Alúmen

Alúmen, commonly anglicized as alum, refers to a family of hydrated aluminum sulfate salts. The most familiar member is potassium aluminum sulfate dodecahydrate, KAl(SO4)2·12H2O. The general formula for alums is AAl(SO4)2·12H2O, in which A is a monovalent cation such as potassium (K+), ammonium (NH4+), or sodium (Na+). The term comes from Latin alumen, meaning bitter salt, from Greek.

Alums are typically obtained by crystallizing from aqueous solutions containing aluminum sulfate and the corresponding sulfate salt of the A cation; they form colorless or white crystals that are soluble in water. They are often used as mordants in dyeing and printing, because aluminum ions form stable complexes with dyes and fabrics, improving color fastness. They also act as coagulants in water treatment, helping remove suspended particles, and as astringents in cosmetics and medicine. In leather tanning, they help to crosslink proteins and stabilize hides.

Safety and handling: alums are generally of low toxicity but should be handled with normal laboratory or consumer precautions. Do not ingest in large quantities; prolonged skin or eye exposure may cause irritation. They should be stored in a dry, well-ventilated area away from incompatible materials.

This brief overview highlights alúmen as a tradititionally important class of compounds with diverse applications in dyeing, water treatment, cosmetics, medicine, and leather processing.