Aluminium Sulfate (Al2(SO4)3): Formula, Properties, Structure and Uses

Aluminium Sulfate is the most common aluminium coagulant. It comes in a variety of solid forms, including block, kibbled, ground, as well as a solution. Aluminium sulfate (Al₂(SO₄)₃) is frequently, but mistakenly, referred to as 'alum' in waterworks practice. It is a white crystalline solid in its anhydrous state. In its solution state, aluminium sulfate appears as a colorless liquid. Aluminium Sulfate is non-toxic and non-combustible in both its forms. It is used as a coagulant and enhances particle collision by neutralizing charge in drinking water and wastewater treatment plants. In this article, we will learn more about aluminium sulfate as we explore its formula, structure, properties, and applications.

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What is Aluminium Sulfate?

Filter Alum or Dialuminum trisulfate are other names for aluminium sulfate. In its anhydrous state, it is a white crystalline solid, while in its solution state, it is a colorless liquid. Both types are non-combustible and non-toxic.

Aluminium Sulphate

Aluminium sulfate is water-soluble but not ethanol soluble. It is odorless and has a sweet, moderately astringent flavor. It emits poisonous sulfur oxide gases when it decomposes. Aluminium is corroded by aluminium sulfate solution. This chemical is made in the lab by mixing sulphuric acid with aluminium hydroxide.

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Aluminium Sulfate Formula

Aluminium sulfate is an ionic chemical compound, which implies that it contains both positive and negative ions. When an atom or molecule loses or receives electrons, it becomes an ion. Molecules can be either monoatomic (containing only one atom) or polyatomic (containing many atoms). The majority of ionic compounds have one metal atom that is a positive ion and one radical or negative ion that is a negative ion. When it comes to Aluminium Sulfate, the positive ion is Aluminium, which is represented by Al³⁺. The radical is a negative-charged sulfate ion, (SO₄)^2-. Because all ionic compounds are electrically neutral, the aluminium and sulphate ions react in a molecular weight ratio that cancels their electrical charges.

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Aluminium Sulfate Formula

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Aluminium Sulfate Structure

Here is how the compound aluminium sulphate looks like: 

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Aluminium Sulfate Properties

Al₂(SO₄)₃ is the chemical formula for Aluminium Sulfate. It's a chemical substance that's commonly used as a coagulating agent in drinking water purification, paper production, and wastewater treatment plants.

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• In its anhydrous state, it is a white crystalline solid. It is, however, colourless in liquid form. 
• Both of these types are non-toxic and non-combustible. 
• Aluminium sulphate is water-soluble but not ethanol soluble. 
• It has no odor and a somewhat astringent and sweet flavor. 
• When it decomposes, it releases highly deadly sulphur oxide fumes. 
• Aluminium is also corroded by the Aluminium Sulfate solution. This is created in the laboratory by combining Aluminium Hydroxide and Sulphuric Acid.
• Aluminium Sulfate has a molecular mass of 342.15 gm/mole (molar mass).
• Aluminium Sulfate has a density of 2.672 gm/cm³.
• Aluminium Sulfate has a boiling temperature of 214^oC and a melting point of 770^oF.

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Preparation & Production of Aluminium Sulfate 

i) In the laboratory-

• Aluminium sulfate is made by mixing freshly precipitated aluminium hydroxide with the right amount of sulphuric acid. The liquid is then evaporated and allowed to crystallize. Pure, glossy crystals, granules, or powder are available.

2Al(OH)₃ + 3H₂SO₄ → Al₂(SO₄)₃ + 6H₂O

• Heating aluminium metal in a sulfuric acid solution also produces aluminium sulphate.

2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂↑

ii) From the schists of alum-

Iron pyrite, aluminium silicate, and numerous bituminous compounds make up alum. Upper Bavaria, Bohemia, Belgium, and Scotland are all home to these. These are either roasted or exposed to the air. Sulfuric acid is produced during the roasting process. It reacts with the clay to make Aluminium Sulfate, which is similar to what happens when the air weathers. After that, it is extracted using water and an Aluminium Sulfate solution with a specific gravity of 1.16. This solution is left to sit for a while before being evaporated till the iron (II) sulphate crystallises on cooling. It is then decanted from any sediment after being drawn off and evaporated until it reaches a specific gravity of 1.40.

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iii) From cryolite

When cryolite is used as an ore, it is combined with calcium carbonate and heated, resulting in the formation of sodium aluminate. The sodium aluminate is then extracted with water and precipitated with sodium bicarbonate or carbon dioxide and current passed through the solution. Sulfuric acid is then used to dissolve the deposit.

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iv) From bauxite or clay-

The material is calcined from clays or bauxite, then combined with sulfuric acid and water. Then it's gradually brought to a boil. Because the synthesis of Aluminum Sulfate is exothermic, no external heat is required if concentrated acid is used. It is then allowed to stand for a while before the clear solution is extracted.

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Applications of Aluminium Sulfate 

• Aluminium sulfate is used in the production of paper.

• It's also used to create a variety of prints on fabric.

• It is used as a waterproofing agent and an accelerator in concrete.

• Aluminium sulfate is utilised in the production of firefighting foam.

• It is also utilised in water treatment plants for sewage treatment.

• Aluminium sulfate is utilised often as a fireproofing agent.

• It is used to make baking soda.

• It is employed in the dyeing of clothing.

• Aluminium sulfate is used in gardening to help balance the pH of the soil.

• Water purification employs the use of aluminium sulphate.

Uses of Aluminium sulfate

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Things to Remember

• Aluminium sulfate is a colourless liquid in its solution form and a white crystalline solid in its anhydrous form. Both types are non-combustible and non-toxic.
• Millosevichite, a rare mineral, contains the anhydrous form of Aluminium Sulfate. For example, it is found in volcanic areas and on coal-mining waste dumps that are burning.
• In some industries, aluminium sulfate is referred to as alum or papermaker's alum. In general, the term "alum" is used to refer to any double sulphate salt. Its formula is XAl(SO₄)₂.12H₂O, where X is a monovalent cation such as potassium or ammonium.
• Aluminium sulfate is created by reacting freshly precipitated aluminium hydroxide with the appropriate amount of sulphuric acid. The liquid is then evaporated and allowed to crystallise.
• Aluminium Sulfate is used as a coagulant. In the purification of drinking water and wastewater treatment plants, it encourages particle collision by neutralising charge.

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