Lime plays two important roles in the production of soda ash and sodium hydroxide.
One of the major sources of soda ash (Na2 CO3) and caustic soda (NaOH) in North America involves the refining of naturally occurring trona ores. These ores are mixtures of carbonates, bicarbonates and impurities that must be refined to produce marketable products. Combining the bicarbonate-containing liquid with lime is one of the processes used to convert the bicarbonates in the trona to carbonate form.
By increasing the lime dosage, either the trona or soda ash can be converted to caustic soda, a higher-value product. In this process, lime is first slaked and converted to calcium hydroxide (Ca(OH)2). Next, the lime slurry is combined with soda ash (Ca(OH)2) + Na2CO3). This yields caustic soda and limestone (2NaOH + CaCO3). The limestone from this reaction can be recycled to make lime.
Soda and caustic-soda solution are essential ingredients in an array of industrial operations. These include pulp and paper and glass making, water treatment, flue-gas treatment, the manufacturing of soap, detergents and bleach, the refining of petroleum products and alumina, along with many other uses in the chemical-processing industry.