Aluminum with fluoride, complexes

The rate (kinetics) and the completeness (fraction dissolved) of oxide fuel dissolution is an inverse function of fuel bum-up (16—18). This phenomenon becomes a significant concern in the dissolution of high bum-up MO fuels (19). The insoluble soHds are removed from the dissolver solution by either filtration or centrifugation prior to solvent extraction. Both financial considerations and the need for safeguards make accounting for the fissile content of the insoluble soHds an important challenge for the commercial reprocessor. If hydrofluoric acid is required to assist in the dissolution, the excess fluoride ion must be complexed with aluminum nitrate to minimize corrosion to the stainless steel used throughout the facility. Also, uranium fluoride complexes are inextractable and formation of them needs to be prevented. 

Direct analysis with the fluoride lon-selective electrode requires addition of total ionic strength adjustor buffer solution (TISAB) to the standard and to unknown samples Some advantages of this addition are that it provides a constant background ion strength, ties up interfenng cations such as aluminum or iron, which form a complex with fluoride ions, and maintains the pH between 5 0 and 5 5 According to the manufacturer s claim, reproducibility of direct electrode measurement IS 2 0%, and the accuracy for fluonde ion measurement is 0 2% [27]... 

Aluminum metal is produced from aluminum oxide by electrolysis using the Hall-Heroult process, whose story is detailed in our Chemical Milestones Box. The melting point of AI2 O3 is too high (2015 °C) and its electrical conductivity too low to make direct electrolysis commercially viable. Instead, AI2 O3 is mixed with cryolite (Na3 AlFfi) containing about 10% CaF2. This mixture has a melting point of 1000 °C, still a high temperature but not prohibitively so. Aluminum forms several complex ions with fluoride and oxide, so the molten mixture... 

Assay of beryllium metal and beryllium compounds is usually accomplished by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryllium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryllium content of the sample is calculated from the titration volume. Standards containing known beryllium concentrations must be analyzed along with the samples, as complexation of beryllium by fluoride is not quantitative. Titration rate and hold times are critical therefore use of an automatic titrator is recommended. Other fluoride-complexing elements such as aluminum, silicon, zirconium, hafnium, uranium, thorium, and rare earth elements must be absent, or must be corrected for if present in small amounts. Copper—beryllium and nickel—beryllium alloys can be analyzed by titration if the beryllium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

Loweth et al. [120] showed that fluoride induces apoptosis in clonal pancreatic fi cells and in the cells of normal rat islets of Langerhans. The process may reflect the formation of AlF41 since it was inhibited by the aluminum chelator desferrioxamine. Recent studies provide evidence that apoptosis of pancreatic fi cells is important in the early etiology of diabetes mellitus. Treating thymus lobe cells with aluminofluoride complexes also provoked apoptosis of a wider range of thymocyte subtypes [121] with an accumulation of inositol phosphates. The responses to aluminofluoride complexes were not prevented by inhibitors of tyrosine kinases, suggesting that unidentified G-proteins which couple to phospholipase C activation may also be capable of initiating apoptosis by a route independent of the T cell receptor. 

Fluoride binds Al + strongly, and at the 1 ppm level where it is added to acidic drinking water, most aluminum appears as AIF2+ and as neutral AIF3. " In mixed complexes of Al +, ADP, and F , the ternary complex appears with the frequency expected statistically on the basis of binary complex stabilities." Contrary to a common misconception, when bound to proteins (such as G-proteins), fluoride complexes of Al + do not contain a tetrahedral, four-coordinate metal ion but hexacoordinate Al + with six donor atoms. " ... 

Simons (143) in a recent review of catalysis concludes that the catalytic activity of hydrogen fluoride must be related to its high acidity. For reactions in the hydrocarbon phase where the dielectric constant of the medium is too low for free ions, we would have to consider complexes of the type Ar HF and Ar HF BF3 which do not exclude ionic mechanisms. For reactions of methylbenzenes with liquid hydrochloric acid or hydrochloric acid and aluminum chloride, similar complexes might be found, and the existence of HAICI4 or HBF4 as such in the medium is unnecessary for an explanation of catalytic action. 

The fluoride complex is sufficiently stable to permit fluoride ions to compete successfully with hydroxide ions for aluminum ions. 

In a follow-up article appearing in the April 2005 issue. Null and Feldman describe the neurotoxic and toxic effects of fluoride on the brain and thyroid gland. For instance, increased brain concentrations of aluminum compounds or complexes were observed in animal studies where aluminum or sodium fluoride was administered, the connection being that presence of aluminum is sometimes associated with Alzheimer s disease. The call is to Stop Huoridation Now. ... 

By catalytic alkylation with hydrogen fluoride, sulfuric acid, or aluminum chloride-hydrocarbon complexes, all in the liquid phase. 

The thermodynamic data for fluoride complexes of aluminum, from published literature (12), were recalculated to zero ionic strength by means of the Debye-Hiickel equation. These, with stability data from our experiments with aluminum hydroxide species, provide a basis for deciding which complexes will be predominant when pH and dissolved fluoride concentrations are known. Conclusions drawn concerning the hydroxide species show that the polymeric aggregates of Al(OH)3 should be considered colloidal and they are not included in this calculation as equilibrium solute species. Hydroxide complexes of significance are the monomer A10H- and the anion Al(OH)4". Fluoride complex species constitute the series AlFn " where n ranges from one to six. 

Defluorination efficiency decreases with increasing AI " " content (see experiments 1—7 in Table 11), probably due to the formation of positively charged aluminum fluoride complexes. 

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