First, sodium metabisulfite:

Sodium metabisulfite is a white or yellow crystalline powder or small crystal with a strong SO2 odor, a specific gravity of 1.4, soluble in water, and the aqueous solution is acidic. When it is in contact with a strong acid, it releases SO2 to form a corresponding salt. When it is left in the air, it oxidizes. It is Na2S2O6, so the product cannot be stored for a long time. Above 150 degrees Celsius, SO2 is decomposed. 
The shape is a crystalline powder 
with a 98% 
particle size of 150 mesh.

Second, classification 
Sodium sulfite is divided into industrial grade and food grade

Third, packaging 
Common packaging: 25Kg / bag 
V. Application:  
For the production of insurance powder, sulfadimethylpyrimidine Aniso, caprolactam and other purification of chloroform, phenylpropane sulfone and benzaldehyde. The photographic industry is used as a fixative for the fixer. The perfume industry is used to produce vanillin. Used as a preservative for brewing industry, a rubber coagulant and a bleaching agent for cotton bleaching. Organic intermediates, dyes, and tanning are used as reducing agents for electroplating, wastewater treatment of oil fields, and as a mineralizer for mines. 
Industrial 
use in printing and dyeing, organic synthesis, printing, tanning, pharmaceutical and other departments; as a preservative, bleaching agent, loosening agent in food processing. 
Used as a chemical reagent 
(printing and photography, etc.), as a bleach mordant, as a reducing agent rubber coagulant, also used in organic synthetic pharmaceuticals and spices. 
It can also be used as a chromatographic reagent, preservative and reducing agent for dyes and the pharmaceutical industry. 
Sodium metabisulfite has a stronger reducibility and is similar to sodium sulfite. Our regulations can be used for candied fruit, biscuits, sugar, rock sugar, sugar, candy, glucose, liquid glucose, bamboo shoots, mushrooms and canned mushrooms. The maximum use is 0.45g/kg. Residues of candied fruit, bamboo shoots, mushrooms and canned mushrooms, grapes and blackcurrant concentrate (in terms of SO2) are less than 0.05g/kg; residues of biscuits, sugar, vermicelli and other varieties are less than 0.1g/kg; residues of liquid glucose The amount must not exceed 0.2g/kg. 
The food industry is used as a bleaching agent, preservative, bulking agent, antioxidant, color protectant and preservative. 
The pharmaceutical industry is used to produce chloroform, phenylpropyl sulfone and benzaldehyde. The rubber industry is used as a coagulant. The printing and dyeing industry is used as a dechlorination agent for cotton bleaching and a cotton scouring aid. The leather industry is used for leather treatment, which makes the leather soft, full and tough, and has the properties of waterproof, anti-folding and abrasion resistance. The chemical industry is used to produce hydroxy vanillin, hydroxylamine hydrochloride, and the like. The photosensitive industry is used as a developer or the like. 
For analysis. preservative. reducing agent. Antioxidant

6. Preparation: The production process route of sodium metabisulfite has two methods: dry method and wet method. 
(1) Dry method. Stir the soda ash and water in a certain molar ratio. When the Na2CO3.nH2O is formed into a block shape, put it into the reactor, keep a certain gap between the block and the block, and then pass through the SO2 until the reaction is finished, and remove the lumps. The finished product is crushed. 
(2) Wet method. Adding a certain amount of soda ash to the sodium hydrogen sulfite solution to form a suspension of sodium sulfite, and then introducing SO2 to form sodium metabisulfite crystals, which are separated by centrifugation and dried to obtain a finished product.