Water Treatment & Effluent Treatment – As a Coagulant
One of the most important uses of Alum is in water treatment and purification.
In water Alum controls: - Turbidity - Suspended solids - Total organic carbon (TOC) - Biochemical oxygen demand (BOD)
When added to water, it causes microscopic impurities to clump together into larger and larger particles. These clumps of impurities will then settle to the bottom of the container or at least get large enough to filter them out of the water. This makes the water safer to drink. On the same principle, aluminum sulfate is also sometimes used in swimming pools to decrease the cloudiness of the water. Alum is used to make many products you use daily. Even the water you drink is filtered using aluminum sulfate!
In the past, Alum was used in making paper, although synthetic agents have mostly replaced it. The Alum helped to size of the paper. In this process, aluminum sulfate was combined with rosin soap to change the absorbency of the paper. This changes the ink-absorbing properties of the paper. Using aluminum sulfate means that the paper was made under acidic conditions. Use of synthetic sizing agents means that acid-free paper can be produced. Acid-free paper does not break down as fast as paper sized with acid.
Dyeing Fabrics- As a mordant
Alum is used as a mordant in the dyeing process. A mordant is a substances that aids the dye with becoming printed on a fabric. When dissolved in a large amount of water that has a neutral or slightly alkaline pH, the compound produces a gooey substance, aluminum hydroxide. The gooey substance helps dyes stick to the cloth fibers by making the dye water insoluble. The role of aluminum sulfate, then, is as a dye “fixer,” which means that it combines with the molecular structure of the dye and the fabric so the dye doesn’t run out when the fabric gets wet.
Alum 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.