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Show INTER-MOUNTAI- jamss W. Neills Roasting Hearth. important invention, designed to reduce the cost of treatment of pyrites An has recently been perfected by James W. Neill of this city. There ores, Mr. are many districts throughout the West where this class of ores predominates, notably the Trail Creek country, British Columbia, and as it has N MINING REVIEW. 5 mical point is to ship as or, after the free sulphur is burned off, which point is attained without the aid of much fuel. To attain this point the Neill roasting hearth has been devised and patent for this device is now pending. The accompanying cuts give the outlines of the furnace in section. Figure roasted ore to fall away from the furnace into suitable bins. For the successful operation of the furnace the ore should be crushed to about one-inc- h pieces, or finer. Therefore, with the furnace a crusher is necessary, and an engine to drive this and also to drive the fan which furnishes the blast for the hearth. For this purpose a small fan, similar to those used for blacksmith forges, is best adapted, as the pressure needed is but light. The plant is most suitably located on a side hill, so that the ore will pass through the crusher into the ore bins, thence being fed into the furnace, whence it falls into a brick-line- d bin below, to be shipped when cooled. Such ings shaded, grates perforated, and sheet iron work plain lines. This cut shows the dust chamber of sheet iron, which is attached to the flue and settles the dust in pockets, while the smoke passes out through the end of the chamber into a stack. The blast enters the hopper under the grates through a hole in the back bed plate, indicated in figure 2. Any fine material which falls through the grates can be removed by opening the hole provided for this purpose at the bottom and back of the hopper, also indicated in figure 2. The furnace is 12 feet 4 inches by 4 feet 3 inches, outside dimensions, each side of the hearth having a grate surface of 6 feet by 4 feet; the side and back plates of cast iron are 2 feet high, the perforated grate plates each 4 feet by 2 feet, and each of these is perforated of an by about 1200 holes, inch in diameter. The heaviest of these plates, the back plates, which are 6 feet by 2 feet, weigh close to 800 pounus each. All these cast iron plates are bolted firmly together after reacning point of erection, hoppers bolt under frame plates, hood fits over sides, so that the erection of the furnace is exceedingly simple. The whole is supported by railroad iron resting on posts at the ends and corners, giving room enough underneath the furnace for the an arrangement can be easily attained iron-mono-sulphi- de, shows a section through the length demonstrated that this prelimin- of the furnace (one side only). The ary treatment greatly reduces the cost shaded parts are cast iron plates 1 of transportation and reduction, its inches thick. The grates show the pergeneral adoption should follow. An ex- forations through which the blast perimental plant at Bingham, which forces itself into the furnace. The light has been in operation for some months, lines indicate the sheet iron hood above has demonstrated the merits of the the furnace proper, and the hopper bemethod. The Mining Review is in- low the grates. debted to the inventor for the follow2 gives a cross section, cast Figure ing diagrams and description of the 1 been invention. The miner who produces a pyrites ore carrying only 10 per cent silica can gain nothing by the ordinary methods of wet concentration, as this method will in all cases leave about 5 per cent of the silica in the concentrates and this saving in silica will not repay the losses inevitable in the operation. For ores carrying up to 10 per cent silica, or for the concentrates resulting from the wet concentration of ores higher in the direct shipment to the smelter results in a large loss to the miner, owing to the freight which he has to pay on the moisture and on the sulphur contents of the ore. The mineral silica, pyrite contains 46.7 per cent of iron and 53.3 per cent sulphur when pure. That means that an ore carrying 10 per cent silica would, if the balance is pyrite, carry 48 per cent sulphur, on which the shipper will have to pay freight and smelter charges. The remedy which suggests itself is to roast the ore, thereby removing the sulphur and effecting the saving in freight due to the difference in weight between the raw and the oxidized product. This difference is theoretically 33.3 per cent if we oxidize all the iron to the of pure pyrite from oxide (Fe S2 to Fe2 03), but in the practice of metallurgy this perfection is not attained. Some of the sulphur remains in the product as the protoxide (Fe O), so that the actual reduction in weight varies, sometimes being as much as 40 per cent, sometimes less than the theoretical. To effect such a complete roast requires a large and expensive plant, first for crushing the ore to the proper size and, second, for the roasting. The expense of the operation is also quite high, as much fuel has to be burned etc. The first half of the sulphur contents of pyrites, called the free sulphur, is easily driven off. The ore once ignited, this sulphur burns by itself. The reduction of weight by the loss of this free sulphur is larger than by the driving off of the latter half, as this first loss takes place without the oxidizing of the ore, therefore the reduction of weight is almost absolute; that is to say, the difference in weight between iron (Fe S2) and iron sulphide (Fe S) is 26.7 per cent while, as before stated, the theoretical difference in weight for complete oxidation is only 33.3 per cent and in pracdi-sulph- ide di-sulph- ide tice say about 35 per cent. Therefore it is evident that for the shipper of pyrites ores the most econo one-four- th on the dump of most mines. The furnace when erected presents the appearance of a large double open with cast iron back and sides and sheet iron hood in place of a chimney. The grate is made of perforated cast iron plates and covers an air tight box, into which the wind is blown, forcing itself through the holes in the grates and so through the charge. The front of the furnace remains open all the time, as the workman is constantly adding to the charge or working out the roasted material. The operation of this furnace is simple in the extreme. To start up, the lights a fire of chips and kindling on the grate, adds to this some coal, or better charcoal, turns on the blast and as soon as the fire is well under way scatters some of the ore over this burning fire, a little at a time. The sulphur in this ore quickly ignites, and as it does so, more and more is added, the fire is worked so as to cover the entire surface of the grate, and as the heat increases the depth of the ore bed is also increased till the grate is covered to the depth of several inches. It will at this period present the apfire-plac- e, fur-nacem- an pearance of a bed of material through which innumerable little tongues of fire and streams of sparks shoot, driven by the blast, and it makes a very pret- - |