Uses of Aluminum Sulfate

Aluminum sulfate has many different uses in everyday life and is used in several important industries. In fact, you may be exposed to it every day without even knowing it!

Household Uses

Some of the most common uses of aluminum sulfate are in the home. This compound is commonly found in baking soda, although there is some controversy over the appropriateness of adding aluminum to the diet. Some antiperspirants contain aluminum sulfate because of its antibacterial properties. Finally, the compound is an astringent component in hemostatic pens designed to stop small wounds from bleeding.

Dyeing fabrics

Another use of aluminum sulfate is in dyeing and printing on fabrics. When dissolved in large amounts of water with a neutral or weakly basic pH, the compound produces a sticky substance, aluminum hydroxide. The sticky substance helps the dye adhere to the fabric fibers by making it insoluble in water. Aluminum sulfate thus acts as a dye "fixative", meaning that it binds to the molecular structure of the dye and the fabric so that the dye is not depleted when the fabric becomes wet.

Water Treatment

The most important use of aluminum sulfate is in water treatment and purification. When added to water, it causes tiny impurities to collect into larger and larger particles. These clumps of impurities then settle to the bottom of the container, or at least become large enough to filter them out of the water. This makes drinking water safer. Based on the same principle, aluminum sulfate is sometimes used in swimming pools to reduce the turbidity of the water.

Gardening

Other interesting uses for aluminum sulfate around the house are gardening. Because aluminum sulfate is extremely acidic, it is sometimes added to very alkaline soils to balance the pH of plants. When aluminum sulfate comes in contact with water, it forms a solution of aluminum hydroxide and very dilute sulfuric acid, which changes the acidity of the soil. Gardeners growing hydrangeas use this property to change the color of the hydrangea flowers (blue or pink) because this plant is very sensitive to soil pH.

Paper making

In the past, aluminum sulfate was used for paper making, although most synthetic agents have replaced it. Aluminum sulfate helps to adjust the size of paper. In this process, aluminum sulfate combines with rosin soap to change the water absorption of the paper. This changes the paper's ink absorption characteristics. The use of aluminum sulfate means that the paper is made under acidic conditions. Using a synthetic sizing agent means that acid-free paper can be produced. Acid-free paper does not break down as fast as paper sized with acid.

Although you may not know it, aluminum sulfate is used to make many of the products you use every day. Even the water you drink is filtered with aluminum sulfate!