How soda ash is made

Most soda ash starts as salt water and limestone, and the plant recycles its own ammonia over and over.

stations: 8
things upstream: 14
raw sources: 9
steps from the ground: 4

The short version

Soda ash is made by bubbling carbon dioxide from burnt limestone through salty brine that has been loaded with ammonia. Baking soda crystals drop out of the liquid and are heated to leave sodium carbonate. The ammonia is then recovered and reused. Where natural trona is mined nearby, it can simply be baked instead.

Dissolve salt into brine

Salt from the ground or from evaporated seawater is dissolved in water until the liquid is saturated. This brine supplies the sodium for the whole process.

Goes in
Rock salt Water
Load the brine with ammonia

Ammonia gas is absorbed into the brine. The plant buys very little of it, because almost all of it is recaptured at the end and sent back here.

Goes in
Ammonia
Burn limestone for gas

Limestone is heated in a kiln, which gives off carbon dioxide gas and leaves quicklime behind. The gas feeds the next station and the lime is saved for the last one.

Goes in
Limestone
Bubble gas up through the brine

Solvay's absorption tower stood 24 m tall. Carbon dioxide rises through a slow downward flow of ammoniated brine, and white crystals of sodium bicarbonate form and sink.

Goes in
Carbon dioxide
Filter out the crystals

Filters pull the bicarbonate from the liquid that is left, which is rich in ammonium chloride. Crystals are washed and carried onward.
Heat the crystals to ash

Calcining drives off water and carbon dioxide, leaving dry, white, anhydrous sodium carbonate. Released gas is captured and sent back to the tower.
Recover the ammonia

Quicklime from the kiln is slaked with water and mixed into the ammonium chloride liquid, which frees the ammonia as a gas. Calcium chloride solution is the only real waste.

Goes in
Quicklime Water
Calcine mined trona instead

Near natural deposits, such as the Green River beds in Wyoming, miners dig the mineral trona and heat it to get sodium carbonate directly. It skips every station above.

Goes in
Trona

End of the lineSoda ash Next it goes into laundry detergent, fiberglass, lithium carbonate and 10 more.

Worth repeating

Soda ash is named for the ashes of salt-loving plants, which people burned for centuries to get an alkali for glass and soap.
Large trona deposits were found near the Green River in Wyoming in 1938, and they let American plants produce soda ash more cheaply than the Solvay route.
The key reaction was spotted in 1811 by the French physicist Augustin Fresnel, decades before Ernest Solvay made it work as a factory process.