HOO CHEMTEC supplies Sodium Metabisulfite (SMBS), CAS No. 7681-57-4, for reverse osmosis dechlorination, industrial water treatment, mining, textile processing, pulp and paper, food processing, and other industrial applications.
Sodium Metabisulfite is a white crystalline powder used as a dry sulfur-based reducing agent. In water treatment, one of its main applications is reducing residual chlorine before chlorine-sensitive equipment, particularly polyamide reverse osmosis (RO) membranes.
Our standard industrial-grade Sodium Metabisulfite is typically supplied at 97% minimum assay, subject to the agreed product specification. Bulk supply is available in 25 kg bags, palletized bags, jumbo bags, and customized export packaging.
For international B2B orders, HOO CHEMTEC can provide product specifications, batch COA, SDS, TDS, packing details, container-loading information, and applicable export documents.
Need a quotation? Send your required grade, assay, application, quantity, packaging requirement, and destination port.
Sodium Metabisulfite at a Glance
| Property | Information |
|---|---|
| Chemical name | Sodium Metabisulfite |
| Common abbreviation | SMBS |
| Other name | Sodium Pyrosulfite |
| Chemical formula | Na₂S₂O₅ |
| CAS No. | 7681-57-4 |
| Molecular weight | 190.11 g/mol |
| Appearance | White or slightly yellowish crystalline powder |
| Main function | Reducing agent |
| Typical industrial assay | 97% min |
| Main water-treatment use | Dechlorination |
| Common applications | RO, water treatment, mining, textile, pulp and paper |
The final product specification should always be confirmed against the supplier’s current technical data sheet and batch Certificate of Analysis (COA).
What Is Sodium Metabisulfite?
Sodium Metabisulfite is an inorganic sulfur compound with the formula Na₂S₂O₅. It dissolves in water and forms bisulfite-related reducing species that can react with oxidizing substances.
This reducing property makes SMBS useful for dechlorination, redox control, selected mining processes, textile dyeing, pulp and paper production, and permitted food-processing applications.
SMBS is often compared with Sodium Bisulfite, Sodium Sulfite, and Sodium Thiosulfate. These are different chemicals with different formulas, physical forms, concentrations, storage requirements, and dosing systems.
For an industrial buyer, the choice is therefore not simply a matter of chemical name. The existing dosing equipment, storage conditions, logistics, process requirements, and total delivered cost all matter.
Sodium Metabisulfite Specifications
There is no single specification that fits every SMBS application.
For water treatment, the focus is usually on assay, insoluble matter, dissolution behavior, and batch consistency. Food-processing applications may require tighter impurity limits and specific regulatory documentation. Mining customers may place more emphasis on process performance and cost per unit of active chemical.
A typical industrial specification may include:
| Parameter | Typical Industrial Requirement* |
|---|---|
| Sodium Metabisulfite content | ≥97% |
| Appearance | White crystalline powder |
| Water-insoluble matter | As agreed |
| Iron | As agreed |
| Heavy metals | Grade- and application-dependent |
| Packaging | 25 kg bags, jumbo bags, or customized packaging |
*Values are for reference only. The final specification, impurity limits, and packaging details should be confirmed before ordering.
For repeat industrial purchases, batch consistency is as important as nominal purity. A batch COA allows the delivered material to be checked against the agreed specification and provides a useful record for comparing shipments over time.
Sodium Metabisulfite for Water Treatment and RO
Sodium Metabisulfite is used in water treatment primarily as a reducing and dechlorinating agent.
One of its most common applications is removing residual chlorine before a downstream process that is sensitive to oxidizing agents.
Typical uses include:
- RO pretreatment
- Dechlorination before membrane systems
- Industrial process-water treatment
- Selected wastewater-treatment processes
- Chlorine removal
- Redox control
Sodium Metabisulfite for RO Dechlorination
Many polyamide RO membranes are sensitive to free chlorine. Prolonged exposure to chlorine can oxidize the membrane and affect salt rejection and service life.
A typical pretreatment sequence is:
Raw Water → Pretreatment → Chlorination → SMBS Dosing → Mixing/Contact → Cartridge Filtration → RO Membrane
The actual process arrangement varies by plant.
The important point is that SMBS needs adequate contact with the chlorinated water before the water reaches the membrane. A dosing-pump setting alone does not demonstrate that dechlorination is complete.
The system should be checked for:
- Incoming free-chlorine concentration
- Water flow rate
- SMBS assay
- SMBS solution concentration
- Dosing-pump output
- Injection location
- Mixing efficiency
- Contact time
- pH and temperature
- Changes in raw-water quality
The most useful operating check is residual chlorine after SMBS dosing and before the RO membrane.
SMBS Dosage for Chlorine Removal
SMBS dosage calculations should distinguish between a theoretical chemical requirement and an actual plant operating dose.
For chlorine reported as Cl₂ equivalent, the theoretical stoichiometric requirement commonly used for SMBS dechlorination is approximately 1.34 kg of pure Na₂S₂O₅ per 1 kg of chlorine as Cl₂.
For a commercial SMBS product, the starting product requirement can therefore be estimated as:
SMBS product dose = Chlorine load × 1.34 ÷ SMBS assay fraction
For example, with:
- Free chlorine = 1.0 mg/L as Cl₂
- SMBS assay = 97%
The theoretical product requirement is:
1.0 × 1.34 ÷ 0.97 ≈ 1.38 mg/L
This is a calculation starting point, not a universal operating dosage.
Actual chemical demand can be affected by:
- Product assay
- Chlorine concentration
- Water flow
- Other oxidizing substances
- Mixing efficiency
- Contact time
- pH
- Temperature
- Measurement accuracy
- Operating margin
For this reason, the dosing rate should be validated by measuring residual chlorine downstream of the SMBS injection point.
Important note on dosage calculations
Do not size an SMBS dosing system from a theoretical ratio alone.
For example, if the feed-water chlorine concentration changes from 0.5 mg/L to 2.0 mg/L, the chlorine load changes substantially even when the water flow remains constant. The SMBS feed rate must respond to the actual oxidant load.
Monitoring and Troubleshooting SMBS Dechlorination
A stable dechlorination system relies on process measurements rather than a fixed dosing rate.
| Parameter | Why It Matters |
|---|---|
| Incoming chlorine | Determines chemical demand |
| Downstream chlorine | Confirms dechlorination performance |
| Water flow | Determines total chlorine load |
| SMBS solution strength | Determines active chemical delivered |
| Pump output | Confirms actual feed rate |
| Mixing/contact time | Affects reaction completion |
Common Problems
| Problem | Possible Cause | Recommended Check |
|---|---|---|
| Chlorine remains before RO | SMBS dose is too low | Check chlorine load, solution strength, and pump output |
| Chlorine residual fluctuates | Source-water quality changes | Increase monitoring frequency and adjust dosage |
| Calculated dose is correct but chlorine remains | Poor mixing or insufficient contact time | Review injection point and piping |
| SMBS solution loses performance | Poor preparation or prolonged storage | Check solution preparation and storage conditions |
| Product becomes lumpy | Moisture exposure | Inspect packaging and warehouse humidity |
This approach is more useful in plant operation than relying on a fixed SMBS dosage calculated from historical conditions.
Sodium Metabisulfite Grades and Applications
Industrial Grade Sodium Metabisulfite
Industrial-grade SMBS is commonly used for:
- Water treatment
- RO dechlorination
- Wastewater treatment
- Mining and mineral processing
- Textile processing
- Pulp and paper
- Leather processing
- Industrial chemical processes
For these applications, buyers normally compare assay, impurity limits, physical condition, batch consistency, packaging, documentation, and delivered cost.
Food Grade Sodium Metabisulfite
Food-grade Sodium Metabisulfite may be used as a preservative, antioxidant, or processing aid where sulfites are permitted.
It is commonly identified as E223 / INS 223, but food-grade status does not mean that the material is approved for every food application.
Permitted uses, maximum levels, labeling requirements, sulfite declarations, and documentation vary between markets.
For food-grade purchasing, the intended application and destination market should therefore be established before the quotation is finalized.
Sodium Metabisulfite vs Sodium Bisulfite
Sodium Metabisulfite and Sodium Bisulfite are closely related sulfur-based reducing agents, but their physical forms and handling requirements are different.
| Factor | Sodium Metabisulfite | Sodium Bisulfite |
|---|---|---|
| Formula | Na₂S₂O₅ | NaHSO₃ |
| Typical form | Dry powder | Often liquid solution |
| On-site preparation | Usually required | Often ready for direct metering |
| Storage | Dry storage; protect from moisture | Suitable liquid chemical storage |
| Transport | Dry chemical shipment | Liquid chemical transport |
| Dosing | Dissolution system required | Often direct liquid metering |
SMBS is a practical choice when a plant has dry-chemical storage and solution-preparation equipment.
Sodium Bisulfite can be more convenient when the plant already has liquid storage and metering infrastructure.
The better choice depends on the existing system, storage capacity, labor, logistics, process requirements, and delivered cost.
Packaging, Storage and Handling
HOO CHEMTEC can supply Sodium Metabisulfite in:
- 25 kg moisture-resistant bags
- 25 kg bags on pallets
- 500 kg jumbo bags
- 1,000 kg jumbo bags
- Customized packaging, subject to confirmation
For SMBS, moisture protection is particularly important. Packaging should therefore be matched to the shipping route, storage period, warehouse conditions, unloading method, and container-loading plan.
Storage
Store Sodium Metabisulfite in a cool, dry and well-ventilated area.
Keep the product tightly sealed in its original packaging and protect it from moisture.
Avoid contact with acids and incompatible materials. Acid contact can release sulfur dioxide, so appropriate ventilation, personal protective equipment, and SDS-based handling procedures are important.
The current SDS for the specific product should always be used as the primary reference for handling and emergency procedures.
Sodium Metabisulfite Export Supply
For international B2B orders, HOO CHEMTEC can support:
- Product specifications
- Batch COA
- SDS and TDS
- Commercial Invoice
- Packing List
- Certificate of Origin, where applicable
- Shipping marks
- Container-loading information
- Buyer- or destination-specific documents, subject to confirmation
Before shipment, the order should clearly establish:
Grade → Assay → Quantity → Packaging → Palletization → Destination Port → Incoterms → Documents → Delivery Schedule
This reduces the risk of specification or documentation changes after the order has been confirmed.
Why Source Sodium Metabisulfite from HOO CHEMTEC?
HOO CHEMTEC supplies Sodium Metabisulfite for water treatment, industrial production, distribution, and bulk export.
We can support customers with:
- Industrial-grade SMBS, typically 97% minimum assay
- Food-grade or application-specific requirements
- 25 kg and jumbo-bag packaging
- COA, SDS, and TDS
- Container-loading planning
- Export documentation
- Destination-port supply requirements
- Repeat-order packaging and specification consistency
For an RO dechlorination inquiry, send the water flow, incoming chlorine concentration, required quantity, packaging preference, and destination port.
These details allow the quotation to be based on the actual application rather than a generic product description.
Request a Bulk Sodium Metabisulfite Quote
Looking for a Sodium Metabisulfite supplier for water treatment or industrial applications?
Send HOO CHEMTEC:
- Required grade
- Assay
- Application
- Quantity
- Packaging preference
- Destination port
- Required documents
- Target shipping date
We can confirm the available specification, packaging option, documentation and quotation basis for your bulk order.
Contact HOO CHEMTEC for Sodium Metabisulfite specifications, COA, SDS and bulk export pricing.
