Sodium metabisulfite, also called sodium pyrosulfite, is an inorganic compound with the chemical formula Na2S2O5. It appears as a white to slightly yellowish crystalline powder or granular solid with a sharp, pungent sulfur dioxide (SO2) odor. When dissolved in water it readily forms sodium bisulfite (NaHSO3), and in the presence of acids or moisture it releases sulfur dioxide gas, which is the source of its preservative, antioxidant, reducing, and bleaching properties. Because it delivers a high concentration of available SO2 in a stable, easy-to-handle solid form, it is one of the most widely used sulfiting agents in industry. Weifang Hailei Fine Chemical Co., Ltd supplies it in food grade, industrial grade, and mining flotation grade.
The sulfur dioxide (SO2) content is the single most important quality parameter for sodium metabisulfite because virtually all of its functions depend on releasing SO2. Pure Na2S2O5 has a theoretical SO2 equivalent of about 67%, and commercial grades are commonly specified at 65% available SO2 or higher. Buyers use the SO2 figure to calculate dosage in applications such as dechlorination, food preservation, and flotation. A low SO2 content usually indicates dilution or poor production control, which forces users to add more product to achieve the same effect and increases their total cost.
Sodium metabisulfite is manufactured by absorbing sulfur dioxide (SO2) gas into an aqueous solution of sodium carbonate (soda ash) or sodium hydroxide. The reaction forms a sodium bisulfite/sulfite solution, which is then crystallized and dried to yield the anhydrous metabisulfite salt. The quality of the raw sulfur and the purity of the alkaline feed largely determine the final product's purity, color, and impurity profile. Being located in Weifang, Shandong — one of China's major inorganic-salt chemical production bases — Hailei benefits from a mature raw-material supply chain and consistent production conditions.
The three grades differ mainly in purity requirements, impurity limits, and intended end use, even though the principal assay may be identical. Food grade is produced and handled to meet food-contact requirements and carries tighter limits on impurities such as arsenic, heavy metals, and iron; it is used where the product may enter food or feed. Industrial grade is intended for technical applications like water treatment, pulp bleaching, and textiles, where food-grade purity is not required. Mining flotation grade is optimized for mineral processing — as a depressant, cyanide-destruction reagent, or reducing agent — and is typically supplied to a specification that balances purity with cost for high-volume use. Hailei supplies food grade 96.5%, industrial grade 96.5%, and mining flotation grade.
In food processing, sodium metabisulfite acts as a preservative, antioxidant, and bleaching agent, and is widely known as food additive E223. It inhibits the growth of molds and bacteria, prevents enzymatic and non-enzymatic browning, and preserves color and freshness in products such as dried fruits, fruit juices, wines and beers, canned and frozen seafood, and certain vegetable preparations. It is also used to sanitize winemaking equipment and to stabilize the flavor of bottled beverages. When sourcing for food use, buyers should specify food grade and confirm that the supplier's impurity limits and handling practices are suitable for food-contact applications.
One of the most important industrial uses of sodium metabisulfite is the removal of free chlorine and chloramine from water. It reacts rapidly with residual chlorine, reducing it to harmless chloride, which protects reverse-osmosis membranes and other downstream equipment from oxidative damage. It is widely dosed in municipal water treatment, power plants, and industrial wastewater facilities as a cost-effective dechlorination agent. Compared with gaseous or liquid alternatives, the solid powder is easy to store, meter, and apply, which is why many plant operators prefer it.
In mineral processing, sodium metabisulfite serves primarily as a flotation reagent, most commonly as a depressant and reducing agent. It is used to depress pyrite and other sulfide minerals so that target minerals such as copper, molybdenum, lead, or zinc can be selectively floated. It is also applied in cyanide detoxification, where its reducing power helps neutralize residual cyanide in process effluents, and as a general oxygen scavenger in pulp circuits. Mining flotation grade is formulated for these high-volume, cost-sensitive duties and is typically supplied in bulk.
In the pulp and paper industry, sodium metabisulfite functions as a bleaching and reducing agent. It is used to brighten mechanical and recycled pulp, to remove residual oxidants after chlorine or peroxide bleaching stages, and to help stabilize brightness by counteracting yellowing. It also acts as a chemical oxygen scavenger to protect process equipment from corrosion. The industrial grade is the standard choice for this sector.
In textile processing, sodium metabisulfite is a versatile reducing agent used in dyeing, printing, and stripping operations. It helps reduce and fix certain dyes, removes unfixed or unwanted color in the stripping or "discharge" of dyed fabric, and is used in bleaching and after-cleaning steps. Its mild, controllable reducing action makes it useful where stronger reducing agents would damage fibers. Textile mills typically specify industrial grade for these applications.
Beyond the sectors already covered, sodium metabisulfite is used across a wide range of industries. It serves as an oxygen scavenger and reducing agent in some oilfield and industrial water systems, as a chemical intermediate in manufacturing other sulfites and chemicals, and in the treatment of photographic chemicals and gold-recovery solutions. It also appears in rubber and latex processing, leather treatment, and various cleaning and preservation formulations. Its combination of strong reducing power, low cost, and easy handling makes it a common input wherever a controlled source of SO2 or a reducing environment is needed.
Choosing the right grade starts with identifying whether your end product has food-contact or regulatory sensitivity. If the material may enter food, beverages, or feed, select food grade and confirm that it meets the relevant food-additive specifications for your market. For technical uses such as water treatment, pulp, textiles, and general industrial chemistry, industrial grade is normally the economical choice. For mineral processing, ask about mining flotation grade, which is tailored to flotation and cyanide-destruction duties. Sharing your full application details, dosage method, and target market with the supplier will help them recommend the most suitable specification.
When evaluating sodium metabisulfite, buyers typically review a certificate of analysis (COA) covering assay (Na2S2O5 content), available SO2, iron (Fe), heavy metals, arsenic, water-insoluble matter, and appearance/color. Food-grade material should also be assessed against the food-additive requirements applicable in the destination country, while industrial users focus mainly on assay, iron, and water-insoluble content. Ask the supplier to explain which test methods are used and whether third-party testing is available. Always request a COA for each batch so you can track consistency over time.
The "96.5%" refers to the minimum assay (purity) of Na2S2O5 in the product, expressed as a percentage by weight. Both food grade and industrial grade at Hailei are specified at 96.5% main content, but the two grades differ in their impurity profiles and suitability for end use. Food grade is manufactured and controlled to meet food-contact requirements, with stricter limits on elements such as arsenic, heavy metals, and iron, and is handled under conditions that protect its food-safety status. Industrial grade is intended for technical applications and may allow slightly higher levels of certain impurities that are irrelevant outside food use. Buyers should therefore select by end use rather than by assay number alone.
Sodium metabisulfite is moisture-sensitive and releases SO2 on contact with water, so packaging must be sealed and moisture-resistant. It is commonly supplied in 25 kg PE-lined woven polypropylene bags, or in larger jumbo bags (500 kg–1,000 kg) for bulk industrial and mining buyers. Inner polyethylene liners and heat-sealed closures protect the product from humidity during ocean freight and warehouse storage. Hailei can also arrange palletized loads, shrink-wrapping, and custom labeling or private labeling to suit the buyer's market.
Sodium metabisulfite should be stored in a cool, dry, well-ventilated area, away from moisture, acids, and oxidizing agents. Because it gradually releases sulfur dioxide — especially in damp or acidic conditions — the storage area must be kept dry and the containers tightly sealed when not in use. It should be kept away from heat, direct sunlight, and incompatible materials such as strong oxidizers, and industrial grade should not be stored alongside food products. Following these rules preserves product quality and reduces SO2 odor in the warehouse.
Minimum order quantities (MOQ) and lead times depend on grade, packaging, and destination. A common MOQ is one 20-foot container (around 20–27 metric tons in 25 kg bags), although trial quantities in smaller batches are often possible for qualified buyers. Lead time is typically a few weeks for container quantities, depending on production scheduling and the shipping route. Buyers should confirm the current MOQ, production window, and vessel availability with the supplier at the quotation stage to plan purchasing and logistics accurately.
The price of sodium metabisulfite is driven mainly by the cost of its raw materials — sulfur/sulfur dioxide and soda ash (sodium carbonate) — plus energy, packaging, and freight. Because it is a commodity chemical, market supply and demand, exchange rates, and ocean-freight rates also cause prices to move over time. Grade and packaging (small bags versus jumbo bags), order volume, and delivery terms (FOB, CIF, etc.) all influence the final unit price. Working with a source factory can reduce intermediary markups and give buyers more transparent pricing.
A reliable supplier evaluation covers manufacturing capability, quality control, and documentation, not just price. Look for a source factory with stable production and a genuine quality system, request samples and batch COAs, and ask for references or trial orders. Confirm that the supplier can provide the necessary documents for your market, such as a COA, MSDS/SDS, and, where required, certificates for food-grade use. Responsiveness, stable specifications across batches, and clear logistics support are also strong signals of a dependable long-term partner.
Sodium metabisulfite is a reducing agent, not an oxidizer, and it releases sulfur dioxide when it contacts water or acid. Transport classification varies by region and by the exact formulation, so the governing documents are always the current Safety Data Sheet (SDS) and the regulations of the shipping and destination countries. In general, it is shipped in sealed, moisture-resistant packaging and must be kept segregated from acids, oxidizers, and moisture during transit. Always share the full SDS with your freight forwarder and confirm the applicable class, UN number, and packaging requirements before shipment.
The main hazard of sodium metabisulfite is the release of sulfur dioxide (SO2) gas, which is irritating to the eyes, skin, and respiratory tract and can trigger reactions in sensitive individuals. Workers should use appropriate personal protective equipment — such as gloves, safety goggles, and, where ventilation is limited, respiratory protection — and handle the product in well-ventilated areas. Avoid contact with acids and water, and keep sulfite-containing materials away from people with known sulfite sensitivity or asthma. Proper training and clear SDS-based handling procedures should be standard in every facility that uses the product.
Weifang, Shandong is one of China's most important production bases for inorganic salts and industrial chemicals, giving buyers access to mature raw-material supply, well-established logistics, and experienced manufacturing. Sourcing directly from a source factory (源头厂家) like Weifang Hailei Fine Chemical Co., Ltd removes intermediary layers, which can improve price transparency, quality traceability, and communication on specifications. Direct factory relationships also make it easier to arrange custom packaging, consistent batch quality, and reliable export documentation for global B2B buyers.
A professional supplier should provide a full set of supporting documents, including a certificate of analysis (COA), a Safety Data Sheet (SDS/MSDS), and commercial documents such as the proforma invoice and packing list. For food-grade material, ask about the documentation needed to demonstrate suitability for food use in your destination market. Good suppliers also offer samples for evaluation, technical guidance on dosing and handling, and help with shipping arrangements and customs documents. Clear, complete documentation from the start reduces the risk of customs delays and specification disputes.