Sodium Bisulfite

About This Product

Sodium bisulfite, sodium hydrogen sulfite with formula NaHSO3 and CAS number 7631-90-5, is supplied as a clear to pale yellow solution, typically 38 to 40 percent, or as a white solid. In water it exists in equilibrium with metabisulfite and releases sulphur dioxide under acid conditions. It acts as a reducing agent, and that single property explains its uses. In reverse osmosis pretreatment it is dosed to remove residual chlorine from feedwater: thin-film composite membranes are oxidised and permanently destroyed by free chlorine within hours of exposure, yet chlorine is needed upstream to control biofouling, so it must be scrubbed out immediately before the membranes. Sodium bisulfite reduces free chlorine to chloride almost instantly and is the standard means of doing it. In boiler feedwater it scavenges dissolved oxygen, which would otherwise pit and corrode steel. In effluent treatment it reduces hexavalent chromium to the trivalent form for precipitation. It is corrosive and releases sulphur dioxide on contact with acid, so it must be stored away from acids and in ventilated areas. It is used in reverse osmosis dechlorination, boiler water oxygen scavenging, chromate and cyanide waste treatment, pulp bleaching and textile processing. Bio Green Chem supplies sodium bisulfite to specification on assay as SO2, iron, pH, density, colour and heavy metals.