Alum – Potassium aluminum sulfate – Potassium alum

Description

What is Alum?

Alum is a naturally occurring chemical compound known as a double salt, consisting of aluminium, sulfate, and an alkali ion such as potassium or ammonium. The most common form is potassium alum with the chemical formula KAl(SO₄)₂ 12H₂O. It is a colourless, white crystalline powder that is readily soluble in water. Without further specification, alum is also called potassium aluminium sulfate.

Properties and Uses of Potassium Alum

Alum plays an important role in various traditional and modern processes due to its unique chemical properties. In papermaking, it was traditionally used to improve the properties of the paper. It was added to the pulp to strengthen the structure and make the paper more resistant to ink. This causes the fibers to absorb less ink, which allows for sharper printing. This application is less common today, but it remains a historically important ingredient in the development of the paper industry.

In tanning, potassium alum is an essential aid. It is used in the tanning of leather to preserve and soften the hides. Due to its astringent action, it stabilizes the fibers in the hide, making the leather more supple and resistant to wear. It is mainly used in the production of white leather, where the leather gets a smooth, light finish without dark discolorations.

Alum is often used as a mordant in textile dyeing. It improves the adhesion of dyes to the fabric and thus ensures better colour fastness. By pre-treating fabrics with this substance, the chemical reaction between the fibres and the dye is optimised, resulting in more intense and durable colours.

Alum is widely used in water purification. It acts as a coagulant and helps remove dirt particles and other impurities from water. It causes small particles to clump together into larger flocs, which then sink to the bottom or can be easily filtered. This process makes it a widely used substance in the treatment of process and industrial water.

In horticulture, alum is valued for its ability to lower soil pH. Acid-loving plants, such as hydrangeas, benefit from the addition of this substance to the soil. By making the soil more acidic, it creates an optimal environment for these plants, which is most evident in the vibrant colors of hydrangeas.

FREQUENTLY ASKED QUESTIONS – FAQ

Is potassium alum the same as alum?

Yes, potassium alum is a common form of alum. It is a general term for a group of double salts of aluminum and sulfate, combined with another ion such as potassium or ammonium. Potassium alum (KAl(SO₄)₂ 12H₂O) is the most commonly used variety and is often simply called “alum”.

Is Alum Dangerous?

When used correctly, alum is not classified as toxic. It may be irritating to skin or mucous membranes, especially to sensitive individuals. Avoid inhaling the powder and avoid contact with eyes.

What forms of alum are there?

The two most common forms are:

• Potassium alum (KAl(SO₄)₂ 12H₂O) – widely used in water treatment, textile dyeing and tanning.
• Ammonium alum (NH₄Al(SO₄)₂ 12H₂O) – often used in similar processes, depending on specific needs.

Both variants have similar properties, but the choice depends on the application.

Is Alum Poisonous?

Alum is not considered toxic when used normally in industrial applications. However, in large quantities or over long periods of exposure, it can cause irritation to the skin, eyes, or respiratory tract. Caution should be exercised when handling this powdered form.

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