Sodium Metabisulfite

About This Product

Sodium metabisulfite has the formula Na2S2O5 and CAS number 7681-57-4, supplied as white crystals or powder with a pungent sulphurous odour. Dissolved in water it hydrolyses to bisulfite, so it is chemically equivalent in use to a bisulfite solution while being far more convenient to handle. That equivalence with a physical advantage is the reason it exists as a separate product. A bisulfite solution is roughly 60 percent water by weight, so shipping it means shipping water, and it has a limited shelf life because the sulfite slowly oxidises to sulfate in the drum. The solid metabisulfite carries much more available sulphur dioxide per tonne, is stable in sealed packaging for far longer, and can be made up to whatever strength the application needs at the point of use. Against that, it must be dissolved before dosing, which needs mixing equipment, and the powder releases irritant sulphur dioxide when handled. It performs the same functions: dechlorination ahead of membranes, oxygen scavenging, reduction of hexavalent chromium, and bleaching and antimicrobial control in industrial processes. It is used in water treatment and dechlorination, mining and gold processing, pulp and paper, leather tanning, textile bleaching and photographic processing. Bio Green Chem supplies sodium metabisulfite to specification on SO2 content, assay, iron, selenium, insolubles and heavy metals.