Potassium alum

Potassium alum or potash alum is the potassium double sulfate of aluminium. Its chemical formula is KAl(SO₄)₂ and it is commonly found in its dodecahydrate form as KAl(SO₄)₂·12(H₂O). It is commonly used in water purification, leather tanning, fireproof textiles, and baking powder. It also has cosmetic uses as a deodorant and as an aftershave treatment. Its mineral form is known as kalunite (rock form) and kalinite (fiber form).

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Characteristics

Potassium alum crystallizes in regular octahedra with flattened corners, and is very soluble in water. The solution reddens litmus and is an astringent. When heated to nearly a red heat it gives a porous, friable mass which is known as "burnt alum." It fuses at 92 °C in its own water of crystallization. "Neutral alum" is obtained by the addition of as much sodium carbonate to a solution of alum as will begin to cause the separation of alumina. Alum finds application as a mordant, in the preparation of lakes for sizing hand-made paper and in the clarifying of turbid liquids.

Mineral form and occurrence

Potassium alum is a naturally occurring sulfate mineral which typically occurs as encrustations on rocks in areas of weathering and oxidation of sulfide minerals and potassium-bearing minerals. Alunite is an associate and likely potassium and aluminium source. Found at Vesuvius, Italy,East of Springsure,Queensland, Alum Cave, Tennessee, and Alum Gulch, Arizona in the United States.

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