US2696298A

US2696298A - Hydraulic classification of minerals

Info

Publication number: US2696298A
Application number: US113831A
Authority: US
Inventors: Donald N Griffin
Original assignee: Deister Concentrator Co Inc
Current assignee: Deister Concentrator Co Inc
Priority date: 1949-09-02
Filing date: 1949-09-02
Publication date: 1954-12-07
Anticipated expiration: 1971-12-07

Description

Dec. 7, 1954 D. N. GRIFFIN HYDRAULIC CLASSIFICATION OF MINERALS 2 Sheerls-Sheet 1 Filed Sept. 2. 1949 INVENTOR- D N. GRIEEIN DONAL ATTORNEYS.

lam-6n BY Dec. 7, 1954 D, N, GRlFFlN 2,696,298

HYDRAULIC CLASSIFICATION OF MINERALS Filed Sept. 2, 1949 2 Sheets-Sheet 2 FIG. 3.

FIG, 4.

7 INVENTORi DONALD N. GRIFFIN ATTORNEYS.

United States Patent HYDRAULIC CLASSIFICATION OF MINERALS Donald N. Griflin, Fort Wayne, Ind., assignor to The Deister Concentrator Company, Fort Wayne, Ind., a corporation of Indiana Application September 2, 1949, Serial No. 113,831

6 Claims. (Cl. 209-159) This invention relates generally to vortex classification, and particularly to a process and apparatus for cleaning and classifying coal and other minerals.

Hydraulic classifiers have long been used in the ore dressing art as a means for separating various fractions, as for instance particles of high specific gravity from particles of low specific gravity, and for separating particles of large size from particles of small size. In the ordinary hydraulic classification, the spigot product is frequently a mixture of large size particles of low specific gravity with smaller size particles of higher specific gravity.

Although hydraulic classifiers of the type having an open bottom sorting column have been satisfactorily employed in classification problems arising in the various mineral treating arts for a long period of time, the art has generally recognized a definite limitation upon the capacity of such classifiers, and in particular it has been considered impractical to operate them with a sorting column of a diameter greater than about three and onehalf inches. 'Although, in isolated instances, attempts have been made to construct hydraulic classifiers with open bottom sorting columns of a diameter up to ten inches, the results with such larger size sorting columns have been uniformly discouraging. Such results have led the workers in the art to believe that, where the sorting column is of a diameter in excess of three and one-half inches, the column is unstable and is subject to surging and channeling for very substantial distances above the quiescent zone, a fact which in itself defeats the purpose of the classifier. Consequently hydraulic classification has been limited in its utility to operations where the tonnage of mineral required to be processed by an individual cell was but a few tons per hour (of ore having much higher specific gravity than coal).

In the cleaning of coal, vastly greater processing capacities are required for a classifier, and no hydraulic classifier having a sufficiently high capacity has heretofore been made available. The tabling of coal is a much faster operation than the tabling of other minerals. An ordinary coal cleaning table has a capacity of about twenty-five tons per hour. To keep such a table fully supplied with classified coal would require a hydraulic classifier having a production capacity many times that heretofore available. While the hydraulic classification of coal preparatory to tabling was proposed, and laboratory tests reported, in Technical Publication No. 76 of the American Institute of Mining and Metallurgical Engineers, the proposals contained in that publication were unsuccessful on plant scale, apparently because of failure of the hydraulic classification phase, to perform efiiciently at the high magnitude of production rate required.

In one modern process of treating coal contaminated with a high percentage of pyrite and considerable slate, the run-of-mine coal is first crushed to pass a three-inch screen, then separated into fractions above and below onequarter inch. The plus one-quarter inch material is then subjected to gravity separation into fractions which, for example, respectively sink and float on a medium having a specific gravity of 1.55. The sink fraction from this separation is refuse. The float fraction from the aforesaid gravity separation is subjected to another gravity separation, using, for example, a medium having a specific gravity of 1.32. The float fraction from the last-mentioned separation is clean coal, but the sink fraction contains coal in which is locked a considerable quantity of impurities, such as pyrite and slate. The latter, that is, the sink fraction, is then recrushed to pass a one-quarter 2,696,298 Patented Dec. 7, 1954 ICC inch mesh, and is added to the minus one-quarter inch mesh material from the first screening operation, thus yielding a mill product which, though containing a high percentage of recoverable coal, is nonetheless contaminated with substantial quantities of impurities which must be removed in order to adapt the coal to metallurgical use. While this mill product may be tabled to accomplish some separation of the impurities from the coal, such a tabling operation without intermediate classification would yield large volumes of middlings and render the operation economically unfeasible. While it might appear that a supply of classified feed, adequate to keep a cleaning table operating at capacity, could be achieved by paralleling a multiplicity of small capacity hydraulic classifiers, such a solution of the problem is impractical, not only from the standpoint of space requirements and initial cost, but from the operating standpoint, and in particular because the consolidation, on one table, of spigot products from a plurality of classifiers introduces such complexities and difficulties into the tabling operation and so reduces the efficiency thereof that those skilled in the art seek to avoid it.

Accordingly the object of the invention, generally stated, is to providea hydraulic classifier capable of handling tonnages of large magnitude, such as are encountered in coal cleaning operations.

A further object of the invention is to provide a process of hydraulic classification having a high capacity.

Other objects will become apparent as the disclosure proceeds.

The present invention is predicated upon the discovery that open bottom hydraulic sorting columns, having a diameter of twelve inches or more, do not lose their stability and do not surge and channel (as has been heretofore observed in connection with sorting columns having diameters of between three and one-half and ten inches), provided the hydraulic water be introduced into the classifier tangentially, so as to produce a swirl or vortex within the sorting column, and provided further that the spigot discharge be both discontinuous and incomplete. It has been observed that a vortex sorting column having a diameter of twelve inches will maintain stability to an extent sufiicient to accomplish the desired classification if due care is exercised in regulating feed, input of hydraulic water, and spigot discharge. As the diameter of such a sorting column is increased above twelve inches, it becomes markedly less sensitive to the several variables constantly encountered in practical operation. At a diameter of sixteen inches, the performance of such a sorting column is wholly dependable and not affected, in the practical sense, by the variables normally expected in plant scale operation. The diameter of the sorting column in such a vortex classifier may be increased as desired, within practical limits, Without encountering instability of the column, surging, or channeling, which has heretofore been observed in such columns having a diameter of between three and one-half and ten inches. Sorting columns having a diameter of thirty inches have been successfully operated in accordance with the present invention.

In the practice of the present invention, it is important that the discharge of solids at the spigot be intermittent and so coordinated with the feed that at no time is the accumulation of solids in the quiescent zone completely exhausted. Unless the spigot discharge is so prolonged that the material emerging changes in appearance from that of a falling stream of wet solids to that of a gushing spout of liquid (a difference which is readily noticeable even to an unskilled eye), the stability and efiiciency of the sorting column is not disturbed by intermittent spigot discharge.

In the vortex classifier of the present invention, wherein the diameter of the sorting column is relatively great as compared with those heretofore considered practical, it is not necessary to maintain any fixed ratio of diameter to length of sorting column. For example, sorting columns having diameters of sixteen, eighteen, twenty-one,

twenty-four, twenty-six, twenty-eight, and thirty inches reduced below the figure just indicated, provided the particles are given a suflicient time period within the sorting column to separate themselves, one from the other. The upper limit to the length of the sorting column is solely a matter of practical consideration, it being in most instances desirable to avoid excessive length.

In the design of vortex classifiers having the order of size contemplated by the present invention, the character and screen analysis of the material being treated, the tonnage requirements, and the viscosity of the mixture within the sorting column are to be taken into consideration. It is desirable first to determine the ascending velocities of hydraulic Water necessary respectively to float a selected number of size fractions of the mineral to be classified. A battery of vortex classifier cells is provided, one for each fraction selected for spigot product. Having determined the velocities of the ascending hydraulic water just short of sustaining the several fractions, the input tonnage of mill product is analyzed and the several cells in the battery (which respectively produce different fractions at their spigot discharge) proportioned so that each sorting column handles its share of the load. The diameter of the sorting column in the respective cells is proportioned so that, with its anticipated load of mineral at any increment of time, sulficient hydraulic water will be present to maintain the viscosity of the mixture in that sorting column within a range at which classification can occur. For example, with coal, and with most other minerals which would be so treated, the mixture within the sorting column at any increment of time should average between fifteen and thirty-five per cent solids. If, for example, it is determined that a twenty-five per cent solids content of the mixture within the sorting column is preferable for the operation, it is evident that hydraulic water must be continuously supplied in the proportion of three parts to one of mill product (of the fractions occupying the sorting column) being fed. The optimum diameter for any given sorting column is therefore that which provides the volume of water necessary to maintain the desired concentration, and at the same time assures an ascending velocity of the water within the sorting column at the rate predetermined to cause all of the mineral, except that selected to sink in that cell, to float therein.

Referring now to the drawings for an embodiment illustrating a battery of eight cells designed for the classification of coal:

Figure 1 is a view in side elevation of the battery of cells, partly broken away to reveal the relationship of the components;

Figure 2 is a plan view of the classifier shown in Fig- M ure 1;

Figure 3 is a sectional view taken along line 33 of Figure 1; and

Figure 4 is a sectional view taken along line 44 of A,

Figure 3.

Upon a suitable framework a series of

cells

1, 2, 3, 4, 5, 6, 7, and 8 are mounted. The respective cells are provided with external cylinders 11, 12, 13, 14, 15, 16, 17, and 18, respectively, all of the same size in the embodiment shown, and concentrically within said exterior cylinders each cell is provided with an

interior sleeve

21, 22, 23, 24, 25, 26, 27, and 28, respectively. The interior sleeves vary in diameter, as shown in the drawings, and as will be described hereinafter. At the upper ends of the exterior and interior cylinders, the two are connected together by an annular ring 9, so as to provide an annular space 10 between the exterior cylinder and the interior sleeve in each cell.

The lower end of each respective exterior cylinder is provided with a cone 19, which leads to a spigot 20.

Arranged above the several cells is a launder 29 having a feed compartment 30 at one end. Adjacent the feed compartment 30 is a weir 31, which defines one side of the zone of activity of cell 1. The other side of the zone of activity of cell 1 is defined by a weir 32 which, as shown in Figure 1, extends to a higher elevation than weir 31. Weir 32 separates the zone of activity of cell 1 from that of cell 2, and comparable weirs 33, 34-, 35, 36, 37, and 38 (which progressively decrease in elevation) separate the zones of activity between the other cells of the battery, so that mill product fed into feed compartment 30 moves over weir 31 into the zone of activity at cell 1, then the floats from cell 1 move over weir 32 into the zone of activity of cell 2, and the floats from cell 2 move over weir 33, etc., until finally the floats from cell 7 reach cell 8. However, some of the finest portions of the floats, i. e. the slimes, may be eliminated at each cell by discharge over walls 39, now to be described.

The walls of the launder, which determine the hydraulic head upon all cells, are the longitudinal walls 39 which terminate at an elevation below feed compartment 30 and are separated therefrom by a wall 40. In the embodiment shown, the walls 39 extend at a uniform elevation across the battery of cells, but it will be understood that, in keeping with a common practice in the art, the walls 39 may be sectionally adjustable, or inclined, so that overflow of slimes may take place throughout the entire length thereof, or at selected regions therealong, as desired.

Extending lengthwise of the launder 29 and arranged to receive slimes which flow over the top edges of walls 39 is a pair of troughs 41 having inclined bottoms 42 leading to a discharge outlet 43. Such an arrangement of feed compartment, launder, and troughs is conventional and well understood by those skilled in the art of hydraulic classification.

Each of the several cells 1 to 8, inclusive, is provided with a hydraulic Water inlet 44, fed from a header 45 and controlled by a valve 46, one for each cell. In order to produce a swirling of the hydraulic water in the annular space 10, and within the interior sleeves of the respective cells, the inlet 44 is arranged to enter the cells in a tangential direction, as clearly shown in Figure 4.

The spigots 20 at the bottom of each cell are controlled by suitable quick-opening and quick-closing valves, which may be, and preferably are, of the character disclosed in the copending application of Spencer A. Stone and Don A. Weber, Serial No. 720,426, filed January 6, 1947, and now abandoned. The several valves may be actuated in unison by a common drive 47, but said valves are individually adjustable so as to vary the proportion of open-time to closed-time during each cycle of operation of the drive 47.

Arranged beneath each of the spigots 20 is a trough 48 arranged to receive the spigot discharge from the cell thereabove and to convey the same to the succeeding treating apparatus, such as a cleaning or classification ta e.

In the embodiment shown in the drawings, which is designed particularly for the treatment of coal, but is nonetheless adaptable to the treatment of other minerals, the diameters of the interior sleeves of the respective cells increase from left to right, as follows:

Sleeve 21, sixteen inches Sleeve 22, eighteen inches Sleeves, 23, 24, twenty-one inches Sleeves 25, 26, 27, twenty-three inches Sleeve 28, twenty-seven inches By thus reducing the area of the interior sleeves, it is apparent that, with a given input of hydraulic water, the ascending velocity thereof will be greater through sleeve 21 of cell 1 than through sleeve 22 of cell 2, etc., and consequently heavier and larger particles will be floated in cell 1 than in cell 2, etc. The particular embodiment shown in the drawings was designed for the treatment of coal at a feed rate of one hundred tons per hour, the feed to tank 30 being minus one-quarter inch material, including about fifteen per cent of slate, pyrite, and other refuse. In a typical operation, cells 1 and 2 were adjusted to separate refuse from coal, the purpose being to maintain the spigot discharge from cells 1 and 2 free of coal. Accordingly, cell 1 has its hydraulic water input adjusted at a rate such as to float solids having a specific gravity less than 1.70, and cell 2 has its hydraulic Water input regulated so as to float all solids having a specific gravity less than 1.55 (the relatively finer size fractions of +1.55 specific gravity also float at cell 2). The spigot discharge product from cell 1 contained 2.7% floatable on a test medium having a specific gravity of 1.70, and 97.3% sinks in said test medium. Of the floats on the 1.70 specific gravity test medium, the mean mesh was 5, while the mean mesh of the sinks was 8.

Cell 2 receives floats from cell 1. Analysis of its spigot discharge revealed 13.2% float on a 1.55 specific gravity test medium, 8.3% sink in 1.55 specific gravity medium, float on 1.70 specific gravity medium, and 78.5% sink in 1.70 specific gravity medium. The mean mesh of the there fractions of spigot discharge from cell 2 was 5, 6, and 10, respectively. Thus, cells 1 and 2 separate from the coal a considerable proportion of the refuse material, such spigot discharge being practically free of coal.

In contrast to cells 1 and 2 (which were designed and adjusted to yield refuse material as a spigot product), cells 3 to 8, inclusive, are designed and adjusted to effect a classification of the coal and extraneous matter sized in accordance with the standards by which hydraulic classification is judged. Analysis of the spigot product from cells 3 to 8, inclusive, show the following results when tested on media having specific gravities of 1.40,

1.55, and 1.70:

It is, therefore, to be distinctly understood that the invention is not limited to the details of the embodiment described, but that the principles thereof are applicable at large to classification problems where large tonnages are involved. It is contemplated that, in adapting the process and apparatus to the treatment of the various minerals, those skilled in the art may modify and adjust the same in order to meet the characteristics of the mineral being treated. Accordingly, it is to be distinctly understood that such modifications and adaptations are contemplated by and within the scope of the appended claims.

Having thus described the invention, what is claimed Spigot Products Percentage by Weight Mean Mesh Cell No 3 i 4 5 6 7 8 3 4 5 6 7 8 gloat 01111.40 77. 2 79. 3 88. 6 85. 4 93. 5 85. 0 7 7 9 10 14 24 ink in .40 g a 1 5 11.1 11.4 7. 4 9. 5 4.2 9.8 8 9 12 16 20 32 in in 5. Float on 1 7O 3. 1 2. 3 1. 3 1. 9 0. 8 1. 7 9 9 16 24 28 42 Sink in 1.70. 8. 6 7. 0 2. 7 3. 2 1. 5 3. 5 16 24 32 42 65 80 From the foregoing test results, it is readily apparent that in the discharges from the individual cells, the mean particle sizes of the various specific gravity fractions decrease sharply as the specific gravities of those fractions increase. Moreover, in the discharges from successive cells, the mean particle sizes of comparable specific gravity fractions decrease. Thus, clear-cut classification is obtained and the standards of hydraulic classification are fulfilled.

In the coal cleaning operation in which the device described is being currently employed, the spigot discharges from cells 3 to 8, inclusive, are conveyed respectively to coal cleaning tables, which efficiently separate the residual refuse material (being of higher specific gravity and much smaller mean mesh than that of the coal in any given spigot product) from clean coal, without the production of a middling fraction. An efficient two product separation of this nature is economically desirable and would be impossible without effective hydraulic classification ahead of tabling.

In the operation referred to, the overflow from all cells into launder 41 consists of fine coal (minus 28 mesh) together with finer refuse (minus 100 mesh) which, after being thickened, is separately tabled. In the case of coals which are relatively free of finely divided extraneous matter, tabling or other cleaning of the overflow is not necessary.

The apparatus above described is capable of consistently processing coal at a rate in excess of one hundred tons per hour, and the spigot product from the individual cells is amply sufiicient to keep a coal cleaning table supplied at near capacity. The spigot products of cells 5, 6, 7, and 8 contain such a small quantity of high specific gravity (i. e., refuse) material that, for most uses, the coal does not require subsequent tabling, but where, as in some metallurgical uses, it is desirable to remove the last possible particle of refuse, the spigot products may be tabled. The increased percentage of heavy gravity material in the spigot product from cell 8 is attributable to the finely divided form in which occurred much of the pyrite in the particular coal being treated.

While the particular embodiment which has been disclosed in detail was designed for, and is successfully operating in the treatment of, coal and, while repeated reference has herein been made to the treatment of coal, it is not thereby to be understood that the invention is limited to the treatment of coal. On the contrary, the apparatus and process are equally applicable to the treatment of any mineral where large tonnages are involved as, for example, in sand and gravel operations, in iron ore cleaning, and in phosphate rock recovery. Indeed, with appropriate adjustment in the areas of the sorting columns and proper regulations of the input of hydraulic water to achieve an ascending current velocity appropriate for the sinking and floating of selected fractions, the apparatus is readily adaptable to the treatment of many mineral in large volumes.

and desired to be secured by Letters Patent is:

l. A hydraulic classifier having an exterior cylindrical wall, an open bottom sorting column located within the exterior wall, said sorting column having a diameter of at least twelve inches, means for inducing a swirl of hydraulic water in the sorting column, said exterior wall providing a quiescent zone below the bottom of the sorting column terminating in a spigot, and means for intermittently opening and closing the spigot.

2. A hydraulic classifier having an exterior cylindrical wall, an open bottom sorting column located within the exterior wall, said sorting column having a diameter of at least twelve inches, means for introducing hydraulic water tangentially into the interspace between said exterior wall and said sorting column, said exterior wall providing a quiescent zone below the bottom of the sorting column terminating in a spigot, and means for intermittently opening and closing the spigot.

3. The hydraulic classifier of claim 2 wherein the sort ing column has a diameter of at least sixteen inches.

4. The hydraulic classifier of claim 1 wherein the spigot is provided with a constrictor valve.

5. In the art of hydraulic classification, the process comprising, feeding heterogeneous comminuted material into the top of an open bottom sorting column, said sorting column having a diameter of at least twelve inches, moving hydraulic water in an ascending direction through the sorting column while maintaining a swirling motion therein, regulating the ascending velocity of the hydraulic water in the sorting column to inhibit sinking of selected fractions of the comminuted material and permit sinking of other fractions, collecting the sinking fractions of the comminuted material in a quiescent zone below the sorting column, and intermittently yet incompletely discharging the collected material from the bottom of the quiescent zone.

6. The process of claim 5 wherein the sorting column is at least sixteen inches in diameter.

References Cited in the file of this patent Report of Investigations, R. I. 3844, December 1945.