Alumunium Sulphate Application
Aluminium sulfate may be made by dissolving aluminium hydroxide, Al(OH)3, in sulfuric acid, H2SO4:
2Al(OH)3 + 3H2SO4 + 10H2O → Al2(SO4)3·16H2O
Aluminum is used in packing industry as cans and foil. Owing to the high ratio of Al3+ in aqueous solutions, the ion proteolyses part of the water envelope and forms hydroxo complexes. It can also complex with electron-rich species, such as fluoride and chloride. Commercial aluminum compounds in chemical industry are:
- Alum: Various isomorphous double sulfates composed of trivalent metals and univalent metals, especially aluminum potassium sulfate, AlK(SO4)2·12H2O, a white, crystalline compound. Alums have the general formula M2SO4·MIII2(SO4)3·24H2O, where M is one of alkali metals (potassium, sodium, rubidium, caesium, silver. thallium or ammonium), and MIII denotes one of the trivalent cation (e.g., aluminum, chromium, iron, manganese, cobalt, or titanium). In aqueous solution, alums show all the chemical properties that their components show separately. These salts are used in water purification, leather tanning, coagulation agent for rubber latex, mordant dyeing, fireproofing textiles, modifying concrete, baking powder, preparation of lakes, clarifying of turbid liquids and as astringents.
Aluminium Sulfate is used in water purification and as a mordant in dyeing and printing textiles. In water purification, it causes impurities to coagulate which are removed as the particulate settles to the bottom of the container or more easily filtered. This process is called coagulation or flocculation.
When dissolved in a large amount of neutral or slightly-alkaline water, aluminium sulfate produces a gelatinous precipitate of aluminium hydroxide, Al(OH)3. In dyeing and printing cloth, the gelatinous precipitate helps the dye adhere to the clothing fibers by rendering the pigment insoluble.
Aluminium sulfate is sometimes used to reduce the pH of garden soil, as it hydrolyzes to form the aluminium hydroxide precipitate and a dilute sulfuric acid solution. Aluminium sulfate is the active ingredient of some antiperspirants; however, beginning in 2005 the US Food and Drug Administration no longer recognized it as a wetness reducer.
