US1673891A - Method of preparing flotation concentrates - Google Patents

Description

June 19, 1928. 1,673,891

H. J. STEHLI METHOD OF PREPARING FLO'IATION GONCENTRATES Filed July 50, 1926 ATTORNEY Patented June 19, 1928 UNITED STATES HENRY J. STEHLI, OF CEDAR GROVE, NEW JERSEY.

METHOD OF FREPARING FLOTA'IION CONCENTBATES.

Application filed July 30, 1926. Serial No. 125,858.

By the modern methods of concentration of ores for the purpose ofseparating values from the accompanying earthy material or gangue, the ores are frequently ground to 1 almost flour fineness and the resulting concentrates, after having as much water removed as possible b means of filters, are still wet and at best lilVe the consistency of soft putty. Ores of this character are usually sintered as a preliminary to treatment in smelting furnaces to remove sulphur if that is necessary, but chiefly to produce a coarse product favorable for subsequent blast furnace smelting. Such ores may have to go through a considerable amount of handling before they are delivered to the sintering plant, and in their wet, stick; condition are very difficult to put into an discharge out of cars, draw out of hoppers or bins, or handle through chutes, elevators, conveyors, etc. The treatment which I describe below makes such ores easy to handle, as they can be put in cars, bins, etc., or be drawn out through chutes or conveyed in elevators or conveyors without sticking to the containers. As a requisite for successful sintering the material to be sintered should be fed onto the sinterin machine in a loose bed permeable to t e air currents. Such concen- 30 trates present a diflicult problem, since in their wet plastic condition they do not offer a mass sufliciently permeable to the air currents in the sintering machine, and if the concentrates are mixed up in some form of mixing or disintegrating device the particles stick together again almost immediately, giving an impervious bed, or at best, one that is irregularly permeable. The air currents, choosing the permeable spots, leave untouched the denser areas. This results in a very unsatisfactory, partially sintered product full of unsintered fines or of fines {ugh in sulphur, which cause high dust osses.

,To avoid the foregoing objections the usual methodis to mix such concentrates with other materials. Such procedure is only partially satisfactory, as the resulting mixture contains a large proportion of the 5 lastic concentrates in relatively large l,; f;'.,'l umps, as from the size of an egg down to the size of a walnut, which have not become broken up and thoroughly mixed through the charge. Such lumps, because of their M impermeabilit'y to air, cause unsintered spots 01' islands in the sinter bed, and, as a re sult, high sulphur content in the sinter cakes and serious dust losses.

{is the tonnage of ores treated by the flotation process is daily growing greater, and the amount of other ores available to mix with them is daily growing smaller, the problem has reached an acute stage.

It is well known that a charge to successfully sinter must contain a certain amount of water, which may vary from 8% to 12%. It is, of course, possible to subject the wet concentrates above mentioned which contam, as they come from the filters, 15% or moreof Water, to a process ofdrying. In practice this is unsatisfactory not only on account of the cost but because such material cannot be readily dried to a uniform vmoisture content. It can be completely dried but the resulting dried material consists of baked lumps which are hard to break up again, and when broken up they form fine dust. It is not feasible to stop the drying at a point where the material will still contain from 8% to 12%-moisture became this drying action is uneven. The partially dried mass would consist of some completely dried dusty material and a quantity of large lumps dry and baked hard on the outside and still very wet on the inside, making a material unsuitable for a sintering charge and one which would be almost impossible to mix satisfactorily.

The object of the present improved method is to so treat and mix the concentrates referred to that they will readily flow through bins, chutes, etc., and when fed on the bed of a sintering machine they will form a loose, open mass, readily permeable to the air currents, and which when sintered will give solid cakes thoroughly agglomerated and free from dust.

In the preparing of concentrates I proceed as follows:

I divide the wet plastic ore concentrates or fines into relatively small lumps, pellets, nodules or the'like of such a size, that they will give the maximum of large air passages while at the same time be themselves of a size such as to most efficiently undergo the desired reduction in treatment on the sintering machine, and I coat the lumps, etc., with a suitable dry powder-like or pulverulent material that 'will adhere to the lumps and thereby keep them separated in the mass so that the lumps will not stick to other and will thereby provide a permeab e mass in which spaces between the lumps will permit the assage of air. The material for coating the umps or the like may comprise dry ore, flue dust, lime or any other suitable dry material, of which there is always some to be found available among materials to be smeltered at any smelter. Under some conditions it may be found desirable or economical to dry a certain percentage of the concentrate to be sintered, say 10%, and use the same in powder form for the purpose of coating the lumps and the like. The wet plastic concentrates may be divided into the small lumps, pellets or the like by any suitable means. The wet plastic concentrates may be forced through a machine on the order of the ordinary meat grinder which will serve to divide or chop the concentrates into small lumps or pieces, the size of which will be governed by the character of the machine, or other well known machines adapted for dividing masses into small pieces may be used for the purpose. In order to economically and expeditiously coat the aforesaid lumps of wet concentrates the lumps, pellets or the like may be delivered into a revolving drum containing the dry powderlike material used for coating the lumps. and as the latter drop into the revolving drum they immediately begin to roll around in the powder and accumulate a coating of the dry powder-like material until the lumps are no longer sticky on the exterior and will not pick up any more of the dry material. The drum may be provided with interior cups or shelves in the same manner as in an ordinary concrete mixer, which mixer may be used for the purpose if desired. The cups or shelves, as the drum revolves, lift a certain amount of coated lumps, pellets or the like and also an amount of the dry material or ore up above the mass in the drum and pour the. same out onto an inclined chute. The chute may have a perforated bottom, such as one made of screen cloth, and maybe caused to shake in such a manner that the dry material unattached to the coated lumps or the like will fall back into the drum while the coated lumps will roll along the screen-bottom chute and may be directed into the sintering machine hopper, or to any other desired place, whereby the coated lumps are separated from the mass of dry coating material. The mesh of the screen should be smaller than the coated lumps or pellets so that as the latter run down over the screen and fall into the hopper of the sintering machine the excess of fine dry coating material will pass through the screen and be returned to the mixing drum. If desired the aforesaid chute may have a solid bottom and the coated lumps and some of the dry coating material may be delivered from the chute' to an outside screen which will serve to separate the coated lumps from the remaining dry material, which lumps may pass to the hopper of the sintering machine in any desired way.

While some fine concentrates do not possess this sticky character-for instance, the zinc flotation concentrates from the Joplin districtthey nevertheless, because of the exceedingly small interstices between the very minute particles, do not present good conditions for sintering. These passages between the particles are so small that the air currents can be drawn through them (because of friction) only under an excessively high suction. Such a high suction has a tendency to pull a good deal of the material from the bed at points where the coherence of the bed is the least, and the result is the production of flue dust and loss of values. Therefore, one of the main objects of my method is to increase the size of the air openings through the one bed. The smaller the nodules the smaller will be the size of the air passages, and the greater the resistance to the suction. On theother hand, if the nodules are made too large, or if the material is not nodulized at all, but fed on the bed in the shape of big plastic lumps, then while the individual air passages are large enough, they are not sufficiently disseminated through the mass to produce even sintering and homogeneous sinter.

In the foregoing description it is to be assumed that the fines or concentrates possess a suitable sticky or plastic character. whereby the material of the lumps will adhere together. Most flotation concentrates contain a certain amount of clayey matter or hinder which makes it possible to produce the relatively small plastic lumps or nodules before referred to that can be rolled in the dry coating material. Some fine concentrates do not possess such a sticky or plastic character, there being no such clayey binder present. For instance, in the zinc flotation concentrates from the Joplin district, and because of the exceedingly small interstices between the very minute particles such ores do not usually present good conditions for sintering. The passages between the par ticles are so small that the air currents can only be drawn through them under an exceedingly high suction which has a tendency to pull some of the material from the bed at points where the coherence of the bed is the least, and the result has been the production of fine flue dust and loss of values To such a natural n0n-sticky or non-plastic concentrate water may be added to make momentary lumps but they will have insuificient coherence to hold their form during the rolling and coating process I have described or during subsequent handling, so that when they break up they produce an exceedingly fine moist mass. In order to prepare such natural non-sticky or non-plastic fines or concentrates for-the production of lumps to be coated with the dry powder 1 add to such concentrates a relatively small amount of plastic material, such as fire clay, whichneed not be more than 5%, (and frequently may be less than 5%), mix the mass, and add a suitable amount of water to the mixture (if it. is not already present) to' impart to such natural non-sticky or non plastic flotation concentrates the desired plastic condition which will make it possible to produce therefrom the lumps, nodules or the like previously referred'to of such a character that they will retain their shape, and they may be treated in exactly the manner previously described for coating the lumps with the powdered material. Such natural non-sticky or non-plastic concentrates are thereby produced in a. form in which sintcringmay take place much more rapidly than if no binder is added because of free air passages between the lumps in the sinter bed,'whereas when such non-sticky fine concentrates are placed directly on a sinter bed they present exceedingly small interstices between the very minute particles and do not present good conditions for sintering.

The lumps or pellets of concentrate coated with powdered material as described will be wet. or damp on the interior, suitable for sintering. The dry coating will keep the lumps or pellets from sticking to ether or coalescing into a solid impermeable mass.

Such coated lumps or pellets are fed into a sintering machine of any well known make and will present a loose bed of substantially uniform permeability with a multitude of air passages between the lumps or pellets which will be ignited, and said passages will facilitate the passage of air currents through the sinter bed in the process of sintering and thus promote uniform and rapid sintering of the concentrates. For some cases it is desirable, while making a uniformly sintere'd product, to retain as much sulphur as possible in the sintered product for subsequent reuses in a blast furnace. This is par- ,ticularly the case with copper concentrates high in copper where sulphur is required to make matte in the blast furnace. In other cases, such as, for instance, lead or zinc ores, it is desirable to eliminate the sulphur as far as possible. These variations can be effected by regulating the size of the lumps or pellets according to my invention. The smaller the pellets are in size the greater will be the elimination of sulphur in sintering, and the larger the size of the pellets the smaller will be the elimination of sulphur in the sintering. It is manifest, therefore, that in accordance with my method the metallurgist has a means of regulating the sulphur content of his sinter within a wide range, while at the same time always making a properly sintere'd product even when the material to be sintered consists of flotation concentrates or similar materials comprising extremely tine or pulverulent particles and which are plastic when wet, because of the ability to regulate the size of the coated over the present practice of sintering ores of the character referred to herein. Furthermore, my improved sinter cakes from such ores are more advantageous for use in smelters than the known sinter cakes because of the regularity of my product which will be more readily reduced with less ore losses, or irregular furnace operation, and at less costthan heretofore.

The accompanying drawing diagrammatically illustrates a machine in which the lumps, pellets, nodules or the like may be formed from the concentrates and mixed with the powdered material for delivery to the hopper of a sintering machine. numeral 1 indicates a cylinder in which a rotative screw or worm 2 is provide for forcing the material 3 to be divided, such as lumps of concentrates and attendant fines, which are delivered into the cylinder through the intake opening 4 and are forced from the cylinder by the screw through any desired number of outlet holes at-5. The delivery outlets 5 are shown located within a rotative drum 6 into which the cylinder 1 extends through a. side opening 8. The lumpslpellets or the like 3 drop from cylinder tlei'nto the drum, which drum is provided on its interior with any desired number of cups or shelves 7. At 8 is an inclined chute shown having a perforated portion 9 within the. drum, the chute extending through the side opening 8 of the drum, the outer portion 8 of the chute being shown imperforate so that the coated lumps or the like will slide along the chute for deposit as in a hopper 10 of a sintering machine, elevator, chute or bin. The powdered material for coating the lumps or the like is indi cated at 11 within the drum, and when the drum rotates the lumps will be rolled around with and within the powdered material for coating the lumps, and such material and the coated lumps will drop from the cups or shelves upon the perforated portion of the screen, the material falling through the screen into the bottom of the-drum while the coated lumps or the like slide down the screen to the hopper. Any suitable or well- The known means may be provided for shaking the screen. The screw 2 and the drum 6 may be rotated in any well known or desired way.

Having now described my invention what I claim is:

1. The method of preparing plastic ore fines for sintering consisting in dividing a mass of wet fines into lumps and coatlng the lumps with a powdered material to prevent the lumps from adhering to one another and to provide air passages between the lumps in a mass.

2. The method of preparing plastic ore con'centrates for sintering consisting in dividing a mass of wet concentrates into small lumps and coating the lumps with a dry powdered material to cause the lumps to remain separated in a mass with air passages between the lum s. r

3. The metho of preparing plastic wet material for sintering consisting in dividing a mass of plastic material into small lumps, dropping the lumps into dry coating material, moving the lumps and the said dry material about to cause a suflicient amount of the dry material to adhere to the surfaces of the lumps to prevent the lumps from sticking to one another, and then separating the coated lumps from the excess dry material.

4. The method of preparing plastic flotation concentrates for sintering consisting in dividing the plastic concentrates into small lumps, depositing the lumps in dry material adapted to adhere to the surfaces of the lumps, causing the mass of material and lumps to be rolled together until the lumps are coated with a sufficient amount of the dry material to prevent the lumps from sticking to one another, and separating the coated lumps from the dry material.

HENRY J. STEHLI.

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