Crystalline Arsenates of Zirconium and Hafnium J. R. GUMP AND G . R. SHERWOOD W a y n e U n i w r s i t y , Detroit, Mich.
varying conditions upon the character of the arsenate precipitate-in other words, shows how to get a good precipitate with zirconium which can be filtered and washed rapidly, rather than the common gelatinous kind which is so annoying.
SALYTICAL separations and determinations of elements in
A Groups I11 and IV of the periodic chart are often very diffi-
cult because of the formation of precipitates of poor quality. For example, the separation of zirconium from other positive ions by the precipitation of zirconium phosphate is often not nearly as effective as might be predicted on the basis of solubility differences. This is because it is very difficult to wash out occluded ions from a gelatinous, noncrystalline precipitate. Larsen, Fernelius, and Quill ( 2 ) have pointed out hox the character of this precipitate can be improved. Willard and Freund (3) have further improved the process by forming the precipitating ion in the solution. Recently, it has been shown ( 1 ) that mandelic arid nil1 quantitatively separate zirconium from most interfering ions. Before the latter two publications appeared, the authors began an investigation to find if the separation of zirconium and hafnium could be improved by forming the arsenate ion in solution, through oxidation of arsenite. This paper shows the effvrt\ of
EXPERIMENTAL
E\periments were carried out to determine the effect of varying the concentration of hydrochloric acid present, sulfuric acid present, zirconyl ions, and arsenite ions. The starting material was always air-dried zirconvl chloride or oven-dried (but not ignited) zirconyl hydroxide which was subsequently dissolved in hydrochloric acid. Nitric acid was employed as the oxidizing agent. Excess acid (usuallv hydrochloric) was used to prevent the formation of a basic Precipitate. Table I indicates that varying the concentration of hydrochloric arid had very little effect upon the crystal size and filterability of the arsenate precipitate Although all these precipitates were good, those formed where the hvdrorhloric acid was o n l ~0 6 N and I .2 A- were slightlv better. Table I. Effect of Hydrochloric Acid Concentration In another series of experiments, 11.77 grams of zirconium Rere used, and 14.9 grams of sodium arsenite, 30 ml of concentrated Weight of zirconium, 1 1 . 7 7 11.77 11.77 11.77 6. hvdrochloric acid, and 20 ml. of 6 iV nitric acid were added The Concentrated hydro- 30 60 120 240 volume of solution was 600 ml. at beginning of heating and 500 chlorie acid, ml. nil. after heating (Table 11). Normality of solution 0 . 6 1.2 2.4 4.8 Table 11 shows that the concentration of sulfuric acid is of in hydrochloric acid great importance. Although not listed in the table, the authors Sodium arsenite 14.9 14.9 14.0 11.9 added, g. have determined that if no sulfate ions are present-i e., if pure 6 N nitric acid added, 20 20 20 20 airconyl chloride is employed-the zirconium arsenate precipitate ml. is semicolloidal. Concentrations in the range of 1.2 to 1.8 Y Concentrated sulfuric 30 30 30 30 for sulfuric acid are evidently most satisfactory. Higher concenacid added, ml. trations of sulfuric acid not only produced precipitates of poorer Volume of solution a t 600 600 600 600 beginning of heatquality, but induced humping of the solutions while they were ing, ml. being heated. The molar ratio of sulfate ion to zirconyl ion Volume after heating, 500 500 500 500 should always be kept above 1; in fact, the authors’ experience ml. indicates that the best results are secured when this ratio has a Type of precipitate Crystalline Crystalline Crystalline Crystalline value of approximately 2 (note the excellent DreciDitate listed - Filtered Rapidly Rapidly Rapidly Rapidly first in Table 111). Time of settling, min. 2 2 2-3 3-4 Here we find the limits within which the concentration of zirconyl ion can Table 11. Effect of Sulfuric Acid Concentration be varied. If 600ml. of solution contain C o n c e n t r a t e d sulfuric acid 10 20 30 60 100 10 to 25 grams of zirconium, excellent added, ml. results can be expected. Table 111 also Normality of solution in SUI- 0 . 6 1.2 1.8 3.6 6.0 furic acid rather clearly points out the solubility Type of precipitate Sinall crystals Crystalline Crystalline Semicolloidal Colloidal limits of zirconium arsenate under these conditions. Filtered Fairly wcll Rapidly Rapidly , Poorly Very poorly In a fourth series of experiments, 10 2 2 Hours Hours Time of settling, min. Other remarks Bumping Bumping 10.i grams of zirconium were used, and 30 ml. of concentrated hydrochloric acid and 30 ml. of concentrated sulfuric Table 111. Effect OC Zirconyl Ion Concentration acid were added. The volume of soluWeight of zirconium, g. 23,;,4 11.77 5.9 3.0 2.9 1.7 tion was 600 ml. a t beginning of Concentrated HCI, ml. 60 30 30 30 30 30 heating and 500 ml. after heating. Sodium arsenite added, g. 29.8 14.9 7.6 3 3.7 3.7 In all cases the precipitate was 6 iV nitric acid added, ml. 40 20 10 7 5 5 crystalline and the solution filtered Concentrated sulfuric acid 30 30 30 30 30 30 added, ml. rapidly. Volume of solution at begin- 600 600 600 600 fiOO 600 Tablc IV shows the effect of varvning of heating, ml. ing the concentration of the arsenite Volume after heating, ml. 200 500 500 500 400 500 ions. Evidently within these limits the Type of precipitate Crystalline Crystalline Crystalline Crystalline Cloudy i’-one concentration of sodium arsenite is not Rapidly Rapidly Filtered Rapidly Rapidly .. .. important; all precipitations were rather Time of settling, min. 30 sec. 2 2-3 2-3 .. .. satisfactory. ~~
496
V O L U M E 2 2 , NO. 3, M A R C H 1 9 5 0 Table IV.
497
Effect of Arsenite Concentrations
Sodium arsenite to precipitate 6 .V nitric acid added, mi. Tinielieatedoversame type Bailie, min.
.ill Zr
p:’l
Zr
‘1, Zr
35
20
17
45
51
51
Zr 10 45
‘ / r Zr 8 45
I/(
Zr
tion of arsenate ion within the solution. If optimum conditions are employed, a precipitate of much better quality is obtained than the ordinary phosphate, hydroxide, or arsenate.
5 45
L I T E R i T L R E CITED
(1) Kumins, C. A, ~ L L CHEM., . 19. 376 (1947). (2) Larsen, E. lf.,Fernelius. IT. C., and Quill, L. L., Zbtd., 15, 513 SUM.\IARY
A systematic study has been made of the factors involved in the precipitation of zirconium :md hafnium arsenates by the fornia-
(1943).
(3) U’illard, H. H., and Freund, Hariy, Ibzd., 18, 195 (1946). RECEIVED N a y 31, 1949.
Colorimetric Determination of Cobalt with Nitroso R Salt in the Presence of Copper .A. J. M i L L &.VI) K. S . YOUNG, C e n f r u l Laboratory, S k a m z , .Vorlhern Rhodesia
IIAS been recognized that copper interferes in the coloriI Tnietric determination of cobalt ivitli nitroso It salt, when tlie
usual procedure is followed for small quantities of cobalt in nietallurgical and similar products. Although LlcSaught ( 3 ) stated that copper up to 100 inicrogrania does not interfere with the deterniination of l microgram of cobalt, in his procedure the usual rernoval of copper with hydrogen sulfide is followed. In a later paper (4)he advocates the separatiori of copper when deter1iii1iing cobalt in animal tissues, but lound that for plants and soils the separation was not necessary. Other investigators ( 1 , 2, 5, B), presumably working with much larger quantities of cobalt arld copper, have always removed the copper. In this laboratory it has been found that by slightly niodifying the procedure, quantities of cobalt in the ~‘arigeof 0.1 to 0.5 my. can be determined in the presence of I O t o 12 nig. of copper. REAGENTS
Kitloso R salt solution, 1 gram dissolved in water and made up to 500 ml. Sodium acetate solution, 500 grams of sodium acetate trihydrate dissolved and made up to 1 liter with water. Phosphoric-sulfuric acid mixtures, 150 ml. of concentrated phosphoric acid and 150 nil. of coriceritrated sulfuric acid, made up to 1 liter with water.
Fvith little or 1 1 0 lowering of tlie result. K i t h 23 to 25 mg. of copper the results were slightly l o ~ vand ivere not rectified by the addition of more sodium acetate. It is essential to boil the ssniples for 1 minute before the addition of nitric acid; otherIr-iue the color of the cobalt complex will not be fully developed. The subsequent boiling of the acid addition is not so important, as vigorous boiling for 1 to 2 minutes will decolorize the iron complex, but it is not advisable t o prolong this beyond 2 minutes. I n the authors’ procedure the samples are not filtered until :Lfter the color has been developed. After the initial fuming, residual insoluble matter has no effect on the cobalt color, and the elimination of washing and evaporating solutions materially reduces the time for routine work. Some typical results obtained with this procedure are given in Table I. The samples were those used in this laboratory as standards, and the values for “cobalt present” represent averages of closely agreeing results obtained by standard colorimetric, gravinic,ti,ic., r,oteritioriiett,ic~. arid talrctrolytic procedures for cobalt.
Table 1.
Kecovery of Cobalt i n Presence of Copper CU Present
Sample
PROCEDURE
‘V
Take such a weight of sample, or aliquot after decomposition, that the quantity of cobalt present is not over 0.5 mg. and the copper does not exceed 10 to 12 mg. If this ratio of copper to cobalt is exceeded, remove copper by hydrogen sulfide or electrolysis. Decompose the sample with nitric and hydrochloric acids, with the addition of bromine for sulfides and hydrofluoric acid for silicates. Add 5 ml. of phosphoric-sulfuric acid, evaporate to strong fumes, and continue for 5 minutes. Cool, take up in 20 ml. of water, and boil. Add 30 nil. of sodium acetate solution, and 10 ml. of nitroso R salt solution, and boil vigorously for exactly 1 minute, Add 10 ml. of nitric acid to the boiling samples and if all the flocculent precipitate does not dissolve add 2 to 3 ml. more acid. Continue boiling for a t least 1 minute, but do not prolong this operation beyond 2 minutes. Cool and dilute to 100 ml. with water. Filter through dry Whatman S o . 40 papers and dry funnels into dry 250-ml. flasks. It will suffice to filter only 40 to 50 ml. Measure the absorption of the solutions in a photoelectric colorimeter in the usual m y against a suitable blank and read the concentrations from a calibration curve prepared with measured amounts of cobalt (6).
Copper reverberatory slag
0 . G3 0.63 0.63 0.71 0.71 9.29
Electric furnace slag Copper converter a l s g
cu
.\dded 110
..
11.5 23 11:5
co Present
co Found
“ /ti
%
0 63 0 63 0 63 2 27 2.27 4 95
0.63 0.63 0.61 2.27 2.25 4.94
SU.\I>IARY
13y increasing the sodium acetate arid nitric acid in the nitroso It salt procedure for cobalt, 0.1 to 0.5 mg. of the latter may be determined in the presence of 10 to 12 mg. of copper. This niodification, together with the practice of filtering the sample only after the developmPnt of color a t the end of the determination, wsults in a considerable saviug of time. LITERATURE C I T E D
(1) Allport, N. L., “Colorimetric Analysis,” London, Chapman and DI SCU SSIO 5
If not more than 5 ml. of phosphoric-sulfuric acid are added to a, 0.25-gram sample, it is only necessary to fume the latter strongly, and neutralization with sodium hydroxide is not required. Samples fumed to complete dryness and those having 4 rnl. of phosphoric-sulfuric acid present gave the same results. With 30 nil. of sodium acetate and 10 ml. of nitric acid, cobalt could be determined in the presencr of 10 to 12 mg. of copper
Hall, 1947.
(2) “B.D.H. Book of Organic Reagents for Analytical Use,” Lon(3)
don. British Drug Houses Ltd.. 1948. McNaught, K. J.. .inaZust, 64, 23-7 (1939).
(4) Ibid., 67, 97-8 (1942).
( 5 ) Sandell, E. B., “Colorimetric Determination of Traces of lletals,” (6)
New York, Interscience Publishers, 1944. Young, R. S., Pinkney, E. T., and Dick, R., I m . E m . CHEM., ANAL.ED.,18,474-6 (1946)
RECEIVED .ipril 26, 1949
