Blanqueador - Classes of Bleaches - Reducing Bleaches

Reducing Bleaches

Sodium dithionite (also known as sodium hydrosulfite) is one of the most important reductive bleaching agents. It is a white crystalline powder with a weak sulfurous odor. It can be obtained by reacting sodium bisulfite with zinc

2 NaHSO3 + Zn → Na2S2O4 + Zn(OH)2

It is used as such in some industrial dyeing processes to eliminate excess dye, residual oxide, and unintended pigments and for bleaching wood pulp.

Reaction of sodium dithionite with formaldehyde produces Rongalite,

Na2S2O4 + 2 CH2O + H2O → NaHOCH2SO3 + NaHOCH2SO2

which is used in bleaching wood pulp, cotton, wool, leather and clay.

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