US2203601A - Separating fragmentary materials - Google Patents

Description

June 4, 1940.

v. RAkowsKY ET AL SEPARATIN G FRAGMENTARY MATERIALS Filed Feb. 18, 1939 SEPARATING ZONE Sp. GI. 2,6

m My m r wwdw kmH m; r r wyw 9 W Patented June 4, 1940 SEPARATING FRAGMENTARY MATERIALS Victor Rakowsky, Joplin, M6,, Ray W. Arms, Evanston, Ill., and Grover ,3. Bolt, St. Paul, Minn, assignors to Minerals 'Beneficiatlon Incorporated, Chicago, I ware ll., a corporation of Dela- Application: February 18, 1930, Serial No. 251,250 Claims, (0l. 209-113) This invention relates to separation of the constituents of ores in which the concentrate to be recovered therefrom has a specific gravity of 2.6 or more. In the oredressing art there are many known processes that take advantage of the difierent specific gravities of the constituents oi the ore to effect a separation of such constitucuts one from another in a mixed ore feed. Fundamentally, density (mass per unit volume) is the controlling factor in such gravity separating processes, but it is more convenient to use the expression of density in the c. g. s. system known as specific gravity. The force of gravity acting upon a particle of any solid causes it to fall through a fluid environment, such as air. or water, at a rate depending on the relative density of the particle and the fluid through which it falls. The shape of the particles, the viscosity of the fluid and other contributory factors afiect the rate of fall, but density is the most important factor with particles of equal size.

Minerals of high density fall at a greater rate.

through any given fluid medium than those of low density. This attribute, known in the art as falling velocity, has been utilized in processes for separating one mineral from another. When single particles are considered, or when there are so few particles that they fall through the fluid unobstructed by others, they fall under "free settling" conditions, but when the particles are crowded in the fluid they obstruct each other in their fall and they are said to be falling under "hindered settling conditions. These principles apply to particles of the same size, but falling velocities are also dependent on' the size of the particles. A small dense particle may fall at the same rate as a larger but less dense particle. 0

Therefore, attempts heretofore made to separate ores on the basis solely of their falling velocity in a given medium have not produced satisfactory results because of the many sizes of particles in any given ore feed.

When a separating medium composed of finely comminuted solids suspended in water is used, the specific gravity of the medium depends on the proportions of water and such solids in the medium, and if the proportions of solids is high (it may be as high as 80% or more) the specific gravity of the medium is also high. Under such conditions the solids of the medium are under extreme hindered settling conditions, and the different sized grains of solids of themedium will tend to settle at the same rate. Therefore, in such high specific gravity suspension mediums (containing 70% or more of solids) very little force is required to maintain all of the comminuted solids of the medium in suspension, and thus maintain constant the specific gravity of the medium. When pre-sized ore particles are added to such medium the smallest particle in the ore is so much larger than the largest grain of the comminuted solid in the medium that it is not materially affected by the extreme hindered settling conditions of the medium itself. In effeet, the ore particles may be regarded as under free settling conditions in a medium which is itself governed by hindered settling conditions. According to the present invention when it is desired to treat any ore the concentrate from which is to have a specific gravity in excess of 2.6, we suspend in a liquid, such as water, finely comminuted solids of high specific gravity, such as iron, steel, galena, etc., in such proportions as to produce a separating medium having a specific gravity between 2.6 and 3.6, the exact speciflc gravity selected being dependent upon the character of the ore to be treated and the specific gravity of the concentrate to be recovered therefrom. This medium is composed of not less than 70% nor more than 85% of said comminuted solids suspended in water of from 30% to 15% both by weight of the entire medium. Such a mixture will produce a medium of a specific gravity ranging, as indicated above, from 2.6 to 3.6 and it is essential that this specific gravity of the medium once established, be maintained in the separating zone. The important point is that the specific gravity of the separating medium once established must be kept constant in, the separating zone. According .to the present invention the specific gravity of the medium once established, is kept constant in the separating zone by imparting a very slow upward movement to the medium through the separating zone sufficient to prevent settling of any of the comminuted solids of the medium itself but which is not suflicient to prevent sinking of the small particles of the desired concentrate.

When' v a separating medium of constant specific gravity taken of these conditions to prevent settling of the solids of the medium without interfering with the settling of the. small particles of the desired concentrate. This is accomplished by imparting a very slow upward movement to a medium having not less than 70% of solids and at a rate intermediate the settling rates of the solids of the medium and the small particles of concentrates in said medium when quiescent.

By providing a supply of medium of the same composition as that in the separating tank and then slowly and continuously introducing such medium into the tank below the separating zone and out of the tank above the separating zone, the following highly important results are accured:

1. The specific gravity of the medium is main- I tioned medium is fed into the tank from below and the slimes and sands are eliminated with the overflow;

7. There is a continuous movement of the whole body of medium into, through, and out of the tank, and hence no treatment of the medium in the tank to maintain its specific gravity constant is required;

8. By reason of the slow rate of upward movement of the medium turbulence and eddies in the medium are avoided, since this upward fiow of the, medium is in no sense an agitating current;

9. Separation of the ore particles is effected strictly on the basis of difference in their specific gravity and classification, i. e., separation according to size does not occur.

Certain known processes are more or less adle quate for the separation of certain classes of ores, thatis, ores in which the valuable constituents are a great deal heavier than the tailings (waste) and in which the valuable constituents break cleanly fromthe waste when crushed. They are, however, totally inadequate to produce eflicient separation or concentration of ores, such as iron ore, for example, in which, when crushed, the particles do not consist entirely either of the valuable or of-the waste variety. .In such ores the waste or "tails contains a certain amount of iron and the valuable iron particles always contain more or less of the deleterious substances,

such as silica, inherent in its chemical composition, and thus are not readily separable by crushing. In such an ore the amount of middlings, i. e., material very close to the desired separating gravity, is quite high and the separating process must be extremely accurate to be commercially practicable.

Rising currents of the prior processes mentioned are not effective on such a difiicult class of ores unless the feed is very closely sized, because in such processes classification, i. e., separation according to size, will occur rather than separation according to specific gravity of the particles with the result that fine particles of concentrate will be lifted into the waste.

In the process of the present invention the velocity of the upwardly moving medium at the separating zone must be intermediate the falling velocities of the comminuted solids in the medium and the concentrates when the medium is quiescent. Under these restricted conditions remarkably superior results are secured. By the practice of any process heretofore employed for the separation of ores, such as iron, where a concentrate of 2.6 or above is desired, it has been found commercially impossible to secure a concentrate that is not largely contaminated with middlings, i. e., particles consisting of a mixture of waste and particles whose specific gravity very nearly ap-' proaches the specific gravity required in the separating zone. The specific gravity of such middlings, in other words, is intermediate the.

specific gravity of the waste (tailings) of the ore and that of the desired concentrate. tamination of the concentrate of prior processes sometimes amounts to 10% or more unless too much of the ore which should go to concentrate is passed over to waste. By the process of the present invention, however, less than 1% of the material which should have been discarded as fioat is found in the concentrate, and in the tailings not more than 2% of the material which should have gone to concentrate is found. These are the figures that have been absolutely demonstrated in commercially treating certain iron ores, and this is a result never before attained by any commercial process for the separation of iron ore. These figures may vary somewhat in different ores but in every case it will be found that the amount of contaminating material found in the concentrate is greatly decreased below that of contaminating material in concentrates produced by any other process; and on the other hand the amount of valuable material in the waste that should have gone to concentrate is much less than any other process of separating such ores.

It will be understood by those skilled in the art that the ore or other materials to be subjected to the separating process should ordinarily be crushed to a certain maximum size to free the valuable mineral from the waste or tailings to a sufficient degree to make separation practicable. From such a crushed ore it is preferable to remove the smaller sizedparticles therefrom by screening. washing or otherwise, and thus remove grains of concentrate having a settling rate approxi- ,mately that of the comminuted solids of the medium. This to the end that the settling velocity of the solids of the medium be less than that of the smallest particle of the heavy material of the ore to be separated. By "settling velocity is meant the falling velocity which is soon reached after the particle is introduced into the separating medium when quiescent. It will be understood that while it is essential to maintain the upward movement of the medium at the separating zone at a rate indicated, nevertheless the rate of movement of the medium below the separating zone need not necessarily be maintained at precisely the same rate as that which must be maintained in the separating zone. Another important advantage of the process of the present invention over processes heretofore employed for the separation of ores is found in the fact that socalled fiats which occur in many ores are not carried over into waste if said fiats are of such specific gravity that they should settle as a par of the concentrate.

The con- The restricted conditions oi. the present invention may be enumerated as follows:

1. The fluid medium must contain between 70 and 85% of, solids by weight of the entire medium. If less than 70% minimum of the solids be employed, it would be necessary to employ an upward movement of the medium strong enough to involve classification, i. e., separation according to i the size of the particles, instead of according to the specific gravity thereof. It more than 85% of the fluid medium is composed of solids the medium would be too viscous to be employed as a separating medium.

, 2. The fluid medium must have a rising rate of movement suificiently high to support the comminuted solids of the medium itself. The rate of upward movement is very low because under the superhindered settling conditions of a mixture of 70% or more of fine solids with the water, the settling rate of said solids is very low.

3. The upward movement of the fiuid medium must not prevent the settling in the medium of .the smallest grain of concentrate in the ore feed.

Preferably the minimum size in ore feed should be such that the upward movement of the medium used does not even approach the settling velocity of the finest heavy particles in the ore feed.

4. The upward movement of the medium is sufflcient to carry off with the tailings the intermediate gravity material (middlings) which would accumulate in the container it the medium were static.

. Various forms of apparatus may be employed in practicing the invention, one of which is diagrammatically shown in the accompanying drawing.

In said drawing, I indicates a suitable separating tank having a medium inlet pipe 2 to which the medium is supplied through pipe 3 controlled by valve 4. The specific gravity of the medium is established by mixing a finely comminuted heavy solid, such as steel, iron or galena,with water in such proportions that the solids shall constitute not less than 70% nor more than 85% o! the mixture. The exact proportions must be such as to produce a medium whose specific gravity is intermediate that of the tallings" or lighter ore particles which it is desired to eliminate and that of the heavier ore particles which it is desired to retain as concentrates. For the purpose of illustration, this specific gravity is indicated in the drawing as 2.6. Ore is fed through suitable chutes 5, 5 and the particles whose specific gravity is 2.6 or less immediately begin to rise in a zone opposite the points where the ore feed enters, which zone is diagrammatically indicated at 6 as the separating zone. The ore particles whose specific gravity exceeds 2.6 immediately fall through said zone and down to any desired point of removal, as at I, while the tailings with some medium overflow the top of tank I and into-a launder 8.

It will be seen that the medium enters the tank I below the separating zone and flows upward through said zone and out over the top of the tank into the launder 8 and some medium may pass out with the concentrates at I. The rate of upward flow through the separatory zone is so controlled (by any suitable means, as the head in the medium in pipe 2) that the rate or flow in the said zone is intermediate the falling velocities of the solids of the medium and the smaller particles of concentrates in said medium when quiescent. The necessary result of .this is that none or the comminuted solids or the medium at the separating zone settle and all particles or the ore feed whose specific gravity does not exceed that of the medium are discharged at the top 01' the tank.

By withdrawing occasional samples of the medium from the tank and testing the specific gravity thereofit may be readily determined whether or not it has the desired specific gravity. If it should appear that the specific gravity in the tank is falling below that required it is evident that'the specific gravity oi the medium flowing into the tank should be increased. If it should.

appear that the middlings are not being carried out with the waste (tails) the rate of upward flow oi the medium is increased through valve 4 until it is just sufiicient to carry over the middlings.

It will be' noted that the medium in the tank illustrated enters well belowthe separating zone. The result of this is that disturbing currents and whirlings of the medium at and near the point of entrance into the tank are dissipated before the medium reaches the separating zone.

It will be noted-that the velocity of the up ward movement of the medium gradually increases from the base or the truncated conical portion to the point of overflow into the launder 8. By maintaining the velocity of upward movement of the medium at such a rate that, in the separating zone, such velocity will be intermediate the falling velocities of the comminuted solids in the medium and the ore concentrates when said medium is quiescent, the waste and middlings will-be discharged into the launder and the concentrates will settle, and thus tendency of middlings toaccumulate is avoided. Below the separating zone the velocity of the medium is somewhat less than that in the separating zone, and hence ofiers a less resistance to the settling of the particles of ore concentrates in a tank of this construction. It will thus be'seen that the specific gravity of the medium in the tank remains. constant, middlings and'tailings are rapidly removed at the top of the tank and the movement of medium below the separating zone does not interfere with the settling of the concentrates.

When ore is fed into the tankin a wet condition, as in common practice, the water accompanying the ore tends materially to dilute and hence change the specific gravity of the medium if the main body of the medium as a whole re mains in the tank, even though there be some overflow at the top. Attempts to correct this change in specific gravity are resorted to by many of the prior processes by introducing additional medium into the tank having a specific gravity designed to cheat this result. .By the present invention, however, any of the moisture entering the tank with the ore feed is at once swept out of the separating tank, together with,

the tails and middlings, with the result that it does not in any wayafi'ect the specific gravity 'of the oncoming medium. The result is that the ore feed constantly meets and is acted upon by a separating medium of the desired specific gravmiddlings as well as the tails. Moreover, the diameter ofthe discharge opening at the top of the tank is much less than that at any other point in the tank above that where the medium enters the tank. This restricted discharge opening produces a uniform mushroom-like discharge entirely around the discharge mouth, and thus avoids any direct cross current of discharge. Moreover, by thus restricting the outlet at the top of the tank the rapidity of outlet flow at the top is much increased thereby insuring'the eiiicient discharge of tails and middlings, while at the same time maintaining the low rate of upward fiow of the medium at the separating zone. 5 It will be understood that the term tails" as herein used is meant to define all of that portion of the ore feed whose specific gravity is less than that of the medium at the separating zone; that by middlings is meant all of those 29 particles of the ore feed whose specific gravity is such that it would tend to remain in the separating zone but for the upward movement, of the medium; and by concentrates is meant all of those ore particles. whose specific gravity is greater than that of the medium at the separating zone and which settled through the medium toward the bottom of the tank.

What is claimed is: 1. The process of separating ores which con- 30 sists in preparing a liquid separating-medium of not less than 2.5 specific gravity and composed of comminuted solids suspended in water, flowing said separating medium upwardly through a separating tank, the rate of fiow of the medium continually increasing as the medium moves upward, and introducing the ores into the medium at a zone where the velocity of the medium is intermediate its maximum and minimum velocities and where the falling velocities of the solids of the medium and the heavier ore particles in said medium when it is quiescent.

2. The process of separating ores which consists in preparing a liquid separating medium of a specific gravity not less than 2.5 and of constant specific gravity from the top downward by suspending comminuted solids in water, ascertaining the falling velocities of the solids in said medium, when quiescent and the heavier ore particles to be separated, and imparting an up ward movement of constantly increasing velocity to the medium from a lower point in the separating tank to the outlet thereof and introducing the ore particles into the medium intermediate the upper and lower portions of the tank and at a point where the velocity of the medium is intermediate the falling velocities of the solids of the medium and the heavier ore particles in said medium when it is quiescent.

3. The process of separating ores which consists in preparing a separating medium of a specific gravity not less than 2.5, and composed of comminuted solids suspended in water, passing said medium upwardly through a separating tank at a constantly increasing velocity, and introducing the ore particles into said medium below the surface thereof and in a zone where the velocity of the medium is intermediate the falling velocities of the solids of .the medium and the heavier ore particles 'in'said medium when it is quiescent.

I 4. The process of separating ores which consists in preparing a separating,medium of a constant specific gravity not less than 2.5 by suspending comminuted solids in water, continuously passing said medium, upwardly through taining the velocity of the current at said zone a tank and discharging it therefrom through an opening concentric with the ,tank, introducing the ore particles to be separated into the medium below the surface thereof, and maintaining the upward velocity of the medium at the zone of introduction intermediate the falling velocities of the solids of the medium and the heavier ore particles in said medium when it is quiescent.

5..Ihe process of separating concentrate ore particles from tails'and middlings which con- 1 sists in introducing into a tank a liquid gravity separating medium'x -ot not less than 2.5 specific gravity and in whic when quiescent the tails would float and the concentrates would sink and composed of not less than 70% comminuted 1 solids and not more than 30% water, both by weight, imparting an upward currentto said medium at a velocity which increases from a lower point in said tank to its upper outlet, and introducing-the comminuted ore into saidcur- 2 rent below the surface of the'medium and at a point where the upward velocity of the medium is less than the falling velocity of the concentrates in said medium when quiescent but greater than the falling velocity therein of the middlings. 2

6. The process of separating ores which consists in preparing a liquid gravity separating medium of a constant specific gravity in excess of 2.5 and composed of comminuted solids sus pended in water, the solids and water being in 3 proportions to form a liquid medium of the required specific gravity, continuously passing said medium in an upwardly moving current through a tank, introducing the ore particles to be separated into the tank below the surface of 3 the medium, permitting the concentrates to settle in said medium and sweeping out the tails and middlings in said current by maintaining a current velocity at the point of introduction of the ore particles intermediate the fall- 4 ing velocities of the solids of the medium and the ore concentrates in said medium when it is quiescent.

'l. The process of separating ore particles which consists in preparing a liquid gravity sep- 4 arating medium composed of not less than 70% comminuted solids and not more than 30% water mixed in proportions to produce a liquid medium having aspecific gravity intermediate the specific gravities of the ore particles to be separated, passing said medium in an upwardly moving current through a separating tank, and introducing the ore particles into said medium v ata point below its surface and maintaining said current at said point of introduction at a .velocity intermediate the falling velocities in said medium when quiescent of those ore particles whose specific gravity exceeds that of the medium and of the solids of the medium, whereby middlings are swept out of the tank with the tails" by said current.

8. The process of separating ore particles which consists in preparing a liquid gravity separating medium composed .of not less than 70% comminuted solids and not more than 30% water, mixed in proportions to produce a liquid medium having a specific gravity intermediate the specific gravities of the ore particles to be separated, pass ing said medium in an upwardly moving current through a separating "tank, the velocity of the current constantly increasing from a lower point in the tank to an upper outlet, introducing the ore particles into said medium-at a. circumferential zone below the surface thereof, and mainintermediate the fallingvelocities of the ore concentrates and the solids in the medium when said medium is quiescent.

9. The method of separating ore particles of different specific gravities which consists in preparing a liquid gravity separating medium of constant specific gravity in excess of 2.5 and composed of comminuted solids and water mixed in proportions to produce a liquid medium having a specific gravity intermediate the specific gravities of ore particles to be separated, passing the said medium upward through a tank with a constantly increasing velocity, introducing the ore particles into said medium below the surface thereof and at a point where its velocity is less than the falling velocity of the concentrates and greater than that of the middlings in said medium when quiescent, and sweeping the tails and middling's in said current out of the tank through an opening concentric with said tank and above the point of introduction of the ore particles.

10. The process of separating ore particles the desired concentrates of which have a specific gravity in excess of 2.6 which consists in introducing into a tank a separating medium having a specific gravity of not less than 2.6 and composed upward velocity of the medium is less than that of the falling velocity of the desired concentrates in said medium when quiescent and greater than the falling velocity of the middlings in said medium when quiescent.

VICTOR RAKOWSKY. RAY W. ARMS. GROVER J. HOLT.

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