What is Sodium Metabisulfite CAS 7681-57-4?

Sodium metabisulfite, also called sodium pyrosulfite or disodium metabisulfite, is an inorganic sulfite salt with the formula Na2S2O5. It is supplied as a white to slightly yellow crystalline powder and acts as a reducing agent, antioxidant, preservative and dechlorination agent.

Why is Sodium Metabisulfite used in water treatment?

It rapidly reduces free chlorine and chloramines to chloride, making it useful for dechlorination of process water, wastewater and reverse-osmosis feed water. It can also reduce hexavalent chromium to trivalent chromium in some wastewater treatment systems.

What happens when Sodium Metabisulfite dissolves in water?

It dissolves to form bisulfite and sulfite species and can release sulfur dioxide, especially in acidic solution. The resulting solution is reducing and has antimicrobial activity, so dosing should be controlled to avoid excess sulfite or sulfur dioxide.

Is Sodium Metabisulfite available as food grade?

The listing covers industrial and food grades. Food-grade sodium metabisulfite is used as a permitted preservative and antioxidant where regulations allow, often associated with E223, but sulfite sensitivity, labeling and destination-market limits must be considered.

What are the main industrial applications of CAS 7681-57-4?

Typical uses include water and wastewater dechlorination, textile bleaching and antichlor treatment, pulp and paper, leather processing, photography, gold recovery or cyanide treatment, and other chemical reduction processes.

Which specifications should I check before ordering Sodium Metabisulfite?

Confirm the grade, Na2S2O5 purity, SO2 content, pH, iron, heavy metals, arsenic and water-insoluble matter. Food-grade material should also meet the preservative purity limits and regulatory requirements of the destination market.

Sodium Metabisulfite CAS 7681-57-4

Sodium Metabisulfite (CAS 7681-57-4) is an inorganic compound functioning as a reducing agent and antioxidant within industrial water treatment processes and bleaching operations. Chemically identified as Sodium Pyrosulfite or Disodium Metabisulfite, this white crystalline powder acts effectively to neutralize oxidizers and remove excess chlorine in aqueous systems. Sodium Thiosulfate is another reducing salt used where dechlorination is the defined requirement. As a versatile Sodium Disulfite component, it is widely utilized for its stability and reactivity in various technical formulations. We ensure bulk supply capabilities for this material, providing access to competitive factory pricing and customized specifications to meet specific processing requirements. Full technical documentation, including MSDS, TDS, COA, is available to support compliance and safety protocols.

CAS: 7681-57-4
Synonyms: Sodium Pyrosulfite, Disodium Metabisulfite, Sodium Disulfite, Disodium Pyrosulfite
Einecs: 231-673-0
Molecular Formula: Na2S2O5
Grade: Industrial Grade / Food Grade
Package: 25kg PP/PE liner bags, 500kg/1000kg Jumbo bags (Customizable)

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Product Description

Sodium Metabisulfite is an inorganic compound that appears as a white or slightly yellowish crystalline powder with a slight odor of sulfur dioxide. It is highly soluble in water, forming an acidic solution. As a strong reducing agent, it is chemically active and readily oxidizes to sodium sulfate when exposed to moist air. Our product is produced using advanced chemical synthesis processes to ensure high purity (≥96.5%) and low impurity content, making it suitable for demanding applications in water treatment, mining, and textile processing.

1 Physicochemical Properties

2 Applications

3 Storage Conditions

4 Safety Precautions

Physicochemical Properties

Parameter	Specification (Industrial Standard)
Appearance	White or light yellow crystalline powder
Purity (as Na2S2O5)	≥ 96.5%
Sulfur Dioxide (SO2) Content	≥ 65.0%
Iron (Fe)	≤ 0.005% (50 ppm)
Water Insoluble Matter	≤ 0.05%
pH Value (5% Solution)	4.0 – 4.6
Arsenic (As)	≤ 0.0002% (2 ppm)
Heavy Metals (as Pb)	≤ 0.001% (10 ppm)
Solubility	Soluble in water (approx. 54g/100ml at 20°C)
Odor	Slight sulfur dioxide odor

Applications

Water Treatment: Used effectively for dechlorination (removing excess chlorine) in reverse osmosis (RO) systems and for the reduction of hexavalent chromium to trivalent chromium in wastewater.
Mining & Mineral Processing: Acts as a depressant and flotation agent in the mining industry, particularly in the extraction of gold and processing of copper/lead/zinc ores.
Textile & Dyeing: Serves as a bleaching agent for wool and cotton, a dechlorinating agent after bleaching, and a mordant in the dyeing industry.
Paper Industry: Used for bleaching paper pulp to improve brightness.
Chemical Synthesis: utilized in the production of sulfones and resins; used as a reducing agent in organic synthesis.
Food Industry (Food Grade): Used as a preservative, antioxidant, and color fixative in processed foods to prevent browning and spoilage.

Storage Conditions

Environment: Store in a cool, dry, and dark warehouse (below 25°C is ideal).
Air Exposure: The product oxidizes easily. Keep containers tightly closed when not in use.
Incompatibility: Store separately from oxidants, strong acids, and direct heat sources. Never store with acids as toxic sulfur dioxide gas will be released.
Shelf Life: typically 12-24 months if stored correctly in unopened original packaging.

Safety Precautions

Respiratory Protection: Wear a dust mask or respirator. Inhalation of dust or gas (SO2) can irritate the respiratory tract and cause asthma-like symptoms.
Skin & Eye Protection: Wear protective gloves, safety goggles, and protective clothing to prevent contact. It causes irritation to eyes and skin.
Handling: Use in a well-ventilated area. Avoid generating dust.
Emergency: In case of contact with eyes, rinse immediately with plenty of water for at least 15 minutes and seek medical advice.

FAQ - Technical & Supply Chain

Q:
What is Sodium Metabisulfite CAS 7681-57-4?

A: Sodium metabisulfite, also called sodium pyrosulfite or disodium metabisulfite, is an inorganic sulfite salt with the formula Na2S2O5. It is supplied as a white to slightly yellow crystalline powder and acts as a reducing agent, antioxidant, preservative and dechlorination agent.
Q:
Why is Sodium Metabisulfite used in water treatment?

A: It rapidly reduces free chlorine and chloramines to chloride, making it useful for dechlorination of process water, wastewater and reverse-osmosis feed water. It can also reduce hexavalent chromium to trivalent chromium in some wastewater treatment systems.
Q:
What happens when Sodium Metabisulfite dissolves in water?

A: It dissolves to form bisulfite and sulfite species and can release sulfur dioxide, especially in acidic solution. The resulting solution is reducing and has antimicrobial activity, so dosing should be controlled to avoid excess sulfite or sulfur dioxide.
Q:
Is Sodium Metabisulfite available as food grade?

A: The listing covers industrial and food grades. Food-grade sodium metabisulfite is used as a permitted preservative and antioxidant where regulations allow, often associated with E223, but sulfite sensitivity, labeling and destination-market limits must be considered.
Q:
What are the main industrial applications of CAS 7681-57-4?

A: Typical uses include water and wastewater dechlorination, textile bleaching and antichlor treatment, pulp and paper, leather processing, photography, gold recovery or cyanide treatment, and other chemical reduction processes.
Q:
Which specifications should I check before ordering Sodium Metabisulfite?

A: Confirm the grade, Na2S2O5 purity, SO2 content, pH, iron, heavy metals, arsenic and water-insoluble matter. Food-grade material should also meet the preservative purity limits and regulatory requirements of the destination market.

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