Aluminum sulfate.octadecahydrate

V. Matsuguma et al, KogyoKayaku 33(4), 214-22(1972) CA 78, 6074(1973) (Combustion preventive chemicals for coal mine expls. II. Inorganic compds. Effective compds were aluminum nitrate nonahydrate, aluminum sulfate octadecahydrate and magnesium sulfate heptahydrate)... 

Aluminum sulfate octadecahydrate [7784-31 -8]y Al2(S0 2 I8H2O, and its aqueous solutions are used primarily in the paper (qv) industry for sizing and as a flocculating agent in water (qv) and wastewater treatment. This material is often called papermakers alum or alum. Because this salt is precipitated from aqueous solution, aluminum sulfate hydrate [17927-65-0] Al2(SO 7/H2O, can have variable composition and is sometimes referred to as cake alum or patent alum. The solid commercial hydrate, generally written as the 18-hydrate, is typically dehydrated to correspond to from 17.0 —17.5% Al O where n = 13 14 (1,2). This dehydrated form is called dry alum, ground or lump. Aluminum sulfate solutions are typically 7.5—8.5% Al O and are known as liquid alum. 

Aluminum sulfate octadecahydrate, Al2(S04)3 I8H2O, is the most common soluble salt of aluminum. It is prepared by dissolving bauxite in sulfuric acid. The salt... 

Hydrates. Aluminum sulfate hydrates, Al2(SO H20, where n ranges from 0 to 27 have been reported (3—6). Relative decreasiag vapor pressure studies iadicate the presence of an octadecahydrate, hexadecahydrate, dodecahydrate, dihydrate, and the anhydrous salt, assumiag that basic aluminum sulfates are not formed duriag the dehydration (3). 

Solubility. The aqueous solubiUty of a typical commercial aluminum sulfate, Al2(SO H20, where n = 14-18, is shown compared to the solubihty of the octadecahydrate in Table 1 (2,8). Differences in solubiUties probably result from small amounts of impurities such as iron, and the slight excess of AI2O2 base present in technical grade commercial aluminum sulfate hydrate. 

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