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The conveniences, the comforts, and luxuries conferred on Society by the many important Inventions of the present century, must naturally excite a desire to know the origin and progress of the application of scientific principles, by which such advantages have been gained. Practically considered, those Inventions are of much greater value than the discoveries of Science on which most of them depend; and the scientific inquirer who confines his views to abstract principles, without looking beyond them to the varied methods of their application to useful purposes, may be compared to a traveller who, having toiled arduously to gain the top of a mountain, then shuts his eyes on the prospect that lies before him. The knowledge to be gained by such inquiry is eminently practical, and of a kind which those engaged in any of the pursuits of life can scarcely fail to require. A History of Inventions almost necessarily implies a description of the mechanisms and processes by which they are effected; so far, at least, as to render the principles on which their actions depend understood.

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The possibility of cheap electric power for a number of mining areas in this country has suggested to many the idea of electric smelting of nonferrous ores in small units at or near the mines. The electric smelting of nonferrous ores was tested fairly thoroughly 20 years ago by United States Bureau of Mines and by others, and the fact that it did not achieve continuing workable, success in any instance is sufficient proof that it offered no advantages at that time.

Lyon and Keeney thoroughly investigated the problems, covering the possibilities with iron ores, copper ores, lead ores, zinc ores, complex. They decided that, excepting iron ores, aluminum, and ferroalloys, electric smelting was in the experimental stage. It is the purpose of the present paper to survey the technical and economic changes that have taken place and to determine whether electric smelting of nonferrous ores offers any more promise today than 20 years ago.

The following factors need to be considered especially:. While most of the current interest in electric smelting relates to pyritic gold ores, actually more data are available on other ores, notably zinc and copper.

Accordingly, we shall consider the status of electric smelting of several types of ores individually, based on the factors enumerated. In , Lyon, Keeney, and Cullen reviewed the status of electrio-furnace zinc metallurgy in the following terms:. In the metallurgy of nonferrous metals, the electric smelting furnace has had a greater application for the treatment of zinc ores than in the metallurgy of any of the other nonferrous metals except aluminum the process has not been applied to any great extent because of the difficulty of condensing the zinc vapor produced in smelting in the electric furnace.

The cause of this difficulty has not yet been definitely determined. With few exceptions the work has not been done on a very large scale, and so it may be said that the electric smelting of zinc ores is still in the experimental stage. The foregoing note on smelting zinc ores is followed by a description of the electric-furnace process in Sweden. Roasted zinc-lead-silver slime was being smelted, but many difficulties presented themselves, although it was expected that they would be overcome.

Electrothermic or thermoelectric smelting may be defined as the reduction of an ore by means of an electric current.

It may be said that more than two-thirds of the zinc metal produced in the world is derived from the retorting or distilling of roasted concentrates; the rest results from the electrolytic or wet treatment of ores. For retorting, the heat, which is applied outside, is derived from natural gas, producer gas, waste heat, coal, or other combustibles.

Retorting is not smelting; it is not simple, and losses are rather high. Neither is the smelting of zinc ores simple; in fact, in general it is impracticable. The first electric furnace for the reduction of zinc ores was devised in Little was done then until , through to ; but the production of zinc as metal was difficult, most of it being condensed as blue ponder.

Later, the electrolytic treatment of ores more or less directed attention away from electric smelting. Because of the imperfections in retorting and in electrolytic processes, the United States Bureau of Mines and the Missouri School of Mines and Metallurgy undertook an investigation into the electrothermic metallurgy of zinc. The greatest obstacle encountered in all the attempts to smelt zinc ores electrically, and one that has caused the failure of many otherwise promising attempts, has been the difficulty of condensing the zinc vapor obtained from the smelting furnace to liquid zinc.

In the earlier work, the major part of the zinc was invariably obtained as blue powder, which clogged the condensers and had to be remelted to obtain a marketable product. Complex as is this problem, many complexities arise in smelting ores.

Zinc is oxidized by the carbon dioxide formed; the zinc vapor is diluted by carbon monoxide and is sulphidized by sulphur and sulphur dioxide; also, fine dust is likely to be carried into the condenser by the rush of evolved gases. The electric smelting of zinc ores for the production of spelter can now be termed metallurgically feasible.

The question of cost then becomes of paramount importance. Up to the present time, the plants in Norway and Sweden are the only ones that have been able to achieve success. Little data on their costs are available, but the plants have been able continuously to maintain and expand their operations during more than 15 years.

They are favored by having very cheap power available, and it is probable that their process would not be practicable in this country the United States. Judging from published reports, their metallurgical results are not as good as have been obtained in much of the work in this country. The largest single item of cost in the electrothermic process is electric power. An electric smelter must be near cheap power. A conservative estimate of the requirements of a properly constructed, continuously operating furnace of 5 to 10 tons daily capacity would seem to be 3.

This consumption should be lowered by larger and standard operations. Somewhat more power than that stated may be required by low-grade ores. In the Western States, 24—hour continuous power can be obtained at rates of 0. It is metallurgically possible to recover at least 90 to 95 percent of the zinc from an ore in an electric furnace in regular operation. Also, most of the proposed electrothermic processes recover lead, copper, and the precious metals as bullion and matte or as a product in desirable shape for blast-furnace treatment.

Low-grade and complex ores offer no difficulty in the electric furnace, and the presence of impurities is not detrimental. The cost of an electrothermic zinc plant will be less than that of either a retort or an electrolytic plant if power is purchased. The process has the additional advantage that units of 10 tons are practicable. Each of the three processes -retort, electrolytic, and electrothermic — has its particular field and there are undoubtedly places in this country where the electrothermic process could be profitably applied.

In the 13 years that have elapsed however, it has been impossible to find any cases, either here or abroad, in which electrothermic zinc smelting has been profitable, in spite of some rather extensive trials, especially that at Trollhattan, Sweden. The attempts to smelt zinc ores in the electric furnace in Sweden have been described by Landis. Gustav deLaval began to experiment in the field of electric zinc smelting in and by he had developed a practical but intermittent furnace at Trollhattan, Sweden.

By he could smelt roasted sphalerite using coke as a reducing agent and lime as a flux and he applied for the first of a long series of patents. In a company was organized, and large plants were built at Trollhattan, Sweden, and at Sarpsborg, Norway. The former was much the larger, employing 22 furnaces,, each of horsepower, during the World War. The early furnaces were single-phase, with bottom contact and one movable top electrode.

The newer furnaces, which had greater hearth area, were provided with two top electrodes and no bottom connection. One of these was merely suspended in the furnace and lowered as consumed. Zinc was recovered partly as liquid metal and partly as powder. As developed to the Trollhattan process was one of all—electrothermics involving the use of four different types of electric furnace on zinc and a fifth for lead refining, if lead was present.

The sulphide ores ware roasted in a multihearth furnace and mixed to make the charge as nearly self—fluxing as possible. The smelting operation was carried out in a closed, arc-resistance type of electric furnace. The reaction was essentially one of reduction and volatilization, the gangue of the ore being fluxed to produce a fusible slag. The furnaces were charged from overhead bins, the charge consisting of a pre-mixed roasted ore, flux, and coke breeze; and if copper was present in the ore, enough sulphur was left in the charge to produce a-low-grade matte.

This smelting furnace handled all off-grade slags and mattes, together with any residue of zinc dust not liquefied in the rotary furnace and the various residues from the refining furnaces. This gas stream passed to water-cooled condensers, where the metals dropped out in the form of a powder and mechanical screw conveyors were provided for continuously discharging the powder through a suitable seal. The carbon monoxide passed out through a water seal and burned at the exit stack.

The character of this flame was an important guide to the furnace operator. The zinc-lead powder removed from the condensers was collected in metal containers, which were carried to bins placed above the rotary furnaces. A large part of the powder was rolled into liquid, which was tapped from the rotary furnaces at intervals. Eventually, the lead-zinc alloy was liquated and yielded refined zinc slabs and lead pigs, also an iron-silver-copper cake that was sold.

The power consumption, calculated back to the original zinc ore from Burma, was kw. The total consumption per metric ton of 57 percent material on the three furnaces was 3, kw. In spite of years of work recorded in volumes of literature, and an expenditure of large sums of money, there is not a single electrothermic zinc smelter operating anywhere in the world.

In this industry the electric furnace plays only a secondary part today. They make zinc oxide and are operated by the St.

Joseph Lead. Lawrence Co. In the plant are two Herreshoff hearth roasters, three Dwight-Lloyd sinterars, Cottrell precipitators, sulphuric-acid equipment using vanadium pentoxide as catalyst, and preheaters, eight Gaskill patented electrothermic furnaces arranged to make baghouse zinc oxide, which is advertised as lead-free. Six 1, kw. The process is described by George F. The plant was designed to treat tons of concentrates daily.

The furnaces have a bore of 57 inches and are 37 feet over-all in height. Electrical contact with the charge is made by means of three pairs of carbon electrodes; the charge itself constitutes a resistor 57 inches in diameter and 24 feet long. About 18 hours is required for the passage of the charge through a furnace, each of which consumes 29, kw. The voltage averages The final product varies according to customers wishes, but a typical example is As is seen by the foregoing description, these electric furnaces are not actually smelting the zinc concentrates; but use is made of electric heat to volatilize the zinc which is condensed as oxide.

The coke serves a double function — to provide the resistance oath for the electric current and the carbon for reduction of the zinc. The refractories used in the electrothermic furnaces are described by Winfield B. It was found that electrical features of the furance introduced more than the usual limitations in refractories. The furnace wall is composed of circular sections of refractories supported on steel skew-rings, which are electrically insulated from the furnace columns.

The major refractory problems pertain to tho silica and iron solution attack at high temperature. Exact dimensions of shapes is of importance, also. Experimentation finally evolved a mix of low-alumina grog minus mesh, with control of the amount of minus mesh , a ball clay, and 9 to 10 percent water.

The texture is uniform, the refractory has a metallic ring when struck, and the porosity averages 15 percent. Low porosity is an important feature in any refractory for this type of furnace. The possibilities of metallic-zinc production by reduction with solid fuel and electric heal would seem to have been fairly well exhausted. The economic possibility of the natural-gas reduction process developed in the Metallurgical Division of the Bureau of Mines remains to be determined, however.

Maier, of the Bureau of Mines, had discussed the use of methane for reducing zinc oxide and predicted equilibria at various temperatures for the more important reactions. Doernor extended the study. The gas used contained The experimental retort need not be described.

Electric Smelting Furnace of Ore

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For more than fifty years DK Holdings has been at the forefront of manufacturing and developing diamond based grinding and cutting tools. Ed Hill discovers more about its approach to composite tooling. The ISO accredited company produces diamond tools for a broad range of applications and materials ranging from stone, glass, ceramics, hard metals and composites. Its cutting tools and abrasives products can be found in industries as diverse as high-end engineering, food production and medical tool manufacturing. It exports to more than 50 countries and employs around 90 staff. DK Holdings range includes electroplated, vacuum brazed, resin-bonded and flexible tools for cutting, drilling, profiling, grinding and polishing. Its composite products include saw blades, bandsaw blades, holesaws, drills, routers, machinery and grinding wheels. That led by natural progression into the aerospace and other composite sectors.

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The possibility of cheap electric power for a number of mining areas in this country has suggested to many the idea of electric smelting of nonferrous ores in small units at or near the mines. The electric smelting of nonferrous ores was tested fairly thoroughly 20 years ago by United States Bureau of Mines and by others, and the fact that it did not achieve continuing workable, success in any instance is sufficient proof that it offered no advantages at that time. Lyon and Keeney thoroughly investigated the problems, covering the possibilities with iron ores, copper ores, lead ores, zinc ores, complex. They decided that, excepting iron ores, aluminum, and ferroalloys, electric smelting was in the experimental stage.

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