Aluminium sulphate

Mode of degradation in actual use

Administrative data

Endpoint:

mode of degradation in actual use

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Reliable without restrictions. Guideline study.

Data source

Reference

Reference Type:

review article or handbook

Title:

PRIORITY SUBSTANCES LIST ASSESSMENT REPORT of Aluminium chloride, nitrate and sulphate,

Author:

Canadian Environmental Protection Act, 1999 ,

Year:

1999

Bibliographic source:

Environment Canada Health Canada, p. 17 2008

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: (CEPA 1999)

GLP compliance:

not specified

Type of study / information:

ASSESSMENT REPORT

Test material

Test material information

Constituent 1

Reference substance name:

Aluminium sulphate

EC Number:

233-135-0

EC Name:

Aluminium sulphate

Cas Number:

10043-01-3

Molecular formula:

Al2(SO4)3

IUPAC Name:

Aluminium sulphate

Details on test material:

- Name of test material (as cited in study report):aluminium sulphate

Results and discussion

Any other information on results incl. tables

Aluminum sulphate will not degrade in surface water and goes into solution without undergoing chemicals decomposition.Aluminium ions will remain as aluminium ions.

 

When released into water, the aluminum sulphate hydrolyses to form aluminum hydroxides.

Reactions between aluminum sulphate, water and associated “impurities” result in the formation of a floc, which separates from the water phase to form alum sludge. A small fraction of the aluminum can stay in the water in either colloidal or dissolved form.The different reactions involved in the formation of aluminum hydroxide in aqueous solutionwasdescribed; the overall reaction can be represented by the following equation:

Al2(SO4)3+ 6H2O<=>2Al(OH)3⁰+ 3H2SO4

The aluminum hydroxide present in sludge is expected to remain mostly solid following release into surface water.Experiments were showed that less than 0.2% of the aluminum hydroxide present in sludge was released in supernatant water at a pH of 6 and less than 0.0013% was released at pH 7.65. In both cases, aluminum hydroxide was present mostly in particulate form. At these pH values, aluminum solubility is low and kinetics favour the formation of solid aluminum hydroxide.

 

The anhydrous form occurs naturally as a rare mineral millosevichite, found e.g. in volcanic environments and on burning coal-mining waste dumps. Aluminum sulphate is rarely, if ever, encountered as the anhydrous salt. It forms a number of different hydrates, of which the hexadecahydrate Al₂(SO₄)₃•16H₂O and octadecahydrate Al₂(SO₄)₃•18H₂O are the most common. The heptadecahydrate, whose formula can be written as [Al(H₂O)₆]₂(SO₄)₃•5H₂O, occurs naturally as the mineral alunogen.

When heated between 770 and 860°C Aluminum sulphatedecomposes to produce Aluminium oxide and Sulfur trioxide.It combines with water forming hydrated salts of various compositions

                  770 - 860°C

Al₂(SO₄)       =>          2Al₂O₃ + 6SO₂+ 3O₂

 Al₂(SO₄)₃+ 6 NaHCO₃→ 3 Na₂SO₄+ 2 Al(OH)₃+ 6 CO₂

When used to treat sewage water, aluminium sulphate will also react with phosphate, as shown in the following reaction:

Al2(SO4)3+ 2PO4^3– <=>AlPO4(s) + 3SO4^2–

Applicant's summary and conclusion

Conclusions:

When is hydrolyzed aluminium sulfate form the aluminium hydroxide precipitate and a dilute sulfuric acid solution