US2815859A

US2815859A - Concentration of phosphatic material

Info

Publication number: US2815859A
Application number: US462470A
Authority: US
Inventors: Clinton A Hollingsworth
Original assignee: SMITH DOUGLASS CO Inc
Current assignee: SMITH DOUGLASS CO Inc
Priority date: 1954-10-15
Filing date: 1954-10-15
Publication date: 1957-12-10
Anticipated expiration: 1974-12-10

Description

Dec. .10, 1957 C. A. HOLLINGSWORTH CONCENTRATION OF PHOSPHATIC MATERIAL Filed 001:. 15, 1954 Conc. Bin- FIG. I

Wusher Undersnze Waste l6 Froth roth Frofluv Tails to Wade 0 23%] q INVENTOR CLINTON A. HOLLINGSWORTH B @mamlfinnmgmpx ld ATTORNEYS CONCENTRATION OF PHOSPHATIC MATERIAL Clinton Holiingsworth, Lakeland, Fla, assignor to Smtth DougiaSs-Company, Incorporated, Nortolk, Va., 21 corporationoftvirginia' Application Qctober 15, 1954,.S1erialNo. 462,470

8 Claims. cr. 209mm- This invention relates to the froth. flotation proce s for concentrating .phosphatic material and more particularly to the separation of silica from phosphaticmaterial by froth flotation, and has for its object. the provision of an improved methodof froth flotation .for separating silica from phosphatic. material.

The main .phosphatic. constituent. of Florida Phosphate res Patent rock, as well-as most native. phosphate .mineralscontaining fluorine, is-fluorapatite (usually referred to as apatite) commonly believed tobea combination of trlcalc um phosphate and calcium fluoride (.Ca F (PQ The grade of the rock .is determined by its tricalciumphos- .phate content, which isusually. designated in the industry as bone phosphate of lime (BPL). Silicais one ofthe chief valueless or gangneconstitnentsot phosphate rock and in the phosphate industry. is commonly determined and reported as insolub1es.(insol.-). For-manypurposes,

it is presently the common. practice throughout the Florida phosphate field to double-floatthe undersi-ze fromnthe washing plant. That is, after concentration ott-heraw rock bywashing andthelike, the undersizeor finesfrom the washer is further concentrated in two stages-of froth flotation. In the first stage,.the .deslimedflo-tationteed is conditioned with caustic soda, fuel oiland a iattyacid such as tall oil, and the conditioned feed is su'bjectedto froth flotation where ,a phosphate product (commonly called a rougher concentrate) is floated and the linderflow (largely silica) is discarded to waste. Thezrougher concentrate normally contains v8 to of silica, and hence its phosphate grade (BPLlis too low to be of much practical value. Accordingly, .the rougher concentrate is de-oiled by scrubbing with sulphuric .acid

followed by desliming. The de-oiled'product (commonly called the amine cell feed) is subjected to .the second stage of froth flotation in the presence of a strong cationic collecting agent, such as an amine, where silica is floated and discarded to waste. The underflow of the second stage of flotation is a high grade phosphate product of low silica content, and is transferred'to storage. In the phosphate field, the phosphate product. is called the concentrate regardless of whether it is the floated product or the underflow, and hence the silica float is called tailings or tails.

Phosphate ores are friable and tend toproducedeleterious amounts of slime during flotation treatment, especially in machines of the agitation type. .Slime has been found to be particularly objectionable in the amine circuit flotation, since the presence of slime necessitates an increased amount of the relatively costly amine reagent with an attendant loss of phosphatic material in the silicatailings in order to obtain the desired low silica content in the phosphate concentrate. In theaforementioned twostage practice, considerable slimes are produced in the .the pulp column, through a porous medium'at the bottom Ice scrubbing of the rougher phosphate concentrate with sulphuric acid, andjhence the de-oiled product is deslimed preparatory to the second stage of froth flotation. But even then, the types, of flotation apparatus presently used in the Florida phosphate field produce objectionable amounts of slime during the flotation treatment due to the violent agitating. action. of the impeller.

In my copending application for Letters Patent of the United States .Ser. No. 452,177, filed AugustfZS, 1954 (Patent ,No..2,.7;5'.8,7,14 .I have described a methodof pneumatic-hydraulictflotation peculiarly adapted for phosphate minerals because of its highly effective aeration without. creatingcslime in. objectionable amount. I have .fiou-n'dthat whenflotation 'is carried out in accordancewith-this method, the firststageiof the present common flotation practice .(in-whichphosphate is floated.) can be replaced ,by arougher froth flotation step in which silica is floated, .therebyeliminating .the present tie-oiling treatment of the tougher- ,phosphate concentrate. The

.presentinvention makesuse of this discovery, and in its broad .aspect involves arr-(improved method of separating silica, as ,a.fl.oat,-.from-phosphaticmaterial by froth .in-the presence of .a st-rong cationic collecting agentand silicais floated'in each. Each step .of flot ation iscarr'ied ou i fla rela ve y e p olunin -.of pu p. an gthedow iward velocity of pulp flow in the columniis. substantially decreased and thecreationof slimesisth'ereby minimized byjintroducing water .ina fine state of .subd'itiisionfmto thereof; in accordance with the invcntionof ,my aforementioned ,appliQafiQIL. .In addition .to ,providingitwo separateand similar steps of froth. flotation,-in which different cationicjlotationagentsmay housed if desired, the method of t the invention contemplates particlegsifzing of the rougher phosphate concentrateintoja coa'rseieed and fine feedfor the second stepot froth flotation, thereby permitting, if desired or necessary reroptimum results, the use of different cationic-flotation agentswwith the eeds of different particlesizc.

The foregoing andothernoyel.features .of theinvention Wi b better understood from the followingdescription t aken'in conjunction'with the accompanyingtdrawn in which:

Fig. 1.,i s a .diagrammaticflow sheet embodying the principles ,otthe, invention, and 1 Fig. .2,,.i s".a. side. elevation,..mostly in: section, of the pneumatic-hydraulic flotation cellor apparatusdescribed in my aforementioned application and especially adapted for practicingthe present invention.

Referring-to thefflows'heetot Fig. 1,. the feedtothe flotation plantis the undersizeor fines from the phosphatelwasherplant having a particle:size'norrnallyminus 14.m.esh, i. e. substantiallyall through a.14 mesh standard Tyler screen. The following is..a typical screen analysis, of the flotation. plantfeed orheads:

Thus, .theflotation heads priced is predominatelyfi. .e.

.morethanhalf) .minus .20rmeshand on- 65 mesh. The

(BPL). The washer undersize is first dewatered in a large hydroseparator 5, the overflow of which is discharged to waste, and the underflow pulp is pumped to storage bins 6. From the storage bins, the pulp is pumped, as required, to a surge bin 7, the overflow of which goes to a relatively small hydroseparator 8. The underflow of the surge bin goes to a rake classifier 9, the overflow of which goes to the hydroseparator 8. The rake product is delivered to a deslimer 10, the overflow of which is returned to the large hydroseparator 5. The settled underflow of the hydroseparator 8 is pumped to the deslimer 10.

The deslimer pulp is delivered to two series (11 and 12) of rougher flotation cells, arranged in tandem, that is the phosphate underflow of the cells 11 is the feed of the cells 12. The silica froths of both cells 11 and 12 are combined and fed to froth-cleaning flotation cells 13. The silica froth (tails) of the cells 13 is discharged to waste, and the underflow of these cells is delivered to a catchall sump or middlings tank 14.

The underflow of the cells 12 (rougher phosphate concentrate) is delivered to a storage sump, from which it is pumped, as required, to particle sizers in which products of two different particle sizes are produced, namely coarse and fine, as feed for the flotation cleaner cells. The following are typical screen analysis of these sized products:

+20 mesh 20 +35 -35 +65 65 +150 150 Coarse teed, percan Fine feed, percent.

Thus, the coarse feed is predominately (i. e. more than half) minus 14 mesh and on 35 mesh, while the fine feed is substantially all minus 35 mesh and predominately minus 65 mesh.

The coarse and fine feeds are delivered to separate rinsers 15 and 16, respectively, in the nature of deslimers. The underflow of the coarse feed rinser 15 is delivered to two series (17 and 18) of flotation cells (cleaners) arranged in tandem. The underflow of the fine feed rinser 16 is delivered to two series (19 and 20) of flotation cells (cleaners) arranged in tandem. The underflows of the cells 18 and 20 (final cleaner concentrate) are combined and deliverd to a dewatering screw classifier 21, and the dewatered phosphate concentrate is discharged to storage bins. The screw classifier overflow is delivered to the middlings tank 14.

The silica froths of the

cells

17 and 18 are combined and retreated in a froth cleaning cell 22, while the silica froths of the

cells

19 and 20 are combined and retreated in a froth cleaning cell 23. The silica froths (tails) of the

cells

22 and 23 are discharged to waste, and the underflow of these cells is conveyed to the middlings tank 14. Middlings from the tank 14 are pumped to the storage bins 6 for the dewatered washer undersize at the head of the flotation plant.

As a general indication of the distribution of the flotation cells in the plant, where there are 6 rougher cells in each series 11 and 12, 4 froth-cleaning cells 13 (of approximately the same size) are provided. In each of the series of cleaning cells (1718 and 19-20) there are 2 cells, and 1 froth cleaning cell (22 and 23) is provided for each series of cleaning cells.

The pneumatic hydraulic flotation apparatus or cell illustrated in Fig. 2 of the drawings is built in separate units or sections which are vertically assembled and secured together to form the complete apparatus. The apparatus illustrated in the drawings is built up of a top unit A, an intermediate unit B and a bottom unit C. The top and bottom units may advantageously be about 2 feet in depth and the depth of the intermediate unit (or units) may then advantageously be from 2 to 3 feet. As many intermediate units B may be assembled in the complete apparatus as required to give the desired over-all depth of pulp column. Usually the assembled cell will accommodate a pulp column of at least six feet in depth. Each unit is provided with at least one group of horizontally disposed air-diffusers 25, so that when the units are assembled the various groups of air-diffusers are superposed and vertically spaced. The air-diffusers are of such construction that air is uniformly introduced into the pulp column in a very finely disseminated state over the entire cross-sectional area of the pulp column.

Each unit comprises a metal frame 26 to which are bolted or otherwise appropriately secured side and

end members

27 and 28, respectively. The side and end members may advantageously be transparent thermoplastic resin plates, such as Rohm and Haas Companys Plexiglas, through which the action of the air-diffusers and the condition of the pulp column can readily be observed. Where the side and end members are of metal or other opaque material, the side members are preferably provided with transparent windows at levels opposite the air-diffusers, as indicated by the dotted lines 27'. The juxtaposed ends of the frames 26 of adjacent units have peripheral flanges 29 for bolting or otherwise appropriately securing the units together.

The bottom unit C has a hydraulic compartment 30' at its lower end which communicates with the main upper portion of the unit through a porous medium 31. While the porous medium is shown in the drawings as consisting of a punched metal plate covered with a bed of lead shot about one inch in depth, the medium may consist of porous tile, punched metal plate, metal screen, heavy canvas and the like. The hydraulic compartment 30 is connected to a suitable source of water through a pipe 32 having a suitable control valve (not shown).

One end wall 23 of the bottom unit C has a lower pulp discharge opening 33 and an upper pulp discharge opening 34 communicating with a common pulp discharge chute 35. The discharge opening 33 is just above the porous medium 31, while the discharge opening 34 is near the top of the unit, and the horizontally disposed air-diffusers are about midway between the two openings with one diffuser positioned in the discharge chute 35. The chute 35 extends across the width of the end wall 28, and is provided at its bottom with a pulp discharge pipe 36. The rate at which water is introduced into the hydraulic compartment 30 is so proportioned with respect to the

openings

33 and 34 and the pipe 36 as to be substantially the same as the rate at which water is discharged in the mineral pulp through the pipe 36.

The top unit A has a feed hopper 37 at the top of one end wall and an adjustable froth overflow weir 38 at the top of the outwardly flaring opposite end wall 28. A perforated plate 39 is horizontally positioned a short distance (normally about 2 inches) below the level of the Weir 38, and extends from the inside bottom of the feed hopper 37 to the first of three vertically disposed (i. e. depending) and horizontally spaced transverse baffles 40. The outward flare of the end wall 23 is such that the top of the unit A is about twice the length of the bottom of the unit, and the horizontally spaced baflles 40 are positioned above the flared end wall. A transverse perforated baflle 4-1 depends from about the center of the horizontal perforated plate 39, with one air-diffuser (nearest the discharge weir 38) on one side of the baflle 41 and the other air-diffusers of unit A on the outer, or feed hopper, side of the baffle 41.

The intermediate unit B is provided with a vertical chamber or channel 42 along that end wall adjacent the flared end wall 28' of the top unit. The channel 42 communicates at its top with the top unit A and at its bottom with a similar but shorter channel 43 at the upper end of the bottom unit C. The channel 43 communicates through an opening 44 with the unit C at a level slightly above that of the group of air-dilfusers of the unit, and the channel 42 communicates through an opening 45 with the ass-sees unit B at a level slightly above that of the group of airdiifusers in the"unit The channels 42-and" 43*areof the same width as their respective units, and are provided with transverse dampers 46 and 47, respectively, forregulating the pulp circulation.- The dampers are adapted to be adjusted by a removable-wrench; shownin dotted lines.

Each of theflotation cellsin the flowsheet of Fig. l is of the type shown in Fig-2 In each the feed-of phosphatic material, inthe fer-m of an a'que'o'us mineralpulp, is delivered through the hopper- 37 into a relatively deep column or body of pulp undergoing froth flotation treatment. The flotation reagent (orre'a gentsD may be mixed with thepulp before or as it is-introdu'ced into the'hoppcr, or part or all of the reagent maybe-introduced at'one or or more lower levels in the:pulp c'olumn.- Where the pulp has been well deslimed, itis preferable to add the reagent with the feed but whenth'efeed c'ontaihsany slime, some or all of the reagent shouldbe introduc'ed 'at one ormore lower levels in. the pulp columnc Aeration takes place at the three (or more) differentlevels atwhich the groups of air-diffusers are positioned, and is extensive in sectional area and gentle and uniform:..ini character. Each group of air-diffusers discharges a denseem'ass oflextremely fine, uniform. and gentle streams of air into the:- pulp column over the: entire cross-sectional'area thereof.

Bubbles from the rising air streams attach themselves to the silicaparticles: selectively conditioned. by the cationic. flotation agent to float, and carry such particles into a layer or column of froth overlying the surface of the pulp body. The perforatedplate39= is. at approximately the liquid level of the pulp column,. and serves'to minimize surface turbulence so that. the overlying layer of froth is relatively quiescent. Asthe'froth passes longitudinally beyond the active influence of the top air-diffusers toward the overflow weir 3'3, it moves over a' relative quiescent body of pulp (adjacent and intdirect'communication with the pulp column") where opportunity is afforded phosphate particles to drop out-of. the froth layer. Thus in effect there areinthe'top unit A an active aerated zone and an adjacent quiescent settling zone. The single air-diffuser in the latter zone' provides aeration; for returning to the froth layer any silica particles in the-immediate vicinity of the boundary between the two zones. The depending transverse battles 40-and 41 diver3t descending phosphate particles away from'theactive aerated-zone of the pulp column and generally inxthe direction of tl e open top of the channel 42. The battle 41: extends more deeply into the pulp column than do-the baflles' 4h, because of its proximity to the air-diffusers. The depending baffles 40 and 41 further tend to minimize circulation of the pulp body directly below the froth layer, and thus induce a quiescence in the pulp body' that is beneficial in guiding the phosphate particles (dropped from the froth layer) toward the open end of the channel 42..

There is a natural downwardcirculation of pulp in the channels 42 and 43, due to the upward impetus that is given the pulp column in the units B and C by the rising air streams from the difiusers 25 in those units. By ad-- justment of the dampers 46 and 47, any desired portion. of the downwardly circulating pulp can be diverted from the channels 42 and 43 through the openings 45' and 44 into the units B and C, respectively. Thus, the channels provide means for short-circuiting phosphate particles to a lower level of the pulp column, and for returning any silica particles to the pulp column, at levels of active aeration. In this manner, as well as in the characteristic arrangement of the air difl'users at several different levels in a relatively deep pulp column, silica particles are given several opportunities of attaching themselves to rising air bubbles thereby minimizing the amount of such particles included in the underflow.

The introduction of a controlled amount of Water from the hydraulic compartment 30 into the lower portion of the pulp column is a characteristic feature of the method,

T he water -so introduced into the pul'p column iscon veniently called the hydraulic water. It promotes=circulanon within the pulpcolumnandprolongs the period of suspension of silicaparticles-and gives them better, longer and more frequent opportunity forattachment to rising air bubbles; The hydraulicwater alsoprevents sandingtlp ofthe cell; since the pulp density of the under-flow-dischar-gods lowered by thewater entering the pulp-column in the region of the und'erflow discharge. The pulp density of the feedto-the' sells 1 1,174 and -l9-i's' generally within the range of- 30 to-7 5.% solids andishigher than the pulp density of-thei-r underflow discharge, which is generally within the range of20 to-40% solids. Generally speaking, the average pulp densitywithin the cells is roughly between 15 and 35% solids. From 25 to 50% of thewater of thepulp column inthese cells is introduced with the feed, and the remaining percent (that is from to 50% is introduced as hydraulic water. The volume of hydraulic water introduced into the unit C (per unit oftime) is substantially equivalent tothe volume of water in the underflowi discharge from-the pipe 36 in thesame time period;

As phosphate particles descend into the unit C, some will be-carried by the pulp stream through the upper openin'g 3'4. into thedischarge chute 35. The simple airdiffuser near the top of the chute offers a further and last: opportunity for any silica-particles to be carried upward by attachment to rising air bubbles. Similarly, ,the remainder ofthelowerrnostair-diffusers in the unit C promote-final cleaning of the pulp stream of silica particlesbefore' discharge of the: pulpthrough the bottom opening 33 intothe ch'ute-35c Withdrawing with: the; underflow discharge of substantially the same volume: of water as introduced into the unit C through it's porous bottom decreases the downward 'velocity of pulp flow and thus provides and insures a relatively quiescent column of pulp above the unit C. This relatively quiescent column of" pulp provides better and: longer contact of silica particles with. air particles, and thusip'romotesseparation of silica. and phosphate particles andiminimizes slime production. In this quiescent column of pulp there are only-gentle circulatory motions resulting from the effects of the rising air streams and the chaunel'stll and 43, and hence little, if any, tendency to create slime.

Normally, the froth column or bed will be from 1 to 5 inches in depth. The depth of froth depends to a large extent upon. the type of flotation reagents employed, some yielding: a voluminous froth while others give very little froth. The depth of froth can be controlled to some extent by the use of different frothingagents, surfaceactive agents, depressants etc. The perforated frothsubduing plate 39 is normally about 2. inches below the level of the adjustable weir 33. The pulp (that is liquid) level may be raised or lowered, in relation to the perforated plate 29, by adjusting the number of filler-bars that make up the adjustable weir 28. Thus, the pulp level should be lowered for a shallow froth bed and raised for a deep froth bed.

It is presently the common practice in the Florida phosphate field to size the raw flotation feed (washer fines) in order toprovide (in the second stage of flotation) a sized amine cell feed, since larger particles of silica do not float with the averagequantity of reagents used, and an increase in the quantity of reagent required to float such larger silica particles results in floating large amounts of phosphate which are lost in the silica tails. In accordance with the present invention, the feed to the first bank of rougher flotation cells 11 is unsized washer fines, and a large proportion of the silica gangue is'removed in this first step of flotation and before the rougher phosphate concentrate is sized preparatory to the second, step of flotation. By dividing the rougher phosphate concentrate intoproductsof two different sizes, different amounts of reagent, or differentreagents, can be used with the 7 coarse feed and the fine feed to give the optimum result with each.

I have found that all silica does not appear to respond in the same Way to flotation treatment. For example, one type of reagent floats part of the silica best while another type of reagent floats the remaining part of the silica best. By floating in two steps of silica flotation, advantage can be taken of this phenomenon. Thus, a different type of cationic collector may be used in the second or cleaner step of the invention than used in the first or rougher step, or perhaps diflerent amounts of the same cationic collector in the two steps of flotation Will give the optimum results. In the present preferred practice of the invention, the first step of flotation of unsized feed (in cells 11, 12 and 13) is carried out with the reaction product of sulphuric acid and a mixture of a fatty amine and liquid hydrocarbon, such as described and claimed in the copending patent application of Jordan L. Wester and myself, Ser. No. 443,692, filed July 15, 1954. Typical of such a modified amine reagent is the reaction product of 4.76% (by weight) of sulphuric acid and a mixture of 19.05% of Armour and Co.s Armoflote S (consisting of about 70% free fatty amine and about 30% nitrile) and 76.19% of crude turpentine. The second step of flotation of sized feed is then carried out with an unmodified amine (i. e. one not reacted upon by sulphuric acid), such as Armoflote S or other suitable fatty amine flotation reagent or other type of cationic collecting flotation agent, usually in conjunction with a suitable frothing agent such as pine oil, crude turpentine or one of the so-called alcohol frothers (e. g. di-isobutyl carbinol). Different quantities of the same unmodified amine, or different cationic collectors, may be used with the sized coarse feed and fine feed, respectively, to give the optimum result with each. While I noW prefer cat-ionic collectors of the amine type, other types of cationic collectors are now commercially available for floating silica and may be used in practicing the invention.

The following table illustrates the broad ranges of BPL and insol. in the principal products of the method, and also gives the more typical BPL and insol. contents generally obtained in plant practice.

Product Approx. Approx.

BPL lnsol.

Percent Percent Initial flotation feed 20-50 73- Generally (around) 35 55 Rougher phosphate con 55-71 30-8 enerally (around) 65 16 Silica float of cells 13 2-10 96-87 Generally (around)... 6 92 Coarse feed to c ls 17 55-71 30-8 Generally (around) 65 15 Fine feed to cells 19....... 55-71 30-8 Generally (around)... 65 15 Coarse phosphate conc. (cell 18). 74-78 6-3 Generally (around) 76 4 Fine phosphate cone. (cell 20) 74-80 6-2 Generally (around) 77 3 Coarse tails from cell 22 -20 93-73 G enerally (around) 88 Fine tails from cell 25... 5-20 93-73 Generally (around) 10 88 In the first rougher step of the invention, the BPL recovery is in excess of 90%, and usually 95% and higher. In the second cleaner step, the BPL recovery is usually at least 95% and frequently as high as 98-99%. The overall BPL recovery of the complete method, that is the amount of phosphate in the initial unsized washer undersize that is recovered in the final cleaner concentrate, is usually at least 85%, and frequently 90 to 95%. The slime loss in the method of the invention is for all practical purposes negligible, contrasted with a slime loss of about 10% in the heretofore common double float practice of the Florida phosphate field. The lost slimes have a relatively high BPL content, and consequently the overall BPL recovery of the flotation plant in the double float practice seldom exceeds 80%. The slimes are delivered 8 to the pond, along with the silica tails, and no attempt is made to recover the phosphate in the bed of settled solids.

I claim:

1. The method of separating silica from an unsized silica-containing phosphate product which comprises subjecting the deslimed and unsized phosphate product to a first rougher step of pneumatic froth flotation in the presence of a cationic collecting flotation agent and in the course of which a silica froth and a rougher phosphate concentrate are obtained, subjecting said rougher phosphate concentrate to a sizing treatment to obtain a product of relatively coarse particle size and a product of relatively fine particle size, and subjecting each of said sized products to separate cleaner steps of pneumatic froth flotation in the presence of a cationic collecting flotation agent, each cleaner step of pneumatic froth flotation being conducted in the presence of a different cationic collecting flotation agent than that present in the preceding rougher step of pneumatic froth flotation.

2. The method of claim 1 in which the rougher step of pneumatic froth flotation is conducted in the presence of the reaction product of sulphuric acid and a mixture of a fatty amine with a liquid hydrocarbon and the cleaner step of pneumatic froth flotation is conducted in the presence of a fatty amine flotation agent unreacted upon by sulphuric acid.

3. The method according to claim 1 in which one of said sized products is subjected to a cleaner step of pneumatic froth flotation in the presence of the same cationic collecting flotation agent as that present in the preceding rougher step of pneumatic froth flotation, and in which the other of said sized products is subjected to a cleaner step of pneumatic froth flotation conducted in the presence of a different cationic collecting flotation agent than that present in the preceding rougher step of pneumatic froth flotation.

4. The method of separating silica from an unsized phosphate product containing at least two types of silica which comprises subjecting the deslimed and unsized phosphate product to a first rougher step of pneumatic froth flotation in the presence of a cationic collecting flotation agent and in the course of which a silica froth and a rougher phosphate concentrate are obtained, subjecting said rougher concentrate to a sizing treatment to obtain a product of relatively coarse particle size and a product of relatively fine particle size, and subjecting each of said sized products to separate cleaner steps of pneumatic froth flotation in the presence of a cationic collecting agent formulated to collect the type of silica predominating in each of said sized products.

5. The method of separating silica from an unsized phosphate product containing at least two types of silica which comprises subjecting the deslimed and unsized phosphate product to a first rougher step of pneumatic froth flotation in the presence of a cationic collecting flotation agent and in the course of which a silica froth and a rougher phosphate concentrate are obtained, subjecting said rougher concentrate to a sizing treatment to obtain a product of relatively coarse particle size predominately minus 14 mesh and on 35 mesh and a product of relatively fine particle size substantially all minus 35 mesh and predominately minus 65 mesh, and subjecting each of said sized products to separate cleaner steps of pneumatic froth flotation in the presence of a cationic collecting agent formulated to collect the type of silica predominating in each of said sized products.

6. The method of separating silica from a mixture of phosphatic material and silica which comprises subjecting an aqueous pulp of the deslimed and unsized mixture to a first rougher step of pneumatic froth flotation in the presence of a cationic collecting flotation agent and in the course of which finely disseminated air is introduced into a relatively deep column of the aqueous pulp at a' plurality of superimposed and vertically spaced levels,

removing a silica froth from the top of the pulp column and a rougher discharging phosphate concentrate in the underflow from the bottom of the pulp column, subjecting said rougher phosphate concentrate to a sizing treatment to obtain a product of relatively coarse particle size and a product of relatively fine particle size, and subjecting each of said sized products to separate cleaner steps of pneumatic froth flotation in the presence of a cationic collecting flotation agent formulated to collect the type of silica predominating in each of said sized products.

7. The method of separating silica from a mixture of phosphatic material and silica which comprises subjecting an aqueous pulp of the deslimed and unsized mixture to pneumatic froth flotation in the presence of a cationic collecting flotation agent and in the course of which finely disseminated air is introduced into a relatively deep column of the aqueous pulp at a plurality of superimposed and vertically spaced levels and water is introduced in a fine state of subdivision into the pulp column at the bottom thereof thereby substantially decreasing the downward velocity of the pulp flow, removing a silica froth from the top of the pulp column and discharging a phosphate concentrate in the underflow from the bottom of the pulp column together with the equivalent of most of the water introduced into the bottom of the pulp column, subjecting said phosphate concentrate to a sizing treatment to obtain a product of relatively coarse particle size and a product of relatively fine particle size, and subjecting each of said sized products to separate cleaner steps of pneumatic froth flotation in the presence of a cationic collecting flotation agent formulated to collect the particular type of silica predominating in each of said sized products, said cleaner steps of pneumatic froth flotation being of the same character as the aforesaid rougher step of froth flotation.

8. The method of separating silica from a mixture of phosphatic material and silica which comprises subjecting an aqueous pulp of the deslimed and unsized mixture to pneumatic froth flotation in the presence of a cationic collecting flotation agent and in the course of which finely disseminated air is introduced into a relatively deep column of the aqueous pulp at a plurality of superimposed and vertically spaced levels and water is introduced in a fine state of subdivision into the pulp column at the bottom thereof thereby substantially decreasing the downward velocity of the pulp flow, removing a silica froth from the top of the pulp column and discharging a phosphate concentrate in the underflow from the bottom of the pulp column together with the equivalent of most of the water introduced into the bottom of the pulp column, subjecting said phosphate concentrate to a sizing treatment to obtain a product of relatively coarse particle size predominately minus 14 mesh and on 35 mesh and a product of relatively fine particle size substantially all minus 35 mesh and predominately minus mesh, and subjecting each of said sized products to separate cleaner steps of pneumatic froth flotation in the presence of a cationic collecting flotation agent formulated to collect the particular type of silica predominating in each of said sized products, said cleaner steps of pneumatic froth flotation being of the same character as the aforesaid rougher step of froth flotation.

References Cited in the file of this patent UNITED STATES PATENTS 2,156,245 Mead et al Apr. 25, 1939 2,176,107 Smith Oct. 17, 1939 2,185,224 Ralston Jan. 2, 1940 2,357,419 Mead et a1 Sept. 5, 1944 2,369,311 Mead et al Feb. 13, 1945 OTHER REFERENCES Handbook of Mineral Dressing (Taggart), published by John Wiley and Sons, Incorporated (New York), 1927, pages 12-14 relied on.

Claims

1. THE METHOD OF SEPARATING SILICA FROM AN UNSIZED SILICA-CONTAINING PHOSPHATE PRODUCT WHICH COMPRISES SUBJECTING THE DESLIMED AND UNSIZED PHOSPHATE PRODUCT TO A FIRST ROUGHER STEP OF PNEUMATIC FROTH FLOTATION IN THE PRESENCE OF A CATIONIC COLLECTING FLOTATION AGENT AND THE THE COURSE OF WHICH A SILICA FROTH AND A ROUGHER PHOSPHATE