Show THE metallurgy OF LEAD WRITTEN FOR THE MINING REVIEW BY H B roasting and sintering wintering Sint ering lead ores in our study of lead smelting smelling sm elting in the ore hearth and in the furnace we have found that the raw galena is usually used directly but in neither instance is it customary to roast the ore previously one apparent exception is that as the smelting smelling sm elting was formerly carried out at barnowitz Tar some roasted ore was added to the charge to shorten the first part of the smelting smelling sm elting but as the roasting period had been lengthened out because of excessive amounts of blende in the ore it constitutes no important exception to our rule that ores for smelting smelling sm elting in the hearth or rich galenas are best smelted smelter raw roasting ore for the hearth has always been found to give poorer results and cost more than using 0 the ore raw thus it is that roasting lead ores has become an important matter only since lead blast furnaces have become something more than the mere adjunct to hearth and smelting smelling sm elting which they once were with the gradual development of lead blast furnaces the long hearth verber atory was for many years the standard for roasting both lead ores and matte furnaces of other types came into limited use of these the bruckner cylinder had a flashy career then the work of huntington and heberlein gained recognition and started a new development revolutionizing the treatment of lead ores and directly leading to that process which is at this very moment being budded into the metallurgy of iron the sintering wintering sint ering of iron ores and iron flue dust a beautifully simple process which may well quiet all alarmist consert conservationists by multiplying our available iron ore reserves many times the long hearth roasting I 1 furnace to a considerable degree em bodies the elements necessary for the successful roasting of lead ores in this type of furnace the air supply can be sufficiently abundant there is an opportunity for an unlimited amount of stirring while the heat may be regulated as desired a gentle heat for the highest lead ores or possibly more for ores less fusible the furnace is not unreasonable elther either in first cost of maintenance it is however costly both as to fuel requirement and labor while its capacity is not large exact details will of course be different at each locality but the ordinary furnace from 40 to 60 feet long and about 14 feet wide hearth area will roast some 12 tons per 24 hours 25 per cent of the weight of the charge if coal is used for n n ja WIN la ba t im i J if i r i i r i roasting furnace with fuse box fuel will be required the labor cost can hardly be less than a ton A battery of six of these ro asters might require labor as f follows each shift 1 I 1 trammer 12 sidemen 2280 2 firemen I 1 13 1 3 services 1 I foreman total if three shifts per 24 hours are used and each furnace roasts 12 tons of material the cost is evidently or per ton the roasting of the matte produced in lead smelting smelling sm elting requires the same careful heat and cont sant stirring that a lead ore would mattes are thus custom customarily airily roasted in this same kind of furnace in in all cases the material is put in the furnace at the flu flue e end and gradually worked forward to the hotter region by the labor of the side men excessive heat will fuse the charge metallic lead may form and with the fused sulphides sulp hides gradually creep into the hearth raising the floor as the mass accumulates one way to remove these masses is to clear the floor raise the heat of the furnace for a few days and then tap from the side of the furnace after daiv ing a bar through the wall huge sows bows of matte and galena are awkward affairs to handle with the equipment usually available in a roaster shed sledging has little effect upon them and drilling for blasting is tedious melting either before or after removing the furnace floor commends itself as the quickest way of getting them out on the other hand that they should be allowed to accumulate at all might require more than metallurgical explanation I 1 knew of one which kept growing and finally raised the floor of the furnace so close to the roof that the output of the furnace was greatly diminished during the digging out of the furnace the output was of course large eno enough ligh but unfortunately tuna tely the material was not well roasted the design of furnace as built by the colorado iron works S shows hows the long hearth and the fuse box at the gra grate e en end many furnaces for the roasting of ores and matte according to present american practice have the simple straight hearth only this agglomeration or even fusing at the end of the roasting after the sulphur is largely Ke removed moved is to furnish a lumpy product for the smelting smelling sm elting in the blast furnace which is the ne next at step in the ore treatment the use of the fuse box requires added labor and entails increased loss of metals by volatilization this idea of sintering wintering sint ering the materials has long been standard practice percy mentions various places on the continent where the lead ores were thus treated at freiberg the sint sinter er had part of the hearth on a higher level than the portion where the final treatment took place thus each charge undergoes during sixteen hours the temperature should be kept high enough to cause the charges near the fire bridge to sinter strongly and become pasty in which state they are fitted for the smelting smelling sm elting process at Ponti baud the furnaces were double decked with fuse box mechern mechernich Me chernich ich had a battery of ten furnaces each with its h hearth earth 32 in by 12 in all the textbooks text books on the subject give numerous and interesting details in connection with this kind of furnace an approved type is the furnace built by frazer and chalmers there is a goodly volume of literature available about ro asters for lead ores we can hardly pon consider sider in detail I 1 the matters of draft materials of construction st ruction design of parts methods or schedules les of and drawing charges the complicated reactions during roasting the sulphur elimination or the practice at numerous plants etc with cheap labor cheap fuel and twelve hour service collins states that the cost of roasting and fusing should not exceed as per ton in our western states these each 85 by 22 feet whatever success see collins metallurgy of lead p may be credited to these ro asters the introduction tro of blast roasting has put them practically out of date none of those at murray were used during 1909 or 1910 the illustration is of a once ex fig I 1 fia D fig fsr 2 avi flo fig 3 roasting furnace of fraser chalmers make conditions are seldom fulfilled and costs may more reasonably be placed around a ton since the development of blast roasting any further progress in connection with ies is evidently out of the question the matter of labor is always serious the work is arduous and exhausting it is a continual struggle to keep the standard high and sulphurs sulp hurs low in the product the loss by volatilization of both lead and silver values is always considerable and precludes the richest ores being treated in this way handling the flue dust and fume is a serious matter while sulphur trioxide is always formed and usually needs particular attention by the method disclosed in the sprague patents the gases can be neutralized in their sulphuric acid content and all fume recovered the successful operation of this method indicates quite unusual metallurgical attainment possibly no better resume of the status of roasting has been given than that by arthur S dwight in his recent paper on the efficiency of ore roasting the paper appeared in school of mines quarterly for november 1911 and ana was shortly afterwards reprinted in the engineering and mining jordanl and abstracted str acted in mining and engineering world extensive installation for the treatment of ores by the use of the bruckner was made at murray utah A descriptive account is given in eng and min jour 1907 p and by W R ingalls it is stated that there were twenty cylinders ten advertised by the colorado iron works bruckner cylinders labored under the disadvantage of making much flue dust and being difficult to keep in condition the heat also required very careful regulation and multiple hearth furnaces the character of ore and requirements to be met are altogether different and have brought splendid results it is a principle of the most vital importance that for oxidizing effects by the use of air the material should allow the air to pass through and not lot simply over its substance constant stirring of the material in contact with air is a poor substitute sti tute it is however better than allowing the material to lie inactive the present mechanical furnaces for roasting copper and zinc ores are based on the principle of constant stirring yet if any means should be devised to operate as perfectly mechanically and submit the ore to a current of air passing through instead of over the mass the present furnaces would quickly be superseded the present success of blast roasting or sinter roasting as I 1 prefer to call it began with the work of huntington and heberlein in europe who first blew air through the material lead ores to be roasted carmic carmichael hael and bradford altered the composition of the charge changed the charge still more greenawalt devised the method of supporting ores on an inert bed while drawing air down through by suction and finally dwight and lloyd made the process continuous we must remember that sinter is a term used by percy in 1870 and that the desirability of both roasting and sinter ing lead ores was even at that time perfectly understood roasting and Z r it 5 X g V 7 at 61 a bruckner roasting cylinder the heap roasting and stall roasting of lead ores has been of small importance in the metallurgy of copper it has been of far greater moment the same may be said of mechanic mechanically ally raked rake d furnaces and the various types of revolving abing lead ores in the has always been desirable but the latter action is always more costly and with rich ores hardly to be attempted on account of lead and silver losses according to hofman ores containing more than 20 per ce cent nt lead j should not be heated hot enough to fully agglomerate the them n we must remember that up blost bl st or down suction treatment has in no iD instance stance been the particular point at issue in the various processes of nf blast roasting now about to be described to be continued H B armour institute of technology |