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9.5 Industrial Chemistry: 6. Solvay Process

Syllabus reference (October 2002 version)
6. The Solvay process has been in use since the 1860's
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Extract from  Chemistry Stage 6 Syllabus (Amended October 2002) © Board of Studies, NSW.
[Edit 9 Jul 09]

Background: The Solvay process is a method of making sodium carbonate from the raw materials sodium chloride, ammonia and calcium carbonate (limestone). This process was first used by Ernest Solvay in Belgium in the 1860s in an attempt to find a use for ammonia.  Ammonia was being produced as a by-product in the coke industry. The successful manufacture of sodium carbonate also made the manufacture of soap and glass less expensive.

About 70 Solvay process plants are still in operation, however, no new plants using this method are being built as it has been replaced by heating the mineral trona (Na2CO3.NaHCO3.2H2O) where this is available and by electrochemical methods. In Australia, commercial sodium carbonate production is carried out, using the Solvay process, by a company called Penrice in Osborne, South Australia. The following is an explaination of the Solvay process (external website).

The overall process can be shown by the equation,

CaCO3(s)   +   2NaCl (aq)   right arrow   Na2CO3(aq)   +   CaCl2(aq)

However, this reaction cannot take place in one step as calcium carbonate will not react with sodium chloride. The reaction is carried out in a number of steps. Ammonia is involved, but is recovered again so does not appear in this equation.

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identify the raw materials used in the Solvay process and name the products.

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describe the uses of sodium carbonate.

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perform a first-hand investigation to assess risk factors and then carry out, a chemical step involved in the Solvay process identifying any difficulties associated with the laboratory modelling of the step.

For any chemical step investigated in the Solvay process, identify any risk factors. You might like to list these in a table such as the one given below. Identify any potential hazards and suggest ways of dealing with them.

To get you started,

Table of Reactions

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identify,  given a flow chart, the sequence of steps used in the Solvay process and describe  the chemistry involved in:

  • brine purification
  • hydrogen carbonate formation
  • formation of sodium carbonate
  • ammonia recovery.

Brine purification

Salt water (brine) is pumped into shallow ponds, where the water is evaporated by the sun leaving salt. This is a mixture of calcium and magnesium salts as well as sodium chloride. The Ca and Mg ions must be removed.

Production of hydrogen carbonate and sodium carbonate

Ammonia Recovery

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process information to solve problems and quantitatively analyse the relative quantities of reactants and products in each step of the process.

  1. A company in South Australia, called Penrice Soda Products Pty Ltd, produces 325 000 tonnes per year of soda ash (sodium carbonate). How many tonnes of calcium carbonate are needed to produce this?  Take the overall equation as,

    CaCO3(s)   +   2NaCl (aq)    right arrow   Na2CO3(aq)   +   CaCl2(aq),


  2. Evaporative basins at Dry Creek near Adelaide produce an average of 650 000 tonnes per year of salt.  This is purified, then dissolved to form a saturated brine solution that is pumped to the Solvay plant.

    Ammonia is dissolved in the brine solution and then the ammoniated brine is reacted with carbon dioxide.

    1. Write an equation for this reaction.
    2. If 50% of the original salt is sodium chloride, what mass of ammonia will be needed to react with it?


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use available evidence to determine the criteria used to locate a chemical industry using the Solvay process as an example.

Some factors that influence the location of a chemical industry
Solvay process as an example - Australia's supplies come from Osborne, SA
proximity to supply of raw materials Osborne is on a 35 km strip of low-lying land along the Gulf of St Vincent.

Coastal location allows easy access to sea water - pumped into ponds for purification & crystallisation.

A limestone quarry in the Barossa Valley sends a trainload of limestone to Osborne each day.
proximity to market Supplies the Australian region.
availability of transport - for raw materials and finished product. Limestone is transported by train.

48 000 tonnes of sodium bicarbonate and 325 000 tonnes of sodium carbonate transported annually throughout Australia by road, rail and sea.
availability of housing, transport, schools & shops for workers & family Osborne is a western suburb of Adelaide which provides these facilities.
facilities for waste disposal Until recently discharged into the Port River, uses are now being found e.g. for land-fill.

Sodium carbonate in Australia. Chemlink (external website)

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discuss environmental issues associated with the Solvay process and explain  how these issues are addressed.

The Solvay process produces less pollution than previous methods of producing sodium carbonate. The reactions take place in a tower, designed by Solvay, and by-products such as ammonia, calcium oxide and carbon dioxide are re-used.

 Some environmental issues include:

Uses of Sodium Carbonate

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