Method of producing a fluorosilicate material from the hieratite group from fly ashes

The subject of the application is a method for producing a fluorosilicate material from the hieratite group from fly ash, consisting of preparing a mixture comprising: (i) fly ash in an amount of 15 to 25% by weight; (ii) potassium hydroxide in an amount of 75 to 85% by weight.

The components are then mixed until a uniform structure is obtained. The resulting mixture is subjected to pyrolysis in a high-temperature furnace at temperatures ranging from 680 to 1020°C, with a heating rate of 10°C/min and a pyrolysis time of two hours at the final temperature, under a simultaneous gas flow composed of 0–20% carbon dioxide and 80–100% nitrogen.

The resulting powder is agitated with 10–40% hydrofluoric acid for 4 to 6 hours, filtered, the residue is washed with distilled water until a neutral pH is reached, and then dried, yielding a fluoro-silicate material from the hieratite group free from fly ash impurities.