BORROWMAN ON PYRITIC CONCENTRATES FOR SILVER A N D GOLD. the use of niter. He adduces, however, the results of but two fusions. Messrs. Ricketts and Miller, in their text-book on “Assaying,” express lack of confidence in the iron method on ore containing much sulphur. No further comment is made. Mr. H. van F. Furman, in his Manual of Practical Assaying,” says the iron method is preferred by most assayers. Again some authorities recommend a charge for the iron method that yields a basic slag, notwithstanding the well-known fact that such slag is likely to carry values. Others, evidently in recognition of this, prefer a charge containing considerably more acid fluxes and some potassium nitrate. Experimental evidence, however, to substantiate the various opinions, is very meagre and on some points entirely lackS.” Owing to the permanent stock of ferric chloride ing. There circumstances lead the writer to make solution in the reservoir the discharge a t r is always some investigations, in the hope of obtaining definite odorless; so is also the air issuing a t 1 ; the only place data as to the relative efficiency of the various treatof odor emission from the drain-system being a t g, ments. I n all of the work 0 . 5 A. T. ton of ore, passed therefore, its connection with the hood is essential. For common laboratory use the reservoir need not through Ioo-mesh sieve, was taken for each charge. be of the given design. An ordinary five- or ten- The fusions were made in a gas muffle, excepting pound, wide-necked bottle will serve the purpose those of a few slags, which were carried on in a crucijust as well. I n this case the siphon-tube g, r , is taken ble furnace. The fusions were started a t low heat and through the sealed stopper with the other tubes, gradually raised to about I Z O O O C., the charges being and the bottle freed of the sediment, whenever neces- in the furnace about forty-five minutes. Morganite sary, by disconnecting the stopper and emptying cupels w’ere used. The fluxes, time of fusion, size of buttons, in short all conditions were kept as nearly the whole contents. This device, when constructed of other acid-proof uniform as possible. The litharge used contained materials on a larger scale, may readily be applied silver, for which corrections were made. in industrial plants in which hydrogen sulphide is For the first work a Leadville, Colorado, pyrite used. was selected. It was almost pure iron sulphide, I n conclusion, i t may not be amiss to call attention carrying a little copper. The reducing power was to the facts that the extra cost of installation of the 9 . I . Three series of four charges were made up. improvements is trifling and the operating expenses Series No. I consisted of assays for the potassium practically nil, while they greatly contribute to the nitrate method, the following charges being used : increase of the “joys” of the laboratory. 0 . 5 A. ’ I ’ . Ore. Grams. Acknowledgment is due my assistants, Messrs. Ferrel and McComas, for the preparation of the draw.... 15.0 ings from which the cuts in this paper were made.
through this drain and made odorless, instead of being poured into the sink with the well-known effects. The chemical process in the apparatus is i s follows: “ The liquor is a n aqueous solution of ferrous chloride, surcharged with hydrogen sulphide gas. The injected air oxidizes the ferrous to the ferric salt, which is partially precipitated in a basic form. The ferric chloride in solution, by the intimate contact with the inflowing, dissolved hydrogen sulphide, immediately causes the latter’s oxidation and decomposition. I n the reaction the ferric salt is again reduced to the ferrous state, while hydrogen chloride is formed, ‘and sulphur liberated : Fe,Cl, H,S = zFeClz zHCl
+
+
+
PERTHAMBOY, N. J., Feb. 24, 1909.
THE CRUCIBLE ASSAY OF PYRITIC CONCENTRATES FOR SILVER AND GOLD.
.... 1 0 . 0 .... 2 8 . 5 Salt cover.. ............................
Series No.
2
as follows: Ore.
was first dead roasted and then fluxed 0 . 5 A. T. Grams.
By GEORGEBORROWMAN.. Received March 22, 1910.
I n evaluating pyritic gold and silver ores containing little or no gangue material, the assayer has recourse to three crucible methods. He may remove the sulphur by preliminary roasting ; he may lessen the reducing power by using potassium nitrate, or desulphurize by employing iron as wire or nails. The literature affords various criticisms, favorable and adverse, on a t least two of the procedures. Mr. R. W. Lodge, in his “Notes on Assaying,” states the belief that loss of silver occurs in certain ores due to
Salt cover.. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Series No. 3 was made up according to the general type of charge usually recommended for the iron method : 0.5 A. T Ore. Grans. h-aHCOs. ....................... 30.0 PbO. . . . . . . . . . 23.0 Borax glass 10.0 4 Iron nails (20-penny). Salt cover.. .............................
.... ... ..................
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY. The slags in all cases were liquid and poured well. dl1 were glassy excepting those of No. 3, which were basic. No matte formed in any case. Cupellation gave the following results : No. 2 .
No. 1. Au Ag. Mgs. 9.01 8.90 8.95 8.95
+
Au
+ Ag.
Au
.
Mgs. 8.87 8.91 8.59 9410
-
__
+
__
8.86
Av. 8 . 9 5
No. 3 . Ag. Mgs. 7.88 7.23 8.29 8.29 8.05
It will be seen that Nos. I and z check closely, while No. 3 is uniformly low. The slags of No. 3 being basic were assayed and found to carry on the average 0.91 mg. With this correction, No. 3 checks the others closely. The same ore was then assayed with the following charge, recommended by Furman : Ore. NaHC03.
0 . 5 A . T. Grams.
............... ...................
35 20 15 5
.......... K N 0 3 . . ................ . 3 Nails (20-penny). . . . . . . . . . . . . . . . Borax glass cover . . . . . . . . . . . . . . . . Two fusions were made; the slags were glassy and no matte formed. Two more charges were run, omitting the nitrate, considerable matte forming in both cases. The two matte-free buttons yielded the following :
+
Au Ag. Mgs.
June, 1910
These results confirm the preceding. The ore used in the last fusions was taken from a different part of the same lot from which the first assays were made, accounting for the differen$ silver value. The gold in this ore was merely a trace, too small amount to show any detectable variations. The experiments were concluded by repeating the above iron method tests on a higher grade ore containing more gold. This was also practically pure pyrite carrying values in the form of auriferous argentite. Four assays were made each with of the two iron methods described above. As a check, four more were run by the niter process. The following average results were secured: Series No. I is from the ironniter fusions; No. 2 from the non-niter iron method; and No. 3 from the straight niter assay: No. 1 . Au Av.
No. 2 . Au Ag. hlgs. 76 5 4
+ Ag.
+
Mgs. 78 28
No 3 . Au Ag Mgs. 79.08
+
Two slags from each were assayed and the following amcunts recovered : No. 1 . Au Ag. Mgs.
No. 2. Au Ag. Mgs.
+
+
3 00 2 67
3 62 3 50
_ .
Av. 2 . 8 3
No 3 Au +. Ag Mgs. 0.93 0 93
__
__
3.56
0.93
Not more than traces of gcld were recovered from the dags. CONCLUSIOKS.
h-0. 1 ....................... 9.17 No. 2 . . . . . . . . . . ....... 9.04
From the foregoing data it seems that with pyrite ores, a t least, the maximum amount of niter can be -4verage. ............. 9 . 1 0 used with imprnity, that in fact results are, if anyThese results, it will be noted, are a trifle higher thing, a little higher by this method. Iron does not than obtained by any method previously. Fur- thoroughly decompose highly sulphuretted ores though man’s charge was further tested by comparing results only silver appears to be carried into the slag. The use obtained from it with those from a charge similar to of considerable silica apparently assists in breaking the one used in the first iron fusions. It was taken up the sulphide, the tendency to matte formation befrom one of the recent text-books and consisted of ing overcome by a little potassium nitrate. The losses, however, even with basic slags are not very the following : 0 . 5 A . T. large, but i t is evident that when greater accuracy Ore. Grams. is desired, the more troublesome niter method should NaHCOa . . . . . . . . . . . . . . . . . . 30 . . . . . . . . . . . . . . . . . 20 be used in preference to the convenient (‘nail” fusion. ................. 3 As might be expected, the comparisons show the Borax glass c o v e r . . . . . . . . . .. results of the roasting method to be satisfactory, Four charges of each were fused. The slags from though higher grade ores might suffer a considerable the latter mixture were basic, the others as before, mechanical loss. In fu ing roasted ores which had glassy. The results of cupellation follow, No. I contained argentite, the writer found that considerable silver was carried into the slag, probably due to beingifrom the nail-niter treatment : incomplete breaking up of silver sulphate in the No. 1. No. 2 . Au -4- Ag. roasting. Au + Ag. _.
. I
Mgs. 13.61 13.64 13.54 13.74
Av.
Mgs. 13.04 13.27 13.17 13.36
-
-
13.63
13.21
UNIVERSITY O F NEBRASKA,
LINCOLN, NEB.
