oxide and carbon (soot) in a stream of chlorine at 600-800 gr. Chloride must be distilled off.
This salt is used as a catalyst for many reactions. Its main role is the formation of adducts with different substances. Wool is etched with aluminum chloride and added to antiperspirants. The compound also plays an important role in oil refining.
Obtaining sodium hydroxoaluminate
How to get sodium hydroxoaluminate from alumina?
To obtain this complex substance, you can continue the chain of transformations and first obtain chloride from oxide, and then add sodium hydroxide.
Aluminum chloride - AlCl3, sodium hydroxide - NaOH.
Al 2 O 3 β AlCl 3 β Na [Al (OH) 4 ]
Al 2 O 3 + 6HCl = 2AlCl 3 + 3H 2 O
AlCl 3 + 4NaOH (concentrated) = Na [Al (OH) 4 ] + 3NaCl 5
But how to get sodium tetrahydroxoaluminate from alumina, avoiding conversion to chloride?
In order to obtain sodium aluminate from aluminum oxide, it is necessary to create aluminum hydroxide and add alkali to it.
It should be recalled that alkali is a base soluble in water. This includes hydroxides of alkali and alkaline earth metals (I and II group of the periodic table).
Al β Al (OH) 3 β Na [Al (OH) 4 ]
Hydroxides cannot be obtained from metal oxides of medium activity, to which aluminum belongs. Therefore, we first restore the pure metal, for example, through hydrogen:
Al 2 O 3 + 3H 2 = 2Al + 3H 2 O.
And then we get hydroxide.
To obtain hydroxide, it is necessary to dissolve aluminum in acid (for example, in hydrogen fluoride): 2Al + 6HF = 2AlF 3 + 3H 2. And then hydrolyze the resulting salt with the addition of an equal amount of alkali in a dilute solution: AlF 3 + 3NaOH = Al (OH) 3 + 3NaF.
And further: Al (OH) 3 + NaOH = Na [Al (OH) 4 ]
(Al (OH) 3 is an amphoteric compound that can interact with acids and alkalis).
Sodium tetrahydroxoaluminate is highly soluble in water, and this substance is also widely used in decoration and added to concrete to accelerate hardening.
About metaaluminates
Beginning alumina producers probably wondered: "How to get sodium metaaluminate from alumina?"
Aluminates are used in widespread production to speed up certain reactions, stain tissues and produce alumina.
Lyrical digression: alumina - this, in fact, is alumina Al 2 O 3 .
Typically, the oxide is extracted from metaaluminates, but the βreverseβ method will be considered here.
So, to get our aluminate, you just need to mix sodium oxide with alumina at a very high temperature.
The reaction of the compound - Al 2 O 3 + Na 2 O = 2NaAlO 2
For normal flow, a temperature of 1200 Β° C is required.
You can follow the change in Gibbs energy in the reaction:
Na 2 O (q) + Al 2 O 3 (q) = 2NaAlO 2 (q), ΞG0298 = -175 kJ.
Another lyrical digression:
Gibbs energy (or "Gibbs free energy") is the relationship that exists between enthalpy (the energy available for transformation) and entropy (a measure of "chaos," disorder in the system). It is impossible to measure the absolute value, therefore changes are measured during the course of the process. Formula: G (Gibbs energy) = (change in enthalpy between products and the starting materials of the reaction) - (temperature) * S (change in entropy between products and sources). Measured in joules.
How to get aluminate from alumina?
For this, the method that was considered above is suitable - with alumina and sodium.
Alumina mixed with other metal oxide at high temperatures gives a metaaluminate.
But you can still fuse aluminum hydroxide with alkali in the presence of carbon monoxide CO:
Al (OH) 3 + NaOH = NaAlO 2 + 2H 2 O.
Examples:
- Al 2 O 3 + 2KOH = 2KAlO 2 + H 2 O (here, alumina is dissolved in potassium hydroxide) - potassium aluminate;
- Al 2 O 3 + Li 2 O = 2 LiAlO 2 - lithium aluminate;
- Al 2 O 3 + CaO = CaO Γ Al 2 O 3 - fusion of calcium oxide with aluminum oxide.
Obtaining aluminum sulfate
How to get aluminum sulfate from alumina?
The method is included in the school program of eighth and ninth grades.
Aluminum sulfate is a salt of the type Al 2 (SO 4 ) 3 . It can be presented in the form of plates or powder.
This substance can decompose into aluminum and sulfur oxides at temperatures from 580 degrees. Sulfate is used to purify water from the smallest particles, it is very useful in food, paper, textile and other industries. It is widely available due to its low price. Water purification is due to some features of sulfate.
The fact is that the polluting particles have a double electric layer around them, and the reagent under consideration is a coagulant, which, when particles penetrate into the electric field, causes the layers to compress and neutralize the particle charge.
Now about the method itself. To get sulfate, you need to mix oxide and sulfuric (non-sulfuric) acid.
It turns out the reaction of the interaction of alumina with acid:
Al 2 O 3 + 3H 2 SO 4 = Al 2 (SO 4 ) 3 + H 2 O
Instead of oxide, aluminum itself or its hydroxide can be added.
In industry, bauxite, the ore known from the third part of this article, is used to produce sulfate. It is treated with sulfuric acid and "contaminated" aluminum sulfate is obtained. Bauxite contains hydroxide, and the simplified reaction looks like this:
3H 2 SO 4 + 2Al (OH) 3 = Al 2 (SO 4 ) 3 + 6H 2 O
Bauxites
Bauxite is an ore consisting of several minerals at once: iron, boehmite, gibbsite and diaspora. It is the main source of aluminum mining, formed by weathering. The largest bauxite deposits are located in Russia (in the Urals), the USA, Venezuela (the Orinoco River, Bolivar State), Australia, Guinea and Kazakhstan. These ores are monohydrate, trihydrate and mixed.
Obtaining aluminum oxide
Much has been said about alumina, but it has not yet been described how to obtain alumina. The formula is Al 2 About 3 .
And you just need to burn aluminum in oxygen. Combustion is the process of the interaction of O 2 and another substance.
The simplest reaction equation is as follows:
4Al + 3O 2 = 2Al 2 O 3
The oxide does not dissolve in water, but it is highly soluble in cryolite at high temperature.
The oxide exhibits its chemical properties at temperatures from 1000 Β° C. It is then that it begins to interact with acids and alkalis.
In vivo corundum is the only stable variation of a substance. Corundum is very hard, with a density of approximately 4000 g / m 3 . The hardness of this mineral on the Mohs scale is 9.
Alumina is amphoteric oxide. It is easily converted to hydroxide (see above), and having turned, it retains all the properties of its group with a predominance of the main ones.
Amphoteric oxides are oxides that can exhibit both basic (properties of metal oxides) and acid (non-metal oxides) properties depending on conditions.
Amphoteric oxides, excluding aluminum oxide, include: zinc oxide (ZnO), beryllium oxide (BeO), lead oxide (PbO), tin oxide (SnO), chromium oxide (Cr 2 O 3 ), iron oxide (Fe 2 O 3 ) and vanadium oxide (V 2 O 5 ).
Salts: complex and not so
There are medium (normal), acidic, basic and complex.
The middle salts are composed of the metal itself and the acid residue and have the form of AlCl 3 (aluminum chloride), Na 2 SO 4 (sodium sulfate), Al (NO 3 ) 3 (aluminum nitrate) or MgPO 4 .
Acid salts are salts of a metal, hydrogen and acid residue. Examples thereof are: NaHSO 4 , CaHPO 4 .
Basic salts, like acidic salts, consist of an acid residue and a metal, but instead of H there is OH. Examples: (FeOH) 2 SO 4 , Ca (OH) Cl.
And finally, complex salts are substances from ions of different metals and the acid residue of a polybasic acid (salts containing a complex ion): Na 3 [Co (NO 2 ) 6 ], Zn [(UO 2 ) 3 (CH 3 COO) 8 ].
It will be about how to get a complex salt from alumina.
The condition for the conversion of oxide into this substance is its amphotericity. Alumina is great for the method. To obtain a complex salt of aluminum oxide, you need to mix this oxide with an alkali solution:
2NaOH + Al 2 O 3 + H 2 O β Na 2 [Al (OH) 4 ]
This kind of substance is also formed by the action of alkali solutions on amphoteric hydroxides.
The potassium hydroxide solution interacts with the zinc base to produce potassium tetrahydroxozincate:
2KOH + Zn (OH) 2 β K 2 [Zn (OH) 4 ]
The sodium alkali solution reacts, for example, with beryllium hydroxide to form sodium tetrahydroxoberylate:
NaOH + Be (OH) 2 β Na 2 [Be (OH) 4 ]
Salt use
Complex aluminum salts are often used in pharmaceuticals, the production of vitamins and biologically active substances. Preparations created on the basis of these substances help in the fight against a hangover, improve the condition of the stomach and the general well-being of the human body. Very useful compounds, as you can see.
Reagents are cheaper to buy in online stores. There is a large selection of substances, but sites are better to choose reliable and time-tested. If you buy something on the "one-day", then the risk of losing money increases.
When working with chemical elements, safety rules must be observed: gloves, protective glass, specialized dishes and appliances are required.
Epilogue
Chemistry is undoubtedly a science difficult to understand, but sometimes it is useful to understand it. The easiest way to do this is through interesting articles, a simple syllable and clear examples. It would not be superfluous to read a couple of books on the topic and refresh the course of the school curriculum in chemistry.
Here, most of the chemistry topics related to the conversion of aluminum and its oxides, including how to obtain tetrahydroxoaluminate from aluminum oxide, and many other interesting facts, were analyzed. It turned out that aluminum has many of the most unusual areas of application in production and in everyday life, and the history of metal production is very outstanding. The chemical formulas of aluminum compounds also deserve attention and detailed analysis, which was consecrated in this article.