Sodium Dithionite Storage & Tank Compatibility

Storing Sodium Dithionite? Start Here

Sodium dithionite (Na₂S₂O₄), widely sold as sodium hydrosulfite, is a powerful water-soluble reducing agent used in textile and vat dyeing, pulp and paper brightening, kaolin clay bleaching, and water-treatment reduction chemistry. The dry powder is a self-heating, spontaneously combustible solid that reacts with moisture and air, so it is normally dissolved and handled as an aqueous solution. In solution it behaves as a sodium oxysulfur salt and is comfortably stored in polyethylene. Because the chemistry liberates heat and can evolve sulfur dioxide as it decomposes, storage demands proper ventilation, cool dry make-up areas, and equipment that resists both the salt and its sulfur-bearing breakdown products. The data below copies the verified chemical identity and pairs it with an honest polyethylene compatibility read.

Is Sodium Dithionite Safe in Polyethylene (HDPE / XLPE) Tanks?

Yes, for the aqueous solution. Dissolved sodium dithionite is a sodium salt of a sulfur oxyacid, and aqueous salt and sulfite-type solutions sit firmly in the compatible column for high-density and crosslinked polyethylene per standard chemical-resistance charts. Polyethylene is not oxidized or swelled by this mild reducing chemistry, which is why PE tanks are a common home for hydrosulfite make-down and day tanks. The cautions are about the chemical's own instability rather than the plastic: the solution slowly decomposes, releasing heat and forming thiosulfates and bisulfites, and on contact with air it can generate sulfur dioxide. Keep tanks vented, avoid heat and contamination, store the dry solid separately in sealed containers away from moisture, and choose EPDM over questionable elastomers for seals. Do not store the dry powder loose in or near a tank, since it is self-heating and water-reactive.

Material compatibility at a glance

For aqueous sodium dithionite (sodium hydrosulfite) solutions, HDPE and XLPE polyethylene are the preferred tank materials, with polypropylene, PVC, and CPVC suitable for fittings and lines. EPDM is a sound seal elastomer. Avoid carbon steel and treat the dry solid with caution because it is self-heating and reacts with water and air.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Treat the dry solid as a self-heating, spontaneously combustible material (GHS H251); store in tightly sealed containers, cool and dry, away from moisture, air, heat, and oxidizers.
• On contact with water or damp air it slowly decomposes, evolving heat and sulfur dioxide gas; provide ventilation and never confine wetted material.
• For fires use flooding amounts of water to cool and stop the reaction; smothering does not work because the material does not need air to burn.
• Wear chemical goggles and gloves; the material causes skin and serious eye irritation (H315, H319) and is harmful if swallowed (H302).
• Avoid mixing with acids or oxidizers, which accelerate decomposition and sulfur dioxide release.
• Contain spills, dissolve dry material in about five parts water, and collect for proper disposal; keep out of drains and surface water (H402, H412).

Common questions

Can I store sodium dithionite solution in an HDPE or XLPE tank?

Yes. Aqueous sodium dithionite (sodium hydrosulfite) is a sodium salt solution and is compatible with HDPE and crosslinked polyethylene per standard resistance charts. Keep the tank vented, because the chemistry can slowly release heat and sulfur dioxide.

Why is the dry powder considered dangerous if the solution stores fine?

The dry solid is self-heating and spontaneously combustible (GHS H251) and reacts with moisture and air, generating heat and sulfur dioxide. Once safely dissolved in water, it behaves as a manageable reducing-salt solution suited to polyethylene.

What does the W on the NFPA diamond mean for this chemical?

The Special W indicates the material reacts with water. Sodium dithionite slowly decomposes on contact with water or water vapor, evolving heat, so the dry solid must be kept dry and the make-up step controlled.

Which materials should I avoid with sodium dithionite?

Avoid carbon steel and uncertain elastomers. The sulfur-bearing decomposition products (bisulfite, thiosulfate, sulfur dioxide) can corrode metals, so polyethylene tanks with EPDM seals and PP, PVC, or CPVC fittings are the safer choice.