Aluminum Sulfate and Alums

Abstract

Aluminum sulfate octadecahydrate, \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{Al}}{_{2}}{(}{\rm{SO}}{_{4}}{)}_{3}{\rm{{\cdot{}}}}18{\rm{H}}{_{2}}{\rm{O}}} $ \end{document} , and its aqueous solutions are used primarily in the paper industry for sizing and as a flocculating agent in water and wastewater treatment. This material is often called papermakers' alum or alum and is sometimes referred to as cake alum or patent alum. The solid commercial hydrate also called dry alum, ground or lump. Anhydrous aluminum sulfate, Al 2 (SO 4 ) 3 , is a specialty item used in food applications. Over 50 acidic, basic, and neutral aluminum sulfate hydrates have been reported. Commercial dry alum is likely not a single crystalline hydrate, but rather it contains significant amounts of amorphous material. In the United States, aluminum sulfate is usually produced by the reaction of bauxite or clay with sulfuric acid. Unfortunately, the term alum is now used for several different materials. Papermakers' alum or simply alum refers to commercial aluminum sulfate. Common alum or ordinary alum usually refers to potash alum which can be written in the form \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{K}}{_{2}}{\rm{SO}}_{4}{\rm{{\cdot{}}}}{\rm{Al}}_{2}{(}{\rm{SO}}_{4}{)}_{3}{\rm{{\cdot{}}}}24{\rm{H}}{_{2}}{\rm{O}}} $ \end{document} , or it can refer to ammonium alum, ammonium aluminum sulfate. The term is also applied to a whole series of crystallized double sulfates having the same crystal structure as the common alums. Some examples of alums are cesium alum, \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{CsAl}}{(}{\rm{SO}}{_{4}}{)}_{2}{\rm{{\cdot{}}}}12{\rm{H}}{_{2}}{\rm{O}}} $ \end{document} ; iron alum, \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{KFe}}{(}{\rm{SO}}{_{4}}{)}_{2}{\rm{{\cdot{}}}}12{\rm{H}}{_{2}}{\rm{O}}} $ \end{document} ; chrome alum, \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{KCr}}{(}{\rm{SO}}{_{4}}{)}_{2}{\rm{{\cdot{}}}}12{\rm{H}}{_{2}}{\rm{O}}>} $ \end{document} ; and chromoselenic alum \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{KCr}}{(}{\rm{SeO}}{_{4}}{)}_{2}{\rm{{\cdot{}}}}12{\rm{H}}{_{2}}{\rm{O}}} $ \end{document} . In industrial practice it is generally the aluminum content of alums that is important. Because aluminum sulfate is widely available, other alums are more in the nature of specialty items.

Re‐evaluation of aluminium sulphates (E 520–523) and sodium aluminium phosphate (E 541) as food additives

“…An (Darragh and Ertell, 2004); in particular, aluminium potassium sulphate (AlK(SO 4 ) 2 •nH 2 O) is the epitome of alums and is generally referred to as ordinary alum or potash alum.…”

“…Double salt compounds of the general formula AlM(SO 4 ) 2 – where M indicates a metal in its 1+ oxidation state – have traditionally been called alums (Darragh and Ertell, ); in particular, aluminium potassium sulphate (AlK(SO 4 ) 2 ∙nH 2 O) is the epitome of alums and is generally referred to as ordinary alum or potash alum.…”

“…Aluminium sulphate (Al 2 (SO 4 ) 3 ∙nH 2 O; n = 0–27) is usually produced by allowing bauxite – a mineral with a relatively high content of aluminium (oxy)hydroxides – or clay to react with sulfuric acid (Darragh and Ertell, ). Clay (e.g.…”

“…However, the commercial product is obtained by adding a solution of sodium sulphate to a solution of aluminium sulphate. After adjusting the ratio of aluminium sulphate and sodium sulphate, water is evaporated to give a hard cake; this is further heated in roasters and ground to a powder of the desired particle size (Darragh and Ertell, 2004).…”

“…Aluminium potassium sulphate (AlK(SO 4 ) 2 •12H 2 O) occurs naturally as a mineral. Commercial aluminium potassium sulphate is manufactured by treating bauxite with sulfuric acid followed by potassium sulphate (Darragh and Ertell, 2004). Alternatively, potassium sulphate is added to a concentrated solution of aluminium sulphate, or the mineral alunite (K 2 Al 6 (SO 4 ) 4 (OH) 12 ) is calcined and leached with sulfuric acid.…”