US2784841A - Hydraulic classification of solids - Google Patents

Description

Marcin EL 1957 R. n. EVANS HYDRAULIC CLASSIFICATION o`F soLrns l 'Sheets-Sheet 2 Filed April 13, 1953 bm 5MM f7 T TO'RNEY Marh 12, 1957 R. D. EVANS 2,784,841

HYDRAULIC CLASSIFICATION DF "sonrns WSW HTTUMEY nited States Patent C HYDRAULIC CLASSIFICATION or soLIns Robert D. Evans, Pierce, Fla., assigner to The American Agricultural Chemical Company, New York, N. Y., a corporation of Delaware Application April 13, 1953, Serial No. 343,511 13 Claims. (Cl. 2ll9158) This invention relates to apparatus and procedure for classifying solids such as mineral material in particulate form, supplied in aqueous pulp and often in an intermittent and varying manner, and for alfording delivery, at a controlled or constant rate, of one or more fractions of the supplied solids, classied by settling rate, e. g. usually by particle size. Although systems and procedural combinations as described hereinbelow may be applied to other materials, for instance, other mineral substances that are mined or transported with the aid of water, or are otherwise availabe for hydraulic cleaning and classification, an important specic aspect of the invention has to do with the production of a classied phosphate product from phosphate ore such as so-called phosphate rock mined by hydraulic or other means in various localities. Certain deposits of mineral phosphate in Florida are mentioned hereinbelow as representative examples of material to which the invention is particularly related.

Heretofore in the treatment of phosphate ore, for instance pebble phosphate from mines at Pierce and Boyette, Florida, and similar or other phosphate rock from other sources, it has been the usual practice to subject the mined material to the operation of a plant called a washer, which embraces a rather complex series of screening and like devices cooperatively designed to achieve some kind of particle size classication of the ore inasmuch as the tine sand contains a larger proportion of unwanted material. A representative washer may include a receiving tub, from which the mined product, in water, is distributed to a num ber of trommel screens arranged in parallel; from the latter, the undersize materials, e. g. particles or pieces of 3/4 inch size, are then passed to a number of further screens, for example ilat screens, which may segregate, say, +14 mesh material and discharge +14 mesh or %4 inch material to another locality. Such operations are employed, for example, where experience has shown that the most valuable phosphate is attainable in the pieces smaller than 3A inch and is then separable, by further screening, to obtain a high quality fraction which is inch and +14 mesh. In the first trommel screen separation, lumps larger than 1%. inch or 2 inch size are commonly discarded to debris piles or ponds, but the plant usually includes disintegrating means such as a hammer mill and a so-called log washer, for breaking up, say, the -11/2 inch inch pieces and delivering the broken-up material to the ilat 14 mesh screens.

Beyond the roughing section the washer plant may also have a surge bin of modest capacity, say several hundred tons, to receive the material roughly classified as 3A inch +14 mesh, which then constitutes feed for further, successive sets of trommel screens arranged to deliver various approximately sized fractions. For instance, certain better classiiied fractions larger than 14 mesh may be deemed appropriate for direct use as high grade mineral phosphate (e. g. for making superphosphate), while -14 mesh material, perhaps together with like fine discharge from the roughing section of the washer, can be delivered 2,784,841 Patented Mar. 12, 1957 ICC to a so-called recovery plant where, by tabling, flotation or other means, a further quantity of high grade phosphate can be concentrated.

It will now be seen that the Washer plant itself involves a complicated set of screens and cooperating devices, requiring a large plant area and considerable investment, as well as much maintenance and attention. Since the installations must be relatively permanent at a selected place, there is apt to be trouble and expense in transporting mined ore to the washer from very remote localities of the pit or held. Moreover, although to a certain extent satisfactory, the classification is sometimes not precise enough for the best possible direct yield of high grade phosphate, and often leaves more rather than less work to be done by the relatively costly operation of the flotation or tabling plant in order to achieve maximum recovery from the mined ore. Furthermore the coordination of the washer with interruptions and variations in the mining operation can be troublesome, in that most economic operation of the washer and likewise the recovery plant may be achieved with a constant supply of untreated ore or washer undersize, respectively; yet such constant supply is almost never possible, because of the nature of mining operations. A problem occurs, too, if it becomes desirable to interrupt screening, hauling or recovery plant operations for a part of the day, while actual mining continues.

An important object of the present invention is to aord procedure and apparatus of a convenient, easily operated and maintained, and highly eiective character, whereby with at most only a rough preliminary screening, the mined ore may be classified in particle size or settling rate and whereby ultimate delivery may be achieved of a sized fraction or fractions, at constant or other controlled rate as desired. A further object is the provision of such re sults, with considerably simpler equipment than that of a conventional washer plant or the like.

A still further object is to provide for accomplishment of more eilicient classification, indeed sometimes to the point of dispensing with a flotation or other special recovery plant, while at the same time the other results indicated above are achieved even though there may be interruptions or large variations in the supply of mined ore, e. g. in pulp form. It may be explained that from the pit where phosphate, for example, is mined or removed with the aid of water, there may be great variation in the amount of pulp, in its percent solids, and in the particle size or size distribution of the solids, but the means and procedure described below are self-accommodating to all such variations and permit the ultimate withdrawal of size-classified products in a controlled manner, i. e. at a selected rate and at desired periods. Thus there is optimum cooperation with further operations such as screening and drying, or recovery operation on the liner solids.

Additional objects are: to afford improvements in classification and preparation of phosphate rock or matrix material; to obviate much complex, unwieldy and diicultly maintained equipment; and to provide great ilexibility in operation, especially in the selection of product fractions.

To these and other ends, the invention comprises a novel, cooperative combination of hydraulic classication, storage and pulp discharge instrumentalities and procedure, which are capable of obviating, if desired, essentially the whole, or at least the major part of the so-called washer plant now utilized in recovering mined phosphate.

In my copending application Serial No. 107,727, led July 30, 1949, now Patent No. 2,708,517, I have disclosed and claimed certain improvements in hydraulic classication apparatus and procedure, whereby unusual results are obtainable with respect to separation of a desired coarser fraction of a feed pulp (e. g. the higher setarea-,set

tling rate fraction) even though the feed may be of relatively dilute character. Specifically, the device of the stated application, which may be called a double column hydrosizer or hydraulic classifier, embraces coordinated utilization of the principles of free settling and hindered settling, in a way to attain superior eiiiciency in the collection of the higher settling rate solids at the foot of a hindered settling region such as is sometim-es called a teeter column.

A preferred form of the double column classifier of my said copending application comprises a lower vertical column having a constriction plate or the like at the foot through which water is admitted at a rapid velocity, for rise through the column to establish teeter (i. e. hindered settling) conditions7 together with an upper, vertical column above the top opening of the lower column. The upper column has a cross-section at least as great as the lower column and extends upward for a considerable vertical extent, being separated from the lower column by a substantial space, abundant for delivery of solids (and liquid) between the two columns. A large tank surrounds the upper column, having a volume of at least several times the latter, and includes a bottom structure that extends below the space between the columns, i. e. so as to open into the lower column. The tank extends above the lclosed head of the upper column and is normally more or less filled with liquid (i. c. water), so that as feed pulp is supplied into the top of the solids descend continuously to the space between the columns in accompaniment with the generally downward flow of water to the same locality.

By a controlled siphon discharge from the otherwise closed top of the upper column, a substantially constant rise of water is provided in that column, so that free settling conditions are there maintained, to permit removal of large volumes of water along with the finer, i. e. slower settling particles which are carried up from the space between the columns. The larger or faster settling particles fall into thte lower column where because of the large proportion of water removed by the upper column, very efficient hindered settling is achieved, and a sharply cut fraction of the coarser particles can be removed at the bottom, i. e. by suitable means distinct from the water-introducing means there. The device, moreover, is self-accommodating to considerable variation in density and volume of the feed.

Referring now to the present invention, a hydraulic classifier of the character described above, or if desired, a plurality of such classifiers, in parallel, are arranged for delivery, preferably by gravity, of their higher settling rate fraction to a very large storage vessel, a preferred feature of the invention being the constitution of thc storage vessel as an open pit in the ground, having, say, a capacity of many thousands of tons. The pit is provided with a constant feed discharge, controllable for withdrawal of pulp at a desired rate and if necessary, in desirably uniform density. With an open ground pit, a discharge arrangement of particularly cooperative advantage for achieving the desired results of the present inventori, is a suction pipe extending to the bottom of the pit and provided with means, e. g. water jet means, for promoting uniform advance of solids into and along such pipe.

Utilizing the described combination of instrumentali ties and operations, size classification of the received phosphate ore is eliiciently carried out, yet the ultimate product delivery, from the storage pit, is obtainable in any desired, fully controlled manner. Fluctuations and interruptions of various sorts in the mining operation and thus in the feed to the hydraulic classifier, are accommodated in that device, and further in the storage pit. Likewise, while the mining and hydraulic classifying operations may be performed essentially continuously, e. g. without interruption or with interruptions at non-determinable times, the ultimate withdrawal of product can, if necessary, be restricted to desired periods, for accommodation to subsequent operations, such as Screening, drying, transportation to storage, or other handling.

Further description of the invention is set forth hereinbelow in connection with the accompanying drawings, wherein:

Pig. l is a flow diagram showing certain examples of procedure in accordance with the invention;

Fig. 2 is a simplified, diagrammatic view, chiefly in vertical section, showing the basic combination of apparatus;

Fig. 3 is a somewhat enlarged plan View of the suction withdrawal means of Fig. 2;

Fig. 4 is a simplied, somewhat diagrammatic View, in three dimensions (from a vertical section), of a hydraulic sizer utilized in the invention; and

Fig. 5 is a schematic plan View of a further layout of equipment pursuant to the invention, suitable for alterna* tives A and B of Fig. l.

While the iiow sheet contained in Fig. l will be largely self-explanatory in view of the foregoing, the various steps and combinations will be better understood after explanation of certain preferred forms of apparatus. Likewise before dealing with the basic combination in Fig. 2, description may irst be given of a presently preferred classifier, in Fig. 4, of thc so-called double column type mentioned above.

In the following explanation of Fig. 4, certain dimensions of one instance of such apparatus are set forth, it being understood that the named values are purely examples (other dimensions being useful, according to the capacity and results desired), except that they illustrate certain important proportions or relationships. Thus one embodiment of the sizer comprises a large upright cylindrical tank lo having a diameter of 30 feet. The tank is open at the top to receive ore pulp for classification (as indicated by arrows 11) and has a conical bottom opening into a vertical, cylindrical column l2 which has an enlarged portion .i4 `at its foot` The column portion 14 is horizontally partitioned by a constriction plate 15 having a plurality of openings through which water may iiow upward rapidly from a lower chamber i6, the water being supplied to the latter through a pipe 17. A normally closed drain l opens through the constriction plate 15. The lower column 12 with its appurtenances as just described, is designed to function as a hindered settling or so-called teetcr column, whereby coarse or faster settling particles of the supplied ore accumulate in the lower part of the column, i. e. above the constriction plate l5.

Disposed centrally in the tank l0, a plurality of inverted vessels Ztl, 2l `and 22 are arranged in nested relation, but with substantial space from each other, so as to provide in effect three coaxial columns which may be filled with solids-carrying liquid. in the specific device described, the columns Ztl, 2l and 2.2 were upright cylinders having diameters respectively of 6, 8 and 10 feet, the lower column l2 having a diameter of 5 feet and being spaced below the open, bottom. ends of the upper columns by an appropriate distance, say 4 or 5 feet, for full ow of supplied pulp into the region between the lower column and the upper ones.

The three columns Ztl, 2i and ZZ have closed tops 24, Z5 and 26 respectively and are provided with individual liquid-withdrawal pipes having one or more openings into the corresponding columns just below the top of the latter, such withdrawal pipes being respectively designated 28, 29 and 3@ and extending through the side wall of the tank it), to an external tailings box 3i. Near their exit ends, the pipes 28, 29 and 3G are respectively provided with adjustable Valves 32, 33 and 34 so as to regulate the flow of liquid through each pipe and thus the upward iiow of liquid in the corresponding column 20, 21 or 22. AsV will be seen, each withdrawal pipe cooperates with its associated column to constitute a siphon-type discharge for the column.

The tank 10 has a surrounding overflow launder 35, which may also drain, as shown, into the tailings box 31, from which a conduit 36 may lead for discharge of the tailings to a locality of further treatment or of disposal.

While valved, drain-type discharge means (as through the pipe 18) of conventional sort may be employed for the recovery of the sized,coarse fraction at the foot of the hindered settling column 12-14, the illustrated apparatus preferably includes siphon discharge means of the character disclosed and claimed in my copending patent application Serial No. 120,240, filed October S, 1949, now U. S. Patent No. 2,714,958. Here shown in diagrammatic fashion, such discharge means may include a long upright pipe 40 (3 inches inside diameter) opening at its lower end into a larger pipe section 41 (e. g. a -inch pipe 2 feet long) within the 8 foot diameter section 14 of the hindered settling column, the open bottom end of the pipe 41 being appropriately spaced, say a few inches, above the constriction plate 15.

At its upper end, conveniently above the top level 42 to which liquid may rise in the tank 10, the siphon conduit extends laterally from the pipe 4() via a further (2-inch) pipe 43 that runs down, outside the tank, into a products box 44, from which delivery of pulp constituting the sized product may be had through a further conduit 45. The elbow coupling 46 joining the pipes 40 and 43 communicates with an upwardly extending tube 47 that opens into a control box 48 and may there be closed by a float valve 49. The box 48 is adapted to receive liquid from a tube 5l) opening into a static tube 51 extending vertically to the foot of the hindered settling column 12-14, i. e. at a locality just above the constriction plate 15. Since the effect of an accumulation of properly sized, coarse (i. e. faster settling) particles at the foot of the hindered settling column represents an increase of density, and thus an increase of pressure to a predetermined value, rise of water in the static tube 51 to such height above the level 42 as is representative of the increase, may be employed to control the siphon discharge. Specifically, the position of the box 48 is adjusted so that when proper pulp density is reached at the foot of the hindered settling column, the iloat 49 closes the tube 47, thus preventing access of air to the siphon system 40-43 and permitting siphon discharge of the pulp product.

To promote upward ow of the solids and to facilitate self-starting of the siphon at desired times, a continuous, minor supply of additional water is furnished to the enlarged pipe section 41, through a water supply line S2, header 53 and tube 54. As will be seen, the desired product solids are thus continuously siphoned from the foot of the hindered settling column through the system 40-43, but only at times when the pulp density at the foot of the hindered settling column is sufiicient to rep resent the desired classification, i. e. the desired (and continuing) accumulation of coarser particles. If the density is insuiiicient, the pressure is not suciently above the normal hydrostatic head of the tank 10, and consequently the water level in the box 48 will drop, causing the float 49 to fall and opening the tube 47 to the atmosphere. Such air relief for the siphon line 40- 43 thus interrupts the discharge of pulp, so that there is no ow through this conduit or at most a minor or intermittent flow of essentially solids-free water.

Thus the siphon discharge is automatically controlled in accordance with the pulp density or pressure at the foot of the hindered settling column, and is such that so long as the desired classification is achieved, essentially continuous flow of pulp of the classied size will be delivered into the product box 44. For a large capacity operation of the sizer, a plurality of these siphon discharge devices may be employed, arranged to operate in parallel, preferably with individual air-relief controls adjusted to operate in succession, i. e.. to close or open as the pulp density becomes progressively greater or progressively smaller at the foot of the hindered settling column, so that the discharge is automatically accommodated to the quantity of product accumulating. Since the supplemental siphon systems may be identical with the one just described, they are merely indicated in fragmentary fashion by portions of upright pipes 40a, 4011 and discharge pipes 43a, 43h and 43C.

Considering the columns 26, 21 and 22 as together constituting a single upper column of capacity equal to the entire cross-section of the outermost shell 22, the hydraulic -sizer functions as first described above. Large quantities of relatively dilute ore pulp are received in the open top of the tank 10, providing es-sentially continuous downward ow of liquid in the tank and downward passage of practically all of the solids, e. g. to the region 60 between the upper and lower columns. A large proportion of the liquid is carried upwardly in the system of upper columns under influence of their siphon discharge through the pipes 28, 29 and 3i] as -adjusted by the valves 32-34; the liner or slower settling solid particles are thus effectively removed. Since the direct, essentially constant upward tlow provides free-settling conditions throughout the vertical height of columns 20- 22, the larger particles settle into and through the space 60, and thence enter the lower column. 12.

By virtue of the water introduced at the foot of the column 12 and the arrangement of the constriction plate 15 or equivalent means, so-called hindered settling conditions prevail for the downwardly traveling solid particles. That is to say, the effective density of the solid and liquid body in this column rises in a manner tending to prevent particles of less than a predetermined size from reaching the bottom, the finer particles being oarried back into or remaining in the space 60, from which they are removed by the water rising in the upper columns 20-22.

The removal of large quantities of water by the upper columns promotes emcient attainment of hindered settling in the lower column 12-14 and correspondingly sharp classification there. The product delivered to the box 44 thus contains no more than a very small proportion of solids finer than a desired minimum which can be determined, at least to a certain extent, by adjustment of the height of the siphon-discharge control boxes 48. Thus during operation with a continuous large supply of feed pulp, the product fraction goes to the box 44 and the tailings or finer fraction, with the major part of the water, to the box 31.

While the device, because of its upper column arrange ment, is self-accommodating to a considerable variation in volume of ore feed, the use of a multiple upper column has a still greater range of accommodation. Thus with a very large volume of pulp feed, all three of the upper columns 20, 21 and 22 are'functioning.. Each of them, however, has an individual control, i. e. as exempllied for the column 22 by an air vent pipe 62 which opens into the top 26 of the column and which at its other end is normally closed by a float valve 63, the arrangement of the float valve being such that it remains closed until the liquid in the tank 10 drops from its uppermost level 42 to a predetermined lower level 65, e. g. slightly below the top 26 of the column 22. Thus if the incoming pulp supply is reduced below that suicient to maintain desired rate of rise in all three columns, the level in tank 10 falls to or below the line 65, opening the valve 63 and admitting air into the head of the column 22. Siphon action through the discharge pipe 30 is interrupted, the latter thereafter merely serving as an overiiow line without inducing the previously substantial upward ow in the column 22, i. e. outside the shell 21.

Similar air-relief pipes 66 and 68 are provided for the successively similar columns 21 and 20 respectively, with are/1,841

corresponding float valves indicated at 67, 69 for opening such lines when the liquid level (in the tank 10) drops to the points 7) or 7l. That is to say, if the ore pulp supply is further reduced and the tank level falls to the line 70, the siphon discharge through the pipe 29 is interrupted and the only upper column then functioning is that constituted by the innermost shell 20.

Ordinarily it is contemplated that there will be at least sufficient minimum feed of ore pulp to keep the level in the tank itl above the line 7l, so that the innermost column 2u always remains in operation. However, when the pulp supply 11 is interrupted and the tank level falls below l, the air vent valve indicated by its float 69 is opened so as to interrupt operations completely. The tank 10 remains correspondingly partly full of liquid, so as to be ready promptly for resumption of sizing ac tion as soon as pulp feed is resumed. Then as the volume of feed increases, raising the water level in the tank, the lioat valves 69, 67 and 63 close in succession, reestablishing siphon flow from the columns and bringing all of them into operation as needed. The arrangement of multiple Lipper columns affords great flexibility in the accommodation of the apparatus to large variations of pulp feed, e. g. by having two or more (here, for example, three) upper columns which are automatically brought into play or removed from operation, as needed.

Turning now to the combination illustrated in Fig. 2 it will be seen that a double column sizer is indicated at '75 and consists of the large tank it), upper columns 2G, 21 and 22, lower, hindered settling column assembly 12-14 and siphon product discharge du, 43 as described above. For removal of very coarse pieces, mud lumps and the like, the ore pulp from the mining pit is passed through one or more trommel screens indicated at 77, the ner fraction, say B1 inch, being delivered into the tank 10 and the large pieces (being essentially of non-phosphatic material) being discharged to the tailings sump 78, which also receives the delivery from the overflow launder 35 and the tails box 3l.

In accordance with the present invention, the sized product, i. e. the desired, phosphate-rich, coarser fraction of the ore pulp is delivered from the products box 44 `ot' the classifier through a discharge pipe 80 into a large storage pit 82, which may be, as shown, simply a large open pit, having sloping walls and excavated in the ground at a convenient locality. It will be noted that for simplicity of illustration all supporting frames and like parts are omitted in IFig. 2, i. e. such as would be required for the sizer 75, the pipe 3@ and various other instrumcntalities.

In further accordance with the invention, withdrawal from the storage pit 82 is effected by one or more under- -flow suction devices, of which one such is exemplified by the suction assembly designated 34. The latter comprises a large suction pipe 85 extending down into the pit, as in parallel relation to the sloping Wall S6, and opening (e. g. downwardly) at 87, the locality of the lower end of the pipe being conveniently a few feet above the bottom of the pit. At its upper end the pipe 85 communicates with a suction pump 88 (see also Fig. 3), driven by a motor 90 and thus delivering pulp from the pit through the discharge pipe 9i of the pump.

For enhancing proper suspension and withdrawal of the solids from the pit 82, for promoting desired uniformity of such pulp discharge, and thus for affording a desired rate of solids delivery, supplemental means are included for agitating the material in the pit and for directing it into and along the pipe S5. Thus a pipe 92 extends down along the main suction pipe 35 and terminates in a T head 93 a short distance below the open end 87, so as to provide discharge openings in opposite directions below and transversely of the suction pipe entrance. Water, as from a header 94 is directed through the pipe 92 and the resulting jets from the outer ends of the T 93 provide effective agitation in the pit, to

keep the solids broken up and` suspended. Another pipe 95, also supplied with water from the header 94, likewise extends along the suction pipe and terminates in a reverse bend 96, projecting into the Vopen end 87 of the suction pipe. Water is thereby directed in a jet inwardly along the pipe in the direction of desired advance of pulp, not only guiding the pulp and creating additional suction for its entry at 87, but' also diluting it for greater effectiveness of the pump 88. A still further pipe 97, supplied with water from the header 94, opens into the suction pipe 85 at an intermediate locality 98, say midway between its lower end and its point of highest elevation at the top of the pit. The water supplied through the pipe 97 further promotes the advance of solids along the pipe 85, especially by creating additional turbulence and dilution.

With one or more of these further instrumentalities (pipes 92, and 97) and very preferably with all of them, efficient delivery of pulp is obtained from the pit, affording a substantially constant rate of discharge of solids, i. e. in weight of solids per unit time. The actual rate can be changed by adjusting the speed of the pump and by selective use of one or more suction pipe assemblies such as the single such device 84 shown in Fig. 2.

The pulp or slurry from the pump outlet 91 may be further treated or handled in a variety of ways. For example, where the system shown in Fig. 2 is located at a mining locality remote from drying and shipping facilities for the mineral phosphate, and where the classi- 'lier 75 may be operated so as to select a product fraction representing in itself a sufficiently high recovery of the phosphate in the ore, the solids from the pit can be simply de-watered and transported by belt or car to the remote facilities, while the tailings are discharged to waste, as via the sump 78. Although more effective de-watering means of conventional character may be em ployed, such as spiral or rake-type machines, Fig. 2 shows for simplicity of illustration, a screen ltl receiving the pulp and draining water into a discharge channel M1, the de-watered solids being appropriately delivered from the end of the screen to a conveyor belt 192. The belt (shown in section) moves continuously past the device 00 to the remote destination (not shown). Conventional details of the belt supporting and return mechanism are mostly omitted from Fig. 2.

lt will now be seen that a basic form of the procedure, e. g. as carried out with the apparatus illustrated in Figs. 2 to 4 inclusive, involves receiving a large, varying and sometimes discontinuous flow of essentially unclassified ore, in water, and the ultimate delivery, for instance on the belt M2 in Fig. 2, of a desired classified fraction at a selected, constant rate continuously over a desired length of time which may be greater or less than a given period of continuous ore pulp supply. Specifically, thc ore puip, which may be very dilute because of the nature of antecedent operations, is delivered through a large containing region (tank 1G) to a space between lower and upper columns. Much liquid and ne suspended solids rise continuously in the upper columns 20-22 with free settling conditions, while in a far more concentrated state the larger particles continuously accumulate and are classified in the lower, hindered settling column. The procedure preferably includes varying the volume of the upward free-settling columns (and their discharges) in accordance with the volume of pulp received, e. g. by using one or more of the columns 2li-22; the withdrawal of product is likewise self-accommodating to variations in quantity, with a plurality of the siphon devices iti- 43. The classified phosphate particles are delivered to a large storage region, at rates varying with the actual reception of the selectable phosphate in the classifying procedure, and a reservoir of product, in water, is accumulated. The process further involves the withdrawal of pulp from this reservoir, preferably by underflow suction procedure with the cooperative action of supplemental water iiow, to yield a desired, constant delivery of the sized product in a controlled manner, e. through the outlet 91 of the pump 88 (Fig. 2). Thus the desired results are accomplished, with full accommodation to interruptions and non-uniformity of ore supply and also to necessary or desired interruptions of ultimate product delivery.

Fig. l illustrates the invention in further detail, including other combinations and further steps in sequence, as may be needed for various purposes. Thus as shown, the pulp of mined phosphate ore in water is usually lirst carried through a set of scalping trommels (in parallel) such as shown at 77 in Fig. 2, where very coarse particles are removed. If desired, all of the trommel oversize but the extremely coarse pieces (e. g. all but those larger than 11/2 inches or 2 inches) may be subjected to operation for breaking up as in the conventional hammer mill and log washer, for return to the circuit so that material of the desired size is fed to the classifier. Material of inch size has been thus commonly selected in the operations with phosphate rock mined in the Florida localities mentioned above. After passing through one or more classifiers (such as at 75 in Fig. 2) the sized product is delivered to the storage pit such as shown at 82 in Fig. 2.

Upon withdrawal of the material from the storage pit a variety of further procedures may be followed. Three examples of these are shown at A, B and C in Fig. l, Example B being specifically illustrated in Fig. 2 in that the delivered pulp is simply de-watered and placed on a belt or other transporting device for conveyance to the drying plant or other locality of `further processing. In many cases it has been found desirable to screen the classified product, as in alternative A (and as may be done, if desired, to the belt-conveyed product of alternative B), e. g. so as to insure that only the material of +14 mesh or other selected size is delivered to the loading bins for transport by railway car to the drying equipment and thence, for instance, to a plant where the mineral phosphate is converted to superphosphate or other product. In some cases, where the classifier effects a particularly sharp cut and its product has very little material finer than a predetermined size (say 35 mesh or 48 mesh) the solids from the pit may need no further screening, and may as in alternative C, be delivered directly to the loading bins, providing of course that the latter have appropriate structure for draining water from the delivered material.

While sometimes the fine tailings from the double column classifier may be of such poor grade as to warrant no further treatment and are simply delivered to debris (alternative A'), it is often profitable to repeat the procedure of the invention (B) upon the tailings, as by supplying them to one or more other double column classifiers of the described type. The sized, coarser fraction goes to another large storage pit, designated as pit No. 2 in Fig. l, in distinction from pit No. 1 which receives the sized product of the first classification. The final tailings from the classifier in process B can go to debris, While the constant underflow from storage pit No. 2 may be directed to a recovery plant, where by belts, spirals, tables, liotation cells or like equipment, valuable phosphate can be concentrated from this moderately fine material. If desired, where the product taken from storage pit No. 1 is screened, the screen under-size can be run into storage pit No. 2, to augment the recovery plant feed. The described iiexibility and other advantages of the invention are particularly important in process B because the critically controlled operations in the recovery plant usually require a highly constant feed of pulp, i. e. especially a constant feed of solids.

illustration of a complete lay-out of equipment embodying schemes A and B of Fig. l is given in Fig. 5.

Specifically in Fig. 5 pulp of mined ore is supplied through scalping trommels 110 to a pair of the double column sizers 112, the over-size from the trommels be@ ing directed to a debris sump 113. The sized, coarse product from the classifiers 112 is directed via pipes 114 into storage pit No. 1, which may be a large open ground pit having top dimensions of the order of feet by 200 feet and a depth, along its center line, of the order of 25 to 28 feet.

The tailings from the sizers 112 are delivered as feed to a further double column classifier 116 which delivers its product fraction via pipes 117 into pit No. 2, while the very fine tailings are discharged into the debris sump 113.

The underflow suction assemblies 120 withdraw product from pit No. 1, delivering it to the screens 121 from which it then passes, less the finer particles, to the load ing bin 122. if desired, the liner material separated by the screens 121 may be returned to pit No. 2 via line 124. From pit No. 2 the suction withdrawal lines 125 remove the pulp at a desired rate, affording delivery of the solids in a constant manner to the flotation, tabling or other recovery plant 127, from which the resulting phosphate concentrate is conducted to a suitable loading bin 128. 1t will be understood that each of the sizers 112, 116, each of their product delivery pipes 114, 117, each of the pits Nos. 1 and 2 and each of the suction Withdrawal assemblies 120, 125 may be respectively identical with the sizer 75, delivery pipe 80, pit 82 and withdrawal assembly 84 of Fig. 2.

With the system of Fig. 5 the mining operations at the pit (not shown) may continue without interruption so long as the scalpng trommels, sizers 112 and 116, and

removal of debris by appropriate pumping (not shown) continue in operation. Since the sizers have no moving parts and since the pulp velocities and pressures in them are relatively low, they require little maintenance and are practically trouble-free. As explained, the sizers, particularly in using multiple upper columns and multiple siphon discharge means (4t), 40a, 4017,. ete), adapt the system to handling large variations in pulp volumes and percent solids which commonly occur in delivery of ore from the mine.

For effectiveness of sizer operation, certain relationships in this device, e. g. as shown in Fig. 4, are usually important. For instance, the diameter of the upper column, or at least the diameter of the smallest upper column shell where the nested group is employed, should be at least about as wide as the diameter of the lower column 12, while the effective vertical height of each of the upper columns and likewise of the lower column should ordinarily be greater than its diameter, and by preference considerably greater; the lower column preferably has a height equal to at least about twice its diameter. The region 60 between the columns should be relatively spacious, for instance as afforded by a vertical dimension at least nearly equal to the width of the lower column. Similarly, the more or less cylindrical entrance area below the edge or edges of the upper column and shells, and bounded at the bottom by the bottom of the tank 10 around the top of the lower column, should be of ample size, i. e. having a total area (measured as if on a vertical cylindrical surface) at least equal to the sum of the lower column cross-section and the total crosssection enclosed by the upper column assembly. With these proportions of parts, effective self-accommodation is achieved with respect to variations in feed supply, as well as ready handling of very large, relatively dilute pulp feeds yet with an eiciently sharp classification in the lower, hindered settling region.

The size of the storage pit 82 (Fig. 2) and the number and capacity of the under-liow withdrawal assemblies determines the duration of any possible interruption be tween the sizing or roughing operation and subsequent processing; for instance with the example given for Fig. 5, it appears economically advantageous to screen (at 121) in 16 hours the amount of material produced by the two ave/aser sizers 112 in 24 hours. The unique arrangement of underilow suction pipes in the storage pits, such as pit No. 1, including the water jets provided from pipes 92, 95. and 97 (Fig. 2) afford a selected, constant flow of solids from the feed, providing of course that the suctions in use are covered with a reasonable quantity of solids. A steady delivery of solids results in maximum screen efficiency (as at 12), and is also a practical necessityy for efficient operation of the recovery plant 127.

The nature of some types of phosphate matrixY is such that the entirety of the fine fraction of the mined material, e. g. the 48 mesh, or sometimes all of the 35 mesh content of the ore delivered by the trommels, has such low phosphate value (measured as B. P. L. content, i. e. so-called bone phosphate of lime) that it can be discarded. The sizers 112 can then be so operated as to recover in the siphon product from the foot of the lower, hindered settling column, practically all of the +35 or +48 mesh particles. ln general, this is attained chiefly by adiustmcut of the siphon product discharge means, here the control valve or valves 49 (Fig. 4), e. g. in that within limits, the lower the density at which the Siphon discharge op crates, the finer is the lower limit of particle size recovered. When such situation prevails, no feed sizer 116 is needed and alternatives B and A of Fig. 1 are followed; the only material sent to the recovery plant is the screen un lersize from the suction product out of the main storage pit. Finally, in some cases, covered by alternative C (Fig. l), the entire product of the rock sizers 112 is useful without further treatment, for instance as electric furnace feed (to make elemental phosphorus) or as mineral phosphate directly employed (after griding) for agricultural purposes.

Extensive tests have borne out the effectiveness of the system and procedure in treating phosphate ore to yield products of satisfactory characteristics, especially as to grade and phosphate recovery. For example, using a double column sizer having only a single upper column and supplying an ore feed (averaging about 40% solids) provided by the coarse fraction of the scalping trommel under-size, the grade `of the product ranged from 64.4 to 72.7% B. P. L. from a feed which varied in B. P. L. content from about 52 to 37%, A typical sieve analysis of the product showed that 96.2% was +14 mesh and 73.3% was +8 mesh, only 1.1% being +20 mcsh. Pai'- ticularly impressive results have been obtained with a double column classier having a multiple upper column as shown in Fig. 4. For instance, where the ore feed varied from 10% to 40% solids and consisted of BA inch material, the average grade of the sized product (in box 44) over a number of runs which together yielded 2,375 tons, was 63.7% B. P. L., the actual variation being from about 6l to 67.5% B. P. L. ln every case, the major part of the product was +14 mesh, and in most runs the +20 mesh material was no more than about 6 to 12% of the total. Large variations in both volume and dilution of the feed were well accommodated. ln one run, the setting of the sizer was such as to cut off very sharply at 48 mesh and such that the product contained only about 3.3% of -35 mesh material, the grade of the product being 63.7% B. P. L. These results compare very favorably with the product of washer operations of the usual type, yet much dilculty, inconvenience and expense of the washer are avoided.

lt is to be understood that the invention is not limited to the specific apparatus and procedures herein set forth but may be carried out in other ways without departure from its spirit,

l claim:

1. Apparatus for settling rate classification of particulate mineral supplied in aqueous pulp and for discharging a high settling rate fraction of said mineral at a controlled rate independent of the rate of supply of said aqueous pulp, comprising: hydraulic classifying means including means providing a downwardly open, free settling upper column and means providing an upwardly open lower column for hindered settling of solids in liquid therein, said columns being vertically spaced and said classifying means including a tank surrounding said upper column means for receiving the aforesaid aqueous pulp and for delivering mineral particles and liquid to the space between'the columns, means for withdrawing liquid from the top of said upper column means, to remove a slow settling fraction of the mineral, means for removing pulp from the foot of said lower, hindered settling column means, to withdraw a high settling rate fraction of said mineral, means at the foot of said lower column means, separate from the pulp-removing means there, for introducing water to provide the aforesaid hindered settling in and above the lower part of said lower column means, receiving vessel means adapted to contain a large body of liquid, said means for removing pulp from the foot of said hindered settling column means having connections to discharge said pulp into the receiving vessel means, and means for withdrawing pulp from said receiving vessel means at a selected rate to provide controlled, substantially constant discharge of the higher settling rate fraction of the mineral, said upper column means of the hydraulic classifying means comprising a plurality of column-defining structures opening downwardly above the space above the lower col-umn means and each having a siphon discharge device at the top for withdrawing liquid to effect rise of liquid in the rcspective column-defining structure, and control means for the siphon discharge devices to bring them into operation in succession in accordance with successive increases in supply of liquid to the tank and to remove them from operation successively in accordance with decreases in the supply of liquid to the tank, the means for removal of pulp from the foot of the hindered settling column means comprising means for adjusting the volume of removed pulp in accordance with changes in the quantity of higher settling rate solids accumulating in said hindered settling column means.

2. Apparatus as described in claim l., wherein the receiving vessel means comprises a large open ground pit and the means for withdrawing pulp from said pit comprises conduit means extending to a lower part of thc pit and pumping means for advancing pulp along said conduit means, to elevate the pulp from said lower part of the pit to an upper locality of discharge.

3. Apparatus for settling rate classification of particulate mineral supplied in aqueous pulp and for discharging a high settling rate fraction of said mineral at a controlled rate independent of the rate of supply of said aqueous pulp, comprising: hydraulic classifying means including means providing a downwardly open, free settling upper column and means providing an upwardly open lower column for hindered settling of solids in liquid therein, said columns being vertically spaced land said classifying means including a tank surrounding said upper column means for receiving the aforesaid aqueous pulp and for delivering mineral particles and liquid to the space between the columns, means for withdrawing liquid from the top of said upper column means, to remove a slow settling fraction of the mineral, means for removing pulp from the foot of said lower, hindered settling column means, to withdraw a high settling rate fraction of said mineral, means at the foot of said lower column means, separate from the pulp-removing means there, for introducing water to provide the aforesaid hindered settling in and above the lower part of said lower col-umn means, receiving vessel means adapted to contain a large body of liquid, said means for removing pulp from the foot of said hindered settling column means having connections to discharge said pulp into the receiving vessel means, and means for withdrawing pulp from said receiving vessel means at a selected rate to provide controlled, substantially constant discharge of the higher settling rate fraction of the mineral, said upper column means of the hydraulic classifying means-comprising Aa plurality of column-defining structures opening downwardly above the space above the lower column means and each having a siphon discharge device at the top for withdrawing liquid to effect rise of liquid in the respective column-deiining structure, and control means for the siphon discharge devices to bring them into operation in succession in accordance with successive increases in supply of liquid to the tank and to remove them from operation succsively in accordance with decreases in the supply of liquid to the tank, the means for removal of pulp from the foot of the hindered settling column means comprising means for adjusting the volume of removed pulp in accordance with changes in the quantity of higher settling rate solids accumulating in said hindered settling column means; andthe aforesaid receiving vessel means comprising a large open ground pit and the means for withdrawing pulp from said pit comprises conduit means extending to a lower part of the pit, pumping means for advancing pulp along said conduit means, to elevate the pulp from said lower part of the pit to an upper locality of discharge, and water jet means associated with said conduit means and extendingV to said llower part of the pit, for agitating the pulp adjacent the conduit means to promote suspension of solids and for assisting advance of solids in liquid into and along the conduit means.

4. Apparatus for settling rate classifica-tion of particulate mineral supplied in aqueous pulp andffor discharging a high settling rate fraction of said mineral at a controlled rate independent of the rate of supply of said aqueous pulp, comprising: hydraulic classifying means having a lower, vertical-walled column, including means at a lower part of said column for rapid continuous introduction of water at regions localized with respect to the cross-section of the column, for upward flow of water in said column, to provide hindered settling of mineral particles falling into the column, means separate from the water introduction means for removal of faster settling material from the foot of said column, an upper vertical-walled column having a cross-section at least as great as the lower column and opening downwardly above the 4top of the lower column in spaced relation thereto, said upper column being closed at its top and having controllable siphon means opening into thetop of said column for removal of solids-carrying liquid at an adjusted rate therefrom,

to provide substantially constant velocity of liquid rise in said upper column from liquid supplied at the open foot thereof, and a tank having a cross-section at least several times the cross-section of the upper column and surrounding the upper column to a level above the top of said upper column, said tank including lower structure extending below said upper column and opening into the lower column at the lower end of the space between the columns, said tank receiving the aforesaid aqueous mineral pulp and delivering said particulate mineral and water to the space between the columns, said tank having overflow means at the aforesaid level, said Lipper column being arranged to provide free settling conditions in the upwardly rising liquid therein for removal by the siphon means of liquid-carried solid particles of lower settling rate than the particles removed at the foot of the lower column, receiving vessel means having a capac-ity equal to a multiplicity of times the capacity of the aforesaid classifier tank, means connected to the removal means of the aforesaid lower column for discharging pulp of said faster settling material into said receiving vessel means, and constant-rate withdrawal means for said receiving vessel means, comprising suction pipe means opening into said receiving vessel means at a lower part thereof and having water jet means for assisting direction of solids and liquid into and along said suction pipe means, to deliver the aforesaid faster settling rate material out of the receiving vessel means at a controlled rate.

5. Apparatus as described in claim 4, wherein the means for removal of faster settling rate solids from the foot of the lower column comprises siphon means opening at the foot of said column and having a siphon tube extending to a locality above the upper level of said tank and downwardly to an external discharge locality substantially below the upper level of said tank, and means controlled in accordance with the pressure of pulp at the foot of said lower column for controlling said last mentioned siphon means to provide flow therein only when the pulp at the foot of the column has a predetermined pressure higher than that corresponding to the hydrostatic head of water alone in said tank and lower column.

6. Apparatus as described in claim 4, wherein the upper column of the hydraulic classifying means comprises a plurality of inverted vessels of different diameters arranged in spaced, nested relation and opening downwardly to the space in the tank above the opening of the lower column means, each vessel being arranged for upward flow therein of liquid-carrying solid particles, under free settling conditions, and each vessel having a siphon discharge device opening into the head thereof, and control means for the siphon discharge `devices to bring them into operation in succession as and when the aforesaid tank is filled with liquid to successively higher levels and to remove them from operation successively in accordance with fall of liquid level in the tank, for changing the total rate of upward flow in the upper column assembly in response to change in the rate of supply of the aforesaid mineral pulp to the tank.

7. Apparatus as described in claim 4, wherein the receiving vessel means comprises an open ground pit having a volume equal to a great multiplicity of times the volume of the aforesaid tank, said hydraulic classifying means being disposed in elevated relation to said pit, for direct flow of pulp from said lower-column discharge means by gravity into said pit.

8. Apparatus as described in claim 4, wherein the receiving vessel means comprises an open ground pit, the suction pipe means comprising a suction pipe extending from ground level to the vicinity of the pit bottom and the water jet means comprising means extending along said suction pipe and having jet delivering means for directing water jets respectively transversely of the lower open end of the suction pipe, inwardly into the open end of the suction pipe and inwardly into the suction pipe at a locality intermediate its ends.

9. Procedure for settling rate classification of -particulate mineral supplied in aqueous pulp and for delivering a high settling rate fraction of said mineral at a controlled rate independent of the rate of supply of said aqueous pulp, comprising: establishing a lower vertical column of aqueous liquid confined by vertical boundaries, introducing and advancing liquid upwards in said lower column from selected lower localities thereof and at a rate controlled to provide hindered settling in said lower column for selective settling to the foot thereof of higher settling rate solids, establishing an upper column of liquid conned by substantially vertical boundaries extending upward from a locality spaced directly above the lower column, said upper column having a cross-section at least as great as that of the lower column, said lower and upper columns being unconned at their upper and lower ends respectively so that they freely communicate at said ends with the space between them, advancing solidscontaining liquid upwards in saidupper column by withdrawing liquid and particles therein of lower settling rate from the top of said upper column, maintaining a body of liquid surrounding said upper column from a level above the top thereof to said space between the columns and filling said space, supplying the aforesaid feed pulp into said body of liquid at the top thereof for travel of liquid and particles downwardly around the upper column to the space between the columns7 said withdrawal of liquid from the top of the upper column being controlled to provide substantially constant rise of liquid in said upper column for elfectuating free settling of higher settling rate soldis therein and thence downwardly through said space into the lower column; withdrawing pulp of high settling rate solids from the foot of the lower column separately from the aforesaid liquid being introduced at lower localities of the lower column and directing said last-mentioned pulp into a large storage region and thereby accumulating a large body of said pulp in said storage region, and withdrawing pulp at a controlled rate from a lower part of said storage region.

10. Procedure as described in claim 9, wherein the withdrawal of pulp from the lower part of said storage region comprises applying suction to the pulp at said lower part and by said suction withdrawing pulp along a -confined withdrawal path of predetermined cross-section, while promoting advance of pulp into and along said path at a substantially constant rate by jetting water into the lower part of the storage region and into the said path.

ll. Procedure for size classification of phosphate mineral material in aqueous pulp and for deliveringy a course phosphate-rich fraction of said material at a controlled rate independent of the rate of supply of said mineral material pulp, comprising supplying said pulp into a region filled with aqueous liquid and thereby delivering the mineral material particles to a lower Zone o1? said region, withdrawing liquid upwardly from said Zone in an upper column under free settling conditions to carry away the Ifiner fraction of said mineral material and at least substantially all of the water of said pulp, simultaneously subjecting mineral material particles falling from said zone to hindered settling in a lower column for continuously accumulating a coarse phosphate-rich fraction of the material at the foot of said lower column, said hindered settling being effected by introducing a stream of fresh liquid at a locally accelerated rate at the foot of said lower column, removing a pulp of said coarse fraction from said foot of the lower column separately from the aforesaid stream of fresh liquid entering the lower column, directing said removed pulp into a large storage region and thereby accumulating a large body of said coarse phosphate-rich fraction in said storage region, and discharging phosphate-rich material at a selected substantially constant rate by withdrawing pulp at a controlled rate from said storage region, the aforesaid procedure also including the steps of selectively modifying the cross-section of said upper column and the total rate of upward liquid withdrawal therein, in accordance with changes in the level of liquid in said liquid filled region, and controlling the removal of phosphate-rich pulp from the foot of the lower column in accordance with the presence and amount of accumulated coarse fraction material at said foot of the lower column.

12. Procedure for size classilication of phosphate mineral material in aqueous pulp and for delivering a coarse phosphate-rich fraction :of said material at a controlled rate independent of the rate of supply of said mineral material pulp, comprising supplying said pulp into a region filled with aqueous liquid and thereby delivering the mineral material particles to a lower zone of said region, withdrawing liquid upwardly from said Zone in an upper column under free settling conditions to carry away the finer fraction of said mineral material land at least substantially all of the water of said pulp, simultaneously subjecting mineral material particles falling from said Zone to hindered settling in a lower column for continuously accumulating a coarse phosphate-rich fraction of the material at the foot of said lower column, said CII hindered settling being effected by introducing a stream of fresh liquid .at a locally accelerated rate at the foot of said lower column, removing a pulp of said coarse inaction from said foot of the lower column separately from the aforesaid stream of fresh liquid entering the lower column, directing said removed pulp into a large storage region and thereby accumulating a large body of said coarse phosphate-rich fraction in said storage region, and ydischarging phosphate-rich material at a selected substantially -const-ant rate by withdrawing pulp at a controlled rate from .said storage region, said procedure also including the steps of eifectuating response iof the classifying action to absence and presence of aqueous mineral pulp supply, by interrupting and reinitiating upward withdrawal `of liquid in the upper column respectively in accordance with absence or presence of liquid in sai-d iilled region at a predetermined upper level thereof, and by interrupting and reinitiating removal of coarse fraction pulp from the foot of the lower column respectively in accordance with absence or presence of accumulated coarse fraction material at said foot of the lower column.

13. Procedure for size classification of phosphate mineral material in aqueous pulp and for delivering a coarse phosphate-rich fraction of said material at a controlled rate independent of the nate of supply of said miner-al lmaterial pulp, comprising supplying said pulp into a region lled with aqueous liquid and thereby delivering the mineral material particles to a lower zone of said region, withdrawing liquid upwardly from said zone in an upper column under free Ysettling conditions to carry away the ner fraction of said mineral material and at least substantially all of the water of said pulp, selectively modifying the cross-section 4of :said upper column and the total rate of upward liquid withdrawal therein, in accordance with changes in the level of liquid in said liquid iilled region relative to predetermined level limits in the upper part of said region, simultaneously subjecting mineral material particles falling from said zone to hindered settling in a lower column `directly below said zone for -continuously accumulating a coarse phosphaterich fraction of the material at the foot of said lower column, removing a pulp of said coarse fraction from said foot of the lower column, the removal of said pulp being modified in accordance with changes in the amount of said coarse fraction accumulating at the foot of said lower column, directing said removed pulp into a large storage region and thereby accumulating a large body of said coarse phasphate-rich fraction in said storage region, and ydischarging phosphate-rich material Aat a selected substantially constant rate by withdrawing pulp at a controlled rate under suction from a lower part of said storage region.

References Cited in the le of this patent UNlTED STATES PATENTS 1,264,688 Schilling Apr. 30, 1918 1,959,212 Miller May 15, 1934 2,019,968 Holloway Nov. 5, 1935 2,360,129 Hebbard Oct. 30, 1944 2,425,551 McKay Aug. 12, 1947 2,442,522 Wiegand June 1, 1948 2,708,517 Evans May 17, 1955 FOREGN PATENTS 9,883 Netherlands Nov. 15, 1923 21,668 Great Britain of 1909

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