1. Principle of sodium ferric chloride method
Sodium fluoride is a colorless and shiny crystalline substance, belongs to the tetragonal crystal system, with a specific gravity of 2.798g/cm³, a melting point of 995ºc, a boiling point of 1704ºc, a specific heat of 1.0205t/8ºc, a solubility of 32.65kg/mol, soluble in water, slightly soluble in alcohol, The aqueous solution is alkaline. It is a fluoride salt with a wide range of uses. It is used as a pesticide, a fungicide, a water treatment agent, a co-solvent for the electrolysis of light metal molten salt, an adsorbent for uf in the nuclear fuel industry, and other manufacturing. Raw materials for fluoride, etc.
The solubility of sodium fluoride given here is 32.65kg/mol. If you need data in other units, you can convert the units yourself. The molecular weight of sodium fluoride is 42.
(1) Concentrate the sodium fluoride aqueous solution and reuse it to remove iron from the pickling waste liquid. The concentration of chromium and nickel ions in the regenerated acid continues to increase,
Decrease the pickling capacity and lead to failure. The spent pickling waste liquid is neutralized, and the roasting precipitate is recovered in the form of oxide.
(2) Approximately allowable composition range in spring steel pickling solution: HF mass fraction is 30-/0-5%, HN03 mass fraction
The number is 3%-100-/0, and the mass concentration of Fe is 20-50g/L.
In the acid solution, ferric nitrate and sodium fluoride react to form a white precipitate, which is filtered to remove the sodium ferric fluoride to make the acid solution
Raw. The reaction formula is as follows:
(3) The acid washing waste liquid reacts with fluoride with equivalent iron content, and the iron in the waste liquid is removed as a solid product.
The pickling solution is regenerated and reused for pickling.
(4) The iron precipitate reacts with sodium hydroxide to produce iron hydroxide and sodium fluoride, and iron oxide is recovered by roasting the iron hydroxide.
2. Reaction mechanism
Sodium iron fluoride reacts with sodium hydroxide to produce iron hydroxide and sodium fluoride, which are dried and roasted to recover oxidation
Iron, the filtrate is an aqueous solution of sodium fluoride, which is reused to remove iron from the waste liquid after concentration. The reaction formula is as follows:
Na2FeF5.H20+3NaOH——Bucket Fe( OH)3 i+SNaF+HiO
2Fe( OH)3+02 -+Fe203+3H20
The chromium and nickel ions in the pickling waste liquid react with sodium fluoride to produce chromium fluoride and nickel fluoride. However, because they are in
It has high solubility in water or acid. It reacts with sodium fluoride with equivalent iron content in waste acid only, and chromium and nickel ions cannot form fluorine.
Compounds, or even if formed, cannot be removed in the solution because of their very high solubility. Thus, the sodium iron fluoride method
Iron can only be selectively removed, and due to the recycling of the pickling solution, the dissolved chromium and nickel ions gradually increase.
Later, when the specified concentration is reached, the pickling bear force disappears. If this pickling waste liquid is neutralized with sodium hydroxide, the resulting
The hydroxide is roasted and the recovered oxide can be reused as nickel and chromium raw materials.