E522 (Aluminum potassium sulfate) is an inorganic chemical compound and is produced by treating bauxite with sulphuric acid, followed by potassium sulphate, or by adding potassium sulphate to a concentrated solution of aluminium sulphate, or by calcination and leaching with sulphuric acid. It is alum.

It appears as a whitish powder or yellowish flakes.

What it is used for and where

Food

Ingredient on the European food additives list as E522, firming

Other uses

• Adjuvant for precipitating bacteria. 
• Mordant in many colours of haematoxylins

Safety

EFSA's Scientific Panel on Food Additives provided a scientific opinion reviewing the safety of aluminium sulphates (E520-523) and sodium aluminium phosphate, acid (E541) as food additives and concluded that there is no concern regarding genotoxicity and carcinogenicity. The Panel concluded that aluminium sulphates (E520-523) and sodium aluminium phosphate, acid (E541) are of no safety concern in current authorised uses and use levels (1).

However, the risk of cumulative intake of aluminium, which may pose a danger to human health, cannot be excluded as this ingredient can be found in widely consumed food products such as bread, various bakery products (2).

• Molecular Formula    AlKO₈S₂    KAl(SO₄)₂
• Molecular Weight   258.21   
• CAS  10043-67-1
• UNII    09OXB01F3O
• EC Number 233-141-3

References_____________________________________________________________________

(1) Wong, W.W., Chung, S.W., Kwong, K.P., Yin Ho, Y. and Xiao, Y., 2010. Dietary exposure to aluminium of the Hong Kong population. Food Additives and Contaminants, 27(4), pp.457-463.

(2) EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS); Younes M, Aggett P, Aguilar F, Crebelli R, Dusemund B, Filipič M, Frutos MJ, Galtier P, Gott D, Gundert-Remy U, Kuhnle GG, Lambré C, Leblanc JC, Lillegaard IT, Moldeus P, Mortensen A, Oskarsson A, Stankovic I, Waalkens-Berendsen I, Wright M, Di Domenico A, van Loveren H, Giarola A, Horvath Z, Lodi F, Tard A, Woutersen RA. Re-evaluation of aluminium sulphates (E 520-523) and sodium aluminium phosphate (E 541) as food additives. EFSA J. 2018 Jul 27;16(7):e05372. doi: 10.2903/j.efsa.2018.5372.