Show THE metallurgy OF LEAD WRITTEN FOR THE MINING REVIEW BY H B I 1 smelting smelling Sm elting in the ore hearth the ore hearth presents a most interesting case of the persistent type idea a condition possibly more often discussed in biological than metallurgical development in the general progress of lead smelting smelling sm elting the ore hearth nourished flourished and became displaced but certain conditions demanded its retention and so it has prevailed under particular local circumstances similar to those originally requiring it little modifications and improvements have resulted as the years pass by still the ore hearth is the same blistering fume blowing part smelting smelling sm elting part roasting contrivance it always has been for smelting smelling sm elting relatively small amounts of the highest grade galena lead ore where silver is not to be recovered and the operations are intermittent or spasmodic the ore hearth with its accessories fits the conditions so tenaciously that neither nor blast furnace can fully oust outfit lit the whole cost of a plant is not excessive either in its large figure or in its cost per ton of annual capacity while the stock of material which is necessarily under treatment and has to be carried is almost nothing more than half the weight of the lead goes straight through the main process and is available for shipment shortly after it is received any grade of fuel is available of which less is required than for smelting smelling sm elting these are the advantages of the ore hearth from another point of view possibly the more scientific one the hearth may imay be considered as a roasting furnace which fits the high lead ores for cupola smelting smelling sm elting during the roasting process for this further treatment some 60 per cent of the lead is recovered in the metallic condition and is ready to mix with the lead from the cupola for final dressing drossin before molding into bars for shipment this incidental smelting smelling sm elting is thus credited to the operation to more than compensate for the numerous and obvious deficiencies of the apparatus considered primarily as a roasting furnace A quotation by percy in his metallurgy of lead is of extreme interest as relating to the antiquity of the hearth its invention having been induced by scarcity of fuel the more ancient log smelting smelling sm elting being so very inefficient and requiring enormous amounts of wood the original description was given il in 1 I the philosophical transactions in 1668 by joseph glandil Gl anvil in writing about the men dip mines they beat the ore with an iron flat fiat piece cleanse it in water from the dirt sift I 1 it through a wire sive the ore tenda tend to the bottom and the refuse lies at top and these are the preparations they make use of before fit for fusion then they have a hearth about 5 foot high set upon timber to be tuond as a windmill wind mill to avoid the inconvenience of upon a it is cast into sand and run into those as they call them which they sell they have a barr to stir the fire a shovel to throw it up and a ladle heated red hot to cast out the once melting is enough the good melts best and the best first there is sometimes half odds in the goodness the best is by its weight there is a flight in the which I 1 I 1 I 1 I 1 I 1 I 1 I 1 I 1 I 1 I 1 if dl C ct L I 1 I 1 I 1 I 1 I 1 U front clev atLon back elevation elev atlon left side elevation ete M WAKE ME 01 NIX a id I 1 d a d h b oai C 3 4 FT a an X ix agg Sect Loii on o n lt nc CD ORE HEARTH ACCORDING TO f ERCY PERCY 1870 1570 shifting wind the hearth contains half a bushel of ore and coal with bellowes on the top the Char coale is put upon the hearth where the ore is laying dry gads upon the top which they call their white boales there is a sink upon the side of the hearth into which the lead runs that holds about an hundred and an half then falling upon the grass those cattel that eat of it they find the taste of it upon their lips to be sweet when the cli chances ances to fly in their faces brought home and laid in their houses house s it kills rats and mice if this flight mix with water in which the oar is basht and be carried away into a streamed st reame reanie it hath biath poisoned such cattel as have drunk of it after a current ot or 3 miles JJ iles what of this flight falls upon the sand they gather up to melt in a hearth and make shot and sheet lead of it they sometimes find flaggs 3 4 or 5 foot under ground but such as they judge cast aside heretofore about 1730 the ore hearth was the only kind of furnace used in derbyshire a center of ancient and modern lead production in 1782 only two hearths were operating there while by 1811 they had all been replaced by furnaces however the hearth bearth continued to be used in northern england and scotland from whence it was first introduced into the united states in 1 1836 8 13 3 6 the ore hearth described in most detail 1 by percy has been copied in the accompanying drawing on a larger scale this particular furnace was one of those at the eld head mining companas Comp anys smelting smelling Sm elting works wensleydale Wensley dale north yorkshire england the bottom of the hearth is a cast iron box set in the brickwork or other resistant t material for instance stone the hood is a prime requisite to collect and carry off the fume as well as to protect the workmen a the hearth bottom or hearth box of cast iron b the work stone a flat plate of cast iron connected with the front edge of the hearth bottom from which it slopes downwards on the sides and lower edge it has a raised border and from the middle of the upper edge to the middle of the lower edge is a groove as shown between b and b in the horizontal section various component parts of the ore hearth though made of cast iron are termed stones the hearth bottom and work stone are cast in one piece but in ore hearths in other localities they are separate castings the groove is intended to conduct the lead into an iron pot h in front as it overflows from the hearth bottom during reduction of the ore ile c c two similar rectangular prisms of cast iron termed bearers resting on and somewhat overlapping the hearth bottom one on each side id d d rectangular blocks of cast iron termed keystones key stones two on each bearer the two in front are shaped at the back so as to form ledges for receiving the ends 0 of the fore stone e the back stone or pipestone pipe stone if f the upper back stone these stones e and f form the back of the hearth through the lower part of the back stone e passes the auyer g the fore stone of cast iron which lies across the hearth with its ends resting respectively between the keystones key stones it can be moved toward the front or back by changing according to the position of the keystones or it may be raised by placing fire bricks underneath it at each end k the feed door through which chic h the workman places a peat before the nozzle and detaches any adherent slag im im the flue of the fireplace fire place under tinder the pot in recently erected hearths heart hs it has been found better to take this flue direct under the hearth bottom and curve it to one corner the space between it and the work stone should be filled in solid with brickwork hearth bottom one foot eleven inches from back to front one foot nine inches wide and one foot deep inside measure the sides and front are inch thick and the back inch mode of conducting the process of smelting smelling sm elting two men are required and a shift lasts eight hours the fuel is coal and peat cut in prismatic pieces from 9 inches to 12 inches long by 21 inches square such a piece of peat is called a from the last shift is thrown on behind the fore osone when about half of the brouse 0 ia o worked in lead begins to flow and then one of the workmen stirs up the contents of the hearth with a poker throwing them forward away from the blast a portion falling on the work stone at this moment the 01 other ol her workman introduces his scraper through the feed dour door and removes any slag from before the blast throwing in front of the nozzle a peat which disperses the blast and keeps open the fire both men then step to the front with their brouse shovels and put back into the hearth what had fallen on the work stone setting up the contents so that the blast shall be well distributed throughout lead now flows freely ore in small quantities is added where the fire seems hottest the stirring up of the contents of the hearth is repeated at intervals of about five minutes where the fire is N kl akk N 24 it ar 1 A 46 iw 5 z 7 M most recent type of Jumbo Furnace Pho toby H B Pul sifter peat and the plural peats is used lead ore is termed bouse in the north of england and the agglomerated masses of ore formed in the process of smelting smelling sm elting are termed brouse or browse the ore at the keld head companas Comp anys works is not previously the blast is varied considerably sider ably according to the nature of the ore operated upon the hearth is supposed to be in working order and the bottom left nearly full of lead after the last shift A small quantity of coal is laid on the hearth bottom and the remaining cavity of the hearth is filled with peats which are well walled up lip in ill front while smaller pieces are thrown in without order behind A few ignited peats are next placed before the nozzle and the blast is let on As soon as all the peats are well ignited a little more coal is added and shortly afterwards a little of the brouse seen to burn badly on oil account of imperfect c t diffusion of the blast at each stirring a fresh peat is placed in front of the nozzle and from the portions which during this manipulation fall upon the work stone lumps of grey giey slag are picked out and laid aside for subsequent treatment in the slag hearth the pieces of brouse are broken up and returned to the hearth after which fresh ore is added when the receiving pot is full of lead the latter is skimmed and ladled into pi pig 1 1 moulds during a shift these operations of stirring ladling etc are performed alternately by the two workmen thus the man mail who has been using the poker ladles out the metal while the other skims it and the latter attends at the feed door while the former uses the poker towards the end of the shift no more imore is charged but the contents of the hearth are afterwards worked up two or three times after which the blast is stopped all the brouse is taken out thrown on one side and separated from the intermingled grey slag lead is ladled from the receive ing pot back into the hearth bottom so as to fill it ready for the next shift this hearth smelted smelter a little over five tons per 24 hours per cent of the lead in the ore being obtained direct and with labor at about per week the cost per ton of ore amounted to some what was known as the american ore hearth originated at the lead mines of rossie new york this being a hearth similar to the scotch except tor for the castings of the lead well which were hollow and permitted of the heating of the blast by circulation cu before it escaped through the one oile or two rs wood was used as fuel and the heating of the blast was supposed to give greater capacity the type was introduced into missouri and trial furnaces erected in bleiberg in Ca rinthia and at in bohemia the hearths at rossie gained a reputation of doing good work and the recovery was about the same as in the older scotch type but the published from flattering after the working out but of the mines at rossie this type receives no further mention A great defect was inherent in all the earlier scotch hearths when it was attempted to operate them continuously or for long shifts this was the tendency for the box to get too hot at the time when percy wrote in 1870 alleviation had resulted by increasing the depth of the bottom t thus allowing it to hold more lead which was of lower temperature percy suggested water cooling to obviate the difficulty fi he also states that certain works had resorted to the simple expedient of allowing air to circulate freely about the exterior of the bottom with much improve improvement e but that this was too novel and important to be divulged to the generality of lead shelters smelters these ideas found their consumption in the two american types of hearths known as the water back and we ane moffet or jumbo hearth the old scotch hearth survives in its original home and according to collins 24 of them are found in a plant at linares spain in the united states the water back and the jumbo are the survivors the new plant at webb city missouri which began operations a year ago in january has six of these jumbo furn furnaces abes this was very well described and illustrated in a paper by lucius L wittich which appeared in mines and minerals july 1911 this new is very well equipped in respect to devices for handling material and design of plant the hearths are five feet long eighteen inches wide and seven inches deep ten openings along th back admit the blast supplied by a no 9 buffalo blower to one side of each work stone the gutter leads the lead to the little cast iron pot over its small fire from this the lead is ladled out into bars at the other side of the stone is the trough filled with water to receive the slag these jumbo furnaces have a base of cast iron rather open on the ends and back which allows of free air circulation exactly as percy said was already practiced over forty years ago the blast enters the hollow castings forming the walls of the hearth at one end and passes to the tu yeres thus helping to cool the castings four shifts each of six hours can be employed each shift will smelt pounds of high grade galena concentrates recovering some GO 60 per cent of the lead direct about pounds or finely ground limestone will be required during each shift 41 i V N view hearth photo by H B Pul 1912 to keep the ore of the right consistency for rapid and complete reduction the working of the charge is not much different from the method already described for the working of the scotch hearth the small supply bins at the back of each working place contain the lead concentrates the soft coal for fuel and the ground limestone for mixing A blast pipe passing along the ground behind the workmen throws a current of air upward for their relief we have already spoken of the hearth as both a roasting furnace and a smelting smelling sm elting furnace it is general custom for each of these chemical operations to be carried out in separate furnaces in other metallurgical operations the hearth carries out both reactions simultaneously the entering air oxidizes the hot galena to oxide and sulphate of lead the lead oxide is then reducible to metallic lead by the glowing coal or any carbon monoxide that may be present the sulphate first formed is also reducible to metallic lead by the same agencies and a supplementary reaction between the raw galena and the lead with formation of sulphur dioxide at the same time quite a good deal of the lead is always blown aw away y as dust and as fume or iced galena and lead which oxidizes to sulphate and oxide this peculiar position of the hearth as both a roasting and reducing furnace is now clear usually more than 60 per cent of the lead in the ore is thus directly recovered as metal what galena remains upon any unreduced sulphate and oxide silica as impurity in the ore which fuses with lead oxide to a lead silicate other impurities of the ore and the added limestone all melted together form the grey slag sla which has to be further smelted smelter in a cupola for some time the new at webb city was more or less controlled by local men interested in mining as well as smelt ing during this time the was open for inspection to the fullest extent during the first days of january in this year the passed into stronger hands and at the time of the authors visit |