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ARCHIVED - PSL Assessment Report for Aluminum Salts

2.1 Identity and physical/chemical properties

Aluminum chloride is also known as aluminum trichloride, aluminum chloride (1:3) and trichloroaluminum (ATSDR 2006). It has the Chemical Abstracts Service (CAS) registry number 7446-70-0 and a chemical formula of AlCl3. In its hydrated form, AlCl3-6H2O, it is called hexahydrated aluminum chloride (CAS No. 7784-13-6). Trade names include Aluwets, Anhydrol and Drichlor.

Synonyms for aluminum nitrate include aluminum trinitrate and aluminum (III) nitrate (1:3). The CAS registry number is 13473-90-0 and the chemical formula is Al(NO3)3. The nonahydrate aluminum nitrate, Al(NO3)3-9H2O (CAS No. 7784-27-2), is the stable form of this compound.

Aluminum sulphate can also be identified as alum, alumsulphate (2:3), aluminum trisulphate, dialuminum sulphate and dialuminum trisulphate. The CAS registry number for aluminum sulphate is 10043-01-3 and the chemical formula is Al2(SO4)3. Alum is often represented as Al2(SO4)3-14H2O. It may be found in different hydrated forms. The commercial product, called cake alum or patent alum, is an octadecahydrate aluminum sulphate, Al2(SO4)3-18H2O.

In addition to these three compounds, aluminum polymers such as polyaluminum sulphate (PAS) and polyaluminum chloride (PAC) are used in water treatment. The general formula for PAS is Ala(OH)b(SO4)c, where b + 2c = 3a; for PAC, the general formula is Ala(OH)bClc, where b/a is usually about 2.5 (e.g., Al2(OH)5Cl). Mixed aluminum polymers may also be used; their general formula is Ala(OH)bClc(SO4)d, and b/a varies between 0.4 and 0.6.

Physicochemical properties of the three aluminum salts are presented in Table 2.1..

Table 2.1: Physicochemical properties of aluminum chloride, aluminum nitrate and aluminum sulphate 1
PropertyAluminum
chloride
Aluminum
nitrate
Aluminum
sulphate
CAS No.7446-70-013473-90-010043-01-3
Molecular formulaAlCl3Al(NO3)3Al2(SO4)3
Molecular weight133.34213.00342.14
ColourWhite when pure, ordinarily gray or yellow to greenishColourless2White, lustrous
Physical stateWhite hexagonal deliquescent or moisture sensitive platesRhombic crystals2Crystals, pieces, granules or powder
Density (g/mL)2.48No data1.61
Melting point (°C)194 at 527 kPa732Decomposes at 770
Boiling point (°C)182.7
(1.00×105 Pa or 752 mm Hg; sublimation temperature)
Decomposes at 135°C2No data, substance has no boiling point
Solubility in water
(g/100 mL)
69.86 (15°C)
(Reacts violently with water)
63.7 (25°C)36.4 (20°C)
Solubility in other solventsSoluble in benzene, carbon tetrachloride,
chloroform
Very soluble in alcohol;
slightly soluble in acetone
almost insoluble in ethyl acetate,
pyridine2
Insoluble in ethanol
pHNo dataAqueous solution is acidicNo data
Vapour pressure (Pa)100
(20°C)
No data0 (20°C)
substance has no vapour pressure
1 Taken from Perry and Green (1984), Budaveri et al. (1989), Lewis (1992), European Commission (2000a,b) and ATSDR (2006)
2 Refers to aluminum nitrate nonahydrate (CAS No. 7784-27-2)

 

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