US2353152A - Method of concentrating minerals - Google Patents

Description

July 11, 1944. L. J. ERCK METHOD OF CONCENTRATING MINERALS Filed May 29, 1941 4 Sheets-Sheet l ITI/UQMZO? L. J. ERCK METHOD OF CONCENTRATING MINERALS July 11, 1944.

Filed May 29, 1941 4 Sheets-Sheet 2 Inven/Zor July 11, 1944. J.-ERCK METHOD OF CONCENTRATING MINERALS 4 Shets-Sheet 3 Ziorney Filed May 29. 1941 L lu T Q w I ,1 \w @v D D u n mm a Mm vw N and a Patented July 11, 1944 METHOD OF CONCENTRATING MINERALS Louis J. Erck, Nashwauk, Minn., asslgnor to Minerals Beneficiatlon, Incorporated, Joplin, Mo., a corporation of Delaware Application May 29, 1941, Serial No. 395,809

8 Claims.

It is an object of this invention to provide a method for concentrating fine ores and coal by the use of relatively inexpensive equipment and with increased eiliciency and recovery as compared with known methods.

A particular object is to provide acontinuous, low cost method for concentrating certain fine minerals, such, for example, as ores of minus one-quarter inch mesh and minerals generally of such character that they cannot be concentrated economically or efliciently by methods in general use such as those involving flotation in heavy density fluid, froth flotation or utilizing log washers and other known equipment.

In practicing my invention I prefer to use one or more machines having a rotary spiral conveyor working in an inclined trough and with a weir at the lower end of the trough, the main concentrator machine being a modified classifier, operated in a novel manner. My preferred procedure is as follows: After determining the maximum size of the material to be treated, whether this material be ore or coal, it is passed over a scalping screen for the removal of any fraction which may be coarser than that to be treated and then the undersize of this screen is fed to suitable apparatus for removing the extremely fine, lighter fraction of the material and slimes. For the latter operation a standard, rotary spiral, classifier may be employed. The fine waste material overflows the weir of the machine which is at the lower end of the inclined trough. A small fraction of the extremely fine iron or other valuable constituent may be lost in this preliminary step or subsequently recovered, if recovery is commercially practical. The bulk of fine ore, together with the coarse ore and coarse silica, is carried up the incline of the trough by the rotar-y spiral and is discharged at the top of the machine, the upper portion of the spiral serving as a dewatering device.

According to my invention the raw mineral or dewatered material from the primary classifier is fed to the main concentrating machine, which is preferably a machine of the rotary spiral, classifier type, so altered as to permit the maintenance of a relatively dense and large mass of the mineral in the trough adjacent to the weir and to agitate this mass in such manner as to work the coarser particles of the lighter fraction (principally coarse silica in the case of iron ores) to the surface while continuously washing out this lighter fraction over the weir of the machine and removing the concentrate or heavier fraction from the upper end of the machine. In

ore concentration work, some fine ore is carried over the weir of the machine with the coarse silica and it is frequently desirable to recover this fine fraction by subsequent treatment. To accomplish this, I have found that the coarse silica and fine ore may be passed over a vibrating screen of suitable mesh to permit the oversize to be wasted or further treated as hereinafter described and the undersize from the screen, comprising principally fine ore, may be returned either to the primary classifier or to the main concentrator to be subsequently recovered from the latter. A number of modifications of and additions to the foregoing basic procedure, within the scope of my invention, are hereinafter described and claimed.

Details of my preferred mechanism and procedure will be understood from the following description having reference to the accompanying drawings in which: i

Figure 1 is a diagrammatic illustration of apparatus and a fiow sheet for utilizing my invention in the concentration of fine ores;

Figs. 2 to 7 inclusive are sections taken respectively on the lines 22, 3-3, 4-4, 5-5, 66

and 'l'l of Fig. l and showing a. typical disposition of the ore mass in the main concentrating machine;

Fig. 8 is a similar section through the primary classifier taken on the line 8-4! of Fig. 1;

Fig. 9 is a plan view of my improved concentrating machine;

Fig. 10 is an elevation showing the normally lower or weir end of the concentrator;

Fig. 11 is a cross section taken on the line llll of Fig. 9;

Fig. 12 is a side elevation of the concentrating machine;

Fig. 13 is a flow sheet diagram, illustrating a modification of the procedure indicated in Fig. 1, and

Fig. 14 is a. flow sheet showing an application of the invention for the cleaning of fine coal and providing for the recovery of pyrite therefrom.

Referring to Fig. 1, an ore feed conveyor is indicated by the numeral l6. This conveyor delivers the ore to a. scalping screen ll of such mesh as to eliminate sizes larger than those to be concentrated. In the case of iron era, the process being particularly applicable to minus one-quarter inch sizes, a screen of the corresponding mesh is employed and the oversize is either wasted or treated by some other suitable method. The undersize material, together with suiil-cient water to cause it to flow is conveyed the trough and communicating therewithl through perforations. This tank extends only from the ore feed box a short distance toward the upper end of the trough 2i. A considerable quantity of water is caused to overflow a weir 28 at the lower end of the trough and this water carries with it much of the fine sand and slimes which are washed from the ore. The overflow is discharged through a conduit 21.

The product of the primary classifier is carried up the trough 2i and is discharged through a conduit 23 to the feed box 29 of the main concentrator indicated by the numeral 33. The upper end section of the screw conveyor 22 has a dewatering effect on the ore and the latter is caused to flow through the conduit 23 by adding water from the pipe 3|. My improved concentrator 30 has an inclined trough 32 formed with an arcuate bottom and provided with a weir 33 at its lower end over which the coarser silica, together with some fine ore, is discharged. A screw conveyor having spiral flights 34 and an axial shaft 35 extends longitudinally within the trough 32 from end to end thereof. The pitch of the flights 34 is such as to gradually work the ore toward the upper end of the trough when the shaft 35 is driven in the appropriate direction. The flights 34 are of the ribbon type having ample openings around the shaft 35 for the passage of liquid toward the weir 33. In operation, the shaft 35 is continuously rotated by an electric motor 36 (Figs. 9 and 12) mounted near the normally upper end of the trough and connected by suitable speed reducing gearing to the upper end of said shaft.

Fixed at suitable intervals onthe outer periphery of the flights 34 is a series of litter bars 31 adapted to perform the important functions of loosening the mass of ore in the concentrator section of the machine and working the coarser tailings to the surface of the mass. These bars 31 extend in parallel relation to each other substantially from the weir 33 to the upper end of the main body of ore or other material to be concentrated. Extending over the corresponding length of the bottom and side portions of the trough 32 is a hutch tank 33 for distributing water under pressure to the mass of material. This hutch tank is subdivided into separate compartments by partitions 33 (Figs. 9'and l2)v extending across the trough and by a central partition 43 extending longitudinally, approximately along the center line of the machine (Figs. 2 to 6 and 11). Water supply pipes 4| severally communicate with the compartments of the hutch tank and each of these pipes has a valve 42 (Fig. 11) for controlling the fiow of water supplied thereby. As indicated in Fig. 9. the hutch tank communicates with the lnteriorof the trough at the bottom and sides thereof through a multiplicity in Fig. 12. This projection is in communication throughout its length with the interior of the trough so that the material fed to the machine is distributed and directed in a corresponding direction in the accumulated mass of mineral.

An outlet opening 44 (Fig. 9) is formed in the bottom of the trough 32 near its upper end for the discharge of the concentrate or heavier fraction of the material into a chute 43 (Fig. l). The weir 33 extends substantially horizontally from one side of the trough to approximately the center plane of the machine and is located at the side of the trough toward which the material is worked upward by the screw flights 34 and bars 31, as indicated in Figs. 2 and 3. A baiiie 43 extending in the plane of the weir prevents the stream with entrained material from passing directly out of the low or launder side of the mass in the trough. The material which passes over the weir is caught in a receptacle 41 mounted on the outer end of the trough and is discharged through an outlet opening 43 at the bottom of this receptacle.

The machine illustrated has the conventional Akins type mechanism for raising the screw conveyor out of the trough and for gradually lowering the conveyor into the trough when the machine is started after a shut down with a mass of material in the trough, to thereby avoid overloads on the conveyor when starting. A crank operated screw 43 is connected to the lower end bearing of the shaft 35 for raising and lowering it. At the upper end of the trough, the motor 33. shaft 33 and driving connections therefor are mounted on a frame which is swiveled on a horizontal shaft 53, as indicated in Fig. 12.

To recover the flne ore from the overflow from the weir 33 and receptacle 41, the overflow material is conveyed to a fine screen 5| (Fig. l) of the vibrating type. For flne iron ore work this screen should have approximately 48 openings to the inch. The oversize from the screen, comprising principally coarse silica, may be wasted and the undersize, principally fine iron ore, is fed to a sand pump 32 and returned thereby through a pipe 53 to the primary classifier feed conduit ll to be further cleaned and finally recovered in the main concentrator product.

Operation of the screw-type concentrator Details of operation for the concentration of iron ore or minus a quarter inch sizes are here set forth by way of example. This material is fed into the feed box 23 of the concentrator 33. together with sufllcient water to render the mass fluid. As the material enters the trough 32 the heavier fractions including much of the coarse iron ore and some coarse silica, together with most of the finer iron ore, settle immediately to the bottom of the trough at the feed point and are started on their upward path by the screw flights 34. The intermediate grade material which is largely silica, together with some of the finer iron ore, is accumulated in the lower end portion of the trough where it forms a dense mass. By proper adjustment of the rate of feed relative to the speed of operation of the conveyor shaft 33, this mass is. maintained to approximately the level of the top of the weir 33, and.

of small perforations 43. By this arrangement water is forced up through the mass of material and j in the trough and as illustrated in Figs. 2 to 6 inclusive, it is con- .tinuouslysupplied with water from the hutch tank 33, the water entering themass from the u perforations 43 and rising to the surface.

As further indicated in Figs. 2 to 6 inclusive, the mass of material, indicated by the numeral N, is maintained-at a somwhat higher eleva- 'tionatthelettsideotthemachinethanatthe right side due to the rotation of the fiights 34 and lifting bars I! in the direction indicated. Along the opposite side of the trough, a stream of water 55 fiows toward the lower end of the machine and carries with it the larger particles oi tailings together with some fine iron ore. Such tailings are gradually and continuously worked tothesuriaceof themassbothbytherising water and by the mechanical lifting action of the rotating bars 31. A bed of fine material 58, largely fine, heavy ore, is maintained between the bottom of the trough and the conveyor flights ll. The stream of water 55 flowing down the side of the trough washes the coarse silica from the surface of the mass to the rear of the machine irom which it is discharged over the weir 33. The bulk of the heavier material is gradually worked up the incline of the trough out of the water, as indicated in Fig. 7. and is dewatered by the upper section oi. the conveyor, being finally discharged through the opening 44 and chute 45.

As indicated in Fig. 8, the primary classifier contains, near the lower end, only a relatively small mass of the ore 51 and a relatively large body or water 58 which is continuously supplied so that it overflows the weir 26 carrying the slimes and fine silica to waste, in accordance with conventional classifier practice. In order to maintain the relatively large mass of material in the main concentrator for my continuous process, the primary classifier must be considerably larger than the concentrator machine.

The density of the mass of iron ore and water in the concentrating section of the machine 30 should be maintained approximately within the limits of 55% to 75% solids, depending on the structure of the ore. This is accomplished by adjusting the valves controlling the hutch water and by controlling the agitation produced mechanically by the screw flights and lifting bars. Concentration takes place in zones throughout the portion of the trough to which the hutch water is supplied, these zones extending approxiinately two-thirds of the length of the trough. Tests during runs of my process with iron ore have shown that concentration takes place generally in three more or less distinct zones, the primary or rough concentration zone being the portion of the mass extending approximately from the cross section through the point of feed to the rear end or weir. Considering the top surface of the mass, there is also what may be termed a secondary concentrating zone extending from the cross section through the point of feed centrally of the trough and upwardly from such section, and a final or third zone extending approximately from the point of feed to the upper end of the mass along the lower or launder side 01 the mass over which the stream 55 fiows.

From the foregoing it will be evident that I maintain in the concentrating machine a long sloping, sorting column of ore from. which the coarser silica or lighter waste material is removed notwithstanding the fact that the treated material is of various sizes as well as difierent specific gravities. Unlike the vertical column, laboratory glass classifier process, it is unnecessary for the success of my process to have all ore and waste particles 01' approximately the same size. It is thus apparent that one of the advantageous features of my invention resides in the economies resulting from obviating successive screening operations.

The fiow sheet shown in Fig. 13 illustrates a modification of the foregoing method or procedure which does not require the use oi a screen to eliminate the coarse silica from the concentrator overflow. As indicated by the legends, the ore is fed to the primary classifier which operates as hereinbefore described to eliminate fine silica and slimes. The product of the primary classifier is continuously ted to the main concentrator as hereinbeiore described and the prodnot of the latter is the concentrate whereas the overflow, instead 01' being screened, is ground in a suitable mill, such as a ball or rod mill, to reduce the coarse silica to such a fine state that it may be eliminated in the primary classifier. The product of the grinding mill is pumped to the primary classifier feed box.

Another important field for the use of my process is in the treatment of fine coal. The principles of operation above described may be applied to the treatment of coal to produce a satisfactorily clean coal product for use in stokers as well as in producing pulverized coal. Much of the finer coal is wasted by methods in general use which ordinarily employ notoriously inefllcient jigs and produce a relatively high priced product.

The flow sheet illustrated in Fig. 14 indicates a modification of my process to adapt it to the treatment of coal and recovery of pyrite therefrom. In this case the primary classifier eliminates slimes together with a small fraction of the fine coal and the product of this machine consisting largely of pyrite, slate and coal is fed to the main screw type concentrator which operates as hereinbefore described, except that the heavier fraction consisting of pyrite and slate is discharged from the upper end of the trough, whereas the overflow from the weir containing the bulk of the coal is fed to a vibrating screen of suitable mesh. The oversize or coarser fraction from the screen is the marketable coal product and the undersize, consisting of fine slate, pyrite and coal is preferably pumped back into the primary classifier. To recover the pyrite from the slate, the product of the main concentrator is fed to a secondary concentrator also oi the screw type. The heavier traction comprising largely pyrite is separated from the slate in the secondary concentrator which is operated as hereinbefore described in detail. The overflow from this secondary concentrator is conveyed to a vibrating screen of suitable mesh to allow the passage of the smaller material containing some coal and fine pyrite. Finally, the undersize material from the screen is pumped to the feed box of the main concentrator, as indicated, while the oversize from the screen, consisting largely of slate, is wasted.

It will be understood that my invention may be employed in the concentration of ores other than iron ore and to non-metallic minerals where there is a fairly wide spread in specific gravity between the desired concentrates and the desired rejects. In the treatment of non-metallic minerals, as in the case of coal, the concentrate is discharged from the concentrator over the weir and the waste or tailings are discharged from the upper end of the trough. For non-ferrous ore treatment it is not necessary to produce a finished concentrate since the end point is usually reached after a further refining process, such, for

example, as oil flotation. With such refining processes my procedure may be used to advantage in discarding the bulk of the waste material. Other modifications of the flow sheets herein described within the spirit of my invention may include the use of three or more concentrator machines and the recirculation of the overflow from one machine to the machine preceding it.

This invention has been used with marked success in concentrating iron ores from the present tailings basins which are made up of ore reiected from the former concentration operations and containing fine iron and porous iron of sizes and types of ore which are extremely difilcult to treat in jigs or other conventional equipment. Fairly good recovery of high grade material has been obtained from material on which jigs show practically no recovery.

By the term dense," as applied to the mass of mineral in the concentrator tank, it is meant that the particles of ore are in contact with each other in a heterogeneous structure such that the coarsest particles of low specific gravity are prevented from settling and the interstices between particles are filled with water. mass is too viscous to permit classification depending on particle size. It sustains and remains separate from the stream of water which is directed toward and over the weir or out thru the elevated outlet, as indicated in Figs. 2 to 4 inclusive of the drawings, removing from the surface Such a of the mass the coarse particles of low specific gravity as well as some of the finer particles of substances of definite chemical composition which are technically described as minerals.

Having described my invention, what I claim as new and desire to protect by Letters Patent is:

l. The method of concentrating minerals containing substantial quantities of particles of substantially all size ranges up to the maximum size of the mineral being treated which comprises continuously feeding such mineral to a concentrator having an inclined trough and an elevated outlet at the lower end of the trough, controlling the rate of feed of solids and water to the concentrator and the rate of discharge therefrom to maintain a dense mass of the mineral containing from 55% to 75% solids within the lower end portion of said trough substantially to the level of said outlet, said mass being too viscous to permit classification depending on particle size, mechanically agitating said mass and percolating water upward through said mass to work coarse particles of the lighter fraction thereof to the surface by a combination of said mechanical agitation and rising water, continuously discharging said lighter, coarse particles together with some of the finer particles and water from the surface of the mass through said outlet and gradually working the heavier fraction of said mass toward the upper end of .said trough and discharging said heavier fraction therefrom.

2. The method of concentrating minerals containing substantial quantities of particles of substantially all size ranges up to the maximum size of the mineral being treated which comprises continuously feeding such mineral to a concentrator having an inclined trough and an elevated outlet at the lower end of said trough, controlling the rate of feed of solids and water to the concentrator and the rate of discharge therefrom taining from 55% to solids within the lower end portion of said trough substantially to the level of said outlet, said mass being too viscous to permit classification depending on particle size, mechanically agitating said mass and iniecting water into the bottom and sides thereof, while gradually working coarse particles of the lighter fraction thereof to the surface by a combination of said mechanical agitation and rising water, directing a stream of water over the surface of the mass and through said outlet to discharge said coarse particles of the lighter fraction together with some of the finer particles from the trough, working the heavier fraction of said mass toward the upper end of the trough and discharging said heavier fraction therefrom.

3. The method of concentrating minerals containing substantial quantities of particles of substantially allsize ranges up to the maximum size of the mineral being treated which comprises continuously feeding such mineral to a concentrator having an inclined trough and a weir at the lower end of the trough, controlling the rate of feed of solids and water to the concentrator and the rate of discharge therefrom to maintain a dense mass of the mineral containing from 55% to 75% solids within the lower end of said trough substantially to the top of said weir, said mass being too viscous to permit classification depending on particle size, mechanically agitating said mass by passing mechanical lifters upwardly therethrough and supplying water under pressure to at least a portion of the bottom thereof whereby coarser particles of the lighter fraction thereof are worked to the surface of the mass by the combined action of the mechanical lifters and rising currents of water, continuously discharging the lighter and coarser particles together with some of the finer particles and water from the surface of the mass over the weir and gradually working the heavier fraction of said mass toward the upper end of said trough and discharging it therefrom.

4. The method of concentrating fine unsized minerals containing substantial quantities of substantially all size ranges up to the maximum size of the mineral being treated and wherein the maximum size of particles does notsubstantially exceed one-quarter inch mesh which comprises continuously feeding the mineral to a concentra tor having an inclined trough and an elevated outlet at the lower end of said trough, controlling the rate of feed of solids and water to the concentrator and the rate of discharge therefrom to maintain a dense mass of the mineral containing not less than 55% and not more than 75% solids within the lower end of said trough substantially to the level of said outlet, said mass being too viscous to permit classification depending on particle size, mechanically agitating said mass and injecting water into the bottom thereof and gradually working coarse particles of the lighter fraction thereof to the surface by the combined action of rising currents of water and said mechanical agitation, directing a stream of water over the surface of the mass and through the outlet to discharge said coarser particles together with some of the finer particles from the trough and working the heavier fraction of said mass toward the upper end of the trough and discharging it therefrom.

5. The method of concentrating fine unsized minerals containing substantial quantities of substantially all size ranges up to the maximum size to maintain a dense mass of the mineral con- 1 of the mineral being treated and wherein the maximum size of particles does not substantially exceed one-quarter inch mesh which comprises feeding the mineral to a concentrator having an inclined trough and an elevated outlet at the lower end of said trough, controlling the rate of feed of solids and water to the concentrator and the rate of discharge therefrom to maintain a dense mass of the mineral containing from 55% to 75% solids within the lower end portion of said trough substantially to the level of said outlet, said mass being too viscousto permit classification depending on particle size, revolving a spiral, ribbon type conveyor .in said mass while mechanically agitating the same by passing a plurality of bars upwardly and laterally through the mass, said bars extending substantially from said outlet throughout the length of said mass, injecting water into the bottom of said mass to thereby work coarse particles of the lighter fraction thereof to the surface by a combination of said mechanical agitation and rising water, directing a stream of water over the surface of the mass and through the elevated outlet to discharge said coarser particles together with some of the finer particles from the trough and discharging the heavier fraction of said mass from the upper end of said trough.

6. The steps ,in the process of concentrating iron ore of minus one-quarter inch mesh and containing substantial quantities of particles of substantially all size ranges up to the maximum size of the particles being treated which comprise, continuously feeding such ore to a concentrator having an inclined trough and an elevated outlet at the lower end of the trough, controlling the rate of feed of solids and water to the concentrator and the rate of discharge therefrom to maintain a dense mass of said ore within the lower portion of said trough substantially to a level as high as said outlet, said mass being too viscous to permit classification depending on particle size, mechanically agitating said mass and supplying suflicient water thereto to maintain not less than 55% and not more than 75% by weight of solids in the mass while percolating water upward through the mass and working coarser particles of the tailings to the surface of the mass by a combination of said mechanical agitation and rising water, continuously washing said coarser particles together with some of the finer particles from the surface of the mass and discharging them through the outlet while gradually working the concentrated ore toward the upper end of said trough and discharging it therefrom,

7. The method of concentrating minerals containing substantial quantities of particles of substantially all size ranges up to the maximum size of the mineral being treated which comprises continuously feeding the mineral to a concentrator having an elevated overflow and a bottom surface a portion at least of which is inclined, the inclined portion extending to an elevation above the overflow, controlling the rate of feed of solids and water to the concentrator and the rate of discharge therefrom to maintain a dense mass of mineral containing from 55% to 75% solids in the lower portion of the concentrator to a level substantially as high as the overflow, said mass being too viscous to permit classification depending on particle size, mechanically agitating said mass and percolating water upward therethrough to work coarse particles of the lighter fraction to the surface of the mass by a combination of said mechanical agitation and rising water, continuously discharging such coarser and lighter particles together with some of the ilner particles through the overflow and gradually working the bulk of the heavier particles from said mass toward the upper end of the inclined portion of the bottom and discharging such heavier particles therefrom.

8; The method of concentrating unsized mineral containing substantial quantities of particles of substantially all size ranges up to the maximum size of the mineral being treated and of sizes not substantially exceeding one-quarter inch mesh which comprises continuously feeding such mineral to a concentrator having an elevated overflow and a bottom surface a portion at least of which is inclined, the inclined portion extending to an elevation above the overflow, controlling the rate of feed of solids and water to the concentrator and the rate of discharge therefrom to maintain a dense mass of mineral containing from 55% to solids in the lower portion of the concentrator to a level substantially as high as the overflow, continuously stirring said mass by mechanical means and percolating water upward therethrough to work coarser particles of the lighter constituents to the surface by a combination of said mechanical stirring and rising water, said mass having higher specific gravity than said coarser and lighter particles and being sufllciently viscous to prevent the rising of said particles to the surface thereof in the absence of such mechanical stirring, continuously discharging such coarser and lighter particles together with some of the flner particles through the overflow and conveying the bulk of the heavier constituents of said mass toward the upper end of the inclined portion of the bottom and discharging them therefrom.

LOUIS J. ERCK.

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