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Sodium dithionite, also known as sodium sulfite, is a white sandy crystal or yellowish powder chemical. Sodium dithionite has strong reducibility and oxidation because of its intermediate valence. Mainly used as bleaching agent in textile and paper industry, it will release a lot of heat and hydrogen dioxide, hydrogen sulfide and other toxic gases when contacted with water. It is also widely used in reducing dyeing, reducing cleaning, bleaching, organic synthesis, wood pulp and paper making and other fields in the textile industry.
1. the industrial production methods include zinc powder method and sodium formate method. The former has higher purity, but the investment is bigger and the production process is longer. The purity of the latter is slightly lower than that of zinc powder method, but the investment is less and the production process is shorter. Zinc powder process is the most widely used industrial method. 99.9% sulphur dioxide is introduced into the water suspension of zinc powder. The reaction is carried out at 35-45 C to form zinc dithionite solution. Then the solution is added to caustic soda solution, and the double decomposition reaction is carried out at 28-35 C under cooling stirring to form sodium dithionite and zinc hydroxide suspension. After filtration, a certain amount of refined salt was added to salting out under cooling stirring. The reaction temperature was gradually reduced from 36 C to below 20 C. After standing, the reaction temperature was heated to 58 60 C for dehydration, followed by alcohol washing, drying, adding a certain amount of soda ash, the finished product of sodium dithionite was prepared. Its Zn+2SO2 > ZnS2O4ZnS2O4+2NaOH to Na2S2O4+Zn (OH) 2
2. Sodium formate was mixed with sodium formate and soda ash (or caustic soda) in the aqueous solution of human alcohol at 75, then 99.9% sulfur dioxide was introduced to react, and then cooled to 45-S5. Two sodium sulfite products were prepared by filtration, ethanol washing, recrystallization, separation and drying. Its 2NaCOOH+Na2CO3+4SO2 to 2Na2S2O4+H2O+3CO2
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