Sodium Metabisulfite: The Multi-Purpose Reducing Agent Powering Global Industrial Sectors
Author : anny EMI | Published On : 30 Jul 2026
Sodium Metabisulfite, also known as SMBS or sodium pyrosulfite with the chemical formula Na₂S₂O₅, is a white-to-slightly-yellow crystalline powder valued globally for its powerful reducing, bleaching, antioxidant and dechlorinating properties. Marked with CAS 7681-57-4, HS code 2832100000 and UN transport classification 1759, this versatile chemical is supplied in four standardized purity tiers: 95%, 96.5%, 97% and 98%, with a minimum bulk order of 5 metric tons packed in standard 25kg bags. Every production batch includes an official Certificate of Analysis (COA detailing purity, moisture, particle size and heavy metal limits), allowing buyers to select the exact grade aligned with their industry’s regulatory and performance demands. This guide breaks down grade selection, core use cases, shipping protocols and critical handling safety for commercial purchasers across all sectors.
The 95% purity grade serves as the cost-effective baseline for low-demand industrial workflows with loose impurity tolerance. It is widely adopted in municipal wastewater dechlorination, basic pulp deinking and non-critical textile bleaching operations. For facilities with high daily chemical consumption and low sensitivity to minor trace impurities, this tier balances budget and functional performance without sacrificing core reducing power. It excels at removing free chlorine from effluent streams to protect downstream filtration equipment, and acts as an affordable bleaching aid for low-grade paper and rough textile fabrics where ultra-bright finish standards are not required.
The mid-tier 96.5% and 97% purity grades represent the most popular all-round choice for mainstream manufacturing. These two grades strike a perfect balance between cost and refined purity, covering mining flotation processing, standard textile dyeing, general water treatment and conventional chemical synthesis. In mineral mining, 96.5%–97% SMBS acts as a selective flotation depressant and cyanide detoxifier for gold leach tailings, separating valuable sulfide ores from waste rock efficiently. For textile mills, it neutralizes residual chlorine after fabric bleaching to prevent fiber brittleness and uneven dye uptake, delivering consistent color results on cotton, linen and synthetic blends. Most mid-sized water treatment plants rely on these grades to stabilize pH and precipitate heavy metal contaminants from industrial discharge before environmental release.
At the top tier, 98% high-purity sodium metabisulfite meets strict food, pharmaceutical, photographic and premium manufacturing standards with ultra-low heavy metal and ash content. Classified as food-safe when produced to food-grade specifications, it functions as preservative E223 for dried fruits, wine fermentation stabilization and antioxidant for seafood and processed meats, inhibiting enzymatic browning and microbial spoilage to extend shelf life. Beyond food production, 98% SMBS is used in lab photographic stop baths and fixer preservatives, halting developer reactions and extending the lifespan of film processing solutions. It also supports precision organic chemical synthesis where impure lower grades would disrupt sensitive reactions and compromise final product quality.
Across all four purity levels, sodium metabisulfite delivers seven core industrial functions: dechlorination for water systems, mineral flotation reducer, food antioxidant/preservative, pulp & paper bleaching, textile dyeing auxiliary, chemical synthesis sulfur dioxide source, and photographic processing additive. Regardless of grade, all shipments follow UN 1759 hazardous cargo protocols requiring sealed, dry transport and proper corrosive hazard labeling. Storage must occur in cool, ventilated warehouses isolated from strong acids and oxidizers, as contact releases toxic sulfur dioxide gas that poses respiratory risks to staff. Mandatory PPE including dust masks, chemical-resistant gloves and safety goggles is required during powder handling to avoid skin, eye and airway irritation.
Our supplier’s full quality assurance system eliminates procurement uncertainty: every batch ships with downloadable COA documentation verifying compliance with global trade standards, while the flexible 5 MT MOQ accommodates small factories, mid-size mills and large industrial conglomerates alike. Whether you operate a food processing plant, mining operation, textile dye house or wastewater facility, matching your sodium metabisulfite purity grade to your workflow’s precision requirements maximizes efficiency, cuts waste and ensures full regulatory compliance for all finished goods and discharge streams.
