New Fire Assay for Osmium and Ruthenium J.
M. KAVANAGH and F. E.
BEAMlSH
University o f Toronto, Toronto, Ontario, Canada
b This research is part of a general investigation of a new fire assay procedure for the platinum metals. The procedure was successfully applied to a roasted concentrate from a natural ore, salted with milligram amounts of osmium and ruthenium. Losses to slags and pot walls were negligible. The effect of the remaining platinum metals upon the recovery of osmium and ruthenium is recorded.
A
FIRE ASSAY procedure, involving the collection of precious metals from ores and concentrates in an iron-nickel copper button, was recently found to be succemful for platinum and palladium (6). The present investigation was carried out to determine its applicability to osmium and ruthenium. Allan and Beamish (1) and Thiers, Graydon, and Beamish (7) investigated the behavior of osmium and ruthenium in the classical lead fire assay. Slag and cupellation losses were found to be high and only under idealized conditions could osmium be collected quantitatively. Lead buttons containing ruthenium could not be dissolved completely by acids and the residues always required a time-consuming treatment to complete the recovery of ruthenium. In the new method the button collection is complete and the osmium and ruthenium can be quantitatively dissolved and distilled by perchloric acid in one operation.
NEW
APPARATUS, REAGENTS, AND MATERIALS
Apparatus. Pyrometrically controlled Williams and Wilson 15-km. Globar-type assay furnace. Fisher-Lindberg gas-air furnace. Pyro-optical Pyrometer, made by Pyrometer Instrument Co., Inc. Spectrophotometer. Beckman Model B distillation assembly. Reagents and Materials. Reagent grade litharge, perchloric acid, hydrobromic acid, hydrogen peroxide, sodium bromate, test lead, thiourea, and thionalide (Eastern Chemical Co., Newark, N. J.). Technical grade borax and soda ash. Roasted concentrate prepared as described by Plummer and Beamish ( 5 ) ,and assaying the same in all constituents. Fortyfive-mesh carbon prepared from Union Carbide carbon bars. Assay flux prepared by mixing 42.4 grams of soda
490
0
ANALYTICAL CHEMISTRY
ash, 27 grams of borax glass, and 9.5 grams of carbon. Thirty-gram and No. 14 assay crucibles made by A. P. Green Co., Weston, Ontario. STANDARD SOLUTIONS
Osmium. Capsules containing osmic acid supplied by Johnson, Matthey and RIallory Co. were broken under 15% caustic solution, the acid was dissolved, and the solution filtered. This solution was made up t o 1 liter with distilled water. Five-milliliter aliquots were added to 20-ml. portions of hydrobromic acid in glass-stoppered bottles. These solutions were left in a cold room overnight a t 10' C., transferred to 150ml. beakers, and evaporated to 5 ml. After filtration and dilution to 50 ml. with water, osmium was determined by thionalide (4). The solution yielded 1.064 mg. of osmium per ml. Ruthenium. A stock solution of ruthenium in 0.5N hydrobromic acid was used in all experiments. The solution yielded 0.540 mg. of ruthenium per ml. Solutions for Salting Samples. Two-, 2.99-, 5.10-, and 9.93-m1. aliquots of standard osmium solution were added to 20-ml. portions of hydrobromic acid and evaporated to 5 ml. Aliquots of standard ruthenium sohtion could be used directly for salting samples. EXPERIMENTAL
Fire Assay. Eighty grams of roasted concentrate were pulverized t o 45 mesh and mixed with 80 grams of flux. One half of this mixture was placed in a 6-inch evaporating dish lined n i t h cellophane and the salting solution added. This mixture was air-dried either a t room temperature for several days or in the steam oven a t 50" to 60" C. for 6 hours. The dried material was pulverized in a mortar and mixed thoroughly. Three to 5 grams of the unsalted portion were placed on the bottom of a 30-gram assay crucible. The salted portion contained in a plastic envelope plus the cellophane liner mas placed on this and the remainder of the unsalted charge, placed so as to enclose the salted material completely. The crucible fusion was carried out as described by Plummer and Beamish ( 5 ) . DISSOLUTION OF BUTTON AND DISTILLATION AND DETERMINATION OF OSMIUM AND RUTHENIUM
The button obtained from the crucible
fusion and weighing 25 to 33 grams was placed in the distillation flask. The trap and receiver solutions, either in the case where osmium was to be distilled separately or together with ruthenium, contained the same solutions as described by Westland and Beamish (8). The receivers for the distillation of ruthenium separately contained hydrobromic acid. Dissolution of the button and distillation were complete after boiling for 2 hours with 300 ml. of perchloric acid. The trap solution was then boiled for '/2 hour, nhile a slow stream of air was drawn through the apparatus. Rapid air passage and trap boiling caused contamination of receiver solutions by acids from the trap. The receiver solutions for the determination of either osmium or ruthenium were evaporated to 5 ml., filtered, and diluted to 50 ml. n-ith water, and the precipitation 'ilas made with thionalide (4, 6 ) . In the determination of both constituents together, the preliminary separation steps (8) were carried out and each constituent was precipitated separately by thionalide. In each case where sulfuric acid had been present during the distillation, the precipitate was coagulated for 5 hours. This acid invariably retarded the precipitation and the extended coagulation time was necessary to overcome its peptizing effect on the precipitate. The results of the button analyses are given in Table I. BUTTON BLANKS
Button blanks prepared and treated as described above were analyzed colorimetrically for osmium and ruthenium. The result showed no trace of either osmium or ruthenium. FILTRATE TESTS
Filtrates from precipitations were evaporated to 10 ml. Each filtrate was treated separately in the distillation flask. In all cases the trap contained 10 ml. of perchloric acid and the receivers 10 ml. of 10% thiourea solution in 1 to 1 water-hydrochloric acid. The filtrate from the osmium precipitation !vas boiled n ith peroxide until the evolution of bromine was completed. The receivers were replaced n-ith fresh solution and the boiling was continued in the presence of 20 ml. of sulfuric acid and 10 ml. of nitric acid. Air was then passed through the apparatus and the trap solution n-as boiled. The collected osmium was determined colorimetrically (2,8).
The ruthenium filtrate was treated with 20 ml. of sulfuric' acid and several 10-ml. additions of nitric acid. This was sufficient to remove organic material and the pot solution was now suitable for a perchloric acid treatment. Thirty milhlitcm were added and fumed for 15 minutcs. The trap \\-as boiled while a current of air was passed through the system. The collected ruthenium n as determined colorimetrically (3,8). The filtrate losses were negligible in all cases n here the coagulation periods recorded above were used in the thionalide precipitations. The results for osmium and ruthenium, either for the chemical and ignition treatments of residues or the spectrographic examinations, were negligible in all the cases investigated. The lead buttons produced in the fire assay of slags (5) were treated in the same manner as the button blanks. The results for osmium and ruthenium were negligible in all cases. In the analysis of pot walls three pots combined and crushed to '/4 inch. Eight hundred and forty grams of flux consisting of 14.3% silica, 30% borax, 27.2% of soda, and 28.5% litharge were added. Extra litharge and flour were added to produce a lead button of approximately 100 grams. The whole was mixed and fire-assayed in a large pot. The lead button produced was analyzed as described above. The results for osmium and ruthenium were negligible. R ere
EXAMINATION
OF RESIDUES FROM PARTING SOLUTIONS
Residues from button partings mere always white in appearance with the bulk of the material being mostly silica, whereas in samples 25 and 26 (Table I), which contained considerable amounts of the other platinum metals, the residues were black, indicating undissolved platinum mc tals. Residues from buttons analyzed for ruthenium were fused with sodium peroxide in a silver crucible and treated with sodium hypochlorite in the distillation flask (7). Collections were made in thiourea solutions. These solutions were analyzed colorimetrically for ruthenium (3, 8). Residues from buttons analyzed for osmium were placed in a Vycor combustion tube in a current of oxygen a t 600" C. Collections were made in thiourea bubbler solutions connected to the tube by a ground-glass joint. The solutions were analyzed colorimetrically for osmium (2, 8). Residues from buttons analyzed for both osmium and ruthenium were treated with hypochlorite in the distillation flask, and the collections were
Table
Sample NO. 1
2 3 4 5 6 7
8
9 10
I.
Button Analyses
Metal
os
os os os os os
os os os
Taken 5.32 5.32 5.32 5.32 5.32 5.32 2.13 2.13 10.56 2.13 5.40
3.18
11
12
Ru
13
Ru
14 15 16 17 18 19
5.40 3.18 2.70 3.18 2.70
...
Metal, Mg. Recovered 5.29 5.25 5.25 5.33 5.26 5.24 2.10 2.10 10.57 2.11
made in 3% peroxide solution. The separations and determinations described by Westland and Beamish (8) for small amounts of osmium and ruthenium were carried out. The residues from this treatment were then placed in the Vycor tube and the oxygen treatment described above was applied. The residues from this treatment were then fused with sodium peroxide and the hypochlorite treatment described above carried out. Finally the residues were examined spectrographically. In all cases the retention of osmium and ruthenium was negligible. SUMMARY
The new fire assay procedure for osmium and ruthenium was successful for the amounts investigated. Losses of either constituent to slags or pot walls were insignificant. I n the presence of sulfate, filtrate losses were observed in the thionalide precipitations if the coagulation periods were less than 5 hours. Milligram amounts of the remaining platinum metals did not affect the recovery and determination of osmium and ruthenium.
Mg.
-0.03 -0.07 -0.07 +O.Ol -0.06 -0.08 -0.03 -0.03
+0.01
-0.02
...
3.18 5.34 3.18 2.70 3.22 2.70 ... 2.67 5.42 5.41 5.34 5.47 5.37 8.05 8.12 8 .24a 2.79 2 . 52b 5.40
2.70 5.40 5.40 5.40 5.40 5.40 8.10 20 21 8.10 22 8.10 2.70 23 24 2.70 25c Ru(Rh, Ir) 5.40-( 1.01, 1.37) (Pt, Pd) (5.02, 5.00) 26 Os(Rh, Ir) 3.18(1.01, 1.37) 3.17 Ru(Pt, Pd) 2.70(5.02, 5.00) 2.67 Excess reagent precipitated from solution. * Air passed through receiver solutions containing ruthenium for 10 hours. e , d Black residues remained after parting. Ru Ru Ru Ru Ru Ru Ru
Error,
...
0.00
-0.06
0.00 0.00
$0.04
0.00
-0.03
+o. 02 $0.01 -0.06
+0.07 -0.03 -0.05 $0.02 $0.14 +0.09 -0.18 0.00 -0.01 -0.03
The losses of osmium and ruthenium in parting were negligible in all cases. Results for several button blanks prepared from the concentrate used in the fire assay experiments showed n o trace of either osmium or ruthenium., ACKNOWLEDGMENT
The authors express their appreciation to Falconbridge Kickel Mines for financial support and leave of absence given to J. M. Kavanagh. LITERATURE CITED
(1) Allan, W,J., Beamish, F. E., ANAL. CHEM.24. 1569 (19521. . , ( 2 ) Ibid., p.' 1608. (3) Ayres, G. H., Young, F., Zbid., 22, 1277 (1950). (4) Hoffman, I., Schweitzer, J. E., Ryan, D. E., Beamish, F. E., Ibid.,, 2 5 ., 1091 (i953j. (5) Plummer, M. E., Beamish, F. E., Ibid., 31, 1141(1959). (6) Rogers, W. J., Russell, D. S., Beamish, F. E., IND.ENG. CHEM.,ANAL. ED. 12,561 (1940). (7) Thiers, R., Graydon, W.,Beamish, F. E., ANAL,CHEM.20, 831 (1948). (8) Westland, A. D., Beamish, F. E., Zbid., 26, 739 (1954). RECEIVED for review October 10, 1959. Accepted December 17, 1959.
VOL. 32, NO. 4, APRIL 1960
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