CAS 7631-90-5
Sodium Bisulphite
Sodium Bisulphite is a reducing agent used to remove chlorine ahead of RO membranes, scavenge oxygen in boiler water and reduce chromium in plating effluent.
Sodium bisulphite (NaHSO₃) reacts rapidly with oxidising agents. Its biggest use in water treatment is dechlorination: free chlorine that protects pipework from bacteria will destroy polyamide reverse osmosis membranes, so bisulphite is dosed just ahead of the RO unit to neutralise it. The same reaction is used to dechlorinate effluent before discharge to rivers.
In industry it reduces toxic hexavalent chromium to trivalent chromium in plating and tannery effluent, scavenges dissolved oxygen from boiler feed water and acts as an antichlor after textile bleaching. It is supplied as a solution or prepared on site from sodium metabisulphite powder, which dissolves to give the same active species.
- CAS number
- 7631-90-5
- Grades / forms
- Technical
- Industries
- Water Treatment
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Typical applications
- Dechlorination of RO and nanofiltration feed water
- Dechlorination of effluent before discharge
- Oxygen scavenging in boiler feed water
- Hexavalent chromium reduction in plating effluent
- Antichlor after textile bleaching
Packing options
- 25 kg PE-lined bags (powder)
- 250 kg HDPE drums (solution)
- 1,000 L IBCs (solution)
Storage & handling
Keep containers closed — bisulphite slowly oxidises to sulphate in air and loses strength. Contact with acids releases sulphur dioxide gas.
Documentation
Certificate of Analysis, MSDS, Certificate of Origin, dangerous goods declaration where applicable, and third-party pre-shipment inspection on request.
Typical specification
- Form
- White powder or 38–40% aqueous solution
- pH (solution)
- About 4.0–5.0
- Odour
- Slight sulphur dioxide
Typical values for reference. The exact specification is agreed before the order and confirmed on the Certificate of Analysis for each batch.
Sodium Bisulphite — frequently asked
In theory about 1.5 mg of sodium bisulphite neutralises 1 mg of free chlorine. In practice RO plants dose around 2–3 mg per mg of chlorine to allow for dissolved oxygen and to keep a small safety margin, confirmed by an ORP or residual chlorine check.
Sodium metabisulphite (Na₂S₂O₅) is a stable dry powder. When dissolved in water it forms sodium bisulphite, so both deliver the same active chemistry. Powder metabisulphite is cheaper to ship; bisulphite solution is easier to dose.
Yes. At a pH of about 2 to 3, sodium bisulphite reduces toxic hexavalent chromium to trivalent chromium, which is then precipitated as chromium hydroxide by raising the pH.
Yes. Chemtrade manufactures and exports Sodium Bisulphite (CAS 7631-90-5) from Surat, Gujarat, India to more than 55 countries, for customers in Water Treatment. Send your grade, quantity and destination port for a quotation within one business day.
Every shipment of Sodium Bisulphite from Chemtrade includes a batch-specific Certificate of Analysis (COA) and Material Safety Data Sheet (MSDS). Certificate of Origin, third-party pre-shipment inspection and destination-specific regulatory documentation are arranged on request.
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