Sediment core sampled from a Minnesota lake. The precipitate is then dissolved in sulfuric acid. By this means, sodium aluminate is formed it is then extracted with water and precipitated either by sodium bicarbonate or by passing a current of carbon dioxide through the solution. When cryolite is used as the ore, it is mixed with calcium carbonate and heated. It is allowed to stand for some time, and the clear solution is drawn off. In the preparation of aluminium sulfate from clays or from bauxite, the material is gently calcined, then mixed with sulfuric acid and water and heated gradually to boiling if concentrated acid is used no external heat is generally required as the formation of aluminium sulfate is exothermic. It is now allowed to stand for some time, and decanted from any sediment. This solution is allowed to stand for some time (in order that any calcium sulfate and basic iron(III) sulfate may separate), and is then evaporated until iron(II) sulfate crystallizes on cooling it is then drawn off and evaporated until it attains a specific gravity of 1.40. The mass is now systematically extracted with water, and a solution of aluminium sulfate of specific gravity 1.16 is prepared. In the roasting process, sulfuric acid is formed and acts on the clay to form aluminium sulfate, a similar condition of affairs being produced during weathering. These are either roasted or exposed to the weathering action of the air. The alum schists employed in the manufacture of aluminium sulfate are mixtures of iron pyrite, aluminium silicate and various bituminous substances, and are found in upper Bavaria, Bohemia, Belgium, and Scotland. Or by heating aluminium metal in a sulfuric acid solution:Ģ Al + 3 H 2SO 4 → Al 2(SO 4) 3 + 3 H 2↑ From alum schists Production In the laboratory Īluminium sulfate may be made by adding aluminium hydroxide, Al(OH) 3, to sulfuric acid, H 2SO 4:Ģ Al(OH) 3 + 3 H 2SO 4 → Al 2(SO 4) 3 + 6 H 2O However, the name " alum" is more commonly and properly used for any double sulfate salt with the generic formula XAl(SOĢO, where X is a monovalent cation such as potassium or ammonium. The heptadecahydrate, whose formula can be written as 2(SO 4) 3♵H 2O, occurs naturally as the mineral alunogen.Īluminium sulfate is sometimes called alum or papermaker's alum in certain industries. It forms a number of different hydrates, of which the hexadecahydrate Al 2(SO 4) 3♱6H 2O and octadecahydrate Al 2(SO 4) 3♱8H 2O are the most common.
Aluminium sulfate is rarely, if ever, encountered as the anhydrous salt.
The anhydrous form occurs naturally as a rare mineral millosevichite, found for example in volcanic environments and on burning coal-mining waste dumps. It is soluble in water and is mainly used as a coagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water and wastewater treatment plants, and also in paper manufacturing. Aluminium sulfate is a salt with the formula Al 2 (SO 4) 3.
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