ANALYTICAL CHEMISTRY
1474 are made with 99% ethyl alcohol prior to ultraviolet measuremmts. Details of the procedure are given by Mitchell et d. ( 6 7 ) and should be followed with scrupulous care. Dilutions required for the method are such as to give absorbances of 0.2 to 0.8 (Equation 1) corresponding to transmittance of 65 to 16%. Thp concentration of acids is then of the order of 0.25 to 1.5 grams per 1000 ml., depending on the diene content. Set the spectrophotometer to give readings at 2300 A. and 2680 A. Determine either per cent transmittance 100 X I/Io, or absorbance. By Equation 1 calculate k 2 3 3 0 and k*e*o. Substitute b values in Equations 5 and 6 and calculate linoleic and linolenic percentages. Determine iodine number on original acid mixture and calculate oleic miti content from Equation 7 . CONCLUSIONS
Thi, proposed system of characterization summarizes anti codifies information on organic acids (Order I ) for easy identification. Four main classes of acids have been established within which the gathering of a minimum of quantitative data leads to identification of individual members. The “drying oil acids” because of their great practical importance received special treatment. Their identification as single acids or in mixtures generally requires tests for quantitative unsaturation, isomerization, and ultraviolet absorption. The system provides an improved and simplified process for identifying of unknown compounds which has general application because so many types of compounds are convertible t o acids. ACKNOWLEDGMENT
The authors wish t o thank Richard King for purification and determination of the values for a-licanic acid used in this studv. LITERATURE CITED
(1) .Im. Oil Chemists’ SOC.,“Official and Tentative Methods,”
rev. ed., Methods KA-951 and CD-125. 1952. (2) Brice. B. -4.. Swain, M. L., Herb, S. F., Xichols, P. L.. Jr., and Riemenschneider, R. W., J . Am. Oil Chemists’ Soc., 29, 279 (1952). (3) Dorinson. A , , McCorkle, AI., and Ralston. A. W., J . Am. Chem. Soc., 64, 2739 (1942). (4) Doss, 11. P., “Properties of the Principal Fats, Fatty Oils, Waxes, Fatty Acids and Their Salts,” New York, Texas Co., 1952. (5) Earle, F. R.. and hlilner, R. T.. Oil arid Soup, 17, 106 (1940). (6) Ellis, B. A. Analyst, 61, 812-16 (1936). (7) Huntress, E. H., and hlulliken, S. P., “Identification of Pure Organic Compounds,” p. 91, 179-85, Xew York, John Wiley 8: Sons. 1941.
(8) Jackson, J. E., Paschke, R. F., Tolberg, W., Boyd, H. AT., and Wheeler, D. H., J . Am. Oil Chemists’ Soc., 29, 229 (1952). (9) Kamm, O., “Qualitative Organic Analysis,” 2nd ed., New York, John Wiley & Sons, 1931. (10) Kass, J. P., and Burr, G. O., J . Am. Chem. Soc., 61, 1062 (1939). (11) Kass. J. P., Kichols, J., and Burr, G. O., Ibid., 63, 1060 (1941). (12) Kass. J. P., and Radlove, S. R., Zbid..64, 2253 (1942). (13) Kaufmann, H. P., Baltes, J., and Buter, H., Der., 70, 903 (1937). (14) Kirk, R. E., and Othmer, D. F., “Encyclopedia of Chemical Technology,” Vol. 6, pp. 269-83, Sew York, Interscience Publishers, 1951. (15) Kuhn. R., Ber., 69, 1764 (1936). (16) RIacKay, A. F., and Bader, A. R., J . Org. Chem., 13, 77 (1948). (17) BIarkley, K. S.,“Chemical and Physical Properties of the Fatty Acids,” pp. 605-6, Kew York, lriterscience Publishers, 1947. (18) Matthem, K. L., Brode, W. R., and Brown, J . B., J . Am. Chem. SOC.,63, 1064 (1941). (19) AIattiello, J. J.. “Protective and Decorative Coatings.” Vol. I V , New York, John Wiley & Sons, 1944. (20) LlcCutcheon. J. W., Org. Syntheses, 22, 76 (1942). (21) Nikusch, J. D. v., Angew. Chem., 62, 475-80 (1950). (22) AIikusch, J. D. v., Fette u. Seifen, 54, 751 (1952). (23) hIikusch, J. D. v., J . Am. Oil Chemists’ SOC.,28, 133 (1951). (24) Zbid.,29, 114 (1952). (25) i\Iikusch. J. D. v.. and Frazier. Charles. IND.ENG.CSEM.. ANAL.ED., 13, 782 (1941). (26) Ibzd., 15, 109 (1943). (27) Mitchell, J. H., Kraybill, H. R., and Zscheile, F. P.. Ibid., 15, 1-3 (1943). (28) lIorrel1, R. S.,and Davis, W. R., J . Chem. Soc., 1936, 1481. (29) Kichols, P. L., Herb, 8. F., Riemenschneider, R. W..et al., J . Am. Chem. Soc., 73, 247 (1951). (30) Nunn. L. C., and Smedley-Maclean. I., Biochem. J., 32, 1974 (1938). , (31) O’Connor, R. T., and Heinselman, D. C., J . d m . Oil Chemists’ Soc., 24, 212 (1947). (32) Paschke, R. F., Tolberg, W.,and Wheeler, D. H.. I b i d . , 30,97 (1953). (33) Riemenschneider, R. W., Wheeler, D. H.. and Sando, C. E., J . Bl’ol. Chem., 127, 391 (1938). (34) Shriner. R. L., and Fuson, R. C., “Systematic Identification of Organic Compounds.” 3rd ed., p. 146, New York, John Wiley 8: Sons, 1948. (35) Strain, H. H., J . Am. Chem. Soc., 63, 3448 (1941). (36) Wendland, Ray, J . Chem. Educ., 23, 3 (1946). (37) White, LIary, and Brown, J., ,J. Am. Oil Chemists’ Soc., 26, 385 (1949). (38) Ibid.,29, 292 (1952). ~I
>-
RECEIVED for review March
1 , 1954. Accepted Jnne 21, 1954. Journal Series, General Mills Research Laboratories.
Paper 180
Fire Assay for Palladium 1. G. FRASER and F. E. BEAMISH, University o f Toronto, Toronto, Ontario, Can. This investigation was carried out to determine the distribution and losses of palladium in the various phases of a fire assay. Of five platinum metals, palladium is the least subject to loss in the slag. While the losses are small, they are in practice irrecoverable by reassay. This work forms part of a systematic investigation of the efficiency of collection by lead. It was undertaken because the fire assay is the only method generally applied to ores and concentrates and hitherto no data have been recorded to indicate the accuracy of the method.
F
OR many years the analysis of ores for the platinum metals has been carried out by fire assay procedures. The literature reveals little justification for this method except by analogy to the success obtained R-ith gold and silver. I n recent years serious doubts have arisen concerning the collection of rhodium, ruthenium, osmium, and iridium by lead (1-3, 5 ) . With these
metals losses to the slag were significant even in the idealized case where no base metals were present. These losses were shown to vary according to the nature of the slag. Base metals when present in the slag caused high iridium losses (30 to 50%). This n a s about ten times the loss of any of the other metals thus far investigated. The literature ( 1 ) reveals one experiment where osmium was fused with a basic flux without collection by lead. Only of the osmium could be recovered from this slag with three reassays. I n a similar esperiment with iridium ( 3 ) only 75y0of the iridium was recovered. The cupellation of osmium was shown to be useless as nearly complete volatilization of osmium occurred ( 1 ), With ruthenium the loss by volatilization n a s negligible but a 10% loss occurred t o the cupel ( 5 ) . It has been shown ( 3 ) that iridium was lost mechanically during the cupellation because of the formation of black scales on the surface of the bead. I n the present paper the authors present data on the collection of palladium by lead from various fluxes, and compare the losses
V O L U M E 2 6 , NO. 9, S E P T E M B E R 1 9 5 4
1475
caused by various base metals. After fusing the various fluxes
Table I.
with palladium, the recovery by assaying the slags is noted. D a t a are presented on the c u p e 11a t i o n of palladiumcontaining lead buttons.
Flux
Composition of Fluxes
SiOz,
NazBiOr,
CEO,
W t . Taken
NazCOg,
PbO,
KNOs, per Assaye % G.
Type of Flux 7% % % % % 1 Glazing flux 20.0 7.5 5.0 27.5 40.0 .. 35 2 Very acid (medium viscosity) 25.7 5.4 6.7 62.6 .. 80 70 27:2 28.5 .. 3 Very acid (low viscosity) 14.3 30.0 4 Basic 11.5 1.8 2.7 20.3 63.7 ,. 113 5 Seutral 26.8 6.1 42.7 24.4 .. 80 6 Neutral 1514 7.7 6.4 44.9 25.6 78 7 OsidiBing (niter assay) 4.0 2.6 ,. 16.9 58.8 l7:7 1336 220 8 Basic (extra litharge) 3.5 4.6 ,. 7.1 84.8 .. 9 Cupel assay flux .. 14.9 .. 28.4 56.7 .. 140 a Enough litharge and flour were mixed with t h e flux t o produce a 25-gram button before salting. b This flux was mixed with ‘/z assay ton of pyritic ore (reducing power = 6.9) and 28 grams of litharge before NO.
EXPERIMENTAL
Method of Salting Fluxes. A standard palladium solution was used to salt the fluxes. The preparation and standardization of this solution have already been described (4).An 8-inch square of cellophane was placed inside a glazed 20-gram pot. Approximately SO% of the required flux was mixed with sufficient flour and litharge to yield a 25-gram button. This charge was placed in the cellophane liner and the standard solution was added to a depression made in the center of the charge. The pot and charge were dried in an oven a t 110” C. for 4 hours. The dried charge was dumped into a large mortar and ground. The cellophane liner was tamped into the bottomof the crucible and covered with the ground charge. The mortar was “washed” with the remaining 20% of the flus which was added as a cover t o the main charge. TVith certain fluxes and larger volumes of standard solution the salted flux formed a hard cake on drying. Because this cake was practically uniform in composition it was not ground but simply covered with the final 20% of the flux. I n the experiments involving prefusion of the palladium and flux, 80% of the flux was placed in a glazed pot without the cellophane liner, extra litharge, or flour. The palladium solution was added and the pot and contents were dried as before. Fire Assay Procedure. The assays were carried out in a Williams and Wilson 15 KVA Globar-type furnace which was pyrometrically controlled. Usually all the samples of a particular flux were placed in the furnace a t one time a t a temperature of 815’ C. The temperature was raised t o 1200° C . as quickly as possible (approximately 2 hours) and the mixtures were poured into conical steel molds. When cool the buttons were separated from the slag, which was ground to pass a S o . 45 standard sieve. This was mixed by rolling on a cellophane square with litharge to replace that lost t o the first button and sufficient flour to form a second button of 25 grams. This charge was assayed in the original pot. The “prefused” samples were fused, poured, and ground as before. In addition the grinder was washed by grinding in it a n amount of unsalted, fused flux equal to the weight of the sample. This wash was added t o the main charge in the same pot used for the fusion. Composition of Fluxes. The composition of the fluxes used in this research are recorded in Table I. Fluxes 1 t o 6 are identical to those used by Allan and Beamish (1). Analysis of Lead-Palladium Buttons. The procedure followed
for the analysis of the lead-palladium buttons has been recorded earlier (4). Buttons containing 1 mg. or less were analyzed colorimetrically and those with 5 mg. were done gravimetrically. When the lead button was dissolved in nitric acid a certain amount of adhering slag remained undissolved. I n the case of the 5-mg. samples this was filtered off on a Whatman No. 42 paper. The filter and residue were added to the ground slag as part of the charge for reassay and counted with the palladium found in the second button. On evaporation of the nitric acid solution a silica residue was obtained which would not dissolve in the dilute nitric acid solution from which the palladium was to be precipitated. This residue was filtered through a second No. 42 paper and assayed by itself using flux No. 6 . The amount of palladium from this assay was added to the gravimetric result to give the true palladium content of the first button. The experimental data obtained are shown in Tables 11,111,IV, VI, and VII. DISCUSSION
From Tables I1 and I11 it is apparent t h a t no one flux is preferable for the over-all recovery of palladium. There is a distinction, however, in the recovery made in the first button and the number of reassays required to give adequate collection. I n Table I1 it can be seen that only acid fluxes cause any appreciable quantity of palladium to come down in the third button. With acid flux No. 2 considerable palladium remained even in the fourth button. Similarly, Table I11 shows that with samples of less than 1 mg., flux No. 2 is the only one in which virtually complete collection is not obtained in the first button. An attempt to locate the unrecovered palladium by spectrcgraphing the ground slag was unsuccessful. I n fact a spectrogram of a slag obtained by fusing flus No. 2 with 10 mg. of palladium showed no palladium lines, although there was evidence that the palladium was distributed uniformly throughout the slag.
Table 11. Distribution of Palladium in Fire Assay (5.00 M g~. . palladium taken) Palladium Found. M g ,
Button Weights, G. Assay No. 91 92 93 72 73 74 54 55 56 63 64
65 48 49 50
Flus Acid Ac/d Acid Acid Acid Acid Basic Basic Basic Seutral h-eutral h-eutral h-eutral h-eutral Seutral
Flus KO. 2 2 2 3 3 3 4
4
4 0
5 5 6 6
6
1st 27 28 27 20 17 20 25 22 23 24 24 20 26 27 26
2nd 17 16 19 23 21 22 22 21 21 22 23 23 20 18 18
3rd 22 27 25 20 18 20 17 14 17 21 20 20 19 20 20
4th 23 21 22
.. ..
.. .. .. .. ..
.. .. ., ,.
Si02 residue 24 22 27 21 21 21 14 15 18 19 16 19 24 22 23
Total
Pd
covered, hlg. 4.90 4.89 4.91 4.92 4.96 4.72 4.77 4,89 4.92 4.94 4.89 4.99 4.90 4.84 4.50
covered, hfg. 0.10 0.11 0.09 0.08 0.04 0.28 0.23 0.11 0.08 0.06 0.11 0.01 0.10 0.16 0.50
4.85 4.91 4.99
0.15 0.09 0.01
1 In In P d ReUnrein 1st button 4.415 4.441 4.418 4.774 4.809 4.550” 4.436 4.597 4.532 4.880 4.804 4.881 4.747 4,749 4.334Q
88 Oxidizing 7 28 25 27 21 4.654 26 26 26 27 4.663 89 Oxidizing 7 90 Oxidizing 7 27 25 27 .. 25 4.727 These numbers were omitted from t h e averages shown in Table V.
SiOp residue 0.025 0,090 0.065 0.060 0.045 0.046 0.038 0.041 0.032 0.048 0.036 0.064 0.017 0.009 0,000
in 1st button 4.440 4.531 4.483 4.834 4.854 4.596 4.474 4.638 4.564 4.928 4.820 4.945 4.764 4,758 4.334
2nd button 0.306 0.203 0.301 0.063 0.069 0.080 0,298 0.245 0.360 0.012 0.048 0.038 0.125 0.088 0.156
3rd button 0.130 0,107 0.090 0,027 0.041 0.040 0.002 0 009 0.000 0.002 0.000 0.004 0.014 0,003 0.007
0.066
4.720 4.730 4.791
0,124 0.165 0.190
0.003
0.067 0.064
0.010 0.009
4th button 0.026 0.052 0.036
.
.. .,, ... , . , ... ...
..
... ...
.. .. .. ...
A N A L Y T I C A L CHEMISTRY
1476
with the palladium. The o u b standing exception to this ob(Samples of 1 mg. and under) servation was the neutral flux S o . 5 , These data explain DifferP d Found, y Total P d Pd ence, Taken, Assay Flux Button W t . , G Recovered the need for several reassays So. Flux So. 1st 2nd 3rd button button button Y Y ? n i t h certain fluxes while one - 1 99 100 65 21 13 22 12 94 Acid 2 23 250 - 48 2020 151 34 17 10 12 95 Acid 2 22 r e a s s a v i s sufficient v,-ith - 13 487 500 439 31 17 2 27 23 21 96 Acid others 1000 - 7 21 20 953 19 21 593 97 Acid 2 24 The best flux found con100 - 8 2 .. 52 3 21 28 .. 90 75 Acid - 9 250 28 .. 240 1 .. 241 3 21 76 Acid tained no silica, however, in 500 2 .. 502 3 25 28 .. 500 1 2 77 Acid normal assaying, the absence 5 .. 105 100 4 27 15 .. 100 + 5 57 Basic 0 250 3 .. 250 4 27 20 .. 247 58 Basic of silica in the sample would 500 20 ,, 505 13 518 59 Basic 4 27 18 rarely be encountered. The 100 21 , , 103 2 105 66 Neutral 5 2; + 5 2 232 - 18 260 5 26 19 .. 230 67 Neutral assay would be further com500 18 .. 497 8 .. 505 5 24 68 Neutral + 5 plicated bv the base metals 100 23 ., 100 3 103 6 23 30 Seutral + 3 - 6 250 2 .. 244 which are almost invariably in6 25 22 .. 242 31 Neutral -11 12 .. 485 500 6 25 22 .. 477 32 Neutral cluded in the sample. A high 9 8 100 2 15 . . 96 2 84 Oxidizing 7 23 - 5 proportion of litharge in the 245 250 18 ,, 238 7 85 Oxidizing 7 27 500 514 20 , . 511 3 86 Oxidizing 7 22 flux is required to slag off these 1014 1000 +~ 141 4 7 22 20 ,. 1012 2 87 Oxidizing base metals I n order to comThis number was omitted from the averages shown in Table V pare the effects of the various base metals flux S o . 8 was Table IV. Distribution of Prefused Palladium Samples in Fire Assay prepared. This flux was rich Total P d Found, y P d RePd Differin litharge and contained only Assay Button W t . , G I n 1st I n 2nd I n 3rd I n 4th covered, Taken, ence, the silica equivalent to oneSo. Flux No. 1st 2nd 3rd 4th button button button button y ? Y half an assay ton of ore that 9 8 Acid 2 25 23 20 19 48 66 39 26 179 250 71 55 330 400 70 99 Acid 2 24 25 21 20 64 109 82 c o n t a i n e d 50% silica. The .. 93 43 .. 500 , . . 100 Acid 2 23 27 27 22 94 amount of base metal oxide 101 Bcid 2 25 26 21 18 215 332 192 80 819 1000 181 7 2 224 22 19 178 37 250 26 3 27 20 78 Acid shown in Table VI was added 19 256 37 8 4 305 15 22 400 95 Acid 3 28 79 to this flux before mixing and 19 284 90 14 2 19 21 390 500 110 Acid 3 27 80 10 1 15 8 .. 217 salting. Because this flux was 4 18 228 250 22 Basic 60 334 16 5 18 15 ., 355 400 45 Basic 4 23 61 extremely corrosive, the pots 375 30 6 411 500 89 4 25 19 15 ., Basic 62 were placed in the furnace a t 39 14 20 21 ., 205 5 23 258 250 - 8 69 Xeutral 21 .. 361 41 14 22 5 23 416 400 - 16 70 Seutral 925" C. and removed a t 22 ., 400 43 18 461 19 500 39 Seutral 5 23 71 1150' C. instead of the 815" 3 8 11 23 163 23 2 214 6 23 24 250 36 23 Keutral 77 234 22 6 339 23 23 23 Neutral 6 22 400 61 24 and 1200" C., respectively, 251 136 36 23 23 8 431 23 500 65 Neutral 6 23 25 normally used. This almoet halved the time the charge was in the furnace and lessened For comparison, Table V is presented inwhich the results for any the danger of the charge "eating" through the pot walls. The results indicate that this flux allows good collection with iron one flux are averaged in three groups: 5-mg. samples; samples and copper. Nickel, however, causes a large loss to the slag. less than 1 mg.; and prefused samples. Per cent recovery is given for the first and second buttons separately and for the over-all recovery. For the purpose of comparison similar percentages were calculated for the other platinum metals investiTable V. Comparison of Average Per Cent Recovery and Flux Type gated earlier (1-3, 5). There is no general agreement in these Flux no. 2 3 4 5 6 papers as to what should be termed a neutral flux; ( 3 ) and (6) 2.4 2.5 0.8 1.0 1.0 Silicate degree (S.D.) conform to the chemist's viewpoint. I n the others and in this Assays on 5-mg. lstbutton 89.7 9 6 . 8 91.2 98.1 95.2 samples of P d 5.4 1.3 2nd button 6.0 0.7 2.1 paper the convention based on the silicate degree is folloxved. Totalrecovery 98,O 9 8 . 8 9 7 . 2 9 8 . 8 9 7 . 4 (The silicate degree is expressed as the ratio of acid oxygen to Assays on less than 1- 1st button 82.7 9 5 . 4 99.9 98.1 9 7 . 4 basic oxygen-e.g., the silicate degree of 2 i\lo.SiOz = 1.0,) Al1.5 2.1 mg. samples of P d 2nd button 5.7 0.9 2.9 Total recovery 98 6 5 6 . 3 1 02.8 99.6 99.5 though this is mainly a question of definition it is mentioned here Assays on prefused 1st button 18.9 6 4 . 0 81.8 84.1 58.0 to prevent the reader from making erroneous comparisons. samples of P d 2ndbutton 25.0 14.0 4 . 7 11.5 20.5 Total recovery 7 8 . 7 8 1 . 3 87.4 99.8 85.5 The recovery from acid flux No. 3 was superior to that from Assays on osmium lstbutton 81.0 5 5 . 1 93.7 98.1 96.9 acid flux S o . 2. Similarly, neutral flux No. 5 was superior to 0.4 0.2 samplesa 2ndbutton 7,4 0.4 0.3 neutral flux KO.6. This was true for osmium as well as pallaTotalrecovery 9 5 . 4 9 5 , 8 9 4 . 3 9 8 . 6 9 7 . 5 dium. These fluxes differed in two main respects, viscosity and Assays on iridium S.D. 2.6 1.8 0.6 1.0 .. saniplesb lstbutton 86.4 9 2 . 2 89.2 silica content. Since the viscosity increases Kith the silica con8.1 6.0 4.3} 86'4 :: 2nd button 93.6 86.4 .. Total recovery 9 8 . 1 9 9 . 5 tent it would seem logical to avoid an excess of silica in assaying 1.6 0.6 .. .. 2.6 Assays on ruthenium S.D. for either palladium or osmium. X similar situation prevailed 93.2 .. .. 94.5 90.5 samplesC 1st buttond with iridium. Slightly less iridium was recovered from the more Assays on rhodium S.D. 1.5 .. ,. .. .. acid flux viith 28% silica than from the flux with 21 % silica. The samples6 1st button 96.6 .. .. .. .. 2nd button 1 . 7 . . . . . . .. reverse appeared to be true for ruthenium but on the basis of the Total recovery 9 8 . 3 .. ,, .. .. single result given for the more acid flux no definite conclusion can a These numbers were calculated from data taken from ( 1 ) . b Calculated from data taken from ( 3 ) . be drawn. I n the ruthenium paper (5) the authors rejected a Calculated from d a t a taken from (6). second result (Sample 732, Table IV) which had a much poorer d These numbers were obtained indirectly b y subtracting t h e per qent ruthenium found i n the slag which was determined by means of a Geiger collection than the one given. counter and radioactive ruthenium. 6 Calculated from d a t a taken from (I) Tables IV and V demonstrate the general reluctance of all fluxes to permit complete recovery after the flux has been fused Table 111.
Distribution of Palladium in Fire Assay
+
~
C
1477
V O L U M E 2 6 , N O . 9, S E P T E M B E R 1 9 5 4 Table VI.
Table VIII.
Effect of Base 5Ietals on Recovery
Cupellation of Lead-Palladium Buttons
Palladium Found, y I-. c
Av. TCrecoT-erg 1 0 2 . 5
99 4
98 6
69.6
11.8
Bead Size P d Taken, y
1.4
(25-gram lead button) 75 Mg. 150 M g . 150 Mg. P d in P d in P d in Bead, y Bead, y Cupel, y
250 I l g . 250 Ilg. Pd in P d in Bead, y Cupel, y
82.8
Prefusrd Samples 250 li5 104 181 162 25 6 193 500 323 280 304 364 43 11 418 724 84 17 825 1000 579 581 629 A v . % recovery 6 4 . 3 51.9d 6 5 . 8 70.0 9.0 2.1 81.1 a Flux prepared by adding 7.5 grams Fez03 t o 220 grams of Flux N o . 8. b Flux prepared by adding 7.5 grams CuO t o 220 grams of Flux So. 8. c Flux prepared by adding 3.7 grams X i 0 t o 220 grams of Flux h o . 8. d All figures are collections in a single assay only with average button size of 32 grams. Since arerage size of b u t t o n from prefused iron samples was only 12 grams (with per cent recovery of 40.41, the figure given is sun1 of recoveries from first assa5- and reassay.
Table VII.
25 M g . P d in Bead, y
Collection by Lead through Interfacial Diffusion
(1000 y of palladium taken) Palladium Founda, y Flux S o Sorrnal flux Prefused flux .? 5 54 ._ 535 201 261 702 490 149 164 583 346 F76 a I n these assays 25 grams of lead were placed in bottom of pot and salted flux placed above lead. T h e fusions were made in regular manner.
Surprisingly, prefusion of the nickel-containing flux did not increase the loss to the slag. Two reassays of the slag failed to recover more than 83% of the palladium. This large interference by nickel was also reported for iridium and to a lesser extent for rhodium. Prefusion with and without iron and copper resulted in a much lo^ er recovery than in the normal assays. As palladium is often encountered in sulfide ores the results of assays with flux S o . 7 are significant. Almost complete recovery \\ as obtained with only one reassay using this flux and onehalf assay ton of a pyritic ore. The recovery of rhodium using this type of flux was complete. The recovery of osmium was slightly less than that obtained with palladium. On the other hand, ruthenium showed an 18% loss to the slag while iridium showed an even greater loss The results of collection by lead through interfacial diffusion are presented in Table 1-11. Generally, the collection of precious metal is effected as the lead falls through the molten flux after the litharge has been reduced. I n this experiment this fall of lead was avoided by placing the lead in the bottom of the pot and covering it with the flux. Thus, the only means of collection is by diffusion of the palladium through the molten flux t o the lead surface. Since in most cases well over 50y0of the palladium was collected, the need for a fluid flux was clearly demonstrated. However, if viscosity n-ere the only governing factor, then the recovery from the prefused samples in these experiments should have also been over 50%. One possible difference in the prefused case is the lack of stirring caused by the escaping carbon dioxide during the fusion. CLPELLATIOA OF LEAD-PALLADIUM BUTTONS
Because serious losses occur with other platinum metals during cupellation, a careful examination of the losses with palladium was therefore undertaken. Preparation of Lead Buttons. A 5 X 5 inch square of lead foil was folded into a cup-shaped container. Standard palladium and silver solutions were added t o the lead container and evaporated to drvness in a steam cabinet. The lead container Jvas carefully folded into a ball and wrapped with a second piece of lead foil ( 2 X 4 inches). The resulting weight of the lead was 25 grams. The lead was placed in the bottom of a glazed pot, covered with 80 grams of neutral flux X o . 5 , fused, and poured as in a
regular assay. This method of preparing buttons was checked by making four buttons Fhich contained only palladium and no silver. Complete recovery of the palladium was possible as indicated by the regular colorimetric procedure for analyzing the lead buttons. Procedure. The lead buttons were placed on reheated, bone ash cupels and cupelled a t a temperature of 980” The cupellation usually lasted about 30 minutes. The beads obtained often had bits of cupel adhering t o the base but no at,tempt was made to clean them. They were dissolved in 10 ml. of 1 to 2 nitric acid and the solution was evaporated to dryness. Care was taken t o avoid cont’act with hydrochloric acid fumes as this precipitated silver chloride which occluded or adsorbed palladium. The evaporated residue was dissolved in water containing 5 drops of nitric acid. After the addition of dimet~hylglyoximethe palladium was extracted and determined colorimetrically in the manner described earlier ( 4 ) . Beads containing no palladium were made in the same manner for use in preparing the colorimetric standards. A new standard solution had t o be prepared by dissolving palladium in nitric acid. This was checked colorimetrically against the old standard solution prepared with aqua regia. Flux No. 9 was found satisfactory for the assay of the used cupels in order to determine any palladium lost to the cupels during the cupellat,ion of the buttons. Only that’ part of the cupels stained by t’he litharge was used in this assay. The white part of the cupel was scraped off with a knife and discarded. The remainder was ground in a mortar and mixed with the flux and flour. This procedure was checked by preparing four silver-free lead buttons containing 10, 30, 50, and 100 micrograms ( y ) of palladium, respectively. These were cupelled in the regular manner and the cupels assayed as described above. The palladium found was 5 , 31, 50, and 105 y, respectively.
8.
Discussion. The results given in Table VI11 indicate that no significant loss occurred during cupellation. This is shown both by the palladium recovery and by the small amount of palladium found in any of the cupels assayed. This is not surprising in view of the fact that palladium alloys readily with both lead and silver. CO~CLUSIONS
The distribution of palladium during the fire assay has been examined. Palladium has been shown to be one of the “bestbehaved” of all the platinum metals thus far investigated in this laboratory. I n all but acid fluxes nearly complete recovery was obtained with only one reassay of the slag. For samples rich in palladium the monoborate flux was the most desirable in all respects. For regular ores the basic flux with excess litharge is necessary to flux the base metals. Collection was good in all cases except where the slags contained considerable nickel. Unlike the other platinum metals cupellation losses wit,h palladium were not significant. ACKNOWLEDGMENT
The authors are grateful for the Canadian Industries Limited Fellowship held by J. G. Fraser while this research was being conducted. LITERATURE CITED
(1) Allan. W. J., and Beamish, F. E., ANAL.CHEM.,24, 1569 (1952). (2) Allen, W.F., and Beamish, F. E., I b i d . , 22, 451 (1950). (3) Barefoot, R. R., and Beamish, F. E., Ibid., 24, 840 (1952). (4) Fraser, J. G., Beamish, F. E., and McBryde, W. 8.E., Ibid., 26, 495 (1954). (5) Thiers, R., Graydon, (1948).
RECEIVED for review January
W.,and Beamish, F. E., I b i d . , 20, 11. 1954.
Accepted LMay 12, 1954.
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