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Caustic soda flakes (sodium hydroxide), is a substance with high alkalinity, which is produced in both liquid and solid forms, and manufacturers of Caustic soda flakes (sodium hydroxide flakes) market its solid form.
 The purity of flake burner determines its quality, and sodium hydroxide flakes with a purity of more than 98% can be considered the best type of this product, which is produced by some manufacturers of caustic soda flake.

for more information see this link:
https://avidanexport.com/introduction-of-manufacturers-of-caustic-soda-flake-98-purity/
 The top producer of sodium hydroxide in Iran