chloric acid solutions of zirconium-free titanium. The titanium and zirconium were separated from the sulfate with an ammonium hydroxide precipitation (2). The combined hydroxides were collected on filter paper, redissolved with hydrochloric acid, and analyzed. The results are shown under sample 4 of Table 111. The precision of the mandelic acid method is almost equal to the precision of the analytical balance used to weigh the zirconium dioxide residue. Based on the U. S. Bureau of Mines analysis of the zirconium used in preparing the synthetic alloys, the accuracy of the method is comparable to the precision. No interference was encountered from such common alloying constituents as iron, aluminum, vanadium, tin, chromium, manganese, and molybdenum. The reports of Kumins and Hahn indicate that copper, cobalt, magnesium, and nickel do not interfere in the amounts usually found in titanium alloys. Hafnium precipitates quantitatively with the zirconium, but these elements are so similar in their properties that no effort was made to dis-
tinguish between them. According to Hahn (I),both the hafnium and the zirconium may be determined with p-bromomandelic acid by solving simultaneous equations. Because the reactions of p-bromomandelic acid with zirconium are so similar to those of mandelic acid, p-bromomandelic acid could undoubtedly be used in this procedure. Niobium interferes, causing high results. Excess sulfate, fluoride, citrate, oxalate, tartrate, and other complcxing agents interfere, causing low and erratic results but with the exception of sulfate and fluoride, are unimportant because they would not be encountered in ordinary analyses. Fluoride may be removed by evaporating to fumes with perchloric acid. Interference from sulfate can be eliminated by precipitating the Zirconium as zirconium hydroxide with ammonium hydroxide and washing free of sulfate prior to precipitation as the mandelate.
appreciation to the U. S. Bureau of Mines for providing the high purity zirconium metal used to prepare the standards, and R. L. Powell, Titanium Xetals Corp. of America, who supervised this research. REFERENCES
( 1 ) Fritz, J. S., Johnson, Marlene, ANAL. CHEM.27, 1653 (1959. (2) Furman, N. H., Scott’s Standard hlethods of Chemical Analvsia.” 5th ed., Vol. 1, pp. 1095-104, Van Xostrand, New York, 1925. (3) Hahn, R. C., AXAL. CHEW21, 1579 (1949). (4) Ibid., 23, 1259 (1951). (5) Hahn, R. C., Webber, Leon, J . Am. Chem. SOC.77, 4777 (1956). ( 6 ) Klingenberg, J. J., Papucei, R. A . ANAL.CHEM.24, 1861 (1952). (7) Kumina, C. A., Ibid., 19,376 (1949). ’
(8) Mills, E. C , Herman, S. E., Analyst
78.256 (1953). (9) &E, ‘ Henry, private communication, August 1958. (10) Suss, Henry, Sam Tour Rept. KO 9141, Sam Tour & Co., 41 Trinity PI., Yew York, N. Y., November 1951.
ACKNOWLEDGMENT
The authors wish to express their
RECEIVED for review February 21, 1957 Accepted September 22, 1958.
Fire Assay for Platinum and Palladium in Ores and Concentrates M. E. V. PLUMMER, C.
L. LEWIS,’
and
F.
E. BEAMISH
Division o f Analytical Research, University of Toronto, Toronto 5, Canada
b This investigation was undertaken partly to provide a t least one alternative procedure to the one generally applicable method for the determination of platinum metals in ores and concentrates. The new fire assay involves a collection of platinum and palladium by fusions with sodium carbonate a t 1450’ C. in a carbon crucible to produce an alloy with ironnickel-copper. The method of parting the iron button and subsequent isolation of platinum and palladium by cation exchange are described.
M
of the platinum metals available to commerce originate from ores which contain about 0.001% of the precious metals. Of the six platinum metals, platinum and palladium practically ah-ays predominate. With most ores osmium values are not known and usually ruthenium and iridium values are known only approximately. For OST
1 Present address, Falconbridge Xickel Mines Ltd., Richvale, Ontario.
254
e
ANALYTICAL CHEMISTRY
these more insoluble metals the values are generally calculated on the basis of the commercial recovery. Analytical determinations in ores and concentrates involve a fire assay in which the platinum metals are concentrated by solvent extraction by lead from a molten solution of the ores with fluxes. Rarely may the assager resort to an entirely wet treatment of the ores or concentrates to convert the platinum metals to dissolved constituents of familiar compositions. The principle of this procedure is good, but no data have been recorded to indicate its efficiency relative to recovery by fire assay. Furthermore, the procedure is time-consuming. A week is usually required and accuracy of recovery of microgram amounts of platinum metals is not encouraged by the multiplicity of extractions, relatively large volumes of liquids entailed, and difficult techniques involved. Fire assay with lead as the collector remains the time-honored method. It is surprising that few data have been recorded to prove its efficiency. This is
partly due to the absence of alternative procedures; the wet procedure may have proved too difficult. However, an examination of the chemistry of the lead extraction from the fused ore introduces some doubt concerning the possibility of complete extraction of some of the platinum metals (1, 2, 6, 9, l a ) . Among the difficulties is the insolubility of some of the platinum metals in fused lead. Iridium resists dissolution to the degree that a good quantitative method for this metal is based upon this property (10). Furthermore. the platinum metals in ores may exist in forms which resist reduction by carbon and subsequent extraction by lead. This question, used too frequently by those who would promote valueless oIes, plagues the conscience of the platinum metal analyst. The fact that it cannot be disregarded is shoJm by the adverse influence of tellurium in the fire assay for gold. The result of these and other problems has been H continued search for a new approach to the assay for plat-
inum metals; particularly to find a collector which would effectively extract the more insoluble platinum metals and be as efficient as lead for the removal of palladium and platinum. Obviously, application of iron and nickel which are the almost constant companions of the platinum metals in natural occurrences would be considered. Rankama and Sahama (19) stated that the platinum metals are strongly siderophilic and by far the greatest part of the platinum metal in the earth is found in the nickel-iron core, in which they are dissolved in iron. However, any application of iron and nickel to fire assay collection must deal TTith the presence of sulfur and the possible tendency for a t least some of the platinum metals to pass into the matte phase. It has been recorded ($0) that the siderophilic platinum metals preferentially enter the metal rather than the sulfide phase when in the presence of both. The literature is encouraging concerning the alloying qualities of iron, nickel, and copper with the platinum metals. Isaac and Tamman (14) stated that iron forms a continuous series of solid solutions with platinum a t high temperatures. At room temperature it is soluble in a-iron to the extent of nearly 50%. A continuous series of solid solutions crystallizes from palladium-iron melts (11). Kurnakow and Nemilow (17) and Kussman and Nitka (18) believed that the system platinumnickel comprises a continuous series of solid solutions above 600" C. The application of some form of carbon to the problem of producing iron and nickel in situ, from a fused melt ,seemed inevitable. Benedicks and Lofquist (6) stated that the presence of carbon in a melt consisting predominantly of iron and sulfur results in a melt splitting into two liquid phases, one of which is metallic and the other sulfidic. The natural iron-nickel content of concentrates might be used and by adding carbon the base metal button might be separated. Archibald and Thornhill (3) found that the addition of Pimilar proportions of nickel and copper to iron as found in Sudbury ores does not materially affect the two liquid phases in the melt. This paper deals with a successful attempt to isolate an iron-nickel-copper button containing the platinum metals from a fused melt of an ore concentrate; the subsequent dissolution of the button; isolation of the platinum metals by cation exchange; separation of the metals by chromatography; and, finally, colorimetric determinations of platinum and pall a d'ium. APPARATUS A N D REAGENTS
High Frequenry Furnace. An Ajax-
Northrup 40-kw. converter with an output of 7700 volts a t a frequency of 10,000 to 20,000 cycles per second. The two furnaces used were of 50- and 17-pound size, both of the tilting type. Assay Furnace. A pyrometrically controlled Williams and Wilson 15 kv.amp. globar-type assay furnace. Graphite Crucibles, made from National Carbon Co.'s graphite pipe grade A.G.R. The larger crucible of the two had an outside diameter of 13.6 cm., an inside diameter of 11.3 em., and a height of 23 em. The smaller had an outside diameter of 10 cm., inside diameter of 7.3 cm., and a height of 14.5 cm. The bottoms \yere made of 1.8-em. thickness from the same grade of graphite rod. The cylinder walls were bored to form a step 0.8 cm. deep and 0.5-cm. tread; the bottom dijks were machined to fit tightly. Pyro-Optical Pyrometer made by the Pyrometer Instrument Co., Inc. Spectrograph, Applied Research Laboratories. Two-meter grating spectrograph (36,600 lines per inch). Spectrophotometer, Beckman Model
B.
Chemicals. Reagent grade litharge and technical grade soda ash, and borax glass. Fisher certified lead sheet (Fisher Scientific Co.), in rolls, 0.005 inch thick was used in the preparation of the silver beads. These were all free of platinum metals. STANDARD SOLUTIONS
Palladium. Powdered palladium sponge, 0.510 gram, was dissolved in aqua regia and then converted to chloride. The solution was filtered, made up to 1 liter with 0 . l M hydrochloric acid, and standardized with sodium salt of dimethylglyoxime. Three 9.98-ml. portions contained 5.07, 5.08, and 5.09 mg. of palladium. Platinum. A standard solution was similarly prepared by dissolving 0.500 gram of platinum metal sponge. The solution was standardized with benzenethiol (8). Three 9.98-m1. aliquots contained 5.00, 5.01, and 4.99 mg. of platinum. hIulticomponent Precious Metal Standard Solution. Aliquots of these standard precious metals solutions were placed in a 1-liter flask with 20 ml. of concentrated hydrochloric arid so that the solution contained 4.06 nig. per liter of palladium, 10.0 of platinum, 4 of rhodium, and 4 of gold. Synthetic Base Metal Solution. Anhydrous iron(II1) chloride (1450 grams), 250 grams of nickel(I1) chloride hexahydrate, and 50 grams of copper(I1) chloride dihydrate were dissolved in water, and 100 ml. of concentrated hydrochloric acid were added. The solution was diluted slightly and filtered through a 32-cm. fluted KO. 14 Whatman filter paper. The filtrate was made up to 10 liters with water. To produce a solution of p H 1.5 containing about 20 grams of iron, 400 ml. of the solution were diluted to 1500 ml. with water. This solution was used for blanks and standards. Ore Concentrate. The concentrate
Table 1.
Taken, 50 50 50 50 50
y
20.4 20.4 2U.4 20.4 20.4
Av . Mean dev.
Analysis of Silver Bead Standards
Recovered, y ChromatoSpectrographic graphic Pt Pd Pt Pd 50.5 50.0 48.5 48.8 49.8 49.5
19.2 19.5 18.3 18.6 19.1 18.9
0.70
0.40
44 44 46 43 43 44.0 0.80
18 18 18 18 17 17.8 0.32
used was made from ores of the Sudbury district, Ontario. The percentages of the main constituents were iron 36.58, copper 3.78, nickel 4.10, sulfur 27.00, silica 20.68, lime 2.08, alumina 4.68, and magnesia 2.08. PREPARATION
OF STANDARD BEADS
Five milliliters of multicomponent precious metal solution were added to a boat made from a 5 X 5 inch square of lead foil. The solution was evaporated to dryness in a steam cabinet, 10 mg. of silver powder were added, and the boat was folded into a ball and wrapped with 2 X 4 inch portion of lead foil. The lead ball mas placed a t the bottom of a fire assay crucible, covered with 50 grams of a mixture of 6 to 1 soda ash to silica sand, and heated to normal assaying temperatures, Blank samples were prepared as above without the precious metal solution. ANALYSIS O F CONCENTRATE FOR PLATINUM A N D PALLADIUM BY CLASSICAL FIRE ASSAY
T o evaluate the efficiencies of the iron-copper-nickel collection of platinum met,als a suitable modification of the classical fire assay with lead and silver as collectors had to be applied. The determination of microgram amounts of platinum metals in silver beads is a difficult process involving a long sequence of extraction techniques. An attempt was made to apply the chromatographic techniques described by Kember and Wells (16). The results on standard beads (spectrographic analyses of silver beads made by Falconbridge Nickel Mines Ltd.) recorded in Table I indicate an accuracy comparable to that of standard spectrographic methods (IS). The chromatographic method was then used for the isolation of platinum and palladium in both the classical assay and the proposed procedures. The modified classical method used was as follows. One assay ton of concentrate was well mixed with 35 grams of soda ash, 15 grams of silica, 38 grams of niter, 250 grams of litharge, and 5 mg. of silver powder, and fire assayed. The lead buttons from two such assays were scorified and then cupelled to give a silver bead weighing about 10 mg. VOL. 31, NO. 2, FEBRUARY 1959
255
To dissolve most of the palladium and some of the platinum, the uncleaned bead was parted with 5 ml. of 1 to 4 nitric acid with slight heating. Five milliliters of water m r e added and the residue was filtered using TT'hatman S o . 42 filter paper. The filtrate, A, containing platinum, palladium, and silver was set aside for the separation of silver as described below. The residue, A, mas treated by an adaptation of a method described by Wichers, Schlecht, and Gordon (81). This residue, which contained platinum, palladium, rhodium, and gold, was placed on a clean piece of absorbant paper and the filter paper opened so that it was folded once. The paper \vas then rolled so that it could be placed in the center of a 20-em. length of hard glass tubing, inch in outside diameter and with a wall thickness of 5 / ~inch. ~ This bomb tube was put aside t o receive residue C, described below. Three milliliters of 0.1M hydrochloric acid TT ere added with stirring to the boiling filtrate L4. The precipitate was alloned to settle overnight array from light. The silver chloride was filtered using a S o . 42 filter paper and this precipitate, B, containing adsorbed palladium was washed with a fe\y milliliters of cold 0.1M hydrochloric acid. The beaker containing filtrate B from the silver chloride precipitation was set aside for analysis as described belon- and replaced by a 30-ml. beaker. The silver chloride precipitate, B, was treated with hot 1 to 5 ammonia t o produce a residue, C, and a filtrate, C. The small dark residue, C, on the filter paper after ammoniacal dissolution of the silver chloride precipitate was rolled as described above and placed in the bomb tube v-ith residue A. The papers were burned in the muffle furnace a t 420' C. for 12 hours. The residue in the tube was reduced in hydrogen at 500' C. for 15 minutes. The tube was sealed a t one end and, when cool, placed in ice. Two and one half milliliters of concentrated hydrochloric acid were added to the tube and after cooling for 15 minutes, 0.2 ml. of fuming nitric acid (90%) was added and the tube was sealed as quickly as possible, preferably by pulling the glass to a fine thread. This bomb tube was then placed in a steel pipe 15 inches long and 1 inch in internal diameter closed at one end, threaded at the other, and containing 20 grams of calcium carbonate. The screw cap of the tube was replaced and the pipe and tube placed in a muffle furnace at 300' C. After 1 hour the bomb was removed, cooled in dry ice for 15 minutes, and opened. The open end was quickly placed under 5 ml. of water in a 30-ml. beaker. The other end of the tube was then opened and the tube washed with water. Glass from the bomb tube was filtered off using Whatman KO. 42 filter paper. This solution was combined with the filtrate B, and with the solution obtained from filtrate C after boiling off the ammonia, adding 5 ml. of 0.1M hydrochloric acid containing a drop of nitric acid, and filtering. Xeither platinum nor palladium was 256
0
ANALYTICAL CHEMISTRY
found in the final sill-er chloride nrecipitate. The combined solutions mere evaporated to a small volume and treated twice with hydrochloric acid and twice with n ater with evaporations between each addition. The sample mas transferred with a little water to a n 8-ml. crucible, evaporated to one drop, and the chromatographic separation made as described belo\y, DETERMINATION OF PLATINUM A N D PALLADIUM BY N E W FIRE ASSAY METHOD
Preparation of Furnace and Charge, Silica sand was used in preference t o carbon black in the preparation of the furnace; otherwise the furnace and fluxes used nere those recorded by Coburn, Beamish, and Lewis (7). The concentrate was passed through a 100-mesh screen. and the oversize containing very fine organic matter was carefully burned, crushed t o pass the 100-mesh screen, and added t o the main sample. One thousand grams of this sample were mixed with 424 grams of soda ash and 270 grams of borax glass, passed through a 45-mesh screen, rolled, and poured into the large crucible. A graphite cover 13.6 em. in diameter, and 1 em. thick with a hole 1 em. in diameter at its center was placed on the crucible. Preparation of Buttons. S l o heat~ ing a t 6 t o 8 kw. until the mixture became molten n a s Pssential to prer e n t t h e charge from boiling out of the cruciblr. At intervals of about 5 minutes, the cover was removed and the temperature a t the top of the charge next to the crucible wall m-as observed. The reaction became most violent at about 1035' C., although no metallic button was formed until 1350' C. was reached. This latter temperature is referred to as the reaction temperature, and the time measured after this temperature is reached is called the reaction time. This period determines the amount of metal formed, maximum amounts being formed after 15 minutes. The ponder was then cut off, the furnace tilted to an angle of about 30' to the vertical, and the charge cooled for 3 hours in this position. The crucible and charge were removed from the furnace and cooled to room temperature. The bottom of the crucible was removed and the button, matte, and slag were mechanically separated, rreighed, and analyzed, as described below. Dissolution of Button. The button mas placed in a 2-liter beaker with 500 ml. of concentrated hydrochloric acid and left on t h e steam bath overnight. The liquid was decanted into another 2-liter beaker. Further concentrated hydrochloric acid was added until the button was completely parted. The volume of the combined mixture mas reduced by evaporation to about 600 ml. Ten-milliliter portions of concentrated nitric acid were added slowly until as much as possible of the residue had been dissolved. Three or more 5-ml. portions of hydrochloric acid were added to expel the nitrous fumes. The solution, subsequently t o be diluted to
6 liters, was tested for acidity by diluting 10 nil. to 100 ml. and observing the pH; if belolv 1.5 it required further evaporation of hydrochloric acid. This button solution was diluted with 500 ml. of n a t e r and filtered, and the filter washed with Kater; this filtrate, A, was kept for later treatment. The insoluble portion of the button was burned at 600' C., reduced in hydrogen and then treated with aqua regia; hydrochloric acid was added to destroy the nitrate, the solution \vas taken to dryness, and 2 drops of concentrated hydrochloric acid were added. Any residue appearing here may be discarded. The sample was diluted to 25 ml. with n-ater and filtered. This filtrate was added to filtrate A; the combined solutions, B, were diluted to 6 liters with mater, and the pH was adjusted to 1.5 with hydrochloric acid. The sample was divided into four approximately equal parts, each being passed through Dowex 50 X 8 (20 to 50 mesh) cation exchange resin. The column of resin vhich was 70 em. long and 4 em. in diameter, having a wet weight of about 700 grams (42 t o 48% moisture), was prepared by passing 3 S hydrochloric acid through it until the eluate contained no base metals. The excess acid was displaced by washing n i t h 2 liters of water. The four parts of solution B were added to the four columns a t a constant rate so that 1500 ml. had passed through in 1 hour. Each column was ~ a s h e dwith 1500 ml. of water. The four effluents were each evaporated to about 10 ml. and tramferred to 150-ml. beakers. and the evaporation 11-as continued to dryness. If sulfuric fumes appeared, heating 11as continued to the removal of sulfuric acid. The organic matter was then destroyed by repeated addition of fuming nitric acid (90%) and 30y0 hydrogen peroxide. Sitrates were then decomposed by hydrochloric acid, and each of the four samples was taken to near dryness. One milliliter of 40% hydrobromic acid was added to each and the samples were evaporated to eliminate selenium. To remove boron. which interfered in the chromatographic separation, the solutions n ere boiled with concentrated hydrochloric acid and pure methanol, and the volumes mere reduced to dryness. Five milliliters of 2% sodium chloride were added and the samples filtered; these filtrates, C. vvere set aside for the addition of the filtrates obtained below. The residues, largely silica which may contain traces of platinum metals, were burned at 400' C., treated n i t h aqua regia, then with hydrochloric acid, and taken to dryness. Five milliliters of mater were added, the solutions filtered, and the filtrates added to filtrates C. The volume of each of the four combined filtrates was 30 ml. These solutions were adjusted to p H 1.5 with hydrochloric acid and each passed through small Dowex 50 X 8 resin columns 4-cin. long and 10 mm. in diameter, which n ere prepared as described. The columns were washed n i t h 80 ml. of distilled water. The volume of each of the four effluents was evaporated to
about 10 nil., combined, and made up to 50 ml. in a volumetric flask. Thiti solution should now be free from nitric and sulfuric acids, the latter derived from sulfur in the button. The elimination of sulfuric acid is required because of its destructive action on chromatographic paper.
Table II.
Position of Metals on Strips
Metal Rh Ir (1st band) Rh I r (2nd band) Pd Pt
A m t . , r RT
+ +
At1
To isolate the platinum metals, the combined eluates were treated by the following modification of the chromatographic method of Kember and Wells (16).
20
5
RL 7
20 50 20
9 42 71 94
13 62 89 100
Table Ill. Analysis
reagent, placed in the 50-nil. volumetric flask, n-as made up of 1 ml. of 0.5% p-nitrosodimethylaniline in 95% ethyl alcohol, 1 nil. of sodium acetatehydrochloric acid buffer of p H 2.2, and 15 ml. of 95% ethyl alcohol. Absorbance measurements n ere made a t 525 mp (8,2j.The above procedures were applied t o iron buttons and the results included in Table 111.
of O r e Concentrate by Three Methods (Ounces per ton)
CHROMATOGRAPHIC SEPARATION OF PLATINUM, PALLADIUM, RHODIUM, IRIDIUM, AND GOLD
The maximum size of ?ample which could be separated by this technique as controlled by the platinum content of the sample. Beyond 60 y of platiniini there n a s interference n i t h the pxlladiuni band.
To facilitate the quantitative addition of the sample to the chromatographic strip, a 6-ml. aliquot of the solution \vas reduced to one drop in an 8-ml. crucible under a 250-watt infrared lamp. One drop each of concentrated hydrochloric acid and 5% sodiuni chlorate Tlere added to the cool solution. The sample was applied by a syringe to a line drann 3.25 inches from one end of a strip 1i.25 inches long of Whatman KO. 3 paper. Small amounts were applied a t a time to the paper with it5 short dimension held vertically and di 3 ing the paper betn ern each application. Five-milliliter aliquots of the pols component precious metal solution nere used for standards and for a control, The crucible and syringe were Ilaqhed six times mith one drop of 5% sodiuni chlorate solution and applied to the above line. Kashing with water or hydrochloric acid interfered with an efficient separation of bands. d jar, 8 inches in diameter and 18 inches tall, accommodated 10 paper strips which dipped into two 15-ml. glass boats containing a 60 : 30 : 10 isobutyl methyl ketone-hydrochloric acid-isoamyl alcohol mixture. The papers nere held up l y strip supports a t a point 2 inches from the end of the paper. Twenty milliliters of solution nere placed a t the lmttom of the jar to aid saturation of the atmosphere with solvent vapor. Separations by downward diffusion nere carried out a t about 24' C. and c.hromatograms were developed for 12 hours. The lid of the jar supporting the papers was removed and placed in a dust-free atmosphere. Excess solvent v a s removed from the boat Iyith absorbent paper. To ascertain the location of the bands the control strip was sCt aside after 15 minutes and sprayed n ith 1M tin(I1) chloride in 3 . 5 X hydrochloric acid. The positions of the metals were given by the usual colors: palladium, brown; platinum, yellow; rhodium together with iridium, yelloworange. The two bands of rhodium with iridium were not reported by Kember and Rells (15). The remaining nine
Lead Button, Co
Iron Button. h B C
0.0184 0.0178 0.0162
0.0152 0.0140 0.0153
D
0.0232"
0.016i"
E
0.030@ 0.0169 0,0009
0.0195b 0.0141 0.0006
Av
.
0.0180 0.0178 0.0133 0.0183 0.0160 0.0182 0.0182 0.0171 0,0014
0.0133 0.0135 0.0135 0,0157 0.0164 0,0168 0.0135 0.0151 0.0015
0.01'70 0.0169 0,0132 0,0168 0.0188 0,0090~ 0,0153 0.0163 0,0014
0.0138 0.0140 0.0134 0,0137 0.0144 0.0078~ 0.0145 0.0140 0,0003
Mean dev. Iron button salted with 0.0058 ounce per ton platinuni. 0.0029 02. per ton palladium. * Concentrate salted wit,h 0.0146 02. per ton platinum, 0.0058 oz. per ton palladium. hmounts subtract,edto produce recorded average values. Eliminated from average. 5
DISCUSSION
Table IV.
Compositions of Button, Matte, and Slag
OF
TABLE 111 RESULTS
The RT and RL values obtained differed only slightly from those of Kember and Wells (16). Measurements were taken t o both trailing and leading edges of the developed band and the relative positions of thP bands are indicated in Table 11.
Results of the analysis of the concentrate by the iron button method compared very favorably with those obtained by the lead assay. The improved precision obtained in the iron button method TYas probably due to the larger sample taken, the platinum and palladium minerals being more uniformly distributed. During the formation of the ironnickel button three phases were formed : metal, matte, and slag. Although generalizations have been made regarding the siderophilic nature of the platinum metals, the quantitative extraction into the metallic phase has never been shown. It n-as desirable to analyze the matte and slag for platinum and palladium and a knon-ledge of the sulfur and nietal content of the three phases was helpful. These are recorded in Table IT.
DETERMINATION OF PLATINUM AND PALLADIUM IN CHROMATOGRAPHIC SECTIONS
DETERMINATION OF PLATINUM AND PALLADIUM IN MATTE AND SLAG
The platinum section of the strip !vas placed in 10 ml. of 3 N hydrochloric acid in a 30-ml. beaker and let stand for 10 minutes with intermittent stirring. The mixture was decanted through Whatman KO.40 filter paper into a 50-ml. volumetric flask containiw 5 ml. of 1M tin(I1) chloride in 3?5M hydrochloric acid (4). A further 10 ml. of 3 M hydrochloric acid were used to extract the platinum from the pulp. Extractions with successive 5-ml. portions of n ater were continued to reach the 50.00-ml. volume. Absorbance measurements were made a t 402 mg. The palladium was extracted froin its section Tyith water. The colorimetric
The classical fire assay combined with the chromatographic determination of the precious metals in silver beads as described above was applied for these determinations. TITO hundred sixtytn.0 grams of the matte mere burned a t 980' C. for 1.5 hours with stirring to remove most of the sulfur, the calcine weighing 232 grams. This was crushed to pass a standard KO.45 mesh sieve and divided into eight portions. Each portion was fluxed with 30 grams of silica sand, 260 grams of litharge, 40 grams of soda ash, and 4.5 grams of flour. Ten milligrams of silver powder were added to one of the crucibles. The eight lead buttons were scorified to-
110-Gram
Button, Grams
hIatte,
Grams
Slag, Grams
strips nere divided a t points bett? een the various ban&.
VOL. 31, NO. 2, FEBRUARY 1959
* 257
Table V.
Platinum and Palladium in Matte and Slag and Total Platinum and Palladium in Sample of Concentrate
Ounces e o n Slag, 543 Grams Total in Sample - Pt PdPt Pd Sample 0 0159 None detected -+ 0.0184 A 0.0147 None detected --, 0 0174 1) 0.0158 0,0146 None detected -+ E Av. 0.0172 0 0151 Mean dev. 0,0010 0 0006 a These values are exactly those obtained by chromatographic treatment of the bead as recorded in Table 111. Matte, 854 Grams Pd Pt 0 0007 Not detected 0.0009 Xot detected 0 0010 Not detected
Effects of Variations in Charge on Products Formed Charge, Grams Products, Grams NO. Concentrate Soda ash Borax Metal Matte Slag 1 1000 424 270 108 630 570 2 1000 530 270 130 592 611 3 1000 424 371 104 580 il0 4 250 895 5iO 104a 811 nil Total copper, nickel, and iron in 250-gram sample of concentrate was about 111 grams. Table VI.
Experiment
Table VII.
Sample KO.
A B Ca
ACKNOWLEDGMENT
Effect of Sulfur on Production of Matte and Button
Sample Kt., Grams
Sulfur in Sample, Crams
1000 1000 200 200
205 56 0 io 0.70
D” Small carbon crucible used.
Flux, Grams Soda ash Borax 270 424 270 424 54 85 54 s5
Products, Grams Button Matte Slag 320 490 97 98.5
398 GO3
nil nil
These values were due to an incomplete isolation of the metal phase, hieh in the case of sample C was the result of a ferv globules of metal becoming attached to the pot wall and also distributed throughout the slag. With careful collection of these small amounts of inetal, as in Sample D, the slag was free of precious metals. Therefore, the matte, if desired, may be eliminated by a preliminary roasting technique. Further simplification of this procedure nil1 be effected by complete control of the size of the button. This ill reduce the time required for the dissolution procedures and for the ion exchange separation. In any case, this method suggests intriguing variations of technique for the recovery of the platinum nictals, and in its present form, pro\ ides the one alternative to the classical fire assay.
402 :iil I04 100
The authors are grateful for a Union Carbide fellowship given to 11. E. V. Pluninier n hile engaged in this work. LITERATURE CITED
(1) Allan, W.J., Beamish, F. E., ASAL. CHEM.24, 1569 (1952). (2) Allen, W. F., Beamish, F. E., Ibid., 22,451 (1950). (3) Archibald, F. R., Thornhill, P. G.,
personal communication.
gether and the resulting button was cupelled. The charge used for the slag \vas 200 grams of litharge and 4 grams of flour for each 29 grams of slag. The lead buttons obtained from 232 grams of slag contained 10 mg. of added silver powder. These eight buttons were also scorified to form one 25-gram button, which was then cupelled. The silver beads were analyzed chromatographically (Table V). The total platinum and palladium in the ore concentrate, including values in Table 111, are also given in Table V. DISCUSSION
The data described above indicate that a fire assay fusion of ore concentrate from Northern Ontario ores with sodium carbonate in the presence of carbon Ti-ill effect the quantitative extraction by a n iron-nickel-copper alloy of the precious metals. The total platinum and palladium values agree extreniely well nith the values obtained by the chromatographic analysis of the silver bead. The slightly lon- values given by the spectrograph are to be expected, considering the values of the standard beads given in Table I. Improvements in this new fire assay method n ill result from efficient control of button size and matte content. While the latter shows only a slight tendency to retain traces of palladium, it is advantageous to reduce the rela258
ANALYTICAL CHEMISTRY
tive quantity of the matte or eliminate it. Yreliminary investigations were undertaken to learn the effect of the amount of matte of changes in the composition of the charge (Table VI). Increases in the relative amount of soda ash increased the size of the button, whereas borax had little effect. Both reduced the quantity of matte. HOWever, experiment 4 shorvs that sufficient increases in the quantities of the fluxes caused the matte and slag to become a single phase, presumably itself a matte-slag, because i t contained a large proportion of sulfur. T o reduce the matte content, the conpentrate was roasted in 6-inch porcelain dishes in the assay furnace a t 980” C. for 1.5 hours, and the sample was stirred a t 15-minute intervals. The cooled calcine was crushed to pass a 45-mesh screen, mixed with flux, and melted as before. The effects of sulfur on the w i g h t of button and matte are given in Table 1-11. The slag from sample C was almost white and had a good glassy appearance. It was crushed to pass a KO. 48 standard mesh screen, fluxed with 5.8 grams of silica sand, 1 gram of borax glass, 1.4 grams of calcium oxide, 10.2 grams of soda ash, 61.5 grams of litharge, 3.3 grams of flour, 10 mg., of silver powder, and fire assayed. r h e silver bead nas analyzed as outlined above giving 25 y of platinum and 2 y of palladium.
(4) Ayres, G. H., Meyer, A. S., Jr., XSAL CHEM.23, 299 (1951). (5) Barefoot, R. R., Beamish, F. E., Zbid., 24, 840 (1952). (6) Benedicks? Carl, Lofquist, Helge,
“Konmetallic Inclusion in Iron and Steel,” Chapman & Hall, London, 1930. (7) Coburn, H. G., Beamish. F. E., Leivis, C. L., ANAL.CHEM.28, 1297 (19513). (8) Currah, J. E., hlcBryde,.W. A. E., Cruickshank, A. J., Beamish, F. E., IXD. ENG. CHEU..AXAL. ED. 18. 120 (1946). (9) Frazer, J. G., Beamish, F. E., ANAL. CHE?L26, 14i4 (1’84). (10) Gilchrist, Raleigh, J . Am. Chem. Soc. 45, 2820 (1923). (11) Grigoriev, A. T . , 2. anorg. PL. allgem. Chem. 209, 295 (1932). (12) Hoffman, I., Beamish, F. E., ANAL. CHEM.28,1188 (1956). (13) Hoffman, I., Westland, A. D., Lewis, C. L., Beamish, F. E., Ibid., 28, 1174 (1956). (14) Isaac, E., Tamman, G., 2. anorg. Chem. 55 , 63 (1907). 115) Kember. Ii. F.. Wells. R. -4.. Analist 80, i 3 5 ( i m j . (16) Ibid., p. 741. (17) Kurnakow, N. S., Nemilow, V. .4., Ann. inst. platine (U.S.S.R.) 8, 17 (1931). (18) X p m a n , A,, Iiitka, H., PhZjsik. 2. 3g, 313 (1938). (19) Ranliama, Kalervo, Sahama, T. G., “Geochemistry,” p. 688, Univ. Chirago Press, Chicago, 1949. (20) Ibid., p. 689. (21) Wichers, Edivard, Schlecht, W. G., Gordon, C. L., J . Research X a t l . Bur. Standards 33, 363, 457 (1944); (R.P. 1614, 1622). (22) Yoe, J. H., Kirkland, J. J., AKAL. CHEM.26, 1335 (1954).
.
RECEIVED for review July 3, 1958. Accepted September 15, 1955.
