US2129760A - Metallurgical process - Google Patents

Description

Patented Sept. 13, 1938 -um'rso STATES PATENT. OFFICE.

, $2,129,100 sm'ranwaoroar. raoca'ss William E. Greenawalt, Denver, Colo. Application um 2c, 1935, Serial N... 37,928

11 Claims.

My invention relates, broadly, to metallurgical processes, and it has, as its more immediate object, simplifying and cheapening of roasting and smelting copper ores or concentrat The proc-- 5 ess will be described in detail for t particular use. i

The general treatment of copper ores, as prac-' ticed at present, is about as follows: The mine.

ore is ground fine and is then subjected to gravity or flotation concentration to produce a. concentrate. concentrate, as a whole, consists of This procedure involves a number of features which, it is believed, can be greatly improved; among which might be pointed out: First, in 5 roasting, in multiple hearth furnaces, there is always produced a large amount of dust, which is considerable of a nu.isance, and its recovery,

through dust chambers and electrostatic precipitators,vor otherwise, involves considerable ex- 1 30 pense. Second, the roasted concentrate from multiple hearth furnaces is not, as a rule, very hot, and a considerable amount of extra heat is required to bring it to a smeltingtemperature. Third, most of-the heat generated in'roasting is peclally' the multiple hearth'type, are expensive to install, they cover considerable space, are rather expensive to operate, and, taken with the dust recovery, offer a condition which appears to be susceptible of considerable improvement.

The present process will now be described, reference may be made to the accompanying drawing, in which Fig. l is a flow sheet in diagrammatic plan, and Fig. 2 a transverse section through the reverberatory smelting furnace on line 2-2 of Fig. 1. Y

The ore, as mined, may be concentrated as usual by gravity or flotation concentration or both combined. The concentrate is washed, as

in an ordinary classifier or other device, to separate the sands from the siimes. The dividing line between the sands and the slimes, for the purpose intended, will have to be determined ex perimentally under the peculiar existing condi--v tlons. Ordinarily only the slimes, or colloids will wasted. Fourth, ordinary roasting furnaces, es-

l be removed. The idea is to remove the slimes which would interfere with the desired percolation of air or other gas through a column, or bed, of the sands. A considerable amount of air or other gas can be percolated through a column of 5 the deslimed sands, even if the sands are quite fine. This can best be done by washing the concentrate as in an ordinary classifier, in which the dividing line between sands and slimes, for L any particular application, can be closely regu- 10 lated.- The idea would be to have a maximum amount of sands and a minimum amount of slimes, consistent with the best subsequent treatment. .While, for the sake of simplicity, it is preferred to subject the concentrate to a. general 7 The sands, freed from slimes, fines, or sticky or oily material, are easily dewatered, without filtering, and can be mixed so as to contain from Etc 12 per cent moisture, and this is usually the most desirable moisture for uniform mixing to get the greatest porosity for the percolationof air or other gases to promote the reactions "which may be carried out in a roasting furnace.

The sands are charged into a shaft furnace, as

a column or bed. A shaft furnace like that described in my co-pending application, Serial No. 655,201 is preferred, which consists, briefly, of a shaft adapted to contain the material to be treated, provided with hollow heating members,

electrically heated inside, spanning the furnace shaft, which are 1 arranged to introduce air or other gas into the interior of the hollow heating members and into the material in the ,furnace shaft. In this way the material may be heated to any desired temperature and the temperature may be controlled independently of the heat 'generated in the roasting process. Any gas maybe introduced into the heated material as desired either for oxidation or reduction.

The sands are preferably charged into the top of the furnace moist and mixed, and preferably roughly screened into the furnace with a view of providing the maximum porosity for the percolation of gases through the wet charge at the topof the sand column.- The sulphur, burned lower down in the shaft, will ordinarily furnish sufli- 5o cient heat to roast the ore and. dry the freshly. charged wet ore. The temperature for the most eflective roasting has to be fairly well controlled; and the percolation of air through the sand column should be uniform. The heat is controlled by means of resistors, or electric heating elements, within the hollow beams, and, since the electric current can be closely controlled, the increment heat necessary for uniform heating to insure effective roasting, can also be closely controlled. There is little danger of too low a tem perature, either in spots or in the furnace as a whole, to insure effective roasting. If the furnace is shut .down it can be started at any time without removing any portion of the furnace charge. g

The capacity of the shaft furnace is mostly dependent on the amount of air that can be passed through the hot charge, and the amount of air that can be passed through the hot'charge will depend on the coarsenessv of the sands. In ordinary concentrates, for any given fineness of grinding, it will depend mostly on the eifective removal of the slimes, colloids, or fines.

Fine particles of pyrites can be almost completely oxidized in a few seconds, as in flash roasting. They can be fairly well oxidized in a few minutes, as in drop shaft roasting. Under ordinary conditions-of bed or column roasting, the time, and hence the capacity, depends largely I on the temperature and on the free access of air,

as is well known, and is illustrated by Valentines determinations, A. I. M. 11., Vol XVIII, which, in part, are as follows:

Oxidation of pyrites, FeSz, with free access of air Sulphur Percent Approximate tem- Duration of in resi- Loss, of sulperature. deg. F. heat due, per per cent phur cent expelled Original pyrite 1 hour 53. 43 1250 1 hour 4. 27 49. 15 92. 05

2 hours 0. 52. 73 98. 68 20 minutes... 0. 78 52. 65 r 98. 54 45 minutes... 0. 08 53. 35 99. 20 minutes-.. 0. 13 53. 29 99. 75 1 hour 0. 65 52. 78 98. 79 15 minutes..- 3. 23 50. 19 93.

I Assume a shaft furnace having a hearth area of 6 x 25 feet and an ore column of 20 feet under the desired temperature, or from 1200' to 1600 deg. F., or from 649 to 8'71 deg. C. The volume of this ore column would be 3000 cubic feet, and, estimating the weight of the ore at pounds per cubic foot, the total weight under roasting treatment would be tons, and this would be the daily furnace capacity if the oreis under treatment24 hours. If the time of treatment is 12 hours the daily capacity would be 300 tons; and if the time of treatment is 6 hours the daily capacity would be 600 tons. Since the temperature of the roasting can be controlled as desired,

'the capacity of the furnace for any particular temperature will dependupon the amount of air or other gas that can be percolated, blown, or blasted, through the ore bed or column, and that is the outstanding reason for separating the slimes from the sands. Clean sands, even if the particlesare small, will permit of a surprisingly large amount of air to be blown through a bed or column of them. The air requirements will depend mostly on the amount of sulphur in the ore to be oxidized.

In ordinary hearth roasting of sulphides in straight line or multiple hearth furnaces it is estimated that from 50 to 70 per cent of the heat is wastedthat is to say it does not perform any useful function. This is mostly due to the fact that the fresh and cold air is introduced into the discharge end of the furnace; this cools the ore the gas is to be converted into sulphuric acid or if the sulphur is to be recovered in elemental form.

The amount of sulphur eliminated in the roasting will depend on the subsequent requirements. Ordinarily, in roasting for copper smelting, enough sulphur is retained in the roasted ore to meet the matte requirements in smelting, and hence the sulphur elimination need not be even approximately complete. In the present process,

, however, the idea is to eliminate more sulphur from the sands than necessary for subsequent smelting requirements, and then to provide the necessary sulphur by feeding the wet raw slimes directly into the smelting furnace. The drying and roasting of the slimes, with the inevitable excessive dusting in roasting and smelting, is, in this way, practically completely eliminated. The sulphur in the raw slimes is regarded more or less in the nature of a constant in furnishing the sulphur requirements for the matte, and the sulphur elimination in roasting the sands is regulated accordingly.

The roasted hot sands are preferably charged into the middle portion' of the reverberatory smelting furnace, and the wet raw slimes at the sides, as shown in detail in Fig. 2. In this way the wet slimes have the least cooling effect. The slimes so charged into the smelting furnace will, under the excessive heat of the smelting furnace, be fused as soon as the exposed surface becomes dry and hence, there will be a minimum amount of dusting in the smelting operation. The sands and the slimes are thus smelted together. can be added to the sands and the slimes anywhere in the circuit.

It will be seen therefore that by the process described, by separating the slimes from the sands, the sands may be cheaply and effectively roasted, preferably in a shaft furnace, with a conservation of heat and without making any, or at least an appreciable amount of dust; that the sands can be charged from the roasting furnace into the smelting furnace at a high temperature and thus conserve heat in the smelting furnace; that by separating the slimes from the the nuisance of drying, roasting, and dusting of the slimes, either separately or with the sands,

is avoided, and hence the entire metallurgical installation and operation is greatly simplified.

Should the slimes have an excess of sulphur for smelting requirements a portion of the slimes may be roasted, preferably in a muffle furnace. Similarly, if the ore contains zinc or lead, the zinc or lead should be floated from the copper, and the zinc or lead-slimes roasted separately from. the zinc or lead sands. In either case the sulphur dioxide gas from the slime roasting may conveniently be introduced into the bed or column of roasting sands in the shaft furnace if the sulphur gas is to be used forsulphuric acid manu-- facture or if the sulphur is to be recovered in elemental form. If the sulphur is to be re- Flux covered in elemental form the concentrated sul- 7 phur dioxide from the shaft roasting furnace is introduced into the sulphur reducing furnace. which is preferably similar to the shaft roasting furnace, filled with carbonaceous material, such as coke. Gas or steam may be introduced into the reducing furnace to promote the reduction.

If the ore contains zinc or lead in appreciable amounts, it may be found cheaper to volatilize the zinc or lead from the roasted sands, ore or concentrate, and then copper smelt the residue. A shaft reducing furnace similar to the shaft oxidizing furnace could be used for this purpose. Such a procedure, in treating complex .ores, might offer considerable advantage over the usual method of very fine grinding, selective flotation, and separately treating the flotation concentrates. In such cases, under the present process, the ore would be crushed, or ground, relatively coarse-say from 6 to 16 mesh. It might be given a rough concentration treatment to eliminate the totally barren'gangue.

In operating the shaft furnace, the sand charge is brought to the reacting temperature, preferably rate of flow of the ore, or sands, through the shaft. As the ore column is lowered, fresh ore is' charged in at the top, preferably wet and well mixed and evenly-and loosely distributed so as to give the greatest porosity and a uniform percolation of the air through the charge.

The sulphur, in theroasting or reacting pa t of the column, is oxidized to sulphur dioxide, and

this, passing upwardly through the charge, beats and dries the moist upper portion before it gets into the reacting zone. If desired, some of the sulphur may be distilled off in the elemental form and escape, with the gas, at the top of the furnace. The furnace gas, passing through the moist or upper portion of the charge, acts as a filter to arrest dust particles which might otherwise escape with the gas. Hence, the escaping gas will be practically freefrom dust. r

The temperature of the furnace will be determinedlargely by-the rate'of flow of air through the charge, but should not exceed from 1200 to 1600 deg. F. After the furnace is in operation, the electrical heating elements simply maintain the temperature desired so that any air coming-in contact with the ore will at once react with the sulphur in the charge. This equalizing, or increment,heat will be relatively small. a v v r The hot roasted 'ore from the shaft furnace is charged directly into the smelting furnace. A

considerable part of the fuel in the usual reverberatory smelting is consumed in bringing the cool, cold, or wet charge to the smelting temperature. In the present oasethe roasted sands could conveniently be charged into the reverberatory smelting furnace at a temperature of from 1200 to 1500 deg. F., and at this charging temperature the capacity of the smeltingfurnacewould be greatly increased-perhaps doubled. In ordinary reverberatory roasting, cold air in great excess is passed over the ore after the greater portion of'the sulphur has been eliminated, and thus the temperature of the roasted ore is greatly reduced. By roasting in a shaft furnace,'as preferred in the present process, only enough air is introduced into the partly roasted ore to completethe oxidation, and the roasted ore can be exhausted from the furnace at or close to the maxiinthe center, as shown in Fig. 2. In either case the molten charge in the smelting furnace will be composed of a mixture of sands, and slimes' which may be charged into the smelting furnace either wet or dry, raw or roasted. It does notv make any essential difference whether the mixing is done before or after the charging, but.it-is greatlypreferred to charge the hot sands and the wet slimes separately as described.

Sulphur, if it can be. profitably recovered, may

make a valuable lay-product in the treatment of carbon, such as coal, coke, or charcoal, and the charge is heated to the necessary temperature usually to 700m 900 deg. C. The sulphur is mostly distilled in elemental form. Since the sands are freed from slimes, the fumes resulting from reducing roasting, will be practically free from dust and may be easily recovered and refined. If the sands are rich in copper or precious metals, the reduced sands, containing a small excess of carbon, may be charged directly into the converter. If natural gas is cheaply available, it may be substituted for carbon as a reducing agent. roasted oxidizingly or reducingly, the roasted product may be charged either in whole or-in part into the smelting furnace or into the converter, depending largely on the nature of the sand concentrate. By charging the roasted high grade sand concentrate directly into the converter and thus eliminating it from the smelting furnace, the smelter slag can be kept relatively low in copper, and the gain in extraction and the reduced cost of smelting would be appreciable.

Separation of the concentrate into sands and slimes may be done in various ways, either during or after concentration. The particular method Whether the sands are to be blast of separation, or at what stage of the concentration the separation is "made, is immaterial in the present process. Ordinarily, the most convenient way will be to concentrate the orein the usual way, and then merely subject the crude con- .oentrate to wet mechanical concentration by means of which any desired separation may be made between sands and slimes. The sands will usually constitute the high grade concentrate.

Copper is usually a constituent of complex ores, frequently occurring in massive deposits. Complex ores ordinarily contain copper, lead, zinc, gold, and silver, associated in varying amounts with iron pyrites and insoluble. The usual treatment of complex ores is, fine-grinding, selective flotation to produce copper, lead, and zinc concentrates,'and a flotation tailing containing about 10 per cent of total values. Each of the concentrates is separately treated to recover the metals in elemental form, with an additional metallurgical loss.

Under the present process the treatment, in

general, is to crush or coarsely grind the ore toa size suitable for eflective' roasting, say to 6 or 16 mesh, separate the fines or slimes from the sands, subject the sands to a reducing roast to. volatilize the lead and zinc, preferably in a shaft furnace. The sulphur may be driven off either as part of the reducing roast or in a preliminary oxidizing roast, and may be recovered in elemental form, if desired. If the ore contains a large amount of barren gangue, it may be eliminated by a rough gravity concentration, which, at the same time, might also serve to separate the sands from the fines. The fines are subjected to selective flotation to produce copper concentrate. Lead and zinc concentrates may also be produced at the same time if desired. The raw copper concentrate is charged into the smelting furnace with the reduced sands, and smelted to matte or blister copper; Copper, in complex ores, is usually in the form of chalcopyrite and zinc is usually in the form of marmatite. Both of these minerals contain a large percentage of iron which cannot be eliminated by any mechanical method of concentration, and hence the concentrates are not usually of a high grade.

It is believed that'complex ore if treated as a whole by volatilization or distillation of the lead, zinc, and sulphur, especially if the recovery of the sulphur can be made profitable, and then smelting the residue containing practically all of the copper, gold, and silver, with suflicient fine sulphide copper concentrate to make a suitable matte, it would be a considerable improvement over the present method of fine-grinding and selective flotation and separately treating the various excessively fine concentrates with all the attendant metallurgical losses. The copper concentrate, if high grade, could be added direct to the converter, if the copper is smelted to matte,

or it might be given an oxidizing roast and added to the reverberatory if it is desired to smelt to blister copper, as would usually be the case in small-scale operations. The lead, in either case, would be recoveredfrom the smelter fumes. If the lead is present in considerable amounts in the ore as crystallized galena it would be desirable to eliminate most of it by a rough preliminary concentration in the separation of the sands from the fines.

The gold and silver would practically all be concentrated with the copper and the metallurgical loss would be almost negligible as compared with the usual method of fine grinding and selective flotation and separate treatment of the respective concentrates.

While shaft roasting of a column of the ore is preferred, especially if the sulphur is to be made available either for the production of elemental .sulphur or sulphuric acid, there may be conditions under which blast roasting of a bed, or shallow column, of the coarse ore or sands through which the roasted product will be in the form of sinter, might be desirable. The sinter is more readily smelted than any other form of the ore, and the necessary flux can, if desired, be added to the roaster charge. With the fines eliminated from the sands the bed of sinter charge may be made quite deep-possibly as much as two feet or more-and the capacity of the roasting or sintering furnace will be exceedinglylarge. Practically all dust is eliminated from roasting through sintering, as also in smelting, and, owing to the porosity of the sinter, and the openness of. the sinter charge, the capacity of the smelting furnace is considerably increased. Concentrated sulphide fines are not adapted to effective blast roasting because .of the limited amount of air that can be passed through a bed of the fines, but with the fines eliminated from the sands, blast roasting of the-sands becomes effective, and the resulting sinter, low insulphur, may advantageously be smelted with the raw fines.

I claim:

1. A process of treating ores of metals comprising, treating the ore to produce sands and slimes, roasting the sands, and smelting the 'roasted sands with the unroasted slimes.

2. A process comprising, treating ores of metals to produce sand and slime concentrates, blast roasting the sands, and smelting the blast roasted sands with the raw slimes to recover the metals.

3. A process comprising, treating copper ore to produce copper concentrate, separating the sands from the slimes, subjecting the sands to a 'reducing roast, and smelting the reduced sands with ing ores to produce copper concentrate, washing the concentrate to separate the sands from the slimes, blast roasting the sands, and smelting the slimes with the blast roasted sands.

5. A process comprising, treating copper ore to produce. copper concentrate, separating the sands of the concentrate from the slimes, blast roasting the sands, charging the slimes into a reverberatory furnace at its sides, charging the blast roasted sands into the reverberatory furnace intermediate the slimes, and smelting the combined charge. 6. A process comprising, treating copper ore to produce a copper concentrate, washing the concentrate to separate the sands from the slimes, roasting the sands, charging the wet slimes into a reverberatory furnace at its sides, charging the roasted sands into the reverberatory furnace intermediate the slimes, and smelting the combined charge.

7. A process comprising, treating ores of metals to produce sands and fines, roasting thesands, concentrating the fines, and smelting the roasted sands with the concentrated fines.

8. A process comprising, treating ores of metals to produce sands andfines, separately roasting the sands, and smelting the roasted sands with the rawfines.

9. A process comprising, treating ores of metals to produce sand and slime concentrates. roasting the sands, and smelting the roasted sands with the unroasted slimes.

10. A process comprising, treating ores of metals to produce metal concentrate. subjecting the concentrate to wet classification to separate the sands from the slimes, roasting the sands, and smelting the roasted sands with the raw slimes.

11 A process comprising, treating sulphide ores of metals to produce sulphide concentrate, subjecting the concentrate to wet classification to separate the slimes from the sands, and separately roasting the deslimed sands. I

WILLIAM E; GREENAWALT.

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