Hydrofluoride decomposition

Another method of raw material decomposition is based on the fluorination of the raw material by the hydrofluoride method. No published data exists on hydrofluoride decomposition of columbite or tantalite concentrates. The interaction can, nevertheless, be discussed based on available information on the decomposition of lithium tantalate, LiTaC>3, and lithium niobate, LiNb03, using the hydrofluoride method [113,118,122]. 

Hydrofluoride decomposition, 263-266 Hydrofluoride synthesis fluorotantalates, 41-47 general information, 38-41 oxyfluoroniobates, 49-54 performance, 46-47, 57 Hydrolysis, 7, 16,317-318 Hydrolysis of... 

The formation of (NH4)3NbOF6 and its decomposition products define the composition of the niobium fluoride compounds that can be prepared by the hydrofluoride method [123-125]. 

Interaction between niobium oxide and fluorides, chlorides or carbonates of alkali metals in an ammonium hydrofluoride melt, yielded monooxyfluoroniobates with different compositions, MxNbOF3+x, where they were subsequently investigated [123-127]. According to DTA patterns of the Nb205 - 6NFL HF2 - 2MF system, (Fig. 18) a rich variety of endothermic effects result from the formation of ammonium monooxyfluoroniobate, its thermal decomposition and its interaction with alkali metal fluorides. The number of effects decreases and separation of ammonium ceases at lower temperatures and when going from lithium to cesium in the sequence of alkali metal fluorides. 

Decomposition of lithium niobate, LiNb03, by molten ammonium hydrofluoride can be performed even at temperatures as low as 130-260°C [122]. The process also enables the separation of niobium and lithium, yielding ammonium oxyfluoroniobate and lithium fluoride. The interaction can be represented by Equation (132) ... 

In general, the process flow chart of raw material decomposition by the hydrofluoride method can be represented as shown in Fig. 117. 

Fig. 117. Possible flow chart of decomposition of tantalum- or niobium-containing raw material by the hydrofluoride method.

Another way of applying the selective extraction method directly on the initial solution is to produce a solution of low acidity. This can be achieved by using the hydrofluoride method for fluorination and decomposition of raw material. As was discussed in Paragraph 8.2.2, the raw material is fluorinated by molten ammonium hydrofluoride yielding soluble complex fluorides of ammonium and tantalum or niobium. The cake obtained following fluorination is dissolved in water, leading to a solution of low initial acidity that is related for the most part to the partial hydrolysis of complex fluoride compounds. The acidity of the solution is first adjusted to ensure selective tantalum extraction. In the second step, the acidity of the raffinate is increased to provide the necessary conditions for niobium extraction. 

The decomposition described in Equation (146) takes place at relatively low temperatures hence, thermal treatment at a relatively slow temperature rate can be sufficient in order to significantly reduce fluorine levels in the final oxides. Nevertheless, treatment at a high temperature rate can lead to another mechanism of ammonium fluoride decomposition yielding gaseous ammonia and molten ammonium hydrofluoride according to the following scheme ... 

Phase transition irreversible, 225 order - disorder, 224-228 reversible, 225, 229, Physicochemical properties of ammonium hydrofluoride, 39 deviations from ideal, 149 ideal system, 148 NbF5 and TaFs, 25 niobium containing melts, 150 tantalum containing melts, 151 M5Nb3OFlg, 234-235 Piezoelectric properties, 245-247 Plasma chemical decomposition equipment, 311... 

The first direct synthesis of 5-fluorocytosine (15) was reported by Robins and Naik,21 in which cytosine (20) was reacted with trifluoromethyl hypofluorite followed by decomposition of the resulting adduct to provide 5-fluorocytosine in 85% yield. Some years later, Takahara disclosed that 15 could be prepared as its hydrofluoride salt in high purity when cytosine was reacted with fluorine gas in the presence of hydrogen fluoride, followed by treatment with methanol.22... 

Electron capture by 02, and approximately simultaneous loss of F from the PdFs" generated by that process, could account for this difference, since the electron affinity of 02 much exceeds that of NO" (280 versus 214 kcal mol" ). But the decomposition could also occur by F capture from the Pdp6 by the 02, since O2F is a weak base, whereas ONF is a strong one. The inability of 02F(,oiv) to dissolve any Pdp4 contrasts with the dissolution of the latter in alkali hydrofluoride solutions or its ready interaction with ONF to make (NO)2PdF6. The enthalpy of ionization of ONF is ... 

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