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There are two industrial methods for producing caustic soda: causticization and electrolysis. The causticization method is divided into soda ash causticization method and natural alkali causticization method according to different raw materials; electrolysis method can be divided into diaphragm electrolysis method and ion exchange membrane method.
Soda ash causticization method: Soda ash and lime are converted into soda ash solution and ashes are converted into lime milk respectively. The causticization reaction is carried out at 99-101℃. The causticization liquid is clarified, evaporated and concentrated to more than 40%. Liquid caustic soda. The concentrated liquid is further concentrated and solidified to obtain solid caustic soda finished product. The causticizing mud is washed with water, and the washing water is used to convert the alkali.
Trona causticization method: trona is crushed, dissolved (or alkali halogen), clarified, and then lime milk is added to causticize at 95 to 100°C. The causticized liquid is clarified, evaporated, and concentrated to a NaOH concentration of about 46%, and the clear liquid is cooled. , salt precipitation and further boiling to concentrate to obtain solid caustic soda finished product. The causticized mud is washed with water, and the washing water is used to dissolve trona.
Diaphragm electrolysis method: add soda ash, caustic soda, and barium chloride concentrate to remove impurities such as calcium, magnesium, and sulfate ions after the original salinized salt, and then add sodium polyacrylate or causticized bran to the clarification tank to accelerate precipitation, and sand filtration Afterwards, hydrochloric acid is added for neutralization. The brine is preheated and sent to electrolysis. The electrolyte is preheated, evaporated, separated into salts, and cooled to obtain liquid caustic soda, which is further concentrated to obtain the finished product of solid caustic soda. Salt mud wash water is used to dissolve salt.
Ion exchange membrane method: After the original salt is converted into salt, the brine is refined according to the traditional method. After the primary brine is filtered through a microporous sintered carbon tubular filter, it is then refined again through a chelating ion exchange resin tower to make When the calcium and magnesium content in the brine drops below 0. 002%, the secondary refined brine is electrolyzed to generate chlorine gas in the anode chamber. The Na+ in the brine in the anode chamber enters the cathode chamber through the ion membrane and the OH- in the cathode chamber generates sodium hydroxide. H+ is discharged directly on the cathode to generate hydrogen gas. During the electrolysis process, an appropriate amount of high-purity hydrochloric acid is added to the anode chamber to neutralize the remigated OH-, and the required pure water should be added to the cathode chamber. The high-purity caustic soda generated in the cathode chamber has a concentration of 30% to 32% (mass), which can be directly used as a liquid alkali product, or can be further concentrated to produce a solid caustic soda product.