Calcium reduction

Much of the vanadium metal being produced is now made by calcium reduction of V2O5 in a pressure vessel, an adaption of a process developed by McKechnie and Seybair. 

Several methods are available for producing thorium metal it can be obtained by reducing thorium oxide with calcium, by electrolysis of anhydrous thorium chloride in a fused mixture of sodium and potassium chlorides, by calcium reduction of thorium tetrachloride mixed with... 

Ion-exchange and solvent extraction techniques have led to much easier isolation of the rare earths and the cost has dropped greatly in the past few years. Praseodymium can be prepared by several methods, such as by calcium reduction of the anhydrous chloride of fluoride. 

The anode residues must be chemically processed to recover the plutonium remaining in the residues. This may amount to about 10% of the feed mass if delta alloy is the feed metal. Either aqueous or pyrochemical processes may be used for anode recovery. One pyrochemical process used for recovery utilizes oxidation of the plutonium with zinc chloride to form plutonium chloride salt, followed by calcium reduction of the PUCI3 contained in the salt phase to produce pure plutonium metal (the impurities follow the zinc metal obtained from the oxidation reaction and are discarded to waste). Impurities more stable than calcium chloride remain in the salt phase and are also... 

We have not demonstrated quantitative phase separation of salt from metal in the oxidation step. Approximately 5% of the gallium was carried over from the feed to the product after the calcium reduction. We are now scaling-up the 100-g experiments to plant-size equipment using magnesia crucibles in the equipment shown in Figure 3. 

The standard free energy changes for these reactions also are given in Figure 4.15. While the free energy for the second step (calcium reduction) is negative at all temperatures (as... 

Fluorides are nonhygroscopic, and their melting points are higher than those of the corresponding chlorides. Besides, the fluoride reduction reactions are considerably more exothermic. The prime examples of the use of fluorides as intermediates are the reduction of uranium tetrafluoride by calcium or magnesium the reduction of rare earth fluorides by calcium, reduction of beryllium fluoride by magnesium and the reduction of potassium tantalum double fluoride by sodium. 

Vanadium metal is prepared from pentoxide, V2O5, by reduction with calcium at elevated temperatures. Presence of iodine lowers calcium reduction temperature to 425°C because of heat of formation of calcium iodide. Pentoxide also may be converted to the trichloride, VCI3, and the trichloride reduced with magnesium metal or magnesium-sodium mixture at high temperatures to form high purity ductile metal. Alternatively, a fused mixture of vanadium chloride, sodium chloride, and hthium chloride may be electrolyzed to produce the metal in high purity. 

The production of vanadium metal essentially is the calcium reduction ot vanadium pcntcixide in Ihc presence of iodine and is known its the McKechiiie-Seyboll process. The reaction is earned out in a steel bomb at about 7(K) C. The end products are vanadium metal, lime, and calcium iodide. A similar iodide process also is used in the production of high-purily zirconium. 

Primary sources of the element are bastnasite and monazite, which contain from 4 to 8% praseodymium. Plant capacity involving liquid-liquid or solid-liquid organic ion-exchange processes for recovering the element is in excess of 100.000 pounds PreOn annually. Metallic praseodymium is obtained by electrolysis of Pr O] in a molten fluoride electrolyte, or by a calcium reduction of PrFj or PrCls in a sealed-bomb reaction. 

Terbium occurs in apatite and xenotime and is derived from these minerals as a minor coproduct in the processing of yttrium. Processing involves organic ion-exchange or solvent extraction operations. Elemental terbium is produced by calcium reduction of anhydrous TbH in a reactor under an inert atmosphere. Both the oxides and the metal aie available at 99.9% purity. 

Cardiovascular In rodents, lymphohistiocytic infiltrates have been observed in the heart and in the perivascular space in various organs. Tissue macrophages in the heart can contain basophilic granules. In monkeys, no changes in ECG, heart rate, or blood pressure have been observed with numerous oligonucleotides. Under conditions when complement is activated, changes in blood pressure and cardiovascular collapse due to hypotension have been observed [55], but we have shown this to be related to complement activation rather than a direct effect on the cardiovascular system. (Of course, other mechanisms for hypotension could occur with other chemistries. For example, if an oligonucleotide formulation or its metabolic products chelates calcium, reductions in ionizable calcium could also produce a hypotensive crisis.) For most PS ODNs the most likely cause of hypotension is complement activation as demonstrated with complement inhibitors. 

The three main processes by which rare earth metals are produced may be listed as (i) electrolysis, (ii) calcium reduction and (iii) lanthanum reduction. The three processes are summarized in Table 1.25. 

Derivation (1) Calcium reduction of vanadium pentoxide yields 99.8+% pure ductile vanadium (2) aluminum, cerium, etc. reduction produces a less pure product (3) solvent extraction of petroleum ash or ferrophosphorus slag from phosphorus production (4) electrolytic refining using a molten salt electrolyte containing vanadium chloride. 

Aromatic hydrocarbons can be reduced to cycloalkenes by calcium dissolved in a mixture of methylamine and ethylenediamine. For example, calcium reduction of p-xylene (57) and anthracene (59) gives 1,4-dimethyl-l-cyclohexene (58) or decahydroanthracene (60) in 84% and 85% yield, respectively (Scheme 4.16). Calcium-amine combinations are different from lithium-amine systems in that they have little or no propensity to reduce internal double bonds despite the large excess of calcium employed. A grayish white precipitate, seemingly calcium alkyl amide. 

Optically active l-halo-l-mefhyl-2,2-diphenylcyclopropanes 61 are used as probes to investigate the mechanisms of calcium reduction [39]. Treatment of 61 with calcium biphenyl (Ca(BPh)2) or calcium naphthalene (Ca(NPh)2) then addition of CO2 gives a mixture of cyclopropane derivative 62 and the corresponding carboxylic acid 63 (Scheme 4.17). Walborsky and Hamdouchi have provided evidence showing that these reactions occur by single electron transfer to yield free radicals... 

F2. Fuhrman, N., et al. The Production of Thorium Powder by Calcium Reduction of Thorium Oxide, Report SCNC-185, 1957. 

Plutonium metal is prepared by calcium reduction of plutonium fluorides or oxides in induction-heated MgO crucibles, under an inert atmosphere of helium or argon. The thermodynamics of plutonium reduction are discussed later in this chapter. 

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