The Ammonia Soda Process

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The Solvay (ammonia-soda) process for the production of sodium carbonate (soda ash)
Generally, the ammonia will react with carbon dioxide and water to produce ammonium bicarbonate (NH4HCO3). Then, NH4HCO3 will react with salt to form sodium bicarbonate. Sodium bicarbonate will be calcined to form sodium carbonate.
The Solvay process comprises of the following steps:
1. Purification of brine
The first step in the Solvay process is brine purification. This step is done to produce a pure sodium chloride solution. Brine contains impurities namely calcium and magnesium salts. Sulfates also can be found in some brines. These impurities have to be eliminated because they will produce unwanted insoluble salts by reacting with alkali and carbon dioxide, thus affecting the quality of the soda ash. Brine purification is carried out when magnesium ions are precipitated as hydroxide with milk of lime (Ca(OH)2) whereas calcium ions are precipitated as carbonate with soda ash (Na2CO3). This process is known as lime-soda treatment. The chemical reactions are as follows:
Mg2+ + Ca(OH)2 → Mg(OH)2 + Ca2+
Ca2+ + Na2CO3 → CaCO3 + 2Na+

2. Limestone burning and lime slaking
The limestone (CaCO3) used must contain low concentration of impurities. The limestone is calcinated with coke in order to form carbon dioxide. This carbon dioxide will be used in the carbonation phase and at the same time, it is also producing calcium oxide which will be used in the recovery of ammonia stage later. The

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