in the wheel, and raised by the wheel so as to dump into the launder c. The boxes d are V-shaped spitzkasten to catch any sulphides in the tailings. Large wheels for handling tailings were probably first used at the Lake Superior Copper Mines, although the idea no doubt originated in Cornwall, England. 68. The Chinese pump shown in Fig. 42 may be used for handling tailings and water with probably more economy than any of the wheels, pumps, or other devices so far described, provided it is intended to charge the lixiviation vats by launders and with tailings. These pumps require comparatively little power to run them. SMELTING PLANTS 69. General Considerations.-Smelting plants must be located with reference, first, to water supply; next, fuel and flux; and lastly, ore. Furnacescannot be worked without water; it is needed for boilers and the modern economical furnaces, which are constructed with water-jackets. The supply of water required for furnaces will be found in Art. 88. Fuel and flux are both necessary items and furnaces should be located so as to have, if possible, railroad transportation for these materials; or if that be not possible, to have good wagon roads at least. Custom smelters are usually situated where cheap fuel can be obtained, for, as the ore must come FIG. 42 This to them, they care naught for the location of mines. 70. The ideal furnace location is one where water is abundant and where fuel, flux, and ore can be delivered with a short haul into the stock piles without extra handling. This, of course, requires a system of railway tracks and trestles connecting with the main haulage railways. It was customary in the past and is so yet in some instances to regard 36- and 42-inch gauge tracks as the proper width for furnace delivery tracks. This idea is erroneous, for it is possible to put in a standard railroad track which has a gauge of 4 feet 8 inches where it is possible to put in the above. If narrower than standard-gauge tracks are used, it causes the rehandling of the fuel and sometimes of the flux and ore. The idea prevailed in the past pretty generally that curves on narrow-gauge roads could be given more curvature, so as to take up less room. The wheel base on two-wheel mine cars of any size is nearly the same as for four-wheel trucks on narrow-gauge cars and the latter is about the same as on broad-gauge cars. The small difference in curvature required for standard-gauge car trucks will not take up much more room than ordinary mine cars, such as would be used to transport ore to the furnace a mile or more. 71. Ideal furnace locations are not always obtainable; but whenever it is possible, locations should be picked where nearby ground will furnish a dumping place for slag. Granulating slag and having it floated away by some stream has been spoken of as an economical method of getting rid of a troublesome furnace product. When such locations are not convenient, but water is abundant, granulating slag and then floating it, as described in Art. 59, to some depression in the ground near by is to be recommended. Again, T the molten slag may be granulated and elevated to dump piles by some of the methods described for the disposal of tailings. Lastly, the slag may be removed to dumping grounds in a molten condition and used for filling up depressions in the surface, if convenient, and if not, for creating. slag heaps. 72. Arrangement of Furnace Plants.-The location of the plant having been determined, the next step is the arrangement of buildings, stock piles, and furnace flues with reference to the furnaces and roasters. The furnaces and roasters must be located with regard to the quantity of ore that may be delivered and also to any possible increase that may occur to double the output in the future. The actual number of furnaces erected should not exceed the output of the mines, but space should be left for additional furnaces and stock piles, should the ore come in greater abundance in the future than the original furnaces can manage. Flues, water, and steam supply should be considered with an eye to an increase in the number of furnaces, and should in each case, whether an increase occurs or not, be in excess of the actual requirements of the plant. The reasons for this are obvious: For instance, if one boiler should give out, there would be too little steam; or if an auxiliary engine of some kind were needed, there would be too little steam power; or, again, in case a furnace were to work badly, it might require an additional blast pressure to cure the trouble; finally, it is economy to have an overabundance of steam supply, rather than a shortage or just enough. The same method of reasoning will apply to keeping an additional furnace in the plant, even though it is idle three-quarters of the time, also reserve engine power, blowers, and water supply. The first cost in such cases will be greater, but it is, nevertheless, cheaper in the long run, because fixed charges about furnaces do not decrease when something goes temporarily wrong, and in furnace work it is a steady output that keeps down expenses. 73. While the arrangement of a furnace plant will depend somewhat on the location, it will also depend in detail on the metallurgist in charge. Details of requirements will necessarily vary, but general details. will not. 74. If the plant is to be permanent, the buildings should be of stone, brick, and iron; but if it is a temporary affair, the buildings may be constructed of light framing and rough. boards. Sometimes corrugated iron is used for sidings, but it is not as durable as wood; neither will an iron or steel roof last as long as a first-class shingle roof. But a smaller fire risk, which even then is large, ofttimes causes the management to favor the metal construction. In case the capital necessary for a large furnace plant is not available and must be derived from profits, any temporary structure will suffice; but while the building may be ramshackle, the furnace and appliances should be first class in every respect. The general plan in this latter case should be thought out as if the structures and entire plant were to be erected at once. 75. The Ore Beds.-The space for ore beds must be large enough to permit one to be building while the other is being drawn upon to supply the furnaces. Two beds, each containing 3,000 tons of ore, are sometimes planned. In such cases all the furnaces in blast are fed from one pile while the other is being made up. In case furnaces are running on one character of ore, ore beds are not necessary, ordinary stock piles being sufficient; but where furnaces are receiving ore from many mines, bedding piles are a necessity. Sulphides and carbonate ores are kept in separate piles, the former usually being dumped in close proximity to the roasting furnaces, from which they are transported to the bedding floor and spread. The carbonate and oxidized ores are dumped nearer the furnace and, consequently, the bedding floor. The beds should be protected from snow and heavy rains. The manner in which the ores arrive is of much importance; that is, whether they come in large or small consignments, at regular or irregular intervals. In case all ores arrive during the summer months, large stock piles may be necessary; this calls for a series of railroad trestles and tracks, if the furnaces are to run throughout the year. In case the ore comes in small quantities at regular intervals, the various ores can be carried, unless they need roasting, direct to the bedding pile. The question of room for the bedding floor requires particular attention only when various ores are to be mixed and smelted. 76. Location of Smelting Plant.-Whenever a hillside is decided upon for a furnace site, the questions to be considered are, can one terrace be obtained for the ore supply, another for the products of the furnace, and yet another for the slag dump? With insufficient fall, the main stress will be laid on having at least two terraces-one for the ore floor and one for the furnace floor. In case but one terrace is possible, preference should be given to the slag dump; the trestles should then be raised to such a height that the stock piles or at least the fuel piles will be above the top of the furnace. In some instances the furnaces must be situated on perfectly level ground, which requires elevators for nearly every product going into and coming out of the furnace. 77. Handling Materials. The principal aim at smelting plants should be to simplify the handling of materials, both loading and unloading, as well as charging. This is done by handling the materials to be moved from one place to another in such a manner that they will fall from and into trucks by gravity. The runways between loading and unloading points should not be long, but still they should not be so short as to crowd and prevent the free movement of apparatus. Tracks, elevators, and scrapper lines should all be arranged with this object in view. |