Table of Contents
Introduction
Potash alum is a chemical compound that is widely used. This is actually a double salt that is commonly used in medicine and water treatment. Potash alum is however known as potassium aluminium sulphate or potassium alum. This is also known colloquially as ‘fitkari.’ Potash alum seems to be an important component of alum, which is one of the most widely used coagulants in water treatment, particularly in low-coloured waters. It contains a large number of highly complex species, including aluminium polymers in conditions that affect the product type, which is further influenced by factors such as dosage, pH, hydroxide supplement rate, and mixing. Because of its versatility, alum is also very adaptable, and various coagulation mechanisms can be manipulated.
Overview
Potassium alum, potash alum, or potassium aluminium sulphate is just a chemical compound with the formula KAl(SO4)2. This is most commonly found as the dodecahydrate KAl(SO4)2·12H2O. This crystallises in neutral solution as an octahedral structure and as a cubic structure in alkali solution, with a space group of Pa -3 and a lattice parameter of 12.18. The compound is by far the most important member of the generic class of compounds known as alums, and it is commonly referred to as simply alum.
Potassium alum has been widely used in water purification, leather tanning, dyeing, fireproof textiles, and baking powder as E522. It is also used cosmetically as a deodorant, an aftershave treatment, and a styptic for minor shaving bleeding.
It has regular octahedra with flattened corners and is very water-soluble. This same solution is astringent and has a slightly acidic taste. Whenever an alum solution is neutralised with potassium hydroxide, the separation of alumina Al(OH)3 begins. Once heated to nearly red heat, it produces a porous, friable mass known as “burnt alum.” This then fuses at 92 °C (198 °F) in its own crystallisation water.
Natural occurrence
Potassium alum dodecahydrate naturally occurs as a sulphate mineral known as an alum-(K), typically as encrustations on rocks caused by weathering and oxidation of sulphide minerals and potassium-bearing minerals.
Historically, potassium alum was obtained from alunite (KAl(SO4)2·2Al(OH)3), which was mined from sulfur-containing volcanic sediments.
Alunite is a potassium and aluminium source that is likely an associate. Its been reported at Vesuvius in Italy, east of Springsure in Queensland, Alum Cave in Tennessee, Alum Gulch in Santa Cruz County, Arizona, and Cebu in the Philippines.
To obtain alum from alunite, it is calcined and then exposed to the action of air for an extended period of time. Throughout this exposure, it is kept constantly moistened with water, eventually falling to a very fine powder. The powder would then be lixiviated with hot water, the liquor is decanted, and the alum crystallises.
The undecahydrate can also be found in the fibrous mineral kalinite (KAl(SO4)2·11H2O).
Industrial production
Traditionally, potassium alum was primarily extracted from alunite.
Potassium alum has become manufactured industrially by combining potassium sulphate with a concentrated solution of aluminium sulphate. Sulfuric acid is typically used to treat minerals such as alum schist, bauxite, and cryolite to produce aluminium sulphate. When there is a lot of iron in the sulphate, potassium chloride should be used instead of potassium sulphate.
Uses
(1) Medicine and cosmetics: In medicine, potassium alum is primarily used as an astringent (or styptic) and antiseptic.
Styptic pencils seem to be rods made of potassium alum or aluminium sulphate that are used topically to reduce bleeding in minor cuts and abrasions, nosebleeds, and haemorrhoids, as well as to relieve pain from stings and bites. After shaving, potassium alum blocks are rubbed over wet skin.
Potassium alum is often used topically to treat pimples and acne, as well as to cauterise aphthous ulcers in the mouth and canker sores because it has a drying effect on the area and reduces irritation. It’s been used to stop bleeding in cases of hemorrhagic cystitis and is used as a treatment for hyperhidrosis in some countries.
(2) Culinary: At high temperatures, potassium alum may be used as an acidic ingredient in baking powder to provide a second leavening phase (although sodium alum is more commonly used for that purpose). In China, for example, potassium alum is frequently used in the leavening of Youtiao, a traditional Chinese fried bread.
(3) Flame retardant: To make cloth, wood, and paperless flammable, potassium alum is used as a fire retardant.
(4) Dyeing: Since antiquity, alum has been used as a mordant to form a permanent bond between dye and natural textile fibres such as wool. It has been used in paper marbling for this purpose.
(5) Chemical flocculant: Since antiquity, potassium alum has been used to purify turbid liquids. It would still be widely used in water purification for drinking and industrial processes, effluent treatment, and post-storm treatment of lakes to precipitate contaminants.
Prior to further filtration and disinfection of the water, between 30 and 40 ppm of alum is added to the water so that the negatively charged colloidal particles clump together into “flocs,” which then float to the top of the liquid, settle to the bottom of the liquid, or can be more easily filtered from the liquid. It works similarly to other similar salts by neutralising the electrical double layer that surrounds very fine suspended particles, allowing them to move. The very same principle is used when increasing the viscosity of a ceramic glaze suspension with alum; this makes the glaze more adherent and slows its rate of sedimentation.
(6) Dissolving iron and steel: Alum solution dissolves steels while having no effect on aluminium or base metals. Steel tool bits that have become lodged in machined castings can be dissolved using alum solution.
Also read: Important Topic: Diamond
FAQs
What is potash alum used for?
Potassium alum has been widely used in water purification, leather tanning, dyeing, fireproof textiles, and baking powder as E522. It is often used cosmetically as a deodorant, an aftershave treatment, and a styptic for minor shaving bleeding.
Is potassium alum safe for skin?
Alum in just about any form can irritate the skin and mucous membranes. Breathing alum can harm your lungs. Aluminium may indeed harm lung tissue. Since alum is a salt, consuming large amounts of it can make you sick.
Is alum powder the same as baking soda?
In the home, alum can also be used as a chemical leavener. It is frequently used as a reactant in baking powders, along with baking soda. However, alum powder and baking soda are not interchangeable.
