Al2SO43

Al2(SO4)3, commonly called aluminum sulfate, is an inorganic compound used primarily as a coagulant in water treatment and in the paper industry. In solid form it is a white, crystalline substance that is highly hygroscopic; commercial samples are typically hydrated, written as Al2(SO4)3·nH2O, and dissolve readily in water to give acidic solutions.

Chemistry and behavior: In water, aluminum sulfate dissociates to Al3+ and SO4^2− ions. The aluminum species hydrolyze to form aluminum hydroxide flocs, releasing H+ and lowering pH. These positively charged hydroxo species neutralize negative colloids, promoting aggregation and precipitation.

Production: It is produced by reacting sulfuric acid with aluminum-containing materials such as bauxite or alumina, yielding aluminum sulfate and water, with subsequent hydration to the commercially used hydrated salts.

Applications: In water treatment, it serves as a primary coagulant to remove suspended solids, color, and phosphates. In papermaking, it acts as a sizing agent and helps improve drainage and ink holdout. It is also used as a mordant in dyeing and in some cosmetic or household applications as an astringent.

Handling and safety: Aluminum sulfate is corrosive and should be handled with protective equipment. Avoid contact with skin and eyes, and minimize inhalation of dust. It reacts with bases and should be stored in a dry, sealed container to prevent hydration and caking.

Environmental notes: Care should be taken to control residual aluminum in treated water, as elevated levels can affect aquatic life and, at high concentrations, pose health concerns if ingested.