A crystalline double sulfate usually encountered as the aluminum sulfate, also known as ammonium alum or just alum, is a which crystalline double sulfate usually encountered as the dodecahydrate, formula(NH4)Al(SO4)2·12H2O. It is used in small amounts in a variety of niche applications. The dodecahydrate occurs naturally as the rare mineral tschermigite.
It is used in water purification, in vegetable glues, in porcelain cements, in deodorants and in tanning, dyeing and in fireproofing textiles. The pH of the solution resulting from the topical application of ammonium alum with perspiration is typically in the slightly acid range, from 4 to 5.
Table 1 Requirement for Ammonium alum
|SI no||Characteristic||Requirement||Method of Test, |
Ref to Clause No. in
|(1)||Ammonium alum [Al2(SO4)3(NH4)2SO4 24H2O] content, percent by weight, Min||99||99||99.5||A-2|
|(2)||Matter insoluble in water, percent by weight, Max||0.15||0.02||0.01||A-3|
|(3)||Alkali and alkaline earths, percent by weight, Max||0.5||0.5||0.15||A-4|
|(4)||Arsenic (as As2O3) parts per million, Max||---||5||3||A-5|
|(5)||Fluoride (as F), percent per weight, Max||---||---||0.004||A-6|
|(6)||Heavy metals (as Pb ), percent per weight, Max||---||0.003||---||A-7|
|(7)||Iron (as Fe ), percent per weight, Max||---||0.002||0.001||A-8|
|(8)||Selenium (as Se), percent by weight, Max||0.006||0.002||0.001||A-9|
|(9)||Chloride (as Cl) percent per weight, Max||---||0.003||---||A-10|
|(10)||pH, not less than||2.9||2.9||3||A-11|