صور الصفحة
PDF
النشر الإلكتروني

wet-concentration mill at Midvale and a sample of ore from the Wasa mine at Hall, Mont., were treated. The Wasa mine ore contains most of the zinc as marmetite, the double sulphide of zinc and iron, in which iron sulphide is thought to be present in solid solution in the zinc sulphide.

The analyses of these four products is given in Table 19, and the screen analyses of the products that were roasted are presented in Table 20.

TABLE 19.-Results of analyses of four zinc products low in lead.

[blocks in formation]

TABLE 20.-Results of screen analyses of zinc ores and concentrates low in lead.

[blocks in formation]

The high-grade concentrate from Joplin, Mo., was almost pure blende of a beautiful orange hue, and any failure to recover all of the zinc could only be due to incomplete roasting. This test gave a measure of the success of the roasting tests that are recorded here. As can be seen from Table 21, roasting this material at 750° C. for five hours rendered only 89 per cent of the total zinc soluble in the leaching solutions. The conclusion is that the roast must have been incomplete. The tailing would have to be reroasted if this were the best work that could be done on a single roast. The work of nearly everyone who has roasted this type of material has shown that well above 95 per cent of the total zinc content can be rendered soluble by sufficiently lengthening the time of the roast, and on that account. little apprehension need be had over any necessity of reroasting the residuc. Also, in these tests an acid efficiency of more than 90 per cent was attained.

TABLE 21.-Leaching zinc blende from Joplin, Mo., after roasting.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][subsumed][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

The roast of the Midvale blende concentrate, as seen in the first part of Table 22, was more successful, possibly because it was finer than the Missouri concentrate. Extractions of more than 96 per cent were obtained, and the acid efficiency was practically 100 per cent. Any lead present was rendered almost completely soluble in brine solution. The lack of agreement between the solution recoveries and the removal of lead as indicated by the analysis of the tailing indicate that about 25 per cent of the lead had volatilized during the roast. The success of this roast showed that with proper grinding the conditions of roasting chosen were designed to give high recoveries of the zinc and the lead.

In the treatment of the middlings from Midvale the recovery of zinc was not so high, possibly through the formation of ferrites during roasting. The results are given in the second part of Table 22. Practically all of the lead, which was present in small amount, was recovered by leaching in brine solution following the sulphuric-acid leaching for zinc.

TABLE 22.-Results of leaching zinc-blende concentrate and zinc-iron middling from Midvale, Utah, after roasting.

[blocks in formation]
[blocks in formation]

26. 18

5.7

41.80

21.4

[ocr errors]

25 57.2 14.30 0.38 13.8 25 57.2 14.30 .32 13.8 1.49 .035 57.2 14.30 .34 13.8 97.6 96.6 1.49 .044 98.3 25 57.2 14.30 .36 13.8 97.5 96.6 1.49 .042 101.5 25 57.2 14.30 30 13.92 97.9 97.4 1.49 .044 103.0

97.4 96.6

1.49 0.042

99.8

97.7 96.6

101.2

[merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]
[merged small][ocr errors][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][subsumed][subsumed][merged small][merged small][subsumed][merged small][subsumed][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

TESTS OF MARMATITE ORE FROM WASA MINE.

Roasting and leaching of the marmatite ore from the Wasa mine gave low recoveries of the zinc; the maximum recovery possible seemed to be about 75 per cent. A 3-hour contact with excess of acid failed to dissolve any more zinc and only used up more acid, reducing the acid efficiency from 100 per cent, as indicated by a 1.5hour leach, to 83 per cent. Low zinc recoveries are to be expected from such ore, on account of the intimate contact of iron and zinc in the mineral. Practically ideal conditions exist in this ore for the formation of zinc ferrite from the iron and zinc oxides formed in roasting, as the purest piece of blende contained about 12 per cent iron. A number of other roasts of this ore were tried, the results of which need not be recorded in this paper, but seemingly no better recoveries of the zinc could be obtained. The data for the first test are given in Table 23.

TABLE 23.-Results of leaching ore from Wasa mine, after roasting at 750°C. for 4 hours.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

The conclusions are that with pure blende ground to pass about 60 mesh, practically all of the zinc can be roasted to a form soluble in sulphuric acid in two to five hours at 750° C., the time of roasting depending on the depth of ore bed used. Where zinc and iron are intimately combined, as in a marmatite ore, it is very hard to get all the zinc into a form soluble in acid, on account of ferrites of zinc forming. If the zinc and the iron in a mixed-sulphide ore are present as a mechanical mixture of pyrite and sphalerite, less ferrite is formed and recoveries of at least 90 per cent of the zinc are possible after a roast of the kind described. Most of these conclusions are not new, but there have not been much data on record to support them; the results presented here will make the truth more evident.

TESTS OF PARTLY OXIDIZED ORES.

As regards partly oxidized ores containing zinc sulphide, the question is whether such ores can be roasted in order to oxidize the sulphide of zinc, while the oxidized minerals of zinc remain unaffected, as far as their reaction toward sulphuric acid is concerned. A prominent example of such partly oxidized ore is that in the Lower Mammoth mine, of Mammoth, Utah.

ORE FROM LOWER MAMMOTH MINE.

Two samples of this ore were treated by roasting. Both of these were almost pure white, claylike material, much decomposed by weathering, and seemed to be completely oxidized, as far as the eye could distinguish. Such an ore would be almost impossible to leach if treated direct, on account of filtering difficulties, but would not be hard to leach after roasting, as the heat breaks up the "colloidal" material in the ore so that it can be filtered. The screen analyses of these two samples are given in Table 24. The results of the tests are shown in Tables 25 and 26.

TABLE 24.-Results of screen analysis of two samples of partly oxidized ore from Lower Mammoth mine, Mammoth, Utah, after roasting.

Size of mesh.

On 20-mesh..

No. 1. No. 2. 15.8

On 35-mesh

On 65-mesh.

On 100-mesh.
On 150-mesh.

On 200-mesh

- per cent..
..do....

....

[blocks in formation]
[blocks in formation]

Through 200-mesh

TABLE 25.-Results of roasting and leaching partly oxidized zinc ore, Lower Mammoth

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]
« السابقةمتابعة »