US2754965A

US2754965A - Beneficiation of nonmetallic minerals

Info

Publication number: US2754965A
Application number: US142981A
Authority: US
Inventors: James E Lawver
Original assignee: International Minerals and Chemical Corp
Current assignee: International Minerals and Chemical Corp
Priority date: 1950-02-08
Filing date: 1950-02-08
Publication date: 1956-07-17
Anticipated expiration: 1973-07-17

Description

July 17, 1956 LAWVER 2,754,965

BENEFICIATION OF NONMETALLIC MINERALS Filed Feb. 8, 1950 4 Sheets-Sheet l PHOSPHATE ORE" FIG. I

WASHER/2 1 5 LOW GRADE/6 3 PEBBLE 4 f T 7 WASHERFINE PEBBLE ows. 9 -|4MESHI +|4MESH I 8 E B 5w SCREENING HIGH GRADE 1 R FINES/ PEBBLE SEPARATOR/H I3 FINES 30A Rs msc SEPARATOR coABsE STORAGE BIN l6 I /I7 INFRA RED TREA MENT /l8 29 ELENiENT I9 24 f 25 ELECTROSTATIC In SEPARATOR 23 l m /20 TAILING FRACTION MIDDUNG CONCENTRATE FRACTION 1 SGAVENGER ELECTROSTATIC l PRODUCT CONCENTRATE FINA TAILS 1 WA ST? 30 IN V EN TOR. JAMES E. LAWVER ATTORNEY July 17, 1956 J, E, wv 2,754,965

BENEFICIATION F NONMETALLIC MINERALS Filed Feb. 8, 1950 4 Sheets-Sheet 2 Fl 2 PHOSPHATE ORE\ WASHER 2 /4 /3 WASHER FINES PEBBLE CONC.

ESH 5 l4 MESH 1; A

3| so DESLIMINGSECTION/ 49 "'5 I I SPRAY DRIER -325 MESH 32 -|4+ 50 IS'ZING SECT'ON T0 WA sTE Z F I SI -325MESH STORAGEU 64 DR|ER MESH -20+325 r 2\ 4 ';B 65 STORAGE B|N\ coARsE BIN FINE III L 35 53 \INFRA RED 4 TREAT IIEIIIT DONOR/37 ELEMENT /65 l /39 ELEcTR0sTATIc.- SEPARATOR 40 1 ,4I /42 TAILING FRACTION) MIDDL'NG CONCENTRATE seI FRACTION 43 SCAVENGER ELECTROSTATIC L RODUCT 57\ I SEPARATOR] (430 CONCENTRATE FINAL TAILS SIZING SECTION'44 59 I /45 -I4+20 MESH 20 MESH-46 INVENTOR. JAMES E. LAWVER ATTORNEY BENEFICIATION OF NONMETALLIC MINERALS- James E. Lawver, Lakeland, Fla., assignor to International Minerals 8: Chemical Corporation, a corporation of New York Application February 8, 1950, Serial No. 142,981

15 Claims. (Cl. 209-127) This invention relates generally to the beneficiation of nonmetallic, nonsilicate minerals and has particular reference to a method for the electrostatic beneficiation of nonmctallic, nonsilicate minerals.

It has long been known that it is possible to beneficiate minerals by electrostatic methods. However, up to the present time electrostatic methods have been successful from an economical and practical standpoint only in isolated instances.

Two general problems confront those interested in electrostatic methods of beneficiation. The first problem concerns the nature of the apparatus employed to create the electrostatic field. This depends primarily on the characteristics of the feed material. These characteristics may be inherent in the feed material or imparted to it by artificial means. Generally, however, the electrostatic apparatus comprises essentially charged and grounded paired electrodes. The grounded electrode may consist of a roller capable of being revolved and the charged electrode of a tube, rod, or a plate having smooth curved surfaces. Also said to be successful are charged electrodes having needle-like points or fabricated. of relatively fine wire.

The second problem confronting those interested in electrostatic methods of beneficiation is the method by which the feed material is advantageously rendered susceptible to the forces exerted in an electrostatic field; In this regard many processes have been developed for treating washer debris obtained, for example, from highgrade phosphate pebble. Likewise, numerous processes have been developed for treatment and beneficiation of comminuted low-grade phosphate pebble or other nonmetallic, nonsilicate ores. Of primary concern in each of these methods is the cost of reagents having a selective aflinity for one of the ore components and required for the production of a marketable product. Such processes are generally employed in tabling, flotation, or other methods in which such reagents are employed.

It has been revealed by Johnson in U. S. Patent No. 2,197,865 that the washery fines may be deslimed and classified into coarse and fine fractions; and that upon treatment with conventional flotation reagents and being frothed, the fines are floated and collected. By this method a rough phosphate concentrate is obtained. It is further taught by this patent that upon screening and drying the rough phosphate concentrate and subjecting the same to electrostatic separation, a marketable product may be obtained. Presumably this process maybe employed upon products obtained at various stages of established processes for the beneficiation of phosphate ore. It is to be noted that in this process the phosphate fraction is rendered susceptible to the forces inv an electrostatic field by selectively reagentizing the feed material United States Patent- 2,754,965 Patented July 17, 1956 with conventional flotation reagents. Thus, this process does not eliminate the use of reagents whose cost, as

previously mentioned, is one of the chief concerns of methods may be mentioned the process disclosed in U. S.

Patent No. 2,168,861 issued to OBrien. It is said-in; this patent that certain types of particled material may be electrified or charged by grounding the material to be separated on a metallic conductor employing, in so doing, a frictional, wiping, or impacting action followed by treatment in an electrostatic field. This method, in addition to being highly complex, produces. considerable wear on the grounded metallic conductor. For practical purposes materials employed in fabricating apparatus to be used in this process are subject to considerable Wear because of the wiping or impacting action employed. it is likewise uneconomical to obtain a beneficiated product by this process. Among. other means of pretreating the material to be beneficiated are said to betreatment of the feed material with acid vapor or subjecting: the feed material to a fabricating plate before subjecting it to an electrostatic field. Mention of other methods; of electrostatic separation may be found in-Industrial andi Engineering Chemistry, volume 32, pages 601 and 602- (1940). According to this reference electrostatic methods of separation may be classified into four categories as, follows: (1) processes depending on differences in con-,

ductance of solids, ('2) processes depending on diiferences;

in contact potentials of solids eitherbetweenthe particles; themselves or of the solids with the surfaces of the sepa; rator unit, (3) processes dependingv on pyroelectric polarization of crystals, and (4) processes depending on relative dielectric constants of the solids and the media in which they are suspended.

It may be implied from the foregoing, that.- of equal importance to conditioning of the feedmaterial for, electrostatic separation is the method of creating the. electrostatic field to which the material is to be subjected: It is likewise important in any beneficiation process, including electrostatic methods, to comminute the feed-.materials sufliciently to obtain a maximum liberation of undesirable inclusions of gangue material from the. dc.- sired mineral values. At the same time, however, it is not desirable to employ a feed material of such a fine mesh that the efiiciency of the process isimpaired,

It is an objectv of this invention to-provide an improved and economical processfor the beneficiation of nonmetal.- lic, nonsilicate minerals wherein electrostatic methods: of separation are employed.

It is a further object of this invention to provide, a. method of imparting and maintaining an appreciable difference in electrical charge between the desiredv components of the feed material and the undesirable. components without previous conditioning of the fced'material with reagents, including those reagents having a selective alfinity for one of the ore components such as are commonly employed in flotation processes.

Another object of this invention is to provide a process for the separation of nonmetallic, nonsilicate minerals or particles from gangue in air ambient, although the various types of particles to be separated are in each case relatively poor conductors and their conductivity is of the same order of magnitude.

These objects as well as other objects of the invention which will become apparent upon a clearer understanding of the same, as hereinafter set forth, may be accomplished by comminuting nonmetallic, nonsilicate ore sulficiently to substantially liberate the desired values from the gangue. The comminuted ore is then dried and treated with infrared waves, by means subsequently to be described, so that upon subjection of said treated ore to a free source of electrons, such as concerns the earth, certain components of said treated ore will develop a marked electrical charge while other components will develop a relatively smaller charge or remain substantially unchanged as to charge. The ore while in the aforedescribed charged condition is subjected to an electrostatic field created by an apparatus subsequently to be described. Ore which has been treated with infrared waves but not subjected to a source of free electrons is capable of taking up differentially additional free electrons. While in this state, some of the orc constituents will take up electrons while other ore constituents remain relatively inert so far as taking up further electrons. Thus the tendency toward electron differentials is increased among the various ore components.

The instant novel process is based on the discovery that the aforesaid gangue material of the nonmetallic, nonsilicate minerals, for example, quartz, feldspar, and chert which comprise the principal gangue material of phosphatic ore, possess the ability, when subjected to infrared waves of sufiicient power density, of acquiring an afiinity for electrons and thereafter an electrical charge from a source external to the gangue components themselves. In the aforementioned U. S. Patent No. 2,197,- 865, it is stated on page 2, column 2, lines 44-46, that silica is to a degree pyroelectric and that its conductivity increases to a certain extent when warm. As previously stated, the differential charge in the instant process is an acceptance or a rejection of electrons, as the case may be, so that at least one of the components possesses an electrical charge and is not merely polarized as in the case of pyroelectric crystals. It has further been discovered that the aforesaid charge on the infrared treated gangue, while present to a very small degree before sub jecting said treated gangue to a source of free electrons, is markedly increased by subjecting the same after treatment with infrared waves to a source of free electrons such as is supplied by the earth. It is preferred, therefore, in the instant novel process to contact infrared treated nonmetallic, nonsilicate ore with an electrical conducting material which is grounded. This is done before subjecting the ore to the electrostatic field, but after infrared treatment or simultaneously with infrared treatment.

In the instant novel process advantage is taken of the aforedescribed phenomena. In this regard it has been discovered further that the phosphatic components of phosphatic ore do not have the same characteristics of acquiring a charge as is exhibited by the gangue, or of acquiring a charge of as large a degree as that produced on the gangue under the same conditions.

The term infrared waves is meant to include those waves of the spectrum having a wave length of between about 1X10 and about 1.5 angstrom units.

By the term power density is meant the concentration of radiation per square inch of ore being treated. The power density is measured in watts per square inch and is to a degree dependent upon the power and spacing of the infrared source, the efficiency of an infrared lamp reflector unit, for example, and to a limited extent (within the range of practice) the distance between the source and the surface of the ore being treated. In this regard reference may be had to the Standard Handbook for Electrical Engineers, section 1866, page 1775, McGraw and Hill (1949). The power density employed in the instant novel process should be between about 4.0 and about 6.0 watts per square inch. The preferred range is between about 4.7 and about 6.0 watts per square inch because of its convenience to obtain.

The length of time of exposure of the ore to be treated at the above stated power density ranges is preferably between about 4 and about 1 minutes, respectively. However, it is not intended to limit the time of exposure or power density to these ranges. On the contrary, since less time of exposure is required if a higher power density is employed, it has been found it is practical to employ exposure times of between about 20 seconds and about 15 minutes with corresponding variations in power density within the ranges set forth above.

The reason for the aforedescribed phenomenon is not fully understood. It is believed, however, that an explanation can be found only after a consideration of advanced physical principles. In this regard reference may be had to Mott and Gurney, Electronic Processes in Ionic Crystals, Oxford Press, 1940, pages 168 to 185, and to Southerland and E. Lee, Developments in the Infrared Region of the Spectrum, in Reports on Progress in Physics, volume 11, pages 147 to 148 (1946-1947).

For a clearer understanding of the instant novel process, reference may be had to the detailed descriptions and tables which follow, and to the accompanying drawings of which Figures 1 and 2, taken together, are diagrammatic flow sheets of a complete process for beneficiating phosphate ore, and Figures 3 and 4 are diagrammatic flow sheets illustrating various alternative processes for beneficiating nonmctallic, nonsilicate ore while eniploying the principles of the instant invention.

It has been found that the type of metallic conductor with which the infrared treated ore is grounded is relevant only as far as the efficiency of the instant process is concerned. Thus, it has been found that an infrared treated gangue of phosphate ore develops a higher relative charge when grounded on carbon, zinc, galvanized iron, or brass than if grounded on a steel donor element.

In this regard, Table I shows the relative charge obtained on Florida silica sand by increasing exposure time to infrared waves. The samples giving the results shown in Table I were grounded on a zinc pan. A sample employed in this table comprises silica sand from which the last traces of phosphatic rock had been removed. The samples were exposed to infrared waves. The source of infrared waves employed was a 1,000 watt, five inch, infrared lamp placed between about 2 and about 4- inches above the sample to be treated. After exposure for the time indicated in column 1, the treated samples were grounded immediately by contact with a grounded zinc pan. The relative charge was measured by contacting an electrometer with the sample to be tested. The relative charge given in column 2 may be converted into coulombs by multiplying the relative charge by 8 l0 This figure is the combined capacitance of the particular electrometer and its antenna used in making the actual determinations and readings. The silica sand employed com prised approximately quartz with the balance containing chert and feldspar.

TABLEI Exposure time Charge 5 secs 0.3 10 secs -03 15 secs 3.0 20 secs ll.0 30 secs -23.l') 45 secs -22.0 1 minute 24.0 2 minutes 39.0 3 minutes --4().() 5 minutes 56.0 10 minutes 9.0 15 minutes 90.0

tion and claims as a donor element.

Table II illustrates the results obtained when a silica. sand sample, similar to that employed in obtaining the data in Table I, has been grounded on a steel pan immedi ately after being exposed for the length of time indicated in column 1 to infrared waves. The relative charge was measured with the same electrometer as employed in obtaining the data recorded in Table I. An inspection of Tables I and II conclusively shows that a higher relative charge is obtainable if the sample is grounded on a zinc pan than if grounded on a steel'pan.

TABLE II Exposure time Charge 5 secs -0.4 secs 0.5 secs 10.0

secs 13.0 30 secs 14.0 1 minute 23.0 2 minutes 26.0 3 minutes 39.0 5 minutes -36.0 10 minutes 43.0

Since zinc and galvanized iron were found to produce a high relative charge on infrared treated phosphatic gangue (i. e., silica), and the magnitude of the charge was substantially the same where zinc or galvanized iron was employed, the term zinc as hereinafter used in the description and claims also is meant to include galvanized iron. Although grounding upon carbon materials, such as graphite, was found to produce the higher relative charge such material obviously does not wear well and is not particularly suitable from an economic standpoint in the instant novel process. Brass and iron donor elements were found to produce a lower relative charge than zinc. However, both brass and iron were also found to be operable. Whatever grounded electrical conducting material is used it is hereinafter referred to in the descrip- The donor ele ment may be composed of any one or more of the materials such as those aforementioned which will when grounded impart electrons to the phosphatic ore gangue contacted with said grounded material. The donor element may be a grounded plate, chute, tray, hopper or the like. When in operation the donor element must be grounded and so positioned that the infrared treated ore, for example silica-containing phosphatic ore, is contacted with it thus imparting a large differential negative charge to the gangue in contrast to the charge obtained on the phosphatic component. The selectively charged ore is then subjected to an electrostatic field for beneficiation.

A further relevant factor in the efficiency of the instant novel process is the particle size of the ore to be beneficiated. The most satisfactory range from an economic standpoint for phosphate ore is that obtained by grinding a substantially dry phosphate ore to between about 14+200 mesh and about 24+2()O mesh, preferably about 24+200 mesh. When ground to this mesh size the phosphatic values are substantially liberated from the gangue, and the gangue may be separated from the phosphate values when treated in accordance with the instant novel process. In the case of Florida apatite or colophony, the gangue comprises essentially about 96% quartz, about 8% feldspar, and about 2% chert.

From the foregoing tables and description it is apparent that four factors are involved in the instant novel process: the length of time, the concentration of radiation of infrared waves with which the ore is to be treated, the type of material employed as the donor element, and the particle size of the ore treated. While not critical, it is preferred ,to employ feed material which has been thoroughly deslimed and is substantially dry. It is to be noted that special types of contacting with the donor element, such as a vibrating plate or a wiping, frictional, or impacting Contact withagrounding plate are not necessary. Rather it is sufi'icient to merely contactthe infrared treated ore with a' donor element. This principle is illustrated in connection with Tables I and II.

, While the principles of the instant process have application to nonconducting, nonmetallic, nonsilicate ores other than phosphate ore, due consideration must be given in any electrostatic beneficiation process to the method of creating the electrostatic field to which the aforesaid charged material is to be subjected. In the instant process it is desirable to employ anapparatus which will minimize the possibility of altering or reducing the previously described charge. Such possibility is increased with the use of electrostatic apparatus which will develop a corona discharge or which will make use of normalv induction as is employed in substantially all conductivity electrostatic separators. Therefore, it is preferred to employ an electrostatic apparatus which has electrodes designed to minimize these effects. The electrodes, therefore, preferably have smooth, curved surfaces. They should be kept at a high direct voltage potential substan tially free of alternating current components. The surfaces of the electrodes which selectively attract or repel some of the components of the feed material should be positioned or formed so that the divergent angle taken by the attracted or repelled components is as wide as possible. This arrangement makes the ultimate separation and collection of divergent and undivergent flowing material by dividers and chutes much more easily accomplished.

The instant process may be applied to nonmetallic, nonsilicate mineral concentrates separated at various stages by conventional tabling or flotation methods of beneficiation. Thus the instant process has application to ground Florida phosphate pebble, deslimed washer debris from high-grade phosphate pebble or concentrates thereof produced in a conventional manner. It may likewise be employed in combination with or in elimination of other familiar methods of beneficiating phosphatic material wherein the feed material has been substantially liberated from its undesired components by customary crushing or grinding. The process also has application to similar stages of beneficiating other nonmetallic, nonsilicate minerals, such as Montana and Tennessee phosphate ores.

For a more detailed illustration of the operation of. the instant novel process, reference may now be had to Figures 1 and 2 which, taken together, are diagrammatic flow sheets of a complete process for beneficiating phosphate ore. The figures are intended merely to illustrate the general application of the instant invention and are not to be considered a limitation thereon. Modification of the process illustrated by these flow sheets while employing the principles of the instant invention will be apparent to those familiar with electrostatic beneficiation processes.

In Figure 1 phosphate ore 1 as mined is pumped into a washer 2 where separation of phosphate pebble concentrate of +14 mesh 3 is made from washer fines 4 of -l4 mesh. The washer fines, as indicated by the letter B, are processed. in accordance with Figure 2, line B" of Figure 1 being the same as line B of Figure 2. pebble is of high-grade pebble 5, it need not be processed any further and may be shipped as a product concentrate. If the pebble concentrate comprises essentially low-grade pebble 6, it is subjected to a grinding process 7 in order to substantially liberate the phosphatic values from the gangue. The latter comprises essentially quartz, feldspar, and chert. The ground material is subjectedto a screening operation 8 and generally sized to a 24 mesh, the coarse material 9 of +24 mesh being recycled to the grinding process 7. The fines 1%) thus obtained are subjected to a conventional separation 11, for example, an air separation. The coarse material 12 of substantially -24+200 mesh is separated from the fine material 13 of 200 mesh which is discarded. The coarse material 12 is again subjected to a separation 14, and the resultant fines (not shown) are combined with the previously obtained fines 13 and sent to discard. The coarse material 15 of -24+200 mesh is placed in storage or a surge bin 16. From the storage bin 16, the material, as needed, is treated with a source of infrared waves 17. This source preferably comprises a battery of infrared lamps properly positioned and of sufficient wattage to give a power density of between about 4.7 and about 6.0 watts per square inch of feed material. The time of exposure of the ore to this source of infra-- red waves depends on the type of ore, its grade, and other factors, such as the rate of production and quality of product desired. The aforesaid negative charge is obtained, as previously stated, by contacting the ore, after treatment with the aforesaid source of infrared waves 17 for between about 15 seconds and about 20 minutes, preferably between about 1 minute and about 2 minutes, with a donor element 18. Alternatively, the donor element may be positioned so that the treatment with infrared waves and grounding upon the donor element takes place substantially simultaneously. If this latter method is employed the preferred time of exposure to infrared waves is between about 1 minute and about 2 minutes. If a galvanized iron donor element is em ployed, the optimum time of treatment with infrared waves is between about 1 minute and about 2 minutes. The ore thus charged is then subjected, preferably immediately after treatment with infrared waves, to an electrostatic field created by a suitable electrostatic separator 19.

Upon passage through the electrostatic field, a phosphatic concentrate 20, which is product 21, a middling fraction 22, and a silica tailing fraction 23 are obtained. The middling fraction 22 is recycled to the source of infrared waves 17 as shown by line 24. The amount of middling fraction, it being a continuously circulating load, is dependent upon the grade of feed material and the amount of middling that the operator desires to carry. Since the middling recycle process is a closed circuit, in starting the operation, the middling circuit must be filled before equilibrium between the amount of feed material put in and the amount of product and tails taken out is reached. If the middling fraction 22 has been originally treated with infrared waves for the optimum length of time, it may be resubjected to the electrostatic separation 19 without repassage through the source of infrared waves 17 as shown by line 25.

The tailing fraction 23 is subjected to a scavenger electrostatic separation 26 where tailings 27 and a phosphatic concentrate 28 are obtained. The concentrate 28 is returned to the source of infrared waves 17 as shown by line 29 for retreatment. As previously noted, the same is done in the case of the middling fraction 22. The concentrate 28 is then again contacted with the donor element 18 and again subjected to an electrostatic separator 19. The final tails 27 are sent to waste 30.

Reference is now made to Figure 2. The washer fines 4, which are of a 14 mesh, are sent to a desliming section 31 where a separation is made of -325 mesh material 32, which is sent to waste 64, and 14+325 mesh material 33. The pebble concentrate is processed in accordance with Figure 1, line A in Figure 2 being the same as line A in Figure 1.

The 14[-325 mesh material 33 is sent to a dryer 34 and then to the dryer storage bin 35. It is then treated in the same manner as previously described when employ ing pebble feed. That is, it is subjected to a source of infrared waves 36, and then contacted with a donor element 37, after which it is subjected to an electrostatic separation 39. The fractions obtained are tails 40, middling fraction 41, and concentrate 42. The latter is product 43. This product may then be sent to a sizing section 44 as shown by line 43a, where the +20 mesh size is 46. Each is separately stored in

bins

47 and 48 re- 8 spectively for shipment. Alternatively, as shown by dotted line 49, the -l4+325 mesh material 33 may be sized into +20 mesh material 50 and 20l325 mesh material 51 and stored in coarse and

fine storage bins

52 and 53 respectively. Materials from

bins

52 and 53 may then be separately processed as indicated by lines 54.

The middling fraction 41 is returned to the source of infrared waves 36 by means of line similar to the flow sheet shown in Figure 1.

Similarly, if the middling fraction 41 has been treated for the optimum length of time with the source of infrared waves it may be resubjected to the electrostatic separation 39 as shown by dotted line 55. The tails 40 are subjected to a scavenger electrostatic separation 56, and the concentrate 57 is returned to the source of infrared waves 36 by means of line 66. The final silica tails 58 are conveyed to waste 59.

The 325 mesh material 32 instead of being sent to waste 64 may, as shown by dotted line 60, be sent to a spray dryer 61 and then to storage 62 from which it may be conveyed, as shown by dotted line 63, to the source of infrared waves 36. After being subjected to the source of infrared waves for the proper length of time, the material is then contacted with the donor element 37 and subjected to an electrostatic separation 39.

The aforedescribed process illustrates one method by which silica-containing phosphate ore may be completely processed dry without the use of any costly flotation reagents. In either of these processes previously described or in other applications of the principles of the instant process hereinafter to be described, the material to be beneficiated may be simultaneously contacted with a donor element and exposed to infrared waves.

Another illustration of a continuous process for beneficiating phosphatic ore by employing the principles of the instant novel process is the individual separation by electrostatic means of a phosphate concentrate, a middling fraction, and a tailing fraction by conventional means other than by treatment with infrared waves, and by employing unreagentized feed material. The middling and tailing fractions may then individually be treated with infrared waves within the aforesaid optimum range and contacted individually with grounded electrical conductors. The phosphate concentrates obtained by separate electrostatic separations of the contacted tailing fraction and the contacted middling fraction are then combined with the initially obtained phosphate concentrate.

For further application of the principles of the instant process reference may be made to Figure 3 which illustrates diagrammatically the use of a single electrostatic separator. In the process illustrated by this flow sheet, the sized silica-containing phosphatic feed material is treated with a source of infrared waves 141b, by means of conducting

lines

141 and 141a. The ore is treated with infrared waves for between about 1 minute and about 2 minutes at a power density of between about 4.7 and about 6.0 watts per square inch. The treated material is then grounded by contact with donor element 67 as indicated by line 67a. As previously stated, the exposure to infrared waves and the contact with donor element 67 may be simultaneous. The treated contacted feed material is then processed through electrostatic separator 110, as indicated by line 11011, which comprises a plurality of paired, vertically arranged electrodes, said electrodes being designed to minimize the possibility of corona discharge. The separator also contains properly spaced dividers and chutes which are in turn connected to draw-off lines to be referred to hereinafter. The number of electrodes required depends on, among other factors, the quality and particle size of the material. In this process all of the pairs of electrodes required to produce a marketable product are included in one electrostatic apparatus. The break 136 in the electrostatic apparatus indicates extra height for additional numbers of paired electrodes as required. For example, an over-all total of eight pairs or more is required to produce the product by the method hereinafter described. The product obtained depends upon the quality of the original feed material. Thus, by the process hereinafter described, phosphatic feed material having a bone phosphate of lime (B. P. L.) content of between about and about is beneficiated to between about 75 and about 77% B. P. L.

From the upper portion of the electrostatic apparatus, as shown by lines- 70, '71, 72, header line 73a, and line 73, a final tail 68 is obtained and as indicated by lines '74, 75, 76, header line 1390, and line 139, a rougher concentrate 69 is obtained. The final tail is sent to discard, and the rougher concentrate in a continuous process may be recycled by line 77 to one of several points in the process as hereinafter described. Some of the paired electrodes, including those within the break 136, separate a middling and a rougher concentrate. These products are treatedsimilarly to rougher concentrate 69. From the lower portion of the electrostatic apparatus 110, as indicated by

lines

111, 112, 113, 114, 115, and 116, product 117 is obtained and collected by means of header line 140. The middling fractions, as indicated by draw-off

lines

99, 100, 101, 102, 103, and 133a are also obtained from the lower portion of the electrostatic apparatus. These middling fractions are collected by header line 84. If

valves

83, 138, and 98, of header line 84 are open and all of the other valves in the system closed, the rougher concentrate 69' will: be recycled by line 77 into line 84 and: there combined with the middlings; and together they are returned by lines 84a and 1410 to the source of infrared Waves 141b, valve 83a being open.

If it is desired that the rougher concentrate 69 by-pass the middling section this may be done by opening

valves

82, 97, 98, and 83a. This arrangement of valves causes the rougher concentrate to be recycled to source of infrared waves 1411 without comingling the same with the middling fraction. It is necessary, however, to accomplish this that the middling section be isolated by closing valve 96 on. line 118, valve 138 on line 34, valve 83 on line 84, and valve 95 on line 119. The middling fraction will be allowed to pass through draw-off line 104 into the electrostatic apparatus through, for example, line 119, open valve 94, and line 124, valve 95a on line 133a being closed. By opening any of the

closed valves

86, 88, 90, 92 or 94, the middling may be recycled into the electrostatic separator by any one of

lines

128, 127, 126, 125, or 124, respectively, employing

lines

120, 121, 122, or 123 for this purpose as required. With the middling fractionisolated as above, the rougher concentrate may be, if desired, recycled through source of infrared waves 78 and contacted with donor element 79 by closing

valves

98 and 83 on line 84 and valve 82 on line 81. The infrared-treated, contacted, rougher concentrate is then allowed to pass through valve 97' on line 109 from where it is conveyed by line 135, valve 138 being closed, through open valve 134 and deposited at a point in the electrostatic apparatus 110 below that section which removes the final tail. This will be somewhere in break 136 as indicated by lines 135 and 1350.

If desired, a rougher concentrate may be recycled into the electrostatic separator along with the middling fraction without reheating or recontacting either fraction with the donor element. This is accomplished by recycling the rougher concentrate into line 84, valve 83 being open and valves 80 and 82 being closed. Any number of valves 85,87, 89, 9'1, and 93 on

lines

129, 130, 131, 132, and 133 are open. For example, if valve 87 on line 130 is open, it will receive the rougher concentrate from line 84 as well as the middling fraction from

lines

99, 100, 101, 102 and 103, and. deposit the same into the electrostatic separator at the point indicated by line 127.

It is sometimes desirable for economical separation to retreat with infrared waves and recontact both the rougher concentrate and the middling fractions and deposit them together ata point in the electrostatic separator below that 10 section from which the final tail was removed. This may be accomplished by

first closing valves

83 and 82 and opening valve 80. This will allow the rougher concentrate to be subjected to the source of infrared Waves 78 via lines 1 105, 106, and 107. In the meantime, the middling fraction element 79 where the mixture is grounded.

Valves

137 and 97 being opened and 98 and 138 being closed, the infrared treated grounded material is conveyed by line through open valve 134 and deposited in the electrostatic apparatus at some point below that section which is removing final tail and above that section which is removing product. This point will be somewhere Within the break 136 as indicated by

line

135 and 135a. If desired, however, a mixture of middling and rougher concentrate may be deposited by any one of

lines

124, 125, 126, 127, and 123 at that section of the electrostatic apparatus from which middling and product are removed. This is accomplished by closing valve 97 and opening valve 95. Also open are one or more of

valves

92, 94, 88, 86, and 90. Thus, if valve 86 on line 128 is open, a mixture of middling and rougher concentrate from line 109 will be conducted by

lines

119, 121, 122, 123, and 128 and deposited by the latter line in the electrostatic apparatus at the point indicated by line 128.

The preferred alternative, however, is to recycle rougher concentrate 69 through line 84 by opening valve 83 and closing valves 82 and 80. This rougher concentrate then is allowed to combine with the middling fraction obtained from draw-off

lines

99, 100, 101, 102, and 103. The middling fraction from line 104a is combined With the middling fractions and rougher concentrate collected by line 84 through line 133a and open valve 95a. The mixture of rougher concentrates and middling fractions are then allowed to pass by means of

lines

84 and 84a into line 1410,

valves

138, 98 and 8341 being open, by which means the mixture is conveyed to the source of infrared waves 141b and thence to the donor element 67 as indicated by line 67a for reprocessing. Alternatively, this mixture, instead of passing into line 84a, may be made to pass through line 86a by opening valve 85a and closing valve 83a, valve 83a thus bypassing the source of infrared Waves 14112 and donor element 67.

Reference may-now be had to Figure 4 where still another application of the principles of the instant novel process is illustrated. Instead of employing one electrostatic separator as referred to in connection with Figure 3, at least two and preferably three separate electrostatic separators, each having the necessary dividers, chutes and drawoff lines hereinafter referred to, are employed. A plurality of paired electrodes designed to minimize corona discharge and vertically arranged are employed in each apparatus. The number of paired electrodes employed again depends upon several factors, such as the type of feed material and particle size. The number of paired electrodes required in each apparatus will generally be less than the total number of paired electrodes in a singly employed apparatus as referred to in connection with Figure 3.

Phosphatic feed material containing silica is conveyed by line 142 to source of infrared waves 143. After treatment with the source of infrared Waves 143 for between about 1 minute and about 2 minutes, and power density of 4.7 to 6.0 watts per square inch, the treated feed material is contacted with donor element 144 as indicated by line 143a. The treated contacted feed material is then deposited in electrostatic separator 145 as indi cated by line 1440. As shown by

lines

146, 147, 148, header line 149, and 150, a final silica tail 151 is obtained from the upper portion of the apparatus. As indicated by lines 206 through 213 inclusive and header line 214, a rougher concentrate fraction 152 is also obtained. Below that point on the apparatus from which the final tail is collected, a middling fraction is also obtained as indicated by

lines

153, 154, 155, 156, and 157. This fraction is collected by header line 158. The rougher concentrate 152 is subjected to an electrostatic separator 197, as indicated by line 1520, from which is obtained a phosphate concentrate fraction 200 and a silica tailing fraction 199. The concentrate fraction 200 is conveyed by line 201 to a third electrostatic separator 202. From this separator 202 a final phosphate concentrate 203 and a silica tailing fraction 204 are obtained as indiacted by 202a and 205 respectively. The latter is recycled to rougher phosphate concentrate 152 by line 205.

If valves 160, 138, 161, and 159a are open and the remaining valves in the entire system closed, the tails 199 will be recycled by line 198 into line 158 where the tails and middlings will be combined and the resultant mixture conducted by line 159 to feed line 142 and then to source of infrared waves 143, valve 160a being closed. Alternatively, the mixture of tails and middlings may be conveyed into feed line 161:: by closing valve 159a and opening valve 160a. This procedure may be followed if an economical separation can be obtained without further treatment with infrared waves and further contacting with a donor element.

It is sometimes necessary for economic separation to again expose to infrared waves and recontact both the tail 199 and the middling fractions and deposit the mixture in the electrostatic separator below that section from which the final tail 151 was removed. This may be accomplished by first closing valves 160, 161, and 138,

valves

174, 175, and 169 being opened. The tailing is allowed to enter source of infrared Waves 172 via

lines

198, 162, 163, and 164. in the meantime, the middlings which have been collected from

lines

153, 154, 155, 156, and 157 by line 158 are conveyed by line 176 through opened valve 169 to line 162 where the tail and middling are combined and sent to source of infrared waves 172. When the mixture of tailings and middlings have been exposed to a source of infrared waves 172 for between about 1 minute and about 2 minutes, it is conveyed to donor element 173 by line 165. After being contacted with the donor element 173, the mixture is conveyed by line 167 through

open valves

175, 168, and 170 and deposited by either line 171 or by any of

lines

185, 186, 187, or 188 in the electrostatic apparatus. If it is desired to deposit this mixture in the electrostatic apparatus by line 171, then valves 181, 182, 183, and 184 will be closed and valves 168 and 170 opened. If it is desired to deposit the mixture of middling and tailing in the electrostatic apparatus by, for example, line 187; then valve 168 will be closed, and valve 182 on line 187 will be opened. The other valves not referred to will remain closed. However, any of

lines

177, 178, and 179 or 180 may be employed to deposit the mixture in the electrostatic apparatus at the desired level.

It is sometimes possible to obtain an economical separation by depositing a mixture of tails and middling fractions in the electrostatic apparatus without retreating or recontacting and at a point on the electrostatic separator below that section from which the final tails are removed. This may be accomplished by closing

valves

174, 169, and 175 thus isolating source of infrared wave 172 and donor element 173. Then with valve 160 and any of

valves

189, 191, 193, or 195 on

lines

190, 192, 194, or 196 respectively open, tailing fraction 199 will be conveyed by line 158 to the middling section of separator 145 and conveyed through together, for example, open valve 193 on line 194 to line 187 by which means it is deposited in the electrostatic apparatus.

From this flow sheet it is obvious that other alternatives exist. Thus tail 199 may be again treated and recontacted without commingling with the circulating middling fraction except when placed in the separator. This is accomplished by closing

valves

160, 169, and 138, thus isolating the middling section. The middlings are permitted to circulate by one of several methods, for example, by opening valve 189 and permitting the middling in header line 158 which has collected middling from draw-off

lines

157, 156, 155, 154, and 153 to be conveyed through line 190 to line 185 and deposited thereby in the electrostatic apparatus 145.

Tailing fraction 199, in the meantime, has been conveyed as previously described to source of infrared waves 172 and contacted with donor element 173, etc. The infrared treated contacted tails are then conveyed by line 167 through opened valves 175 and 168 to line 171, valve being open, by which means it is deposited in the electrostatic apparatus.

The following example is given to illustrate the principle of the instant process. It was not run on a closed circuit. Application of the principles of the instant novel process to a closed circuit have been previously illustrated by the aforedescribed flow sheets.

Example About 1,000 grams of unreagentized 14+325 mesh Florida pebble phosphate ore of about 58% bone phosphate of lime (B. P. L.) was placed on a grounded vibrating feeder of galvanized iron. A 1,000 watt, 5 inch, infrared lamp equipped with a reflector was placed approximately two inches above the ore allowing about 56 square inches of feed to be exposed to infrared waves at any one time. From the feeder the treated material was passed almost immediately through an electrostatic field created by eight pairs of vertically arranged electrodes having smooth, convex surfaces opposed. The electrodes were kept at a field gradient of approximately 10,000 practical volts per inch. After 1 pass of this feed material without further infrared treatment through the electrostatic fields, the results indicated in Table A were obtained. This example was run batchwise and not as a closed circuit.

1 1,000 grams of -14+325 mesh phosphate teed (Florida apatite).

This example clearly illustrates one method of employing the principles of the instant novel process and shows the results obtained on an open circuit.

Having fully described this invention, What is desired to be secured by Letters Patent is:

1. A process for concentrating silica-containing phosphatic ore, which comprises comminuting said ore sufficiently to substantially liberate the phosphatic component from the included silica gangue, drying said comminuted ore, subjecting said substantially dry ore to exposure of infrared waves having a power density of between about 4.7 and about 6.0 watts per square inch for a period of. between about twenty seconds and about fifteen minutes, contacting said ore while thus capable of taking up differentially additional free electrons with a donor element, and subjecting said contacted ore as free-falling bodies r 13 to an electrostatic field, thereby separating phosphatic mineral from silica-containing gangue material.

2. A process according to claim 1, wherein the donor element employed comprises essentiallycarbon.

3. A process according to claim 1, wherein the donor element employed comprisesessentially zinc.

4. A process according to claim 1, wherein the donor element employed comprises essentially brass.

5. A process for concentrating silica-containing phosphatic ore, which comprises comminuting said ore sufiiciently to substantially liberate the phosphatic components from the included silica gangue, sizing said comminuted ore into coarse and fine fractions, subjecting the coarse fraction to a source of infrared waves having a power density of between about 4.7 and about 6.0 watts per square inch for a period of between about twenty seconds and about fifteen minutes, contacting said coarse fraction while thus capable of taking up differentially additional free electrons with a source of electrons, subjecting said contacted coarse fraction while in said state as freefalling bodies to an electrostatic field, and segregating individually at least a phosphatic fraction and a silica tailing fraction.

6. A process for concentrating silica-containing phosphatic ore, which comprises comminuting said ore sufliciently to substantially liberate the phosphatic components from the included gangue, drying said comminuted ore, sizing said substantially dry comminuted ore into a l4+325 mesh size phosphatic fraction and 325 mesh size phosphatic fraction, subjecting the coarse fraction to a source of infrared waves having a power density of between about 4.7 and about 6.0 watts per square inch for a period of between about twenty seconds and about fifteen minutes, contacting said coarse fraction while thus capable of taking up differentially additional free electrons with a donor element, subjecting said contacted coarse fraction as free-falling bodies to an electrostatic field, and segregating at least a phosphatic fraction and a tailing fraction.

7. A process according to claim 6, wherein the donor element employed comprises essentially carbon.

8. A process according to claim 6, wherein the donor element employed comprises essentially zinc.

9. A process according to claim 8, wherein the donor element employed comprises essentially brass.

10. A process for concentrating phosphatic ore, which comprises comminuting Florida pebble phosphatic ore to at least a l4 mesh, substantially drying said comminuted ore, separating said dry ore into a coarse 14+325 mesh size phosphatic fraction and a fine 325 mesh size phosphatic fraction, subjecting the coarse fraction to exposure to infrared waves having a power density of between about 4.7 and about 6.0 watts per square inch for a period of between about twenty seconds and about fifteen minutes, contacting said coarse fraction while thus capable of taking up differentially additional free electrons with a donor element, subjecting said contacted fraction as free-falling bodies to an electrostatic field, collecting individually a phosphatic fraction, a silica-containing middling fraction, and a silica-containing tailing fraction, continuously resubjecting said middling fraction to the source of infrared waves, continuously recontacting said middling fraction while thus capable of taking up differentially additional free electrons with a donor element, and continuously subjecting said middling fraction as freefaliing bodies to an electrostatic field; obtaining continuously therefrom a phosphate concentrate and combining the same with the initially obtained phosphatic fraction; subjecting the tailing fraction initially obtained to a source of infrared waves having a power density of between about 4.7 and about 6.0 watts per square inch for a period of between about twenty seconds and about fifteen minutes, subjecting said tailing fraction as free-falling bodies to an electrostatic field, subjecting the phosphate tailing concentrate obtained therefrom to a source of infrared waves having a 'power density of between about 4.7 and about 6.0 watts per ,square inch for a period of between about twenty seconds and about fifteen minutes, contacting said phosphate tailing concentrate while thus capable of taking up differentially additional free electrons with a donor element, subjecting said contacted concentrate as free-falling bodies to an electrostatic field, segregating aphosphatic fraction and a tailing fraction, and combining said phosphatic fraction with the initially obtained phosphatic fraction.

11. A process according to claim 10, wherein the donor element employed comprises essentially carbon.

12. A process according to claim 10, wherein the donor element employed comprises essentially zinc.

13. A process according to claim 10, wherein the donor element employed comprises essentially brass.

14. In a continuous electrostatic process for the beneficiation of Florida pebble phosphatic ore, wherein the comminuted, substantially dry, unreagentized feed material is subjected to an electrostatic field, by which is obtained a phosphate concentrate, a silica-containing middling fraction, and a silica-containing tailing fraction; the improvements comprising continuously subjecting said middling fraction to exposure to infrared waves having a power density of between about 47 and about 6.0 watts per square inch for a period of between about twenty seconds and about fifteen minutes, contacting said middling fraction while thus capable of taking up differentially additional free electrons with a grounded electrical conductor, separately and continuously subjecting said tailing fraction to exposure to infrared Waves having a power density of between about 4.7 and about 6.0 watts per square inch for a period of between about twenty seconds and about fifteen minutes, then separately contacting said tailing fraction while thus capable of taking up differentially additional free electrons with a grounded electrical conductor; effecting separate electrostatic separations by passing the hot contacted tailing fraction and the hot contacted middling fraction as freefalling bodies through an electrostatic field, and combining the phosphate concentrate fractions so produced with the initially obtained phosphate concentrate fraction.

15. In a continuous electrostatic process for the beneficiation of phosphatic ore, wherein the comminuted, substantially dry, unreagentized feed material is contacted with a grounded electrical conductor and subjected as free-falling bodies to an electrostatic field created by means of at least two pairs of vertically arranged, smooth, curved-surface electrodes by which is obtained a phosphate concentrate, a silica-containing middling fraction, and a silica-containing tailing fraction; the improvementscomprising subjecting the feed material to a source of infrared waves having a power density of between about 4.7 and about 6.0 watts per square inch for a period of between about twenty seconds and about fifteen minutes, contacting said feed material within about fifteen seconds and about one minute after the aforesaid treatment with infrared waves with the aforesaid grounded electrical conductor, continuously recycling and resubjecting the middling fraction to a source of infrared waves having a power density of between about 4.7 and about 6.0 watts per square inch for a period of between about twenty seconds and about fifteen minutes, contacting said middling fraction with a grounded electrical conductor, continuously recycling and resubjecting said tailing fraction to a source of infrared Waves having a power density of between about 4.7 and about 6.0 watts per square inch for a period of between about twenty seconds and about fifteen minutes, contacting said tailing fraction with a grounded electrical conductor, effecting separate electrostatic separations by passing the contacted tailing fraction and the contacted middling fraction as free-falling bodies through an electrostatic field, and combining the phosphate concentrate fractions 15 16 so produced with the initially obtained phosphate con- 1,679,740 Overstrom Apr. 7, 1928 centrate. 2,197,865 Johnson Apr. 23, 1940 2,419,876 Birdseye Apr. 29, 1947 References Cited in the file Of this patent OTHER UNITED STATES PATENTS 5 Electrostatic Separation of Solids," by F. Fraas and 653,343 Gates July 10, 1900 O. C. Ralston. Industrial and Engineering Chemistry,

924,032. Blake June 8, 1909 V01. 32, N0. 5, May 1940, pages 600 to 604.

Claims

1. A PROCESS FOR CONCENTRATING SILICA-CONTAINING PHOSPHATIC ORE, WHICH COMPRISES COMMINUTING SAID ORE SUFFICIENTLY TO SUBSTANTIALLY LIBERATE THE PHOSPHASTIC COMPONENT FROM THE INCLUDED SILICA GANGUE, DRYING SAID COMMINUTED ORE, SUBJECTING SAID SUBSTANTIALLY DRY ORE TO EXPOSURE OF INFRARED WAVES HAVING A POWER DENSITY OF BETWEEN ABOUT 4.7 AND ABOUT 6.0 WATTS PER SQUARE INCH FOR A PERIOD OF BETWEEN ABOUT TWENTY SECONDS AND ABOUT FIFTEEN MINUTES, CONTACTING SAID ORE WHILE THUS CAPABLE OF TAKING UP DIFFERENTIALLY ADDITIONAL FREE ELECTRONS WITH A DONOR ELEMENT, AND SUBJECTING SAID CONTACTED ORE AS FREE-FALLING BODIES TO AN ELECTROSTATIC FIELD, THEREBY SEPARATING PHOSPHATIC MINERAL FROM SILICIA-CONTAINING GANGUE MATERIAL.