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Sodium Carbonate

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Name: Sodium carbonate

CAS number: 497-19-8

EINECS number: 207-838-8

Molecular formula: Na2CO3

Molecular weight: 106-----Detail information please click here to download the document in PDF. Sodium Carbonate HERE

Synonyms:
A synonym, which is widely used, is soda ash. Other synonyms are carbonic acid disodium salt, disodium carbonate, calcined soda(Clayton and Clayton, 1993; The Merck Index, 1983; Johnson and Swanson, 1987).

In addition to the anhydrous form, the monohydrate form (CAS nr. 5968-11-6) and the decahydrate form (CAS nr. 6132-02-1) do exist and are placed on the market in very small quantities (comparedto the anhydrous form). Sodium carbonate decahydrate is known as sal soda or washing soda. Although sodium carbonate monohydrate has a different CAS number than anhydrous sodium carbonate, several studies on the sodium carbonate monohydrate have been included in this dossier because the intrinsic properties are expected to be similar to the anhydrate.

1.1 Composition
Sodium carbonate is a white, crystalline and hygroscopic powder with a purity of > 98 %. There are two forms of sodium carbonate available, light soda and dense soda. Impurities of sodium carbonate may include water (< 1.5 %), sodium chloride (< 0.5 %), sulphate (< 0.1 %), calcium (< 0.1 %), magnesium (< 0.1 %) and iron (< 0.004 %). The purity and the impurity profile depends on the composition of the raw materials, the production process and the intended use of the product. For example the purity of the pharmaceutical grade must be higher than 99.5 % in Europe (Pharmacop¨¦e Europ¨¦enne, 1996).

1.2 Physical chemical properties
Sodium carbonate has a melting point of 851ˇăC (CRC Handbook, 1986; The Merck Index, 1983), it decomposes when heated at > 400 ˇăC and therefore a boiling point cannot be determined. Sodium carbonate is an inorganic salt and therefore the vapour pressure can be considered negligible. Its density is 2.532 (20ˇăC) and its water solubility is 71 g/l water at 0ˇăC, 215 g/l water at 20ˇăC and 455 g/l water at 100ˇăC (CRC Handbook, 1986). The octanol water partition coefficient (log Pow) is not relevant for an inorganic substance which dissociates. The average particle size diameter (d50) of light sodium carbonate is in the range of 90 to 150 ¦Ěm and of dense sodium carbonate is in the range of 250 to 500 ¦Ěm.
Sodium carbonate is a strong alkaline compound with a pH of 11.6 for a 0.1M aqueous solution (The Merck Index, 1983; Johnson and Swanson, 1987). The pKa of CO3 2- is 10.33, which means that at a pH of 10.33 both carbonate and bicarbonate are present in equal amounts.

2. GENERAL INFORMATION ON EXPOSURE

Sodium carbonate is produced on all continents of the world and the global number of production sites is estimated to be 50-70. The total world emand of sodium carbonate in 1999 was 33.4 million metric tons (Morrin, 2000).

Sodium carbonate can be produced from minerals which contain sodium carbonate. It is present in large deposits in Africa and the United States as either carbonate or trona, a mixed ore of equal molar amounts of the carbonate and bicarbonate. However, about 70 % of the world production capacity of sodium carbonate is manufactured by the Solvay (ammonia soda) process, whereby ammonia is added to a solution of sodium chloride. Carbon dioxide is then bubbled through to precipitate the bicarbonate, NaHCO3. The sodium bicarbonate is decomposed by heat producing sodium carbonate. The traditional Solvay process is utilised in most parts of the world, with the exception of the U.S., where all production is based on the minerals which contain sodium carbonate. Different qualities of the sodium carbonate are produced based on the final use of the substance (Morrin, 2000; Clayton and Clayton, 1993).Technical, food and pharmaceutical grades are placed on the market.

Globally the major end uses for soda ash are (Morrin, 2000):
ˇôcontainer glass (28 %)
ˇôflat glass (16 %)
ˇôchemicals (18 %)
ˇôsoaps and detergents (10 %)
ˇôother glass (7 %)
ˇômetals and mining (3 %)
ˇôpulp and paper (2 %)
ˇôothers (16 %)

The glass industry is by far the largest single demand sector consuming more than half of the soda ash produced (51%). About 18% of soda ash production is used in the chemical sector, including the production of sodium chromate, sodium silicate and sodium bicarbonate. In the detergent sector, soda ash is used either directly as a builder in detergent formulations, or indirectly in the production of other chemicals used as builders such as sodium tripolyphosphate (STPP) and sodium silicates. Soda ash has environmental applications in effluent and in acid waste neutralisation and is used as a source of alkalinity, in the pulp and paper sectors, in the textiles industry and for brine purification (Morrin, 2000).

The product sodium carbonate is not only used by industry but is also used by consumers. It may be used directly in solutions of sodium carbonate for soaking of clothes, dishwashing, floor washing and for degreasing operations. Furthermore, a large number of consumer products like cosmetics, soaps, scouring powders, soaking and washing powders etc. contain a varying proportion of sodium carbonate. It is also regarded as a ˇ®Generally Recognised as SafeˇŻ (GRAS) substance in food with no limitation other than current good manufacturing practice (CFR, 1999).

2.1 Environmental Exposure and Fate
The high water solubility and low vapour pressure indicate that sodium carbonate will be found predominantly in the aquatic environment. In water, sodium carbonate dissociates into sodium and carbonate and both ions will not adsorb on particulate matter or surfaces and will not accumulate in living tissues. An emission of sodium carbonate to water will result in an increase in alkalinity and a tendency to raise the pH value.

The carbonate ions will react with water, resulting in the formation of bicarbonate and hydroxide, until an equilibrium is established (McKee et al., 1963). It is obvious that both the sodium and bicarbonate ion have a wide natural occurrence (UNEP, 1995).

Background concentration of carbonate!

If carbonate is dissolved in water a re-equilibration takes place according to the following
equations:

HCO3- ˇűˇú CO3 2- + H + pKa = 10.33
CO2 + H2O ˇű ˇú HCO3- + H+ pKa = 6.35

Background concentration of sodium

The sodium ion is ubiquitously present in the environment and it has been measured extensively in aquatic ecosystems. Sodium and chloride concentrations in water are tightly linked. They both originate from natural weathering of rock, from atmospheric transport of oceanic inputs and from a wide variety of anthropogenic sources. The sodium concentration was reported for a total number of 75 rivers in North and South America, Africa, Asia, Europe and Oceania, with a 10th percentile of 1.5 mg/l, mean of 28 mg/l and 90th percentile of 68 mg/l (UNEP, 1995).

Anthropogenic addition of sodium carbonate

The use of sodium carbonate could potentially result in an aquatic emission of sodium carbonate and it could locally increase the sodium and carbonate concentration in the aquatic environment. Specific analytical data or other reliable data about the use of sodium carbonate and the related emissions of sodium and carbonate have not been found.

As indicated before, the emission of sodium carbonate to the aquatic environment will increase the pH of the water. To underline the importance of the buffer capacity, a table is included with the concentration of sodium carbonate needed to increase the pH to a value of 9.0, 10.0 and 11.0 at different bicarbonate concentrations. The data of Table 1 were based on calculations (De Groot et al., 2002).

Human exposure

The substance has been used for a long time, but no accidental exposures have been reported in the medical literature. The production and use of sodium carbonate may result in inhalation, dermal and/or oral exposure.

Inhalation
Inhalation of sodium carbonate dust may occur due to occupational exposure to sodium carbonate. Light soda might reach the upper respiratory tract and will then mainly be deposited there, due to the diameter size. It will hardly be able to reach the lower respiratory tract. Dense soda will hardly be able to reach the respiratory tract at all, due to its diameter size and hygroscopic properties. Inhalation is normally considered negligible for consumer applications due to the low exposure duration and due to the negligible dust formation for most of the products which contain sodium carbonate (e.g. cosmetics, liquid cleaning products).

Dermal exposure
Dermal exposure to sodium carbonate may occur during production and use of the (pure) product sodium carbonate. The pure product is also available to consumers. Solutions of sodium carbonate in water may be used by consumers for soaking of clothes, dishwashing, floor washing and for degreasing operations. Furthermore sodium carbonate is present in many household cleaning products and this can result in dermal exposure. It is also used in cosmetics mostly in bath, skin and hair preparations in concentrations from smaller than 0.1% to concentrations in the range of 10 to 25%. These products may be expected to remain in contact with the skin for an hour at most and may be used repeatedly over a period of many years.

Oral exposure
Sodium carbonate is used in many countries (e.g. USA and EU) as a food additive. Sodium carbonate is a ˇ®GRASˇŻ direct human food ingredient, with no limitations other than current good manufacturing practices (CFR, 1999).

Sodium carbonate is being used increasingly in the production of high performance compact powders for laundry and dish washing.

The combined use of Zeolite A and sodium carbonate may replace the sodium phosphates and is approved by a large number of detergent powder producers.

Sodium carbonate may also be used for the direct soaking of clothes, dishwashing, floor washing and for degreasing operations.

For these same applications, a large number of formulated domestic products, soaps, scouring powders, soaking and washing powders etc. contain a varying content of sodium carbonate.

Sodium carbonate is the main raw material of sodium percarbonate and sodium perborate which is the mainly detergent raw material in the world.