Ammonium sulphate and aluminium sulphate are two different sulphate salts, bonded to different chemical compounds- aluminium, which is an element, and ammonium, which is a charged molecule (ion).

The main distinction between ammonium sulphate and aluminium sulphate is that ammonium sulphate is an inorganic or mineral salt with a chemical formula (NH4)2SO4, whereas aluminium sulphate is a metallic salt with a chemical formula Al2(SO4)3. Below, we provide an overview of these two compounds and list other key differences.

Understanding Ammonium Sulphate (NH4)2SO4

Ammonium sulphate is an inorganic salt containing an ammonium cation bound to a sulphate anion. It can be made by treating ammonia with sulfuric acid.

This inorganic salt has numerous important uses in various industries. It is primarily used as a fertiliser, particularly for alkaline soils. When it enters the soil, ammonium sulphate releases ammonium ion, which forms a light quantity of acid, reducing the pH balance of the soil.

We can also use ammonium sulphate to produce fungicides, insecticides, and herbicides, thanks to its water solubility. In water treatment, it is used in conjunction with chlorine to form monochloramine for disinfection.

Ammonium sulphate can also be used as a fire retardant as it decreases maximum weight loss rates, raises the production of residue, and increases the combustion temperature of the material in flame retardant compositions.

Although ammonium sulphate has been widely used as a wood preservative, this is no longer as common an application due to the compound’s hygroscopic nature, dimensional instability, and faster corrosion.

Understanding Aluminium Sulphate

As mentioned earlier, this is a metal salt that’s highly soluble in water. It is mainly used in the purification of water and as a coagulating agent to facilitate particle collision by regulating charge. It is also used in paper manufacturing and wastewater treatment plants.

Aluminium sulphate exists in two forms: anhydrous and hydrated form. The anhydrous mode (no water bound) exists naturally as a mineral called millosevichite, often found in volcanic sites and after burning coal mining waste environments.

Hydrated aluminium sulphate (with water bound) is much more common than the anhydrous form. When water is bound to aluminium sulphate, various hydrates are formed, including octadecahydrate and hexadecahydrate (18 and 16 water molecules respectively).

Aluminium sulphate is available as a white crystal-like solid that’s extremely hygroscopic and is also called papermaker’s alum or alum. It can be produced in the laboratory by mixing aluminium hydroxide with sulfuric acid. Heating aluminium metal in sulfuric acid can also produce aluminium sulphate.

What Distinguishes Ammonium Sulphate from Aluminium Sulphate?

As discussed in this article, aluminium sulphate and ammonium sulphate have several differences. However, the most distinct one is that one is a metal salt (Aluminium sulphate) with Al (III) cation, while the other one is an inorganic salt (Ammonium Sulphate) with an ammonium anion.

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