K - salt production

Potassium heptafluorotantalate, K2TaF7, or as it is called by its commercial name K-salt, is a starting material for tantalum metal production. K-salt is produced by adding potassium fluoride, KF, or potassium chloride, KC1, to a tantalum strip solution that results from a liquid-liquid extraction process. In order to prevent hydrolysis and co-precipitation of potassium oxyfluoro-tantalate, a small excess of HF is added to the solution [24]. Another way to avoid the possible formation and co-precipitation of oxyfluoride phases is to use potassium hydrofluoride, KHF2, as a potassium-containing agent. The yield of the precipitation depends mostly on the concentration of the potassium-containing salt and is independent of the HF concentration [535]. 

The main properties of potassium heptafluorotantalate in solid, molten and dissolved states were discussed in previous chapters of the monograph and are also collected and discussed in review [536]. 

The particle size of precipitated potassium heptafluorotantalate is one of the more important parameters. In order to achieve a certain particle size, potassium salts are added to the hot tantalum strip solution as a hot solution. The mixture is cooled down at a specific rate in order to enable the precipitation and crystallization of K-salt in the form of small, individual crystals. 

Potassium heptafluorotantalate, K2TaF7, precipitates in the form of transparent needles. The precipitated particles must not be too fine, since fine powder usually promotes co-precipitation and adsorption of some impurities from the solution. Even niobium can be adsorbed by the surface of K2TaF7 developed during precipitation, as shown by Herak et al. [535]. On the other hand, the precipitation of large K-salt crystals should not be strived for either. Laboratory and industrial experience indicates that excessively large ciystals usually contain small drops of solution trapped within the ciystals. This occluded solution can remain inside of the ciystal until diying and will certainly lead the hydrolysis of the material. 

Precipitated K-salt crystals are carefully filtrated and washed so as to separate them from the mother solution. Diying of filtrated K-salt is also a very delicate and important process that must be performed under conditions that avoid hydrolysis of the material. Potassium heptafluorotantalate is sensitive to water, basic compounds and alcohols, especially at elevated temperatures. The main product of K-salt hydrolysis is Marignac s salt. For a long time it was believed that the composition of Marignac s salt is K Ta F However, X-ray ciystal structure analysis and precise chemical analysis of the 

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Only two processes of tantalum metal production are of worldwide commercial significance. These are the electrolysis of fluoride-chloride melts containing potassium heptafluorotantalate, K TaF , and tantalum oxide, Ta20s, and the reduction with sodium of K-salt or K—salt that is dissolved in potassium fluoride-chloride melts. 

Modem refining technology uses tantalum and niobium fluoride compounds, and includes fluorination of raw material, separation and purification of tantalum and niobium by liquid-liquid extraction from such fluoride solutions. Preparation of additional products and by-products is also related to the treatment of fluoride solutions oxide production is based on the hydrolysis of tantalum and niobium fluorides into hydroxides production of potassium fluorotantalate (K - salt) requires the precipitation of fine crystals and finishing avoiding hydrolysis. Tantalum metal production is related to the chemistry of fluoride melts and is performed by sodium reduction of fluoride melts. Thus, the refining technology of tantalum and niobium involves work with tantalum and niobium fluoride compounds in solid, dissolved and molten states. 

It is apparent from DTA studies [1021] of the decompositions of Group IA formates in inert or oxidizing atmospheres that reaction is either preceded by or accompanied by melting. Anion breakdown leading to carbonate production may involve formation of the oxalate, through dimerization [1022] of the postulated intermediate, C02, especially during reaction of the Na and K salts in an inert atmosphere and under isothermal conditions. Oxalate production is negligible in reactions of the Li and Cs formates. Reference to oxalate formation is included here since this possibility has seldom been considered [1014] in discussions of the mechanisms of decompositions of solid formates. 

The condensation of aromatic aldehydes with anhydrides is called the Perkin reaction When the anhydride has two a hydrogens (as shown), dehydration always occurs the P-hydroxy acid salt is never isolated. In some cases, anhydrides of the form (R2CHC0)20 have been used, and then the hydroxy compound is the product since dehydration cannot take place. The base in the Perkin reaction is nearly always the salt of the acid corresponding to the anhydride. Although the Na and K salts have been most frequently used, higher yields and shorter reaction times have been reported for the Cs salt. Besides aromatic aldehydes, their vinylogs ArCH=CHCHO also give the reaction. Otherwise, the reaction is not suitable for aliphatic aldehydes. ... 

Leeser, J.E., J.A.Tomenson, and D.D.Bryson. 1990. A cross-sectional study of the health of cyanide salt production workers. Report No. OHS/R/2, ICI Central Toxicology Laboratory, Alderley Park, Maccles field, Cheshire, U.K. 

K-SALT 1 (KspA) Solubility Product constant - KspA 12.81... 

K-SALT 2 (KspB) Solubility product constant - KspB -5296... 

The most important characteristic of cement is its pore structure and aqueous phase hence, the microstructure of the hardened cement paste via the pore system. It is highly alkaline (pH >13) due to rapid and almost quantitative dissolution of Na and K salts from the cement clinker. The porosity of the paste comprises interconnected and isolated pores, the pore sizes of which are important to the strength and dimensional stability of cement products. Different types of cement are used to meet different performance criteria. Properties can be estimated from compositions and fineness (i.e., particle size and size distribution). In the past, additives... 

Figure 7.18 gives the ratio (K /K)s4 s4 of the calculated equilibrium constants for solution-phase ammonium nitrate compared to the solid salt product at various temperatures and water activities. As the water activity, i.e., water vapor pressure above the solution, increases, the equilibrium constant falls. That is, at higher relative humidities, relatively less HNO, and NH, are found in the vapor phase at equilibrium. This may be why relatively more ammonium nitrate in particles collected on filters evaporates at lower RHs compared to higher ones. 

For prepn of 1,1-DNEt, ADL Rept (Ref 6, p 108) recommends acidifying the K salt by means of 85% phosphoric acid and purifying the resulting product by vacuum distillation behind a barricade. A small amt of boric acid was added before the distillation operation. The water-white distillate boiled at 73—74.5° at 13mm pressure... 

The K salt is rather sensitive to expln by shock, heat or friction. Crysts may expl violently when broken or rubbed in an agate mortar. When heated rapidly in air the subst detonates with a sharp expln, but less violently than the heavy metal azides. On expln in air, a spectacular flame is produced with the liberation of much heat and the formation of numerous products ... 

Homer-Wadsworth-Emmons reactions are C=C-forming condensation reactions between the Li, Na, or K salt of a /1-koto- or an a-(alkoxycarbonyl )phosphomc acid dialkyl ester and a carbonyl compound (see Figure 4.46). These reactions furnish a,/3-unsaturated ketones or 0 ,/3-unsaturated esters, respectively, as the desired products and a phosphoric acid diester anion as a water-soluble by-product. In general, starting from aldehydes, the desired compounds are produced /ra/ov-selectively or, in the case of alkenes with trisubstituted C=C double bonds, -selectively. 

As emulsifiers Na and K salts of glycine, lysine and taurine (total < 0.8 %) as well as N-(2-amino-ethyl)-3-amino propane sulfonate and/or N-(2-amino-ethyl)-2-amino ethane sulfonate (total < 5.0%) are recommended. These emulsifiers are incorporated into the macromolecules and therefore can be found only in very small amounts in the finished product. Esters of montanic acid with ethanediol and/or 1,3-butanediol and mixtures of these esters with unesterified montanic acid as well as Ca salts (total <1.5 %) can be used as lubricants and mold release agents. 

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