Table IV. Results with One Fusion and Leach on Standard Diabase W-1 Containing Added Rhenium
Re added,
Re found,
0.5 0.5 5 5 50 50 500 500
0.46 0.51 4.9 4.9 45.2 45.5 475 463 (1st fusion)
rg.
PP.
l7
/a
Recovery 92 102
42 (2nd fusion)
Table V.
98
98
90.4 91
92.6 8.4
On leaching the melt, most constituents are rendered insoluble either as hydro.;ides or calcium salts, except for rhenium and a small amount of molybdenum. A rather complete separation of the elements is obtained, as shown by the fact that no precipitate is formed in the filtrate from rocks on adjusting the pH to 7.5 with ammonium hydroxide. About 680 and 440 fig. of hIoOa, respectively, were found in the filtrate when 0.5 and 0.3 gram of M o S 2 were tested; 50 ug. and less than 5 fig. of MoOs mere found when 0.5 gram of W-I was taken to which 1 mg. and 100 ug. of 1\1003,respwtiwly, had been added.
Test of Procedure on Mixtures of W-1 and Molybdenite Containing 70 p.p.m. of Re
Mix taken, gram R-1 0.2 0.4 0.025 0.475 hIoSs 0.3 0.1
Re in mix, pg.
21 7.0 1.75
1st fusion 17.6 6.0 1.6
Re recovered, pg. 2nd fusion 3.1
0.9 0.25
Total 20.i 6.9 1.85
more than 90% complete n i t h a single fusion and leach, as shown in Table IT. Experiments with molybdenite concmtrate containing 7 0 p.p.m. showed thnt of the rheniuni 57.4 p.p.m. or about is made soluble by a single fusion and leach. On drying the residue, and fusing again after adding 1 gram of CaCI2.2H20, 11.2 p.p.m, more of Re or about 90% of the remainder was recovered. X third fusion and leach reco\ ered 1 .-I p.p,m. more. Experiments rvhere the same molybdenite m s fused only once but four separate leaching5 with water were made indicated that rhenium cannot b~ leached readily in this manner, 57.2, 4.1, I, and 0.3 p.p.m. being obtained, respectively, in each successive leach. The procedure was tested also on mixtures of M7-l with the same molyhdenite (Table V). Nore than 95% recovery of the rhenium is obtained in two fusions. The percentage recover) of rhenium in the first fusion is greatpi-. the smaller the amount of molybdenite taken. LITERATURE CITED
Applications of Procedure.
The procedure has been applied t o mixtures of a standard diabase W-1 with added rhenium, mixtures of TV-1 a n d molybdenite, a n d a molybdenite concentrate. Samples were decomposed with a mixture of CaO, CaC12, and MgO. The MgO acts as a combustion aid, CaCh decomposes silicates, and CaO fixes molybdenum as insoluble Cahfo04.
Molybdenum and other elements finding their may into the filtrate are separated by extraction of their 8-quinolinates in chloroform from buffered acetate solution as proposed by Poluektov (4). This step is probably unnecessary for samples containing less than a few hundredths of a per cent molybdenum trioside. The recoveries of rhenium added as a solution of KRe04 to 0.5 gram of TV-1 are
(1) Poluektov, N. S., J . A p p l . C h m .
USSR 9, 2312 (1936). (2) Ibid., 11, 534 (1938). (3) Ibid., 14, 695 (1941). (4) Poluektov. N. S..Kononenko. L. I . ' Zavodskaya Lab. 25; Part 5, 548'( 1959).
RECEIVEDfor review June 7 , 1962. Accepted July 25, 1962. Submitted by F. 0. Simon in partial fulfillment of requirements for master of science degree in chemistry a t the American Vniversity, Washington, D. C.
Comparative Study on Determination of Oxygen in Vanadium Metal VELMER A. FASSEL, WAYNE E. DALLMANN, RODNEY SKOGERBOE,' and VIRGINIA M. HORRIGAN? Institute for Atomic Research and Department o f Chemistry, Iowa State University, Ames, Iowa
b A comparative study on the determination of oxygen in vanadium b y the vacuum fusion, inert gas fusion, and d.c. carbon-arc extraction, emission spectrometric, techniques has demonstrated that concordant analytical results can b e obtained b y the three methods. Synthetic standards were employed to validate the absolute accuracy. The experimental conditions for each technique are tabulated.
V
is included among the many metals whose physical and mechanical properties are markedly influenced by the presence of trace quantities of interstitial oxygen (5, 6 ) . ANADIUM
1364
ANALYTICAL CHEMISTRY
To appraise these effects and to provide analytical control during production operations, accurate and sensitive analytical methods for determining the interstitial oxygen content in vanadium metal are required. The classical vacuum fusion (29) and the more recently developed inert-gas fusion (21, 23) techniques have found widest application to the determination of oxygen in metals. Both techniques involve high temperature fusion of the metal specimen in a graphite crucible, under environmental conditions such that the carbon reduction reaction [hl
+ RIxOy] + c
4
bTC
+M +yco
(1)
leads to the quantitative evolution of carbon monoxide. To aid in the quantitative extraction of carbon monoxide, the partial pressure of the carbon monoxide above the fused sample is reduced to negligible proportions either by vacuum pumping or by a stream of inert carrier gas. When either of these furnace fusion techniques is applied to a metal system, quantitative accuracy of the determination depends on affirmative answers to Present address, Department of Chemistry, M ontana State University,Bozemon t, Mont. 2 Present address, Anaconda American Brass Go., Waterbury, Conn.
t n o critical questions: Is the interstitial oxygen content of the sample quantitatively reduced to carbon monoside under the particular environmental and thermodynamic conditions employed? Is all of the carbon monoxide quantitatively transferred t o and measured by the analytical system? I n principle, definitive ansji ers to tlicsc questions can be provided by observations on absolute standard samples containing precisely knob n quantities of oxygen. Unfortunately, the synthesis of absolute metal-oxygen >tandards, especially in the lo)? oxygencontent range, is a singularly difficult task. Furthermore, significant system.itic eri 01's may arise in the preparation oi thc standard samples. Anothcr approach to this aciuIacy validation problem is to study the basic carbon rcduction reaction under markedly diffcrent environmental and thermodynamic conditions. If these condit ions lead to concordant analytical data, a high degree of confidence can be placcd on the determinations. If, in iddition, quantitative osygen recoveries on synthetic standards can be demonYtrated, a n even greater assurance of absolute accuracy is obtained. I n this Iiaper the results of such a study on the dctermination of oxygen in vanadium ineta1 are presented. COMPARISON OF EXPERIMENTAL CONDITIONS
Vacuum Fusion. T h e carbon reduction reaction is performed i n a dyna niic vacuum system. Although this . w u r e s t h e rapid transfer of the carbon monovide from t h e crucible area, t h e nia\inium operating temperature is limited by t h e rate of evaporation of metal a n d carbon from t h e crucible. I n practice. a crucible temperature in ewess of 2000' C. is rarely used, even tor refractory metals, lest the higher tempwature cause excrssive carbon and metal volatilization and deposition of rcactive films on the furnace nalls and tubulations. Sorption of the evolved carbon monoxide on these deposits may lead to serious systematic errois ( 2 ) . Inert Gas Fusion. T h e sample fusion and its reaction with carbon :ire Conducted under a nominal atniosphmic pressure of a n inert gas. As a conqequence, higher melt temperatures can be tolerated before metal vaporization becomes: excessive. T h u s i t is convenient to examine t h e quantitativeness of carbon monoxide evolution a t temperatures several hundred degrees higher t h a n is practical under vacuum fusion conditions. D.C. Carbon Arc, Emission Spectrometric. T h e carbon reduction reaction shown in Equation 1 can also be performed in t h e anode receptacle of a high current, d.?.
Table I.
Experimental Conditions for Determination of Oxygen in Vanadium by Vacuum Fusion Technique
Analysis facility Furnace assembly Crucible and funnel Furnace heater Analytical system Apparatus outgassing Bath outgassing
Blank level Extraction temperature Extraction time hIaximum concentration Samples and flux
Vacuum fusion gas analysis unit, NRC Equipment Corp., Model 912s (17, 39) Guldner-Beach furnace (14). Graphite parts assembled in quartz thimble and suspended by platinum wire hooks within air-cooled borosilicate glass jacket United Carbon Products Co., C-625 graphite crucible, F-703 graphite funnel, -200-mesh UCP-2 graphite ponder packing Lepel High Frequency Corp., induction heater, Model T-2.5B Conventional low-pressure oxidation and selective absorption and condensation separations (69) Crucible temperature slowly raised to 2400" C:. over 1-hour period and maintained a t this temperature until pressure level became less than l o d mm. Hg S o t less than 20 or more than 60 grams of 12-gage platinum xire added at 1700" C. and outgassed a t 1900" C. until pressure level became less than 10-6 mm. Hg Furnace blank,
