cthyleiie, the purging step is iicwsary before a n analysis. The acetylene peak is not completely separated from the other peaks. The peak height calculated from the inversion point before the peak ( H , Iigure 0), gave a reproducibility better tlinn *2%. If the calibration is made under the =me conditions and at the ssme concentration level, about 1 p.p.m. of acetylene conccntr:rtion is memirsble.
LITERATURE CITED
( 1 ) Boggus, J. D., Adams, N . G., .%NAL.
CHEM.30, 1471 (1958). (2) Eggertsen, F. T., Nelsen, F. M., Zbid., 30, 1040 (1958)
(3) Ford, H. W., Rogers, L. H., Division of Physical and Inorganic Chemistry, 133rd Meeting, ACS, San Francisco, Calif., April 1958. (4) Gaulin, C. A., Michaelsen, E. R., Alexander, A . B., Jr., Sauer, R. W., Chem. Eng. Progr. 54, No. 9, 49 (1958). (5) Hausdorff, H. H., in "Va our Phase Chromatography, D. H. besty, ed., p. 377, Butkrworths, London, 1957.
(6) Pietsch, H., Erdd u. Kohle 11, 157 (1958). ( 7 ) Ray, N. H., Analyst 80, 853 (1955). ( 8 ) Rhoades. J. W., Food Research 23. 254 (1958). ' (9) Watson, E. S., Bresky, D. R. (to Perkin-Elmer Corm). Corp.), u. U. s. S. Patent 2.757.2,757,, , 541 (Aug. 7, 19563." 1956). '
RECEIVED for review March 23, 1959. Accepted August 21, 1959. Division of Analytical Chemistry, 135th Meeting, ACS, Boston, Mass., April 1959.
Determination of Lithium in Silicate Minerals and Leach Solutions by Flame Photometry H. L. HOWLING and P. E. LANDOLTI D. little, Inc., Cambridge 42, Mass.
Arthur
b A method to determine lithium both in silicate minerals and in leach solutions was developed in which minerals are brought into solution by a sulfuric acid and hydrofluoric acid treatment, followed by a calcium carbonate precipitation. The lithium is determined using a Beckman DU spectrophotometer with flame attachment in a manner that eliminates repeated calibration and standardization and eliminates the effects of the common interfering ions. This technique can b e applied to a wide variety of lithiumbearing minerals.
I
YEARS, the classical wct r~itthodsfor the deterniiri:~tioii of litliiuin have been suprrscdcd by inore rapid :md specific methods b:tsc!d on flnn~t: photometry. Scver:il of these 1 i w methods are concerned witti tlir tlt~ti~riilinationof lithium in silicate iiiincwls (1, 2, 3, 5 ) . None of these methods is equally applicable to the detc.rinin:rtion of lithium either in silic:ite iiiincbr:ils or in Icach solutiotis. .Ill are ] l l ' l J l i t ' tri report 1ow lit,hiuni v:thies.
x iwcmT
from distilled wati:r. Scparate the crystals from tlic: mothi'r liquor, wash with deminera1izc.d natc'r, and dry them a t 150' C. for 2 hours. This lithium fluoride is substantially frre from alkali metals aiid is suitnhlr for use as a primary standard. CITRATE B C F F E R S O L U T I O E . Boil 2 liters of dist~ill(~t1 \ v a t u and to it add 1 pound of citric, :icitl :tnd 1 pound of dianimoniurn citrate; thrn dissolve, cool, and transfer the liquid to a sterile polyethylene bottlip and rcbfrigeratc. This solution will keep at least one month when refrigerated, but it should be discarded a t the first sign of mold formation. CALCIUJI CARDOSATF:, rcagent grade powder. HYDROGEN PEROXIDE, rcagent grado, 3%. PROCEDURE
For solid samples, weigh out a portion containing 0.5 to 25 mg. of lithium and transfer it to a 50-ml. platinum dish. Moisten the sample with water and treat with 5 to 10 drops of nitric acid, 10 to 20 drops of sulfuric acid, and about 30 ml. ol hydrofluoric acid. Plaw thc tlisli in :i sand bath and c.val)oratc the solution until just moist; APPARATUS add a further 30 ml. of hydrofluoric acid .I Beckman DU s p c c t r o ~ ~ h o t o ~ ~ i c ~ strong t r r and slowly evaporntc the liquid' to sulfuric acid fumes. Cool, then was usrd with flamr attachmcwt No. moisten the sample with water, treat 921 5 and a hydrogen-oxygctri atomizer, with 10 drolis of sulfuric acid, and bur1ic.r No. 4020. T o ensure good evaporate to fumes; cool the sample replication, it is nectwxuy t o maintain again, add about 5 ml. of water, and careful control of the oxygrn and repeat evaporation to dense fumes hydrogen prrssures, especially t h r Litter. without baking. This procedure ensures that any lithium fluoride formed REAGENTS initially is converted to the sulfate. Dilute the cooled residue with about 30 STANDARDLITIIIUMFLUORIDE. Reml. of water by replacing it on the sand crystallize rcagent grade lithium fluoride bath and adding water as necessary to maintain the volume for about an hour. Transfer the solution to a 250-ml. Present address, Basic Atomics, Inc., Erlenmeyer flask, bring to a boil, New York, N. Y. 18 18
ANALYTICAL CHEMISTRY
remove from the hot plate, and treat with solid calcium carbonate to the methyl red end point; add 10 drops of 3y0hydrogen prroxide and, if necessary, more calcium carbonate. Then boil carcfully to expel carbon dioxide. I n thr CNSC of a liquid sample, pipet an aliquot containing 1 to 5 mg. of lithium into a 200 ml. volumetric flask, dilute to about 75 ml. with water, and treat with solid calcium carbonate to the methyl red end point; add 10 drops of 3% hydrogen peroxide and, if necessary, morr calcium carbonate. Fill the flask with 11 ater and shake well. DETERMINATION
Following the prcttreatment of solids or liquors, filter the solution on 11-cm. filter paper, Uliat,man No. 42. Collect the filtrate derivrd from a solid samplo in a volumetric flask to give a lithium concentration in the range 0.005 to 0.050 gram pw litrr, then wash thv fla,sk and prccipitatr, :idding tht' washings to the filtratc. Collect t h r filtrate derived from a liquid sample in a 100-ml. volumetric, flask and transfer to another volumetric flask to give lithium within thr samc' rangr. To the filtrate in the volumetric flask, add 10% of the total volume of buffer solution, dilute to the mark with demineralized water, and mix well. Pour thr solutions and one or more appropriate standards into 5-ml. beakers (Beckman 914) and allow them to stand for 20 minutes to equalize temperatures. Set up the flame photometcxr and run the unknowns. CALIBRATION A N D STANDARDIZATION
This procedure gives accurate and stable standards and eliminates the necessity of reproducing the standard curve or correcting for other variables. Weigh out exactly 0.3736 gram of
lithium fluoride into a platinum dish, moisten the salt with water, add 15 drops of sulfuric acid, and slowly evaporate to dryness on a sand bath. After cooling the sample, moisten it with water, add 10 drops of sulfuric acid, and evaporate down to strong fumes. Cool the sample again, add about 30 ml. of water, and maintain this volume for about 1hour on the hotplat,e; then transfer the solution t.o a 1-liter volumetric flask and dilute to volume to yield a stock solution containing 0.100 gram per liter of lithium. Various fractions of this solution, as shown in Table I, make a suitable series of concentrations for the compilation of a calibration curve. These standard solutions should be stored in polyethylene bottles and refrigerated to prevent spoilage. T o avoid errors in converting lithium assays to the basis of concentrated solutions, results were reported in terms of grams per liter rather than the conventional units of parti? per million. Set up the spectrophotometer as follows:, wave length 671 mp, selector switch 0.1, slit 0.1 mm., sensitivity 5 turns clockwise. Introduce thc 0.050 gram per liter standard and regulate the slit width to give a transmittance reading of about 90%, then nianipulate the wave length to either side of G71 mp to give maximum transmittance. Introduce the remaining standards in series and note the percentage light transmittance of each one. Plot a standard curve 011 two-cycle log-log paper. T o standardize thc instrument and read unknowns, set up the instrument as for calibration, introduce an appropriate standard, set the transmittance to agree with the curve, and adjust the slit width to zero the needlr. Introduce a bracketing standard and check the transmittance for coincidence with the curve. Thrn read th(s unknon.ns. EXPERIMENTAL
I n the investigation of precipitation of possible interfering elements, samples of spodumene ground to -270 mesh were given the hot plate treatment and then treated with several precipitants t o the methyl red end point and to the phenolphthalein end point. Both the precipitant used and the final p H of the solution influenced the lithium reporting, as shown in Table 11. The filter cakes were treated as solid
samples and assayed for lithiurn. Table 111 shows that the discrepancies in Table I1 are accounted for by lithium oxide values reported in the cakes, with the exception of sample B, which still shows 3.6% of the lithium oxide unaccounted for. Tables I1 and 111 show no loss of lithium using calcium carbonate as the precipitant when taken to the methyl red end point. Kallmann (6) also iound occlusion of lithium when using calciurn hydroxide as a precipitant, presumably because of the nature of the precipitant and the final high pH. Qualitative tests showed that an excess of calcium carbonate does not takc the p H appreciably beyond the methyl red end point. Unlike basic lead carbonate, which s h o w variations betwren brands ( 5 ) , calcium carhonat,e givcs consistent results. Additions of sodiuni, potassium, and magnesium up to 20 timcs the lithium content had no nieasurablc effect on the intensity of the lithium tmission. The effects of largcr aniounts were not studied. This is in agrecmcnt with Brumbaugh and Fanus (3)and Williams and A d a m (7’). Ellestad and Horstman ( 5 ) also report no iiitcrference from magnesium h i t claim interfrrcncc from sodium and potassium. Investigation of the effect of pH on the intensity of the lithiiim reading showed a constant maximum in the pH range 1.5 to 3.0. 1:se of the citrate buffer ensures that all samples will fall within this range, whirti is in acccird with Clemmons ( 4 ) . PRECISION A N D ACCURACY
Two samples of a-spoduiiieiie and one sample of partially leached a-spodumene were subjected to replicate assays by the flame photometer method described yielding 3.18 0.01% 3.50 0.02%, and 0.800 f 0.004’%b,lithium oxide, respectively. The precision of the mrthod is f 0.45%. One sample of a-spodumene arid one sample of partially leached a-spodumene were submitted to a n independent laboratory for analysis. These samp!es were analyzed by the described method, yielding 3.61 and 0.800y0 lithium oxide, respectively. The corresponding independent analyses were 3.64 and 0.800% lithium oxide.
*
*
I . Preparation of Standards Buffei solution 50 ml., fin51 volume 500
Table
ml. dtock Solution, MI.
Lithium, Grams/Liter 0.050
350 200 150
0,040 0 030 0 035 0.020 0 015 0 010 0 005
125 100
75 50 25 Table II.
A A C D E
Precipitation Treatments
Lead carbonate M 3.41 Lead carbonate €’ 3.05 Calcium carbonate RI 3.61 Calcium carbonate I-’ 1.95 BasicleadcarbonM 3 47 ate hI = methyl red, P = phcnolphtha-
lein. Table 111.
Precipitation Cake Recoveries
yo Li20 xtmpk
Cake
Total;
-4 B
0.20 0.43 0 1.66 0.13
3.61 3.48 3.61 3.61 3 fin
c
I)
E Treatmcnt. plus cake.
ACKNOWLEDGMENT
‘ltie authors are indebted to thc managements of Basic Atomics, Inc., and Arthur D. Little, Inc., for p i ’ t ~ i i i k sion to publish this work. LITERATURE CITED
(1) Beer, H. L., Precambrian 24, 8 (1951 I . (2) Benson, V. M., ANAL. CHEM.26, 1855 (1954). (3) Brumbaugh, R. J., Fanus, W. E., Ibid., 26,463 (1954). (4) Clemmons, B. H., Bur. hlines, Tus-
caloosa, Ala., private communication, January 1959. ( 5 ) Ellestad: R. B., Horstman, E. I.., ANAL.CHEM.27,1229 (1955). (6) Kallmann, S., IND. ENG. CHEM., ANAL.ED. 16, 712 (1944). (7) Williams, P. E’., Adams, P. B., J . A Cerarn. SOC.37, 306 (1954).
RECEIVED for review December 22, 1958. Accepted August 14, 1959.
VOL. 31, NO. 1 1 , NOVEMBER 1959
a
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