The standard deviation was 4.8 p.p.m. TEL content ranged from 2.3 to 3.1 ml. per gallon. Precision is equivalent t o that observed on the four previous samples. The inclusion of ignition-control additives containing phosphorus or subatitution of a lead alkyl other than tetraethyllead not affect The similarity between deposits from
spark plugs and from lamp chimneys suggests the possibility of using the analysis of chimney deposits t o Predict what types of inorganic deposits will be formed in engines by various fuel ComPOnents. LITERATURE CITED
(1) Am. SOC. Testing Materials, Phil-
adelphia, Pa., "ASTM Standards 0: Petroleum Products and Lubricants,
Method
126659T, 1960.
((3)2Lauer, k ~ ~ ~ ~Friel, ~ ~H P.&9 .~Miller, ~ E. ~ ~ & B. D., "1
J. L.,
J.,
SAE Meeting, Tulsa, Okla., Nov. 5, 1958.
(4) Wear, G.E.C., Quiram, E. R., ANAL. CHEM.21,721-5 (1949). RECEIVED for review May 5, 1961. Accepted Au st 28, 1961. Division of
Petroleum &ernistry, 140th Meeting, ACS, Chicago, Ill., September 1961.
ire Assay Meth G. H. FAYE and W. R. INMAN Mineral Sciences Division, Mines Branch, Department of Mines and Technical Surveys, Ottawa, Ontario, Canada
b Gold is shown to be quantitatively collected in tin in the proposed fire assay method. The assay buttons are arted in hydrochloric acid and the old remains in the insoluble residue of intermetallic compounds. The procedure for treating the residue and selectively extracting the gold into diethyl ether is described. The proposed method has been applied to the analysis of an ore concentrate, a copper-nickel matte, and a number of rock samples. The results agree favorably with those obtained by conventional methods on the same materials. new fire assay method for the determination of platinum and palladium in copper-nickel matte and in ore concentrates was recently reported by Faye and Inman ( 3 ) . In this method, the precious metals are collected in molten tin during the crucible fusion process and the resultant tin alloy is then treated by wet chemical methods to isolate and determine the indjvidual platinum metals. In subsequent work, an attempt has been made to extend the tin collection technique and devise an analytical scheme in which gold and the platinum metals can be determined in a single sample. The behavior of gold in the scheme is studied in the present work. This metal should be isolated a t an early stage in the procedure so that it will not interfere later in the determination of the platinum group metals. I n the reported method for platinum and palladium (3), the samples were given a preliminary acid leach to remove most of the copper, nickel, and iron. Since the publication of that work it has been found that, with certain minor modifications in the procedure, samples of widely varying composition can be
fused directly, even when they contain substantial quantities of copper, nickel, and iron. The present paper describes the successful use of the modified tin collection technique in the fire assay determination of gold in samples of rock, ore, and copper-nickel matte. For comparison purposes, the gold values obtained by the lead collection technique on these samples are also given, as this method is the single acceptable method so far recorded for these kinds of material. APPARATUS AND REAGENTS
Assay furnace and Vycor melting tube, described previously ( 3 ) . Jelras Handy-Melt electric furnace, ,Model B. Spectrophotometer, neckman Model
B.
Standard gold solution. This was prepared by dissolving 100 mg. of Johnson and Matthey Specpure gold sponge in aqua regia. The resulting solution was diluted to 1 liter so that the final volume contained approsimately 60 ml. of concentrated hydrochloric acid and 40 ml. of concentrated nitric acid. The gold content of the solution was determined by a gravimetric method involving hydroquinone ( I ) and was 0.100 mg. per ml. More dilute solutions were prepared from the stock solution by twentyfold dilution. Flus for crucible fusion: Grams 35 50 10-20 10
6-8 SiOl adjusted according to silica content of sample. b The larger quantity of coke taken for samples high in iron. 11
Diethyl ether, analytical reagent, obtained from 3lallinekrodt Chemical Works.
o-Tolidine, analytical reagent, obtained from British Drug Houses Ltd. EXPERIMENTAL PROCEDURE
Preparation of Tin Assay Buttons. The crucible fusion process used in t h e present work was a modification of that described previously (3), in that the fusions were conducted a t approximately 1250" C. for 1 hour and the flux was of the composition given above. With the exception of certain tests involving leaching of copper-nickel matte, all samples analyzed by the proposed method were roasted a t 750" C. for approximately 1 hour before being mised with the flus and taken through the crucible fusion process. When it was known that the sample taken for fusion containpd more than 3 grams of combined copper and nickel, 16 to 25 grams of stick tin were added t o the charge to lower the melting point of the resultant alloy. Analysis of Tin Assay Buttons. For convenience, most assay buttons were melted under nitrogen in a Vycor melting tube, and the molten tin alloy was poured into several liters of water in an enamel pail t o produce a spongy mass as in the previous work ( 3 ) .. However, buttons containing appreciable quantities of copper and nickpl had a comparatively high melting point (600" to 650" C.) and were more easily handled in the Jelrus HandyMelt portable furnace. As before, these buttons were melted under nitrogen and the melts were poured into water to qranulate the alloy. Any large lumps produced in this operation were easily reduced in size with snips. Each sample was then transferred to a 400-ml. beaker and treated with approximately 150 ml. of Concentrated hydrochloric acid. The beaker and contents were heated until the excess tin had dissolved and vigorous evolution of bubbles from the black insoluble residue had ceased. After diluting to approsimately 360 mi. with water and
g
f
'
allowing the residue to settle, the supernatant solution was decanted through a pad of paper pulp (from Whatman No, 31 paper) supported on a filter disk. The residue was washed several times by decantation with 2N hydrochloric acid and the washings mere passed through the filter pad. The residue in the beaker was treated with a mixture of 15 ml. of 12-47 hydrochloric acid and 5 ml. of 30% hydrogen peroxide, and the beaker was heated gently for a few minutes to ensure complete dissolution of the residue. The beaker was then placed under the filter pad and the pad was washed with 20 ml. of 3 t o 1 mixture of 8N hydrochloric acid and 30% hydrogen peroxide to dissolve any fines deposited during decantation. (Chlorine is evolved vigorously from more concentrated mixtures of hydrochloric acid and hydrogen peroxide and this may disrupt the filter pad.) Approximately 50 mg. of sodium chloride were added to the beaker and the solute was evaporated to dryness. Tin was then volatilized from the sample with mixed halogen acids (3). To ensure complete dissolution of the gold, the residue left after the tin volatilization step was treated with a 3 to 1 mixture of 12N hydrochloric acid and 30% hydrogen peroxide, and the solution was then evaporated on the hot plate to approximately 2 ml. The beaker was placed in a water bath and, with the use of a jet of compressed air, the solution was evaporated gently to dryness. The salts were taken up in 5 ml. of 2N hydrobromic acid and washed into a 60-ml. separatory funnel with a further 10 ml. of 2A' hydrobromic acid. The gold was then extracted according to the method of McBryde and Yoe (5) by shaking the solution with two separate 15-ml. portions of diethyl ether. (The volume of hydrobromic acid and ether was doubled when samples contained large quantities of base metals.) The combined ether extracts were washed with three separate 5-ml. portions of 2 N hydrobromic acid and then stripped of gold by shaking with three separate 15-ml. portions of water. The aqueous gold solution was then treated with approximately 50 mg. of sodium chloride and 5 ml. of aqua regia and evaporated on the hot plate t o approximately 2 ml. 147th the aid of the water bath and a jet of air, the solution was finally taken to dryness. I n most cases, the gold content of the residue was determined spectrophotometrically with o-tolidine according to the method of Clabaugh ( 2 ) . When milligram quantities of gold were known to be present, the determination was finished gravimetrically using hydroquinone (I). EXPERIMENTS AND RESULTS ecovery of Gold from Synthetic
Samples. A number of synthetic samples were prepared by mixing 0.5 gram each of copper, nickel, and iron (all as oxides) with t h e flux, and the
mixture was then salted with 40 pg, of Pt, 30 pg. of Pd, 25 pg. of Rh, 10 pg. of Ir, and known quantities of gold in the manner described in the prevous publication (3). These samples were fused to produce tin buttons weighing approximately 20 grams, each of which was then analyzed according to the procedure given above. Their gold contents are given in Table I. The results given in Table 1 show that the recovery of both milligram and microgram quantities of gold from synthetic samples is essentially complete. It was assumed that the low value obtained in Test 12 was due to mechanical loss rather than to incomplete collection. On analyzing the buttons produced in Tests 1 to 8, the gold values averaged about 6 pg. higher than expected. Experiments were then undertaken with blank charges and i t was found that the gold content of the buttons varied with the quantity of stannic oxide used in the charge. The experimental data indicated that the stannic oxide contained approximately 0.00002% gold (approximately 6 pg. of gold per 30 grams of SnQ2). Therefore all the gold values reported in Table I and elsewhere in this paper have been corrected for the gold content of the stannic oxide. Slag Loss. The slags from Tests 10 to 12 were each crushed and mixed with 30 grams SnQz and 5 grams of powdered coke, and fused to produce
Table It.
Test Number 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Table 1.
Recovery of 601d from Synthetic Samples
Test Number
5 10 15 20 20 30 100" 200"
7 10 16 18 21 31 99 211
Milligrams 9
10 11 12
4,996 4.99b 4.9P 4.99b
4.92b 4.96b 4.93b 4 , 80b
a Aliquots of sample solution taken for analysis. b Determined gravimetrically with hydroquinone.
tin buttons weighing approximately 20 grams each. These buttons were analyaed for gold by the procedure given above and contained 0.3, 0.2, and O . l % , respectively, of the gold originally taken. APPLICATION TO COLD-BEARING MATERIALS
To determine its practicability, the proposed method was applied to the analysis of a number of natural goldbearing materials which had been analyzed previously for gold by con-
Determination of Gold in Rocks and
Nature of Sample Rock No. 1, (gossan) Rock No. 1, (gossan) Rock No. 2, (magnetite skarn) Rock No. 2, (magnetite skarn) Rock No. 3, (magnetite skarn) Rock No. 3, (magnetite ekarn) Rock No. 4, (magnetite skarn) Unconsolidated gravel Unconsolidated gravel Flotation Concentrate Flotation concentrate Flotation concentrate Flotation concentrate Flotation concentrate
Gold Taken Recovered Micrograms
Sample Wt. 1 A.T. 1 1 1 1 1 1
A.T. A.T. A.T. A.T.
A.T. A.T. 1/1 A.T. 1/4 A.T. 1 A.T. 1 A.T. 1 A.T. 1 A.T. 1 A.T. Av. :/z A.T. / 2 A.T. ' / 2 A.T. :/? A.T.
Ore
Concentrates
Proposed Assay Conventional Method Method Troy Oz./Ton 0.005 0.003 0.012 0.013 0.063 0.063 0.025 0.204 0.206 0.020
0.005 (2)
...
0 .Ol'. (2) 0.065 (2) 0.02'5'(2)
0.2'1'5' (2)
0,018 0.018
0.021 0,018 0.019 0,054 0.062 0.058 0.055 0.055 0.060 0.055 0.065 0.056 0,060 0,058 0.058
... ... ... ...
o.dii(9) Copper-nickel matte Copper-nickel matte Copper-nickel mattte Copper-nickel matte /z A.T. Copper-nickel matte '/a A.T. Copper-nickel matte :/z A.T. Copper-nickel matte 1 2 A.T. Copper-nickel matte 10 grams Copper-nickel matte Copper-nickel matte 8 grams 6 grams Copper-nickel matte Copper-nickel matte Av . 0.057 (6) Figuree in parentheses indicate number of replicate determinations. In teste 27-32, samples were leached in 12N hydrochloric acid before fusion. In teats 33-37, samples were fused directly after roasting. 27 28 29 30 31 32 33 34 35 36 37
VQL. 33, NO. 13, DECEMBER 1961
e
%915
ventional methods. Table I1 gives both the results obtained by the proposed method and those by the lead collection method for these samples. The flotation concentrate and the copper-nickel matte whose origin and composition were described previously ( 3 ) ,contained appreciable quantities of the platinum-group metals. These materials had been analyzed for gold a t the Metallurgical Laboratories, Falconbridge Nickel Mines Ltd., Richvale, Ontario, by a method in which the fire assay beads obtained by conventional techniques were analyzed spectrographically (.$,6). The rock samples were chosen a t random from a batch of samples which had been previously analyzed by an independent group at the Mines Branch using the classical fire assay method %ith a gravimetric finish. DISCUSSION
Table I1 shows that the results obtained by the proposed method agree favorably with those of the classical fire assay, also that the proposed method is applicable to a wide variety of materials. The leach liquors in Tests 27 to 31 were treated with zinc dust (3) to
precipitate the copper and any gold present. The metallic precipitates were then dried and fused to produce tin assay buttons in the usual way. The leach liquor in Test 32 was evaporated to dryness and the salts were then fused to produce a tin assay button. The assay buttons from these experiments were analyzed by the procedure given above and did not contain detectable quantities of gold. Therefore, it can be concluded that, prior to analysis, the copper-nickel matte can be leached in hot concentrated hydrochloric acid to remove the bulk of the base metals without losing gold. Platinum and palladium in the coppernickel matte are also insoluble during the leaching operation ( 3 ) . However, the results for Tests 33 to 37 in Table I1 show that as much as 0.5-assay ton sample of the coppernickel matte can be fused directly (after roasting) and thus the leaching operation can be avoided. When platinum metals are to be determined, this approach has the disadvantage that most of the copper in the button remains in the insoluble residue on parting in hydrochloric acid and, after extraction of the gold, must be removed passing by the sample solution through
comparatively large cation exchange columns. ACKNOWLEDGMENT
The authors acknowledge the assistance of P. E. Moloughney in performing much of the experimental work. They are also grateful to Falconbridge Nickel Mines Limited for supplying the sample of flotation concentrate and of copper-nickel matte; and to L. L. Lutes for certain gold assays by the lead collection method. LITERATURE CITED
(1) Besmish, F. E., Russell, J. J., Seath, J., ANAL, CHEM.9, 174 (1937). (2) Clabaugh, W. S., J. Res. Natl. Bur. Standards RP1694, 36 119 (1946). (3) Faye, G. H., Inman, R., AXAL. CHEM.33, 278 (1961). (4) Lewis, C . L., Can. Mining Met. Bull., hlarch 1957. (5) McBryde, W. A. E., Yoe, J. H., ANAL. CHEM.20, 1094 (1948). (6) Scobie A. G., Trans. Can. Inst. Mzning ket.48,309 (1945).
d
RECEIVED for review September 8, 1961. Accepted October 4, 1961. Mineral Sciences Division internal report MS-61-61. Published by permission of the Director, Mines Branch, Department of Mines and Technical Surveys, Ottawa, Canada.
Eva poratio n and Residue CYRUS FELDMAN Oak Ridge National laboratory, Oak Ridge, Tenn.
b
Volatilization of
boron is slight in HzO, "Os, H2S04, and HCIO4 a t -75" C. until very low volumes are reached. Substantial losses can occur from HCI solution earlier in the evaporation. Acidifled solutions evaporated to dryness overnight on a steam bath also lose most of their boron. The presence of mannitol can prevent this loss both during and after the evaporation if the solution does not attack mannitol. Boron is volatilized from HzS04 and HC104 solutions a t and above 228" C., but can b e retained in the system b y refluxing.
(
