Caustic Soda Flakes — Frequently Asked Questions

No. Both are anhydrous sodium hydroxide made from the same melt, and a producer's flakes and pearls usually share one specification for NaOH, carbonate, chloride and iron. Flakes are cooled on a drum and scraped off; pearls are sprayed through a prilling tower. The difference shows up in handling: flakes produce more dust and can bridge in hoppers, while pearls flow and dose more evenly. Choose flakes where whole bags are tipped into a stirred tank.

Technical-grade flakes are typically specified at 98–99% NaOH minimum, and the listed grade here is 99.0% minimum. Specify the assay together with maximum sodium carbonate, sodium chloride and iron, because a high assay alone does not guarantee low impurities. If you calculate additions on an NaOH basis, as soap makers and effluent plants do, use the assay on the batch certificate of analysis rather than assuming 100%.

Sodium hydroxide absorbs water vapour from the air, and the damp surfaces of neighbouring flakes fuse together as they re-dry. It also absorbs carbon dioxide, which slowly converts part of the product to sodium carbonate and lowers the effective NaOH content. Caking usually traces back to a torn bag, a part-used bag left open or a humid store. Keep bags sealed and off the floor, and use stock in rotation.

Add the flakes slowly to cold water while stirring, never water onto the flakes. Dissolving releases about 1.1 MJ of heat per kilogram, enough to bring a small batch close to boiling and cause spattering. Use a stainless steel or polypropylene vessel rated for the temperature, never aluminium or galvanised steel. Wear chemical goggles with a face shield, alkali-resistant gloves and protective clothing, and keep an eye-wash station within reach.

Solid sodium hydroxide classifies under HS subheading 2815.11, whether it is supplied as flakes, pearls or granules; only aqueous solutions move to 2815.12. For transport, flakes are UN1823, SODIUM HYDROXIDE, SOLID, Class 8 corrosive, packing group II. National tariffs add further digits and set duty rates, so check the destination tariff, and confirm the classification against section 14 of the safety data sheet supplied with the product.

Yes, on an NaOH basis: 1 kg of 99% flakes supplies about the same alkali as 2 kg of 50% solution. Flakes avoid paying to transport water and suit smaller or irregular consumption, but they add a dissolving step, heat release and dust to manage. Liquid suits high, continuous use with bulk storage and metering pumps. Many sites switch to flakes when usage is too low to justify tank storage.