Hydrofluoride decomposition of natural materials including zirconium-containing minerals

2nd International Symposium on Fundamental Aspects of Rare-earth Elements Mining and Separation and Modern Materials Engineering

材料科学;物理学

Laptash, N.^1 ; Maslennikova, I.^1,2

Institute of Chemistry, Far Eastern Branch of Russian Academy of Sciences, 159 Pr. 100-letiya Vladivostoka, Vladivostok

690022, Russia^1

Far-Eastern Federal University, Sukhanova Str. 8, Vladivostok

690950, Russia^2

关键词: Difluoride;    Double salts;    Fluoride ion;    Fluorinating agents;    Fluorination reactions;    High symmetry;    Natural materials;    Partial substitution;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/112/1/012024/pdf
DOI  :  10.1088/1757-899X/112/1/012024

学科分类：材料科学（综合）

来源: IOP

【 摘 要 】

Recently, interest in ammonium hydrogen difluoride (NH4HF2) as a versatile fluorinating agent for the decomposition of natural materials resumed. It is considered to be a new and more efficient than hydrofluoric acid (HF) reagent in analytical chemistry. Thermodynamically possible fluorination reactions with NH4HF2are exothermic and proceed even at room temperature with the entropy reserve. The fluorination products are of high symmetry phases (tetragonal or cubic) with partial substitution of fluoride ion for oxide (or hydroxide). The fluorination of refractory silicate zircon (ZrSiO4) is kinetically hindered, and its complete decomposition requires the use of a Teflon autoclave at 200oC. The fluorination products are cubic (NH4)3Zr(OH)xF7-x(x ≤ 0.3) and tetragonal double salt (NH4)3SiF7, which can be separated due to incongruent sublimation of (NH4)2SiF6. The mechanism of the latter process is proposed.