Aluminum sulfate is a commonly used industrial chemical. The compound of aluminum, sulfur and oxygen is often a dry crystal, powdery substance that becomes slimy when wet and is non-combustible. The solution, Al₂(SO₄)₃, is also known as “Alum” and has been in use since ancient Egyptian times when it helped the dyeing process.

Today, aluminum sulfate is still used to help print on paper as well as several other industrial purposes, including household products and wastewater treatment.

As a mordant 

Aluminum sulfate is used as a mordant in the dyeing process. A mordant is a substances that aids the dye with becoming printed on a fabric or paper. When mixed with water, aluminum sulfate creates the sludge-like aluminum hydroxide that aids textiles with the absorption of dye. It also makes the fabric’s dye insoluble in water, so that the textile won’t bleed. Although aluminum sulfate has been heavily used this way since since 2000 B.C., only organic dyes require mordants. Modern synthetic dyes do not.

As a coagulant 

Aluminum sulfate’s biggest industrial use is as a coagulant in water treatment plants. As treating wastewater and potable water is such an integral aspect of modern infrastructure, aluminum sulfate is used heavily.

When mixed with water, aluminum sulfate takes a number of forms with differing ionization levels, which can attract pollutants in the water and precipitate out, making them easier to be cleaned. This precipitation is known as sedimentation. The Safe Drinking Water Foundation explained that a majority of municipal treatment plants use aluminum sulfate. Using aluminum-based coagulants can lead to slightly higher aluminum levels in the processed water, but usually at safe levels.

In paper manufacturing 

Like with dyeing, aluminum sulfate has largely been replaced in the world of paper making by modern developments, but it is still used in some paper’s pulp. The acidic chemical has been used to remove impurities from the water used to make paper. It is also used in the pulp itself to help bind materials, neutralize charges and in rosin sizing. Although acid-free paper without Alum has become popular as a more durable option that is less likely to change colors.

Other uses 

Aluminum sulfate has also been used to help control algae growth in ponds, lakes and waterways. Gardeners also use this acidic compound with plants to adjust the pH level particularly basic soil. It has also been used in firefighting foam, deodorant, baking soda, leather making, fertilizer, soaps, drugs and chemical catalysts.

Aluminum sulfate is widely used industrial chemical, that is best known for it’s use as a primary coagulant in water treatment.