Fluoride absorption

G. M. Whitford, D.H. Pashley, Fluoride absorption The influence of gastric acidity, Calcif. Tissue Int. 36 (1984) 302-307. 

FIGURE 12.5 Hydrogen fluoride removal from smelter primary gas collection system via a sieve tray gas scrubber (only a section shown). Note the recycle of acid product for initial hydrogen fluoride absorption from the exhaust gases to maximize the concentration of recovered acid. (Adapted from Ball and Dawson [33].)... 

Cement - ordinary Portland Hydrogen fluoride absorption... 

New bands appear at 1815, 1848 (acid fluoride absorption) and at 1080cm (alkyl fluoride absorption) (Table 10.14). 

Wet cells composed of beds of wetted saran fibers have been proposed for fluoride absorption and tested on a pilot scale (Berly et al., 1954). However, no commercial installations are known. 

L. Holmia, for Stockholm). The special absorption bands of holmium were noticed in 1878 by the Swiss chemists Delafontaine and Soret, who announced the existence of an "Element X." Cleve, of Sweden, later independently discovered the element while working on erbia earth. The element is named after cleve s native city. Holmia, the yellow oxide, was prepared by Homberg in 1911. Holmium occurs in gadolinite, monazite, and in other rare-earth minerals. It is commercially obtained from monazite, occurring in that mineral to the extent of about 0.05%. It has been isolated by the reduction of its anhydrous chloride or fluoride with calcium metal. 

Toxicity. Fluoroborates are excreted mostly in the urine (22). Sodium fluoroborate is absorbed almost completely into the human bloodstream and over a 14-d experiment all of the NaBF ingested was found in the urine. Although the fluoride ion is covalently bound to boron, the rate of absorption of the physiologically inert BF from the gastrointestinal tract of rats exceeds that of the physiologically active simple fluorides (23). 

Bromine Monofluoride. Bromine monofluoride is red to red-brown (4) and is unstable, disproportionating rapidly into bromine and higher fluorides. Therefore, the measurement of its physical properties is difficult and the values reported in Table 1 are only approximate. The uv-absorption spectmm is available (25). 

Nitric oxide and OF2 inflame on contact emission and absorption spectra of the flame have been studied (24). Oxygen difluoride oxidizes SO2 to SO, but under the influence of uv kradiation it forms sulfuryl fluoride [2699-79-8] SO2F2, and pyrosulfuryl fluoride [37240-33-8] S20 F2 (25). Photolysis of SO —OF2 mixtures yields the peroxy compound FSO2OOF [13997-94-9] (25,26). 

Oxygen and nitrogen also are deterrnined by conductivity or chromatographic techniques following a hot vacuum extraction or inert-gas fusion of hafnium with a noble metal (25,26). Nitrogen also may be deterrnined by the Kjeldahl technique (19). Phosphoms is determined by phosphine evolution and flame-emission detection. Chloride is determined indirecdy by atomic absorption or x-ray spectroscopy, or at higher levels by a selective-ion electrode. Fluoride can be determined similarly (27,28). Uranium and U-235 have been determined by inductively coupled plasma mass spectroscopy (29). 

Hafnium tetrafluoride [13709-52-9] is one component in the cladding layer of a proposed zirconium fluoride glass optical waveguide fiber composition which is expected to have a lower intrinsic light absorption than fused quart2 optical fiber (see Glass Fiber optics Fluorine compounds, inorganic-zirconium). 

Pretreatment of the collected particulate matter may be required for chemical analysis. Pretreatment generally involves extraction of the particulate matter into a liquid. The solution may be further treated to transform the material into a form suitable for analysis. Trace metals may be determined by atomic absorption spectroscopy (AA), emission spectroscopy, polarogra-phy, and anodic stripping voltammetry. Analysis of anions is possible by colorimetric techniques and ion chromatography. Sulfate (S04 ), sulfite (SO-, ), nitrate (NO3 ), chloride Cl ), and fluoride (F ) may be determined by ion chromatography (15). 

Although poly(vinyl fluoride) resembles PVC in its low water absorption, resistance to hydrolysis, insolubility in common solvents at room temperature and a tendency to split off hydrogen halides at elevated temperatures, it has a much greater tendency to crystallise. This is because the fluorine atom (c.f. the chlorine atom) is sufficiently small to allow molecules to pack in the same way as polythene. 

All gas absorption proeesses are surfaee area dependent. Henee water fog may be an effeetive means of dealing with emissions of soluble gases, e.g. ammonia or hydrogen fluoride. 

White phosphorus. This element burns in air and can produce severe thermal and chemical burns. It may reignite on drying. After washing, rapid but brief treatment with copper sulphate (to avoid systemic absorption and copper poisoning) is used to convert the phosphorus to copper phosphide which is then removed Hydrogen fluoride. This can form painful but delayed necrosis. Treat with calcium gluconate locally and monitoring of serum calcium levels, with administration of calcium where necessary... 

The proposed mechanism includes the production of HCl from the pyro-hydrolysis of the metal chlorides. Similar reactions are likely for bromides and iodides. Fluorides however are relatively stable and would not be expected to hydrolyse. It was considered that this might account for the inability of fluorides to cause cracking. Hydrogen absorption by titanium alloys exposed to chloride salts at elevated temperatures has been detected and found to be proportional to the amount of moisture participating in the reaction. 

Vibration spectra of fluoride and oxyfuoride compounds correspond to X Me ratios, especially in the case of island-type structure compounds. Analysis of IR absorption spectra provides additional indication of the coordination number of the central atom. Fig. 45 shows the dependence on the X Me ratio of the most intensive IR bands, which correspond to asymmetric Me-F modes in fluoride complexes, as well as v(Me=0) and v(Me-F) in oxyfluoride complexes. Wave numbers of TaF5, NbF5 and NbOF3 IR spectra were taken from [283-286]. 

Opposite behavior was displayed by molten fluoride systems. For instance, no bands were observed in the thin layer emission spectrum of a KF - K2SiF6 melt, whereas increasing the melt layer to 10-20 mm led to the appearance of two intensive bands at 730 and 476 cm 1. These bands correspond to v3 and v4 vibrations of the complex ion SiF62 Solid K2SiF6 is characterized by IR absorption bands at 741 and 483 cm 1 [343]. 

R.L. Davidovich, T.A. Kaidalova, T.F. Levchishina, Atlas of infra-red absorption spectra and X-ray data of complex fluorides of IV and V groups, Nauka, Moscow, 1972 (in Russian). 

---