Molybdenum stripping

Figure 1.31. Tin drop on a striped surface consisted of non-wetted (oxide glass) and wetted (molybdenum) strips. Reprinted from (Voitovich 1992) with kind permission of the author.

Technetium is an artificial element obtained by the radioactive decay of molybdenum. Element 43, named technetium in 1947, had been discovered in 1937 by Carlo Perrier and Emilio Segre in a sample obtained from the Berkely Radiation Laboratory (now Lawrence Berkeley National Laboratory) in California (Perrier and Segre 1937, 1947). By bombarding a molybdenum strip with 8-MeV deuterons in a 37-in. cyclotron, a radioactive molybdenum species (half-life, 65 h) had been obtained which decayed by yff-emission to a short-lived isotope (half-life, 6 h) with novel properties, identified as technetium-99m (Segre and Seaborg 1938). 

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

Sastre, A. M. Alguacil, F. J. Co-extraction and selective stripping of copper(II) and molybdenum(VI) using LIX622. 

Zhang, P. W. Inoue, K. Yoshizuka, K. Tsuyama, H. Extraction and selective stripping of molybdenum(VI) and vanadium(IV) from sulfuric acid solution containing aluminum(III), cobalt(II), nickel(II) and iron(III) by LIX 63 in Exxsol D80. Hydrometallurgy 1996, 41, 45-53. 

Molybdenum(III) Bromide. This compound is conveniently prepared from the elements in an apparatus such as that illustrated in Fig. 6. Bulbs A, B, E, and F are sections of 25-mm.-o.d. Vycor tubing joined together by sections of 15-mm.-o.d. tubing. Bulb B should be 2 to 3 in. long, and bulbs E each about 6 in. long. In a typical preparation, 3 g. of molybdenum foil (cut into small strips) is placed in B, and the apparatus... 

Trace amounts of molybdenum were concentrated from acidified seawater on a strongly basic anion exchange resin (Bio-Rad AG1 X-8 in the chloride form) by treating the water with sodium azide. Molybdenum (VI) complexes with azide were stripped from the resin by elution with ammonium chlo-ride/ammonium hydroxide solution (2 M/2 M). Relative standard deviations of better than 8% at levels of 10 xg per litre were attained for seawater using graphite furnace atomic absorption spectrometry. 

Hua et al. [507] described an automated method for determination of molybdenum in seawater by means of constant-current reduction of the adsorbed 8-quinolinol complex in a computerised flow potentiometric stripping analyser. The complex was adsorbed onto a molybdenum film electrode at -0.2 V and stripped at -0.42 V. The authors report measuring molybdenum at 8.9 1.3 xg/l in reference seawater NASS-1, with a certified value of 11.5 1.9 xg/l. 

Cathodic stripping voltammetry has been used [807] to determine lead, cadmium, copper, zinc, uranium, vanadium, molybdenum, nickel, and cobalt in water, with great sensitivity and specificity, allowing study of metal specia-tion directly in the unaltered sample. The technique used preconcentration of the metal at a higher oxidation state by adsorption of certain surface-active complexes, after which its concentration was determined by reduction. The reaction mechanisms, effect of variation of the adsorption potential, maximal adsorption capacity of the hanging mercury drop electrode, and possible interferences are discussed. 

Colorimetric field tests for TATP and HMTD were described in Section 5 dealing with peroxide-based explosives. This group contains Keinan s PEX [85] (E. Keinan, Personal Communication, February 2006) and the kit developed by Schulte-Ladbeck et al., which involves also a preliminary stage to avoid falsepositive responses by non-explosive peroxides [86]. The color change of molybdenum hydrogen bronze suspension upon reaction with TATP was recommended also as a field test. Exposure of filter paper strips which were soaked in butanol suspension of the molybdenum compound to TATP or hydrogen peroxide vapors rapidly bleaches the blue color [87, 88]. 

Thus there is considerable incentive to find extractants that could tolerate higher quantities of solids in H2SO4 leach liquors. Stripping of uranium from the Amex process extractant and subsequent regeneration of the amine solvent also consume considerable quantities of acid and base. Recovery of uranium from H2SO4 solutions would be simplified if a convenient neutral extractant could be found. An extractant with better selectivity for vanadium and molybdenum than HDEHP and long-chain amines is also desirable. 

Low carbon, nickel, molybdenum chromium alloy ASTM B 564, UNS N10276 (forgings) ASTM B 574, UNS N10276 (bar and rod) ASTM B 575, UNS N10276 (plate, sheet, and strip) ASTM A 494, Grade CW-2M (weldable cast)... 

The determination of phosphorus after precipitation and solvent extraction as molybdophos-phoric acid (MPA) and reduction to molybdenum blue is a classical procedure,30 40 while cerium can be determined directly as molybdocerophosphoric acid (MCPA emax 7300 at 318 nm). A more selective method is to strip excess of MPA by extraction with chloroform, then to decompose residual MCPA and determine the phosphate liberated therefrom as MPA after extraction into isobutyl acetate. Alternatively AAS can be used to determine the amount of molybdenum. 

Molybdenum can also be recovered economically from some uranium leach liquors, particularly those of the USA. When uranium is stripped from amine extractants by solutions of sodium chloride, any molybdenum present remains in the organic phase, and can be subsequently recovered by being stripped into a solution of sodium carbonate. A process has been operated in which the strip liquor is acidified to a pH value of 4.5 and the molybdenum is reextracted into a solution of quaternary amine chloride in kerosene.218 The extracted metal is stripped into a solution containing sodium hydroxide and sodium chloride to produce liquors containing 30-40 g of molybdenum per litre, from which calcium molybdate can be precipitated by the addition of calcium chloride. 

The results of two studies of silicide films are presented in Tables IV and V. For the results shown in Table IV, molybdenum silicides were deposited on vitreous carbon disks. One set was stripped with base (2 N NaOH), and the other set was stripped with acid (HF-HN03-H20, 1 1 10). The study of chromium silicides (Table V) gave similar results. 

Piersma et al. demonstrated that lithium can be electrodeposited from 1-ethyl -3-methyl-imidazolium tetrachloroaluminate ionic liquid, when lithium chloride was dissolved in the melt [3], Platinum, glassy carbon and tungsten were used as working electrodes with molybdenum and platinum foils as counter electrodes. At -2.3 V a reduction peak of Li+ is observed and at about -1.6 V the stripping of lithium occurs. They noticed that the efficiency was much less than 100%. In addition, they were able to demonstrate that the addition of proton sources like triethanolamine-HCl widens the electrochemical window and allows the plating and stripping of lithium (and also sodium). 

The chemical form of phosphorus in the water column available for uptake by biota is important. The biologically available phosphorus is usually taken to be soluble reactive phosphorus (orthophosphate) , i.e. which, upon acidification of a water sample, reacts with added molybdate to yield molybdophosphoric acid, which is then reduced with SnCl2 to the intensely-coloured molybdenum blue complex and is determined spectrophotometrically (Imax = 882 nm). Reduction in inputs of phosphate, for example from point sources or by creating water meadows and buffer strips to contain diffuse runoff, has obviously been one of the major approaches to stemming eutrophication trends and... 

Strips of Cu, Mo, or Ni were placed in a sealed dessicator with an open container of benzyl bromide, and exposed to the vapor for eight days. Corresponding control strips were kept in a dessicator for the same period. All strips were then withdrawn and placed into 50-mL portions of distilled water. Aliquots were withdrawn to test for dissolved metal levels. All dissolved metal concentrations have units of mg/L. Molybdenum concentrations were determined as molybdate ion. 

---