1. Basic Info

2. Physical & Chemical Properties

Physical Properties

1. Appearance: White crystalline powder or crystalline granule
2. Odor: Odorless
3. Solubility: Easily soluble in water; aqueous solution presents alkaline; slightly soluble in ethanol; insoluble in acetone, ether
4. Density (25℃): 2.633 g/cm3
5. Melting point: Decomposes above 150℃ without fixed melting point
6. Hygroscopy: Moderately hygroscopic, easy to absorb moisture in humid air
7. Crystalline characteristic: Anhydrous product is white crystal; easily combines with water to form heptahydrate Na2SO3·7H2O
8. pH value (10% aqueous solution): 9.0–10.5
9. Molecular Weight: 126.04

Chemical Properties

1. Oxidation susceptibility: Strong reducing agent, easily oxidized by oxygen in air to sodium sulfate, must be sealed and isolated from air
2. Reaction with acid: Reacts with dilute hydrochloric acid/sulfuric acid to release sulfur dioxide gas
3. Reducing performance: Can reduce heavy metal ions (Ag?, Cu2?, Pb2?) to elemental metal; used to remove residual oxidants
4. Thermal decomposition: Decomposes at high temperature to generate sodium oxide, sulfur dioxide and sulfur
5. Chelating ability: Forms water-soluble complexes with transition metal ions, shields metal ion catalytic oxidation
6. Photostability: Stable under dark storage; long-term light exposure accelerates aerial oxidation
7. Compatibility: Compatible with neutral/weak alkaline raw materials; incompatible with strong oxidants (hydrogen peroxide, chlorine, potassium permanganate), strong acid

3. Main Application Fields

1. Water treatment industry

   Water deoxidizer for boiler circulating water, removes dissolved oxygen to prevent pipeline corrosion; reducing agent for wastewater treatment to reduce chromate, heavy metal pollutants; dechlorination agent to eliminate residual chlorine after water disinfection.
2. Food industry

   Food-grade reducing agent and antioxidant, used in dried fruits, preserved vegetables, beverages, candies; inhibits enzymatic browning and oxidative discoloration; food bleaching agent for mushroom, bamboo shoots, longan; preservative to extend shelf life. Subject to strict national dosage limits.
3. Printing & dyeing textile industry

   Textile bleaching auxiliary, removes excess chlorine after chlorine bleaching; cotton fabric deoxidizer; printing reducing agent to stabilize dye color; fiber anti-yellowing agent.
4. Photographic chemical industry

   Developer auxiliary and photographic fixer additive, prevents silver ion oxidation and image fading, stabilizes negative film tone.
5. Paper & pulp industry

   Wood pulp bleaching reducing agent, reduces chroma of pulp; antioxidant to avoid paper yellowing during storage.
6. Fine chemical & pharmaceutical industry

   Raw material for producing sodium thiosulfate, sodium metabisulfite; pharmaceutical intermediate reducing agent; antioxidant for drug liquid preparations to prevent active ingredient oxidation failure.
7. Leather processing

   Leather tanning reducing agent, bleaches animal hides, removes excess oxidants during tanning, improves leather texture and whiteness.
8. Other uses

   Laboratory analytical reducing reagent; electroplating additive to adjust plating solution redox potential; flue gas desulfurization auxiliary raw material.

4. Quality Specification Table