METHOD FOR PRODUCING AMMONIUM HEXAFLUOROSILICATE Russian patent published in 1997 - IPC

FIELD: production of ammonium hexafluorosilicate used as starting material for production of highly dispersed silicon dioxide. SUBSTANCE: silicon-containing starting material is subjected to fluorination with ammonium hydrodifluoride in solid phase, at starting mineral material-to-ammonium hydrodifluoride molar ratio equal to 1:(2.5-3.5), at temperatures ranging from room temperature up to 200 C, for period from 4 h to 25 days. Next fluorinated reaction mass is subjected to heating at 450-650 C, followed by condensation of final product. Ammonia liberated in fluorination process step is collected by causing it to pass through water. NH₄HF₂ formed by heating fluorinated mineral material is collected and recycled back to fluorination step. EFFECT: method offers multiple advantages: 1) product purity and yield are improved; 2) economic aspect is better; 3) range of suitable starting materials is broader; 4) method is simple to practise. 3 cl, 1 dwg