Spectrographic Method for Analysis of Recovery A c i d THOMAS WHITEHEAD, J R . ~ ,AND ESTHER VIRGINIA WILLIAMS, Basic Magnesium, Incorporated, Las Vega,, Nev. A rapid spectrochemical method has been developed for determining small amounts of sodium, potassium, calcium, aluminum, and iron in hydrochloric acid solutions. Working curves were constructed on the basis of a series of prepared synthetic solutions. The plate densities of specific lines in certain wave-length regions were adjusted b y the use of suitable filters. Results secured b y this procedure compare favorably with those obtained b y the usual chemical methods.
THE
rapid analysis of by-products and waste materials is of very great practical importance in many chemical processes, particularly if these materials are to be recycled. In the production of magnesium (6) by the formation and electrolysis of anhydrous magnesium chloride, a considerable amount of hydrochloric acid is generated. This acid is recovered and used in one of the preliminary steps in the magnesium production cycle. This hydrochloric acid, commonly called recovery acid, contains small amounts of impurities such as the chlorides of magnesium, sodium, potassium, calcium, iron, and aluminum as well as some carbonaceous materials. The customary methods of analyzing this recovery acid are somewhat limited in their application and are generally time-consuming. However, analyses can be obtained in a comparatively short time by SPectrographic means.
to samples of recovery acid, and the moving plate technique was employed to select those elements most likely to fill the requirements. A series of recovery acid samples was then prepared containing the elements showing promise for use as internal standards in amounts to give satisfactory line densities. A number of exposures were made, and the intensity ratio precision obtained was used as a criterion for the choice of the most desirable internal standards. Working curves were established (Figure 1) by analyzing synthetic acid samples containing varying known amounts of each element to be determined. To each synthetic sample was added a constant amount of the internal standard selected. The relative intensity ratio existing between the selected spectral lines of the element to be analyzed and the selected spectral lines of the internal standard increases with the concentration of the variable element. By plotting, as ordinate, the relative intensity ratio of the element to be determined to the internal standard, and as abscissa, the concentration of the variable element, a working curve was constructed from which satisfactory estimations of the amount of each element in the recovery acid can be secured. Table
1.
Comparison of Chemical and Spectrographic Analysis of Recovery Acids
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placed immediately in front of the slit, and the electrode stand positioned so that an image of the electrodes falls in the approximate region of the collimating lens. By appropriate positioning of the electrodes, uniform line densities were obtained a t the camera position. The slit was adjusted to a width of 30 microns, and, by the use of the wedge on the Hartman diaphragm, the spectrum lines were limited to a height of 2.8 mm.
.5
ANALYTICAL PROCEDURE
A
AN.4LYsIs FOR SODIUM, CALCIUM, IRON, AND
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No3303
ALUMINUM,To 50 ml. of recovery acid are added 50 ml. of distilled water and 5 ml. of an
ANALYTICAL EDITION
August, 1945
treated special graphite electrode, which is dried at 110" C. for approximately one hour. The spectrograph is adjusted to the 2600 to 3600 A. range, Eastman Kodak process plates are used, and two No. 2 cover slips are placed between the slit and the light source. The prepared electrode is used &s the lower electrode and a pointed electrode having a tip 1.2 mm. in diameter as the upper electrode. Samples are burned to completion, using 11 amperes direct current, and analyses are made in triplicate. After exposures are completed, the plates are developed for 2 minutes a t 18' C. in D-19 developer. The cobalt line having a wave length of 3453.5 b. is used &s the internal standard line. Calculations for the various elements are established on the following lines: Fe Na Ca A1
3306.4A. 3302.3 A. 3179.3 A. 3082.2 A.
Concentrations are evaluated from the working curves (Figure 1) established by the use of the series of synthetic solutions. Sodium and calcium are calculated as chlorides, while iron and aluminum are calculated as oxides. ANALYSIS FOR POTASSIUM. To secure sufficient sensitivity for the analysis of potassium, the spectrograph i s adjusted to photograph the 5000 to 10,000 A. range. To secure satisfactory line density levels in this region, and to obtain suitable sampling, a Wratten Filter No. 57 is placed in front of the slit. Eastman Kodak IV N plates used for the analysis of potassium are sensitized for the wavelength region used by placing in '4% ammonium hyroxide for one minute. Strontium is a suitable internal standard for this determination. To 5 ml. of the original recovery acid sample are added 5 ml. of a solutioii containing 29.7 grams of strontium chloride per liter. These are rapidly mixed, and one drop of the mixture is immediately placed on a graphite electrode previously treated with
49 1
kerosene. The procedure from this point is similar to that outlined previously, except that a 15-ampere direct current arc is used to increase the precision. Either K 7664.9 1.or K 7698 A. may be used for the determination of potassium and Sr 7070.1 A. is used as the internal standard line. Potassium is calculated as the chloride. RESULTS AND DISCUSSION
A series of recovery acid solutions was analyzed spectrographically, and the results were compared with those of routine chemical methods, as shown in Table I. Spectrographically, the iron and aluminum oxide values obtained were converted t o R,O* in order to show comparisons with the chemical results in which RIOl was determined as the hydroxides. Qualitative spectrographic analysis of a number of these precipitates showed the presence of appreciable proportions of titanium, copper. and manganese. By slit-height adjustment and camera movement it is possible to secure triplicate exposures of 10 samples and one standard on each plate. The total time necessary for the analysis of 10 samples for sodium, potassium, iron, aluminum, and calcium should not exceed 7 man-hours. LITERATURE CITED
(1) Breckpot, R.,Chimie & Industrie,Special No., 220-9 (1934). (2) Cholak, J., and Story, R. V., IND.ENQ.CHEM.,ANAL.ED., 10, 619-22 (1938). (3) Eastman Kodak Co., Rochester, N. Y.. "Wratten Light Filters", 1940. (4) Hasler, M.F., J. Optical SOC.Am., 31, 140-5 (1941). (5) Owens, J. S., IND.ENO.CHEM., ANAL.ED.,10, 64-7 (1938). (6) Ramsey, R. H., Eng. Mining J., 144, No.10, 61-7 (1943).
Optical and X-Ray Diffraction Studies of Certain Calcium Phosphates WILLIAM F. BALE, JOHN F. BONNER, AND HAROLD C. HODGE, The University of Rochester, School of Medicine and Dentistry, Rochester, N. Y., AND HOWARD ADLER, A. R. WREATH, AND RUSSELL BELL, Victor Chemical Works, Chicago, 111. The x-ray diffraction data, the melting points, the crystallographic systems, and the indices of refraction of 11 calcium phosphates are reported. These 11 calcium phosphates are divided into four groups: a primary calcium phosphate and 3 derivatives, a secondary calcium phosphate and 3 derivatives, P tertiary calcium phosphates, and hydroxylapatite.
M
fraction. All the compounds shown by fusion studies to exist in the CaO-P20s system except tetracalcium phosphate are given in Table I. PROCEDURES
In Table I1 are given the x-ray powder diffraction data for the 11 substances. These data are presented in the same way as the comprehensive data of Hanawalt, Rinn, and Frevel (Y)-i.e., spacing measurements and relative intensities are given with additional notations for the index lines. The procedures for determining the powder diffraction data in Table I1 are given in detail elsewhere (9).
ICKOSCOPIC characteristics and x-ray diffraction patterns of some of the calcium phosphates have been reported, but none of the lists is complete, even of the more commonly manufactured compounds. This paper attempts to present new data to fill some of the gaps in the knowledge of these important compounds (18). In 1938,lO diffraction patterns were published (9),which were taken as repTable 1. Data on Eleven Calcium Phosphates resentative of 10 calcium phosphates. Melting BireTh(1identity of these compounds was Diffraction P$t. fringRefractive Indices Pattern Type ( 9 ) C. System ence No,N ,N o Nm,"! IVS Formula sought by chemical and optical d. 153 Triclinic 1. I primary 1.528 analyses and x-ray spectrography. 1.518 1,501 2. d. 268 Triclinic I1 primary 1.590 1.564 1.552 The diffraction patterns have been 3. 111 primary .1000 . . Amo;phous 1.578 1.518 Ignited primary 4. 1.540 associated with formulas, and by the Tetragonal 1.588' 1.5955 5. CaHPO4.2HL> I11 secondary ... Monoclinic 1.551 present work eleven compounds have 1:5i5 1.540 Triclinic 6. CaHPO4 I secondary 1.63 1.61 1.60 now been identified. They are preIgnited secondary t. 'ii70 Tetragonala 1.6285 7. R-CaxPz07 ... 1,624'' 1350 8. a-CalPzOr ... 1.605 1.60 1.585 sented by formulas in Table I, in t. 1350 9. B-CaaPz01 1gnited't'e;tiary ... 1.620a ... 1.622" 1720 10. a-Car PzOs 1.588" which the following data are also .. 1 .591° 1540 Hexagdnal 11. Ca~a(POds(0Hh Hydroxzapatite 1.610 .. ... given: the x-ray diffraction pattern d. Decomposition temperature. types as published in 1938, the meltt. Transition temperature. ing points, the crystallographic Values reported from the literature. syst,cms, and the indices of re-
