Aluminosilicate ores processed by a fluoride method

Abstract

An innovative method for preparation of mullite-based refractories from aluminosilicate topaz ores is proposed in which the mineral ore is treated with ammonium fluoride; the excess silicon dioxide is removed in the form of gaseous ammonium hexafluorosilicate. The desiliconized mixture is sintered to obtain a lightweight mullite refractory with a fibrous structure.Mullite composed of 72% Al 2 O 3 and 28% SiO 2 finds ever-increasing application in high-temperature technologies; mullite-based ceramics display low heat conductivity and high strength and are in widespread use as heat-insulating and refractory materials. For all its superior thermophysical properties and large natural mineral reserves, mullite production in Russia is still in the early stage of development. The demands of the domestic mullite market are at present mainly satisfied by the supply of ready-made mullite refractories purchased from foreign manufacturers [1,2].In Russia, a few manufacturers are concerned with the production of mullite-based refractory materials. Mullite materials are available from Ogneupory Joint-Stock Co. (Tula Region) and Semiluki Refractory Plant Joint-Stock Co. (Semiluki, Voronezh Region); however, they contain less than 62% Al 2 O 3 and their refractoriness is much inferior to that of pure mullite materials. The best raw materials for production of mullite are quartz-topaz ores. In Siberia, the world's largest deposits of quartz-topaz ores have been discovered with an overall topaz content of 200 million tons. The domestic market demand for topaz is about 300 thousand tons. The precursor concentrate obtained by ore flotation contains some 40% aluminum oxide, 45% silicon dioxide, and 10% hydroxyl fluoride compounds. To extract mullite, part of the silicon dioxide and fluorine should be removed.The processing of quartz-topaz ore includes two major stages: (i) flotation beneficiation in the topaz component and (ii) desiliconization and sintering of the desiliconized concentrate to a mullite condition. A schematic of the process and the averaged composition of initial, intermediate, and final products are shown in Fig. 1.Desiliconization and sintering (mullitization) of the desiliconized semi-finished product are critical and powerconsuming stages of the quartz-topaz-to-mullite conversion. For removing the excess SiO 2 , aluminum fluoride was used; this interacts with SiO 2 and converts it to ammonium hexafluorosilicate [3]. An advantage of ammonium fluoride as a desiliconizing agent is that it can be completely recovered [4]. The cycle of fluoroammonium desiliconization is shown below:

Hydrofluoride Processing of Tailings From Wet Magnetic Separation of Titanomagnetite to Obtain Amorphous Silicon Dioxide

“…(3) (NH4)3SiF7 → (NH4)2SiF6 + HF↑ + NH3↑ (4) Solid-phase sintering of ilmenites, scheelite, wolframite, non-bauxite ores (kaolins, high-alumina shales, anorthosites, alkaline aluminosilicates etc.) with NH4HF2 or NH4F revealed that the fluorating agent is in molten state [12][13][14][15][16]. We also found that mixing and grinding at room temperature lead to intensive wetting of the reaction mixture due to the formation of ammonia and water.…”

“…The separation of tailing components during hydrochemical interaction with ammonium bifluoride in solution is based on the formation of fluorine-containing compounds having various physicochemical properties. The thermodynamic simulation showed that fluorination reactions of silicon-containing oxide phases and most of minerals begin at temperatures below 200 °С and are accompanied by heat release [12][13][14]. The interaction of NH4HF2 with the basic mineral pyroxene CaMgSi2O6 to form poorly soluble and highly soluble simple and complex fluorides is possible under standard conditions according to eq.…”

Hydrofluoride decomposition of natural materials including zirconium-containing minerals

“…In recent years, a simple, effective, and comparatively safe dissolution method with the use of ammonium fluorides (NH 4 HF 2 or NH 4 F) shows great potential for the digestion of geological samples. NH 4 HF 2 was used in innovative method for preparation of mullitebased refractories from aluminosilicate quartz-topaz ores [2] or for the synthesis of mullite from kaolin [3]. A new technique of decomposing beryl ore [4] or a treatment of gold-containing graphite-bearing ores with NH 4 HF 2 to concentrate gold [5] was recently suggested.…”