Progress of the Silver-Lead Metallurgy of the West, During 1874* BY A. EILERS. THE year 1874 marks a decided advance in the metallurgy of the West, in two directions. On the one hand, the technical management has been very materially improved, and on the other, the production has been largely in-creased over that of the previous year.
The technical improvements of greatest importance are the introduction of condensation chambers, or flues, at several works, and the further treatment of the lead- matte produced in the ore smelting. These two are of general im-portance, and although by no means introduced at the majority of works, their adoption at the few where their great importance has begun to be understood will no doubt bring about their universal introduction. To these may be added a third step forward, which for some localities is vital enough, though for
Fig. 1
Fig. 3
others it must still remain doubtful whether it is to be regarded as an improve-ment or not. This is the introduction, at several works in Utah and elsewhere, of water-jackets, in addition to the water-tuyeres used heretofore.
Finally, the year 1874 has witnessed the successful introduction, in one Ter-ritory, of the Ziervogel process, by means of which argentiferous and auriferous copper-mattes, heretofore sent to England and Germany for further treatment, are now deprived of their silver in the most satisfactory manner in loco.
Of contrivances for the purpose of collecting the dust and condensing the fumes, two deserve special attention. These are the long flues built by the Richmond and Eureka companies at Eureka, Nev., and the peculiar chamber
* A paper read before the American Institute of Mining Engineers at the New Haven Meeting, February 1875.
constructed by Mr. AYRES, of the Waterman Smelting Works, at Stockton, Utah.
The flue at the Richmond works is 800 feet long and ends in a wooden stack, 40 feet high, which stands on the side of the mountain behind the works, and the top of which is about 200 feet higher than the charge doors of the furnaces. It receives the fumes from three large furnaces, which smelt 150 tons of ore (mostly fine) per day. The 250 feet flues along the back of the furnaces and thence to the hillside are constructed of strong sheet-iron, plates of which are riveted together in the shape of a pentagonal prism, the two upper corners being slightly rounded off. By means of iron rods this part of the flue is sus-pended horizontally from wooden trestles, with the sharp angle downwards. About 4 feet below the lower extremity of the flue, a car track runs along the entire length. At intervals of a few feet, small sliding doors are inserted along one side and at its lower edge, so that by opening the same the dust can be drawn into the car below. The size of the flue in this part is amply sufficient
Fig. 2.
to receive all the fumes. The accompanying sketch, Fig. 1, shows the size as well as mode of construction.
Further on, where the canal enters under ground, it is still larger, being 9 feet wide on top and 8 feet deep; but from this point on all the way up the hill to the wooden chimney, it is simply a culvert in the ground, without lining of any kind, and closed on top by a sheet iron cover.
In 1873, the total loss at the Richmond works was 20 per cent of the assay value of the ore; in 1874, after the flue had been put up, the loss was reduced to 12 per cent., of which a large proportion is accounted for in the speiss. Only the first 250 feet are cleaned frequently ; the portion under ground re-quires this only at long intervals. Yet in the sheet-iron portion alone there are saved from 9 to 10 tons of dust per day, when the three furnaces are run-ning. The deposit here obtained assays invariably higher in the precious metals than the ore smelted, and, if we assume its value as only $55 per ton, it is easily seen what an immense saving is brought about by this simple con-trivance.
The Eureka flue is also 800 feet long and constructed of galvanized sheet iron throughout.
The condensation chamber at the Waterman Works, near Stockton, Utah, is substantially represented by the accompanying cuts. (Figs. 2 and 3.) At the time of my visit to the works the furnace was in blast, and it was therefore im- practicable to obtain dimensions inside of the chamber. Some of these were, however, furnished to me afterwards by Mr. GEO. P. LOCKWOOD, who super-intended the smelting works at the time. The accompanying cuts show approx-imately the construction of the chamber, which is partly novel, at least as far as the use of the cylinder with Archimedean screw is concerned. In the sketch the letters represent:
F.—Shaft-furnace.
A.—Flue from furnace to chamber.
B.—Smaller compartment of chamber.
C.—Larger " " "
D.—Chimney.
E.—Archimedean screw in sheet-iron cylinder, covered with tar.
b.—Axis of cylinder, revolved by pully, p, on the outside of chamber and gearing inside.
H.—Discharge-valve in bottom of chamber.
d.—Slide-valve in partition wall between the two compartments, opened when the chamber and cylinder are cleaned.
a, d.—Revolving water jets, to keep the sides of the chamber wet.
c.—Level of water in bottom of chamber and cylinder.
In starting the furnace, F, the chamber is cold, and there is an insufficiert draft through the chimney, D, as well as danger of explosions from the flaming furnace. Therefore, the top of the furnace is at first kept partly open. In from 8 to 12 hours the chamber is sufficiently warmed, and the flaming of the fur-nace has ceased so much that the top of the furnace can be closed and the gases directed through the chamber. Passing through A and B, there is no escape, except through the revolving cylinder E, in which, as two-thirds of its size are immersed in water, the flames are thoroughly cooled, and the dust pre-cipitated either in the water or on the walls of C.
The walls of the two compartments of the chamber are cooled and kept wet by the jets a a, which throw water against them in a continuous shower. The uncondensed gases then pass off into the chimney D.
The cylinder in this chamber revolves 65 times per minute, when in action. The velocity imparted to it must of course be commensurate with the quantity of gases evolved from the furnace.
The bottom of the chamber slopes from all sides to the discharge-valve, H, through which the accumulated dust is drawn off every 24 hours into settling tanks outside of the furnace building. From these the clear water is drawn off every 12 hours. The bottom of the condensing chamber is again filled, by means of a hose, after every cleaning.
To keep the water at the level c, an escape is provided, to run off the water brought in continually by the jets a a. The roof of the chamber is constructed of slightly arched 3/8-inch boiler iron plates, which are laid on loosely. There are several improvements, which suggest themselves for this chamber, as, for instance, some way of preventing the settling of dust in A, which can be effected by bringing the top of the arch under A to an angle of about 45 degrees, or by inclining the whole canal steeply upwards or downwards. The size of the chambers is also smaller than it ought to be. In fact, I do not doubt, that with two chambers, at least 16x16 feet and 25 feet high, to be cooled by sprinklers from above, the no doubt troublesome cylinder and screw might be dispensed with altogether.
As the chamber is now, however, it does very good work, saving on the whole about 11 per cent, of the ore smelted as dust. There are no smelting works in Utah, of which as favorable a record in this respect can be given.
In the further treatment of the first or lead-matte, a beginning has been made by several works in Utah, where an increased quantity of sulphurets has been encountered as the mines advanced in depth. Lead-matte has been made for years in the West, and the total loss incurred by disregarding it has been large enough, as I have shown in a former paper; but the amounts of silver and lead thus squandered at individual works were not sufficiently im-portant in the eyes of the inexperienced to induce them to treat a product of which they knew nothing, and which for years was designated as "iron." Since, however, more abundant sulphurets have begun to occur in the ore a very largely increased production of matte has taken place, which in some cases has been equal by weight to the product of lead.
Mr. WARTENWEILER, of the Winnamuck, first began in Utah to roast his matte and to use it in the ordinary way in subsequent ore smeltings as a very wel-come flux. Others, and notably the Sheridan Hill works, have since followed his example. All have found that besides the advantage of extracting the larger part of the lead and silver from the matte there are other very material gains in doing so. Mr. WARTENWEILER says that by using the matte he did not only lessen the quantity of costly iron-ore flux from 20 per cent, to 3.5 per cent, of the charge, but that also the quantity of fuel used per ton of smelting mixture was very largely reduced. His data permit the calculation of the exact saving in the consumption of fuel, which is 28 percent, of the quantity formerly used. In other words, while 409 lb. of coke per ton, or 20.4 per cent, of the charge, were used before roasted matte formed a part of the mixture, only 293 lb. per ton, or 14.6 per cent, of the charge, were necessary after the change was made. The total additional cost in re- handling and roasting the matte (por- tions of it three and four times) is certainly not more than $4 per ton. Even-tually, of course, a small fraction of the original bulk remains as argentiferous and often auriferous copper matte, which is not further treated and sold in that shape.
The introduction of water-jackets instead of fire poof material used in the smelting zone of the shaft furnace is another step forward, which, at least for Utah and Cerro Gordo, where fire brick or other refractory material is exces-sively high, cannot be regarded as of doubtful merit. These jackets are simply hollow iron castings, occupying about 3 feet 6 inches in height on the outside of the hottest part of the furnaces. The water-space is from 2 1/2 to 4 inches. The tuyeres were first cast in one piece with the jacket-sections where the furnaces were round, or the side and back-castings where they were rectan-gular. But it was soon found far better to leave openings and insert wrought iron tuyeres. For when a cast tuyere cracked, which was frequently the case, the whole section or side of the jacket, as the case might be, had to be removed, which is no easy matter with a furnace in blast. Otherwise the appliance proved very satisfactory, the increase in the consumption of fuel being insig-nificant; and there is no doubt that it will be largely used in the future. Where the water used holds appreciable quantities of mineral in solution, a form of the jacket preferable to the present one will undoubtedly be simple cast plates, provided with a water trough at the lower extremity to carry off the water which is continually forced in many small streams against the top.
The introduction of the Ziervogel process for the extraction of silver from copper mattes at the works of the Boston and Colorado Company at Black Hawk, Colorado, has been a perfect success, both technically and financially. The increase in the production of argentiferous and auriferous lead in the far West over that of the previous year has been large. This was not so much due to the erection of additional works as to better management in keeping a number of those in existence regularly at work. The following is a com-parative statement of the production during the years 1873 and 1874 :
PRODUCTION OF WORK-LEAD.
1873. 1874.
Where produced. No. tons. Gold, silver & lead value. No. tons. Gold, silver & lead value.
Nevada . . . . . . . . . . . 12,812 $5,063,235 11,516 $3,865,419
Utah . . . . . . . . . . . . . . 9,566 2,901,191 15,474 4,332,720
California . . . . . . . . . . 4,000 920,000 5,095 1,680,000
Montana, Colorado
and other sources
(estimated.). . . . . . . . 300 144,000 375 180,000
26,678 $9,028,426 32,460 $10,058,139
