Technical Leaflet
Sodium sulfite grades
M 5873 e
July 1999 (rws)
Supersedes issue dated June 1995
® = Registered trademark of
BASF Aktiengesellschaft
Sodium sulfite anhydrous A
Sodium sulfite anhydrous PHOTO GRADE
Sodium sulfite anhydrous FOOD GRADE
Reducing, bleaching and sulfiting agent,
auxiliary for many branches of industry
Chemicals
Sodium sulfite types
Chemical name
Sodium sulfite
Commercial names
Sodium sulfite anhydrous A
Sodium sulfite anhydrous PHOTO GRADE
Sodium sulfite anhydrous FOOD GRADE (E No. 221)
Chemical formula
Na 2SO 3
Molar mass
126.04 g
CAS No.
7757-83-7
EINECS No.
231-821-4
Forms and packs supplied
The products sodium sulfite anhydrous A, PHOTO GRADE and FOOD
GRADE can be purchased in 50 kg and 25 kg sacks. The product can also
be delivered in big bags and road or rail tankers.
Disposable pallets are used, and wrapping is possible at the customer’s
request.
Properties
Sodium sulfite is a white or pale yellowish, odorless microcrystalline
powder. The apparent density is 1400 –1600 kg/m 3.
Sodium sulfite slowly absorbs water on storage in closed containers. This
is associated with oxidation to form sodium sulfate. In open containers,
this process is greatly speeded up.
The absorption of water is accompanied by formation of more or less hard
agglomerates.
Sodium sulfite is readily soluble in water. The solutions show an alkaline
reaction. Exposure to air results in rapid formation of sodium sulfate.
Table 1 Density and composition of sodium sulfite solutions of
various concentrations
Na 2SO 3
concentration
Na 2SO 3
content
g/100 g
g/100 ml
Amount of Na 2SO 3
required for
preparation
g/100 ml
Density
g/100 ml
5
5.23
5.39
104.6
10
10.97
11.31
109.7
15
17.22
17.75
114.8
20
24.06
24.8
120.3
2
Temperature °C
100
80
60
40
20
0
–20
0
5
10
15
20
25
30
Concentration in g/100 g
Figure 1
Solubility of sodium sulfite in water
Product specifications
The values and test methods stated in the product specifications below are those applying when the technical
data sheet was drawn up. Because changes are possible, those interested are requested to ask for the product
specifications currently applying. The only values which are binding are those in the relevant specification sheets
then provided.
Sodium sulfite anhydrous A
Unit
Typical value
Limit
Test method
Na 2SO 3
g/100 g
98.2
min. 97.5
ISO 418-1994 (E)
SO 2
g/100 g
49.9
min. 49.5
calculated
9.2
8.5 –10.5
RCA/Q-S-066
< 20
max. 50
RCA/Q IC-01
max. 10
AES BASF M91/41
max. 10
AAS BASF M90/5
remainder
calculated
pH value (50 g/l)
NaCl
mg/kg
Heavy metals as Pb
mg/kg
Iron
mg/kg
Na 2SO 4
g/100 g
<5
Product specification RCA_NSA_E of Feb. 10, 1999, Rev.: 2
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Sodium sulfite anhydrous PHOTO GRADE
Unit
Typical value
Limit
Test method
Na 2SO 3
g/100 g
99.0
min. 98.3
ISO 418-1994 (E)
SO 2
g/100 g
50.3
min. 49.9
calculated
Insoluble matter
g/100 g
< 0.1
max. 0.5
ISO 10349-3
pH value (50 g/l)
–
9.3
9.0 –10.0
RCA/Q-S-066
Alkalinity (as Na 2CO 3)
g/100 g
–
max. 0.15
ISO 10349-7
NaCl
mg/kg
< 10
max. 20
RCA/Q-IC-01
AgNO 3 test
–
–
fulfilled
ISO 10349-9
Fe
mg/kg
<5
max. 5
AAS BASF M90/5
Heavy metals as Pb
mg/kg
–
max. 10
AES BASF M91/41
Appearance of solution
–
–
fulfilled
ISO 418-1994 (E)
Na 2S 2O 3
g/100 g
–
max. 0.015
ISO 418-1994 (E)
Na 2SO 4
g/100 g
–
remainder
calculated
Product specification RCA_NSPG_E of Feb. 10, 1999, Rev.: 2
Sodium sulfite anhydrous FOOD GRADE
Unit
Typical value
Limit
Test method
Na 2SO 3
g/100 g
98.5
min. 98.0
ISO 418-1994 (E)
SO 2
g/100 g
50.0
min. 49.8
calculated
9.2
8.5 –10.5
RCA/Q-S-066
pH value (10 % solution)
Heavy metals as Pb
mg/kg
–
max. 10
AES BASF M91/41
Fe
mg/kg
<5
max. 10
AAS BASF M90/5
As
mg/kg
–
< 0.1
AAS BASF M90/7
Pb
mg/kg
–
< 0.1
AAS BASF M90/5
Cu
mg/kg
–
< 0.1
AAS BASF M90/5
Hg
mg/kg
–
< 0.03
AAS (cold vapor)
Se
mg/kg
–
< 0.1
AAS BASF M90/8
Zn
mg/kg
–
< 0.1
AAS BASF M90/5
Na 2S 2O 3
g/100 g
–
max. 0.02
ISO 418-1994 (E)
Na 2SO 4
g/100 g
–
remainder
calculated
Product specification RCA_NSFG_E of Feb. 10, 1999, Rev.: 2
Sodium sulfite anhydrous FOOD GRADE is subject to provisional approval
in the EU according to EC directive 96/77/EC (of Dec. 2, 1996) annex III
part B (E No.: 221), in the foodstuffs listed therein and in the stated
maximum amounts, as preservative and antioxidant.
The product also complies with the requirements listed for sodium sulfite
in the Food Chemical Codex, 4th edition (FCC IV) on page 383. These
requirements are the criterion for use in the foods sector for North
America, parts of South America and for many countries outside the EU.
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Finally, this product also meets the requirements listed in the compendium
of food additives specifications of the FAO/WHO Joint Expert Committee
on Food Additives (JECFA), Rome 1992, page 1395.
Chemical properties
Sodium sulfite has reducing, bleaching, sulfiting and preservative effects.
Acidification results in evolution of the pungent and toxic gas sulfur
dioxide. Sulfur dissolves in aqueous solutions of sodium sulfite to produce
sodium thiosulfate.
Applications
In the chemical and chemical engineering industries:
– for producing sodium thiosulfate,
– as reducing agent, for sulfonation and sulfomethylation.
In the manufactured fiber industry:
– for solubilizing the raw materials, as addition to coagulant baths, for
bleaching, for removing sulfur from the yarn.
In the textile industry:
– as antichlor after treatment with chlorine or with compounds which
contain active chlorine.
In the leather industry:
– for sulfiting tanning extracts.
In the explosives industry:
– in the production of trinitrotoluene.
In the rubber industry:
– for stabilizing latex.
In the photographic industry:
– to protect developer solutions from oxidation.
In the food industry:
– as preservative and bleach (restricted use in accordance with the
additive approval regulations E 221).
In the paper and pulp industry:
– quality-improving effect in the CTMP and TMP processes for producing
semichemical pulp and pulp, in the processing of rags and in the
cooking of straw.
Auxiliary in the treatment of water (prevention of corrosion due to depletion
of oxygen, and for removing chlorine from industrial water).
For waste water treatment in the electroplating industry.
For removing oxygen from boiler feed water (as long as the steam temperature is below 300°C and the sodium sulfate which is formed can be
removed by blow-down).
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Safety
Biological effects
Sodium sulfite is an odorless powder. It is not generally irritating for the
skin; however, sensitive people prone to allergies may on prolonged exposure experience reddening of the skin. Lengthy contact with the skin, and
inhalation of the fine dust must be avoided. Contact with acids may lead
to evolution of toxic sulfur dioxide gas.
In water courses, sodium sulfite leads to extensive oxygen depletion,
which may have adverse effects on organisms. However, if properly introduced into adapted biological treatment plants, no impairment of the
degradation activity is to be expected.
Safety advice
According to the data available to us, sodium sulfite is not included as a
hazardous substance in annex 1 of EC directive 67/548/EEC.
Storage and transport
All sodium sulfite types should be stored under cool and dry conditions.
They are stable for 6 months if the storage temperature does not exceed
25 °C and the relative humidity does not exceed 45 %.
If higher temperatures and/or higher humidities occur during storage, this
may lead to a decrease in the SO 2 content and the pH of the aqueous
solution. Similar effects are produced by wide variations in the storage
temperature. The chemical changes may be accompanied by the formation of more or less hard agglomerates. Hard agglomerates are also
caused by increased pressure – for example if pallets are stacked on top
of one another.
Safety data sheet
Further information on the sodium sulfite types is to be found in the
relevant safety data sheets.
Note
The information submitted in this publication is based on our current
knowledge and experience. In view of the many factors that may affect
processing and application, these data do not relieve processors of the
responsibility of carrying out their own tests and experiments; neither do
they imply any legally binding assurance of certain properties or of suitability for a specific purpose. It is the responsibility of those to whom we
supply our products to ensure that any proprietary rights and existing laws
and legislation are observed.
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