When sourcing sodium sulfite for industrial applications, understanding the detailed sodium sulfite specification is one of the most critical steps in the procurement process. Whether you are buying for a power plant boiler system, a textile finishing line, or a pulp mill, the wrong specification can lead to costly equipment corrosion, product defects, or even safety incidents. At Hailei Chemical, we have seen too many buyers overlook key quality parameters, only to face batch rejections and supply chain disruptions. This comprehensive guide breaks down everything you need to know about sodium sulfite specifications, chemical structure, application-driven requirements, and how to select a reliable sodium sulfite supplier that consistently delivers the quality you need.
Sodium sulfite (Na₂SO₃) is a white, crystalline or powdered inorganic reducing agent widely used across multiple heavy industries. It is available in two main solid forms: anhydrous (water-free) and heptahydrate (seven water molecules). The compound is moderately soluble in water, producing an alkaline solution, and is valued for its ability to react readily with oxygen, chlorine, and peroxides. This oxygen-scavenging property makes it indispensable in boiler water treatment, while its reducing strength supports pulp processing, textile bleaching neutralization, and photographic developing.
When you request a quote or review a certificate of analysis, the sodium sulfite specification will typically include a set of physical and chemical parameters. While exact requirements vary by application, the following core specifications are essential for every industrial buyer to understand.
The primary measure of quality is purity, expressed as percent sodium sulfite (Na₂SO₃) content. Typical industrial technical-grade anhydrous sodium sulfite specifications range from 96.0% to 98.0%. For applications demanding higher purity, photographic and analytical grades can exceed 99.0%. However, for most boiler water treatment and pulp applications, 96–98% purity is perfectly adequate. Hailei Chemical’s standard anhydrous sodium sulfite is consistently within this range, with typical batch results at 97% or above. The heptahydrate form naturally carries a lower Na₂SO₃ content (typically 60–62% due to water of crystallization), and the purity is calculated based on dry basis or as-is weight, so always confirm which reporting basis your supplier uses.
Sodium sulfite hydrolyzes in water to produce an alkaline solution. A 1% solution at 25°C typically has a pH between 9.0 and 10.5. This alkalinity is important for corrosion inhibition in boiler systems, but it can also affect processes where neutral conditions are required. Always specify the acceptable pH range if your process is sensitive. A narrow pH specification (e.g., 9.5–10.0) indicates a well-controlled manufacturing process with minimal free alkali contamination.
For power plant applications, iron content is a critical specification. Dissolved iron can deposit on heat exchanger surfaces and catalyze pitting corrosion. A typical industrial-grade sodium sulfite specification limits iron (Fe) to a maximum of 0.002% (20 ppm). High-purity grades may specify iron below 0.0005%. Heavy metals (as Pb) are usually limited to ≤0.001%. Chloride content is another concern, especially for stainless steel boiler systems where chloride-induced stress corrosion cracking is a risk. Many suppliers will specify chloride as ≤0.01% for boiler-grade sodium sulfite. Hailei Chemical’s standard product meets or exceeds these limits, and we provide full impurity profiles on every batch certificate.
For liquid formulation users, water-insoluble residues can clog injection nozzles and cause system fouling. The specification typically limits water-insolubles to ≤0.01% for high-grade material. Even technical grades should stay below 0.05%. Always confirm this parameter if you will be preparing on-site liquid solutions.
Sodium sulfite slowly oxidizes to sulfate when exposed to air and moisture. Proper packaging in sealed polyethylene-lined kraft paper bags (25 kg) or super sacks (500–1000 kg) is essential to preserve the product’s specification until point of use. Shelf life is generally 12 months under cool, dry storage conditions. Specification sheets often include a recommendation to retest after 6 months if long-term storage is expected.
Understanding the sodium sulfite structure helps explain why it performs so predictably in oxygen-scavenging and reducing applications. The anhydrous molecule consists of two sodium cations (Na⁺) and one sulfite anion (SO₃²⁻). The sulfite ion has a trigonal pyramidal geometry with the sulfur atom at the apex, bonded to three oxygen atoms. This structure makes the sulfur atom relatively electron-rich, giving sodium sulfite its strong reducing character. In aqueous solution, sulfite ions readily donate electrons to oxygen molecules, converting to sulfate (SO₄²⁻):
2 Na₂SO₃ + O₂ → 2 Na₂SO₄
This reaction is the cornerstone of boiler water deoxygenation. At elevated temperatures (above 100°C), the reaction is rapid, making sodium sulfite an effective and economical oxygen scavenger. In the heptahydrate form (Na₂SO₃·7H₂O), the same sulfite anion is surrounded by water molecules in the crystal lattice, which increases the formula weight and lowers the effective Na₂SO₃ content. For industrial buyers, the structural difference translates directly into shipping and handling considerations: anhydrous product delivers more active sulfite per kilogram shipped, reducing freight costs.
Different end uses demand different emphasis on specification parameters. Knowing which parameters matter most can save you money by avoiding over-specifying purity and under-specifying critical impurities.
In power plants and industrial boiler systems, the primary purpose of sodium sulfite is to remove dissolved oxygen down to parts-per-billion levels to prevent pitting corrosion. The key specifications here are:
Sodium sulfite is used in the sulfite pulping process and as a reducing agent in bleaching stages. Specification requirements include consistent purity, low heavy metals (to avoid discoloration of paper), and controlled pH. Sulfite liquor in pulping requires a specific ratio of free and combined SO₂, which is influenced by the sodium sulfite purity. Pulp mills often work with a narrow acceptance range of 96.5–97.5% purity to maintain process uniformity. Impurities like chloride and iron are less critical than in boiler water but still must be monitored to avoid process upsets.
After hydrogen peroxide bleaching of cotton and cotton-blend fabrics, residual peroxide can cause dyeing defects and fabric damage. Sodium sulfite neutralizes the excess peroxide quickly and without producing acidic byproducts. For this application, the textile finishing plant needs a product that dissolves completely and leaves no insoluble residues that could stain fabric. Water-insoluble matter is therefore the most strictly controlled specification, often capped at ≤0.02%. Purity can be in the 96–98% range, but the absence of foreign particles is critical.
In black-and-white photographic developing solutions, sodium sulfite acts as a preservative for the developing agent, preventing oxidation. Photographic-grade sodium sulfite specifications demand extremely high purity (≥99.0%) with strict limits on heavy metals, iron, and organic contaminants that could fog the film. This grade is not interchangeable with industrial boiler-grade material; attempting to use technical-grade sulfite in photography will lead to inferior image quality. For buyers in this sector, sourcing from a sodium sulfite supplier that can consistently deliver analytical-grade material is non-negotiable.
Sodium sulfite is sometimes added to lime-sulfide dehairing baths to improve hair removal efficiency and reduce sulfide demand. Leather processing facilities typically use technical-grade anhydrous sodium sulfite with a minimum purity of 96%. The main specification concerns are heavy metals (which could end up in finished leather) and the absence of insoluble particles that would mar leather surfaces.
While this buyer’s guide focuses on industrial specifications, a frequently asked question deserves a brief mention. What is sodium sulfite in shampoo? In personal care products, sodium sulfite functions as a reducing agent and antioxidant, helping to prevent color fading and extend shelf life by scavenging dissolved oxygen. The cosmetic-grade sodium sulfite specification is far more stringent than industrial grades: purity must be ≥99%, heavy metals essentially undetectable, and the material must meet pharmacopeia or cosmetic ingredient monograph standards. Industrial buyers should note that this is a completely different product category with a significantly higher price point, and it is not suitable for industrial applications due to cost. Hailei Chemical supplies industrial-grade sodium sulfite; for cosmetic-grade inquiries, we recommend specialized fine chemical distributors.
When you ask “where can i buy sodium sulfite,” you are likely looking for more than just a vendor with stock availability. You need a supplier that can provide consistent quality, full documentation, and reliable logistics. Here are six criteria to use when vetting a sodium sulfite supplier.
Every shipment should come with a certificate of analysis (CoA) that lists actual test results against the specification. Avoid suppliers that only provide a generic “typical properties” sheet. The CoA should include assay, iron, heavy metals, water-insolubles, pH, and any other parameters agreed in your purchase contract. Hailei Chemical issues a detailed CoA with every order, allowing your quality control team to verify the sodium sulfite specification before offloading.
Ask if the supplier is a manufacturer or a trader. Manufacturers generally have better control over specification consistency because they can adjust reaction conditions (sulfur dioxide absorption into sodium carbonate/sodium hydroxide solution) and purification steps. Hailei Chemical produces sodium sulfite at our modern plant in Weifang, Shandong, with full traceability from raw material reception to finished product shipping.
Look for ISO 9001 (quality management), ISO 14001 (environmental management), and applicable chemical industry certifications. For exports to Europe, REACH registration is mandatory. Our facility maintains these certifications and can accommodate customer-specific audits. Ask your potential supplier if they have recent audit reports available.
Industrial sodium sulfite is typically shipped in 25 kg woven polypropylene bags with inner polyethylene liners, or in 500–1000 kg flexible intermediate bulk containers (FIBCs). Confirm that the packaging is suitable for ocean freight if you are importing. Proper palletizing and shrink-wrapping prevent moisture ingress. Ask about stuffing density and container loading capacity to optimize freight costs. Hailei Chemical loads a maximum 25 tons of sodium sulfite per 20-foot container without pallets, or 20 tons with palletized packaging for easier unloading.
Given international shipping lead times of 4–8 weeks, you need a supplier with consistent production output and flexible inventory management. Inquire about minimum order quantities (MOQs), typical lead times, and the supplier’s track record for on-time delivery. Hailei Chemical maintains a buffer stock of anhydrous sodium sulfite, allowing us to ship within 7–10 working days from receipt of order and payment, subject to prior coordination.
A true partner will help you optimize specification selection and troubleshoot application issues. When contacting a potential supplier, ask whether they have chemists or application specialists who can advise on dosage rates for your boiler system or compatibility with other process chemicals. For buyers new to sodium sulfite, a knowledgeable sodium sulfite supplier can help you avoid costly specification mistakes.
The anhydrous form contains no water of crystallization, while heptahydrate contains seven water molecules per Na₂SO₃ unit. Anhydrous sodium sulfite has a higher effective sulfite content (96–98%) and is preferred where high reactivity and low shipping weight are needed. Heptahydrate crystals are larger, store with slightly better stability in humid environments, but contain only about 60% Na₂SO₃. For boiler water treatment, anhydrous is the standard.
No. Food-grade sodium sulfite (often used as a preservative and antioxidant) requires compliance with food chemicals codex standards and must have very low heavy metals. Industrial-grade product, even at 98% purity, is not safe or permitted for food use. Always specify the correct grade for your intended use.
Store in a cool, dry, well-ventilated area away from moisture and acids. Keep containers tightly sealed when not in use. Even under ideal conditions, gradual oxidation to sulfate will occur. Retesting is recommended after 6 months of storage. If the product has hardened or become lumpy, it may have absorbed moisture and partially oxidized, and its assay should be verified before use.
Yes. The CAS number for anhydrous sodium sulfite is 7757-83-7, and for sodium sulfite heptahydrate it is 10102-15-5. EINECS number is 231-821-4 for anhydrous. These identifiers are important for customs documentation and safety data sheets.
Sodium sulfite is classified as an irritant under GHS. It can cause respiratory irritation if inhaled as dust, and skin or eye irritation upon contact. Safety data sheets (SDS) should be reviewed and PPE (dust mask, gloves, safety glasses) used during handling. Specification-wise, this means your supplier should provide an up-to-date SDS and ensure the product is not excessively dusty if that poses a workplace hazard. Some customers request a maximum dusting potential specification, which we can address through granular product options.
Getting the sodium sulfite specification right from the start protects your processes, your equipment, and your bottom line. Whether you need technical-grade anhydrous sodium sulfite for high-pressure boilers, a controlled particle size for textile bleaching neutralization, or photographic-grade purity, the specification details matter. At Hailei Chemical, we take pride in delivering consistent quality backed by full documentation and expert support. Our team can help you navigate the specification maze and ensure you get exactly the right product for your application.
Ready to source sodium sulfite that meets your exact specification? Visit our sodium sulfite product page for more technical details, or request a quote directly. Our sales engineers will respond within one business day with a tailored offer, including a detailed specification sheet for your batch.