sodium hydrosulfite is used as an auxiliary dyeing agent for cotton fabrics and a bleaching agent for cotton and wool fabrics. It is also used in medicine, mineral processing, copperplate printing, the synthesis of thiourea and other sulfides. In the paper industry, it is also used as a bleaching agent. Food-grade products are used as bleaching agents, preservatives, and antioxidants.
In the cleaning industry, sodium dithionite is used in the home as a bleach for bleached laundry, as a dye remover when laundry has been inadvertently stained with a colored item, and in a high temperature wash cycle. Typical use is about 5 grams per wash. It is found as an ingredient in detergents or bleaching agents.
In water improvement,
sodium hydrosulfite is used as a de-oxygenating agent to purify the water supplied to steam boilers to prevent corrosion problems. It is also found in water treatment products for clarification and softening filters. As sodium dithionite is a strong reducing agent, it reduces oxidized iron (rust and brown scale) to an ionic state (making it soluble in water) during the washing cycle, thus removing both filter charges and the cationic and anionic resins present in the softening filters. Often found in "IRONOUT" type cleaners in both powder and liquid form.
In cosmetics, sodium hydrosulfite is used as an antioxidant and as a reducing agent to keep products stable, color and odorless. The reducing properties also allow the control of the thickness of products.
In the photographic industry, SDT is used to protect developer solutions from oxidation and to leach the fixative (sodium thiosulphate) from film and photopaper emulsions.
In textiles it is used as a bleaching, desulfurising and dechlorinating agent. In the leather trade it is used to sulphonate tanning extracts. In the leather industry, it is used as a highly effective bleaching agent and pigment disintegrator. In textile and fabric preparation, SDT is used as a solvent remover for the reduction of insoluble pigments to soluble ones, and for the bleaching and lightening of very strong pigments such as indigo.
In metalworking, SDT is used to remove silver, copper and iron oxides from antique and historical finds. Due to its reducing properties,
sodium dithionite converts insoluble metal oxides into soluble ones, and at the same time, due to the alkaline medium and the binding of oxygen, it acts as a corrosion inhibitor which prevents the metals from becoming oxides again.
In fisheries, sodium dithionite is used to regulate fish activity.
In the chemical industry, sodium hydrosulfite is also used to purify laboratory reagents. It is used in chemical production as a sulfonation and sulfomethylation agent.