E521 (Aluminium sodium sulphate) is a chemical compound that is rare to find in nature and to obtain the commercial product, a solution of sodium sulphate is added to aluminium sulphate. 

It appears as an anhydrous white or yellowish powder, slowly soluble in water. 

What it is used for and where

Food

Ingredient included in the list of European food additives as E521, firming, buffering, neutralising agent.

Other uses

Buffering and neutralising agent in fish farming.

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).

• Molecular Formula    AlNaO₈S₂
• Molecular Weight    242.10
• CAS  10102-71-3
• UNII    0CM6A697VV
• EC Number   233-277-3

References_____________________________________________________________________

(1) 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.