Reduction With Sodium Metabisulfite or Sulfur Dioxide

Sodium metabisulfite or bisulfite is a commonly used chemical for chromium reduction. The metabisulfite hydrolyzes to sodium bisulfite, and the bisulfite in turn dissociates to sulfurous acid, which reduces the hexavalent chromium at a pH of 2-3. [Pg.194]

Sulfur dioxide is another commonly used chemical for chromium reduction. The reduction occurs when sulfurous acid, produced by the reaction of sulfur dioxide and water, reacts with chromic acid as follows [Pg.195]

Ferrous sulfate (FeS04) or ferrous sulfide (FeS) reduces and precipitates hexavalent chromium in one step. This eliminates the two-step reduction and precipitation required when sulfur dioxide or sodium bisulfite is used. [Pg.195]