US3307790A

US3307790A - Flotation method and apparatus

Info

Publication number: US3307790A
Application number: US266555A
Authority: US
Inventors: Morris I Cohn; Roy D Perdue
Original assignee: Mineral Industries Corp of America
Current assignee: Mineral Industries Corp of America
Priority date: 1963-03-20
Filing date: 1963-03-20
Publication date: 1967-03-07
Anticipated expiration: 1984-03-07

Description

March 7, 1967 M. I. COHN ET AL 3,307,790

FLOTATION METHOD AND APPARATUS Filed March 20, 1963 v 3 Sheets-Sheet z RI I R2 I I 39 TAILING CONDITIONING l y MEANS K Q) -Fi) q; 34 TAILING TO ROUGHER FROTH FU HER TREAT- xmE 0R WASTE /Cl ,02 03 04 w R r s Y ER WATER WATER AY SPRAY F G 6 INVENTORS D. PE RDUE I BY RIS I COHN @1352, @zmZhg Wwxzz ATTORNEYS United States Patent 3,307,790 FLOTATION METHOD AND APPARATUS Morris I. Cohn, Needham, and Roy D. Perdue, Tewksbury, Mass, assignors to Mineral Industries Corporation of America, Needham, Mass., a corporation of Massachusetts Filed Mar. 20, 1963, Ser. No. 266,555 19 Claims. (Cl. 241-5) This application is a continuation-in-part of Serial No. 197,813 filed May 17, 1962, now abandoned.

Flotation is the separation of particles from one another in a slurry or pulp by means of selective attachment of air bubbles. The particles raised or floated by the bubbles form a froth which can be removed from the surface of the slurry or pulp.

Flotation is widely utilized in mineral benefication where it is desired to separation one mineral from another. The froth is frequently termed the concentrate in that it carries one or more valuable or useful minerals in a more highly concentrated state than existed in the pulp fed to the flotation apparatus. The fraction of the pulp which does not report to the froth is commonly termed the tailing.

While the most valuable or desired mineral is in some cases directed to the froth or concentrate with the impurities and undesirable mineral components reporting to the tailing, in other cases the valuable or desired mineral reports to the tailing in a beneficiated state and the impurities and undesirable mineral components are directed to the froth. In the latter case the tailing is considered the concentrate. For example, a recent patent, US. No. 2,990,958, describes the concentration in the froth of an undesired impurity leaving a beneficiated clay in the tailing.

Typical apparatus employed in mineral froth flotation is described in Bulletin No. FB8l entitled, Denver Sub A Flotation, published by the Denver Equipment Company of Denver, Colorado. Such apparatus, referred to as a Denver Sub A Flotation Machine, is understood by those versed in flotation technology and this bulletin is incorporated in this application by reference. Flotation machines or cells of alternate design are available, but fundamentally each design is directed to the generation of a froth and a tailing.

The method of selectively removing a given mineral fraction from a pulp of two or more minerals so that the given mineral will collect as. a concentrate in a froth is still an art, extensive and valid scientific literature on the subject notwithstanding.

The method conventionally comprises adding suitable chemical reagents to the pulp either prior to or during the flotation process to aid in accomplishing the desired separation. In order to avoid detail unnecessary to describe the scope of the present invention, it is sufficient to point out that such chemical reagents can perform one or more of the following functions: enhance or promote the tendency of one or more minerals to report to the froth; cooperate with other reagents by activating one or more minerals so that it or they will respond better to the entire reagent system; depress or reduce the tendency of one or more minerals to report to the froth; increase the amount or strength of froth produced by a given flotation apparatus. Thus, by judicious selection of flotation reagents and the amounts of said reagents employed per weight unit of mineral solids fed to the flotation apparatus, an improved separation can be effected. This is all well known.

Every flotation operation has at least two overall objectives: the generation of as pure a concentrate as possible and the highest possible recovery of desired valuable mineral product from the ore charged to the operation.

3,307,790 Patented Mar. 7, 1967 Reagents and procedures are conventionally selected toward meeting these objectives within economic limitations. Pulp temperature, acidity, alkalinity, total solids and other controllable variables are manipulated so that these two objectives may be optimized.

Prior to the actual flotation, a step termed conditioning is frequently employed to prepare or condition the surfaces of the minerals in the pulp by removing slirnes or interfering components from said surfaces thereby permitting the desired surf-ace phenomenon to proceed between the minerals, the reagent system and ultimately the air bubbles. The conditioning preferably proceeds in the presence of all or some of the flotation reagents, depending on circumstances. Without conditioning, some flotation separations cannot be made in a manner whereby the two objectives mentioned above, i.e., purity of concentrate and high yield, can be economically met. It therefore follows that conditioning with maximum effectiveness is important and considerable effort has been expended by those practi-cing flotation to design effective conditioning apparatus. This apparatus has taken the form of tanks fitted with powerful agitators and other devices whereby the surfaces of the minerals are rubbed or scrubbed to produce fresh surfaces for attachment or reaction with flotation reagents.

In seeking high recovery in any mineral separation process, especially flotation, the higher the yield of valuable component from the ore fed to the separation process, the lower the purity of the concentrate. This follows because as the tailings are stripped of the valuable component, more and more of the unwanted mineral fraction will being to report with the valuable component, thus lowering the over-all purity of concentrate. Thus, in known flotation processes, increase in yield is achieved with considerable sacrifice in purity and vice versa.

It is an object of this invention to provide an improved flotation apparatus and method by which the highest purity of desired mineralin the froth concentrate is achieved with maximum recovery of said mineral from the feed to the flotation process.

It is another object to provide such an improved flotation apparatus and method in which the highest purity of desired mineral in the froth concentrate is achieved with a greater yield than has been heretofore possible with conventional froth flotation methods and apparatus.

It is still another object to provide such an improved flotation apparatus and method by which the purity of desired mineral in the froth concentrate is increased without sacrifice in yield and vice versa.

It is a further object of this invention to provide an improved method of and apparatus for obtaining talc at an exceedingly high purity by means of concentrating said tale in a froth flotation concentrate in an improved manner and simultaneously obtaining a high recovery of t-alc from the ore fed to the flotation process. Said talc recovered by this invention is of sufliciently high purity for cosmetic and other high purity talc applications.

It is a further object of this invention to provide a method of and apparatus for obtaining kaolin at a purity sufficient to meet paper filler and coating specifications by concentrating such kaolin in a flotation froth concentrate in an improved manner and simultaneously ob taining a high recovery of kaolin from the ore fed to the flotation process.

It is a further object of this invention to provide a novel, improved and exceedingly effective apparatus for, and method of, conditioning mineral pulps prior to flotation, such apparatus and method providing improved flotation not only with the novel and improved flotation method and apparatus of the present invention but with other conventional flotation methods as well.

The improved conditioning apparatus and method of proved purity and yields as compared to conventional conditioning techniques.

It is a further object of this invention to provide an improved method of and apparatus for conditioning a pulp or slurryof talc-bearing ore particles so that it will respond better to a subsequent flotation step as compared to conventional conditioning technique-s, thereby .yielding a very pure talc concentrate with high yield.

It is a further object of this invention to provide an improved method of, and apparatus for, conditioning a pulp or slurry of kaolin-bearing ore particles so that it will respond better to a subsequent flotation step as compared to conventional conditioning techniques, thereby yielding a very pure kaolin concentrate with high yield.

It is a further object of this invention to provide a method of, and apparatus for, simultaneously conditioning and selectively delaminating laminar mineral particles such as talc or mica in a pulp of such mineral particles in order to remove interlayer impurities from said lami- .nar particles and expose fresh surfaces of the laminar mineral for contact with the flotation reagents and ulti- .mately the bubbles and thereby affect through froth flotation better separation of said laminar minerals from the pulp at a high purity.

The invention is not drawn to flotation machines per se of any' particular design, but rather is drawn to the flow configurations from machine to machine, water balances, and improved conditioning means in combination with subsequent flotation.

Further objects and advantages will be apparent from the following description and accompanying drawings in which:

FIG. 1 shows diagrammatically the important features of a conventional Denver Sub A Flotation Machine, which is one of several conventional froth flotation machines which may be emplo'yed'in the present invention;

FIG. 2 shows diagrammatically an embodiment of the improved conditioning means of the present invention;

FIG. 3 is an enlargement of a part of the homogenizing valve of the conditioning means of FIG. 2;

FIG. 4 is a section taken along the line 4-4 of FIG. 3;

FIG. FIG. 3;

FIG. 6 shows diagrammatically an embodiment of the is a section takenalong the line 55 of present invention including in combination the improved conditioning and flotation means;

FIG. 7 shows in greater detail the flow configuration between certain of the flotation machines of FIG. 6.

With reference to the conventional flotation machine shown in FIG. 1, an aqueous mineral pulp or slurry is introduced at inlet 1 and is drawn into the rotating impeller 2, the latter being driven by a shaft 3 and pulley 4. The shaft is rotatably mounted in bearing assembly 5. Air is also drawn into the impeller 2 by passing down through the annular 'space 6 created by the shaft 3 and the standpipe 7. Rotation of the impeller at conventional speeds causes violent agitation of the pulp and air. The aerated mass leaves the diffuser 8 and air bubbles generated during agitation, together with attached desired mineral particles, rise to the surface of the liquid pulp, the level of which is maintained by a conventional overflow shown diagrammatically as 8a. Froth containing mineral concentrate is continuously removed from the machine above quiescent froth zone 9 by rotating froth paddle 10 moving the froth over lip 11 into a trough or launder 12. The froth is either recovered as such or is further treated as set forth below in accordance with the method of this invention. The liquid tailing, stripped of at least a portion of the mineral fraction to be concentrated, which has reported to the froth, leaves the machine through the overflow 8a mentioned above and can be subjected to further treatment or discarded from the flotation circuit. The improved flotation method and apparatus of the present invention does not lie in this machine per se, which is conventional, but rather to the flow configuration between a plurality of such machines or other flotation machines, which configuration will be described hereinafter.

The conditioning means, heretofore never employed in the practice of mineral ore flotation, comprises applying a high fluid pressure on a liquid pulp or slurry of minerals to be conditioned to force it to flow in the form of a thin film edgewise and at a high velocity by virtue of reduction of such high pressure to a lower pressure, through a highly restricted opening or gap in the nature of a fraction of an inch formed by closely spaced, hard surfaces, to thereby impart shearing, turbulence, shattering, impact, and cavitation forces on the mineral particles.

Preferably the pulp or slurry is discharged from the opening at a high velocity against a hard impact surface directly in front of the opening. Discharge against the hard impact surface provides optimum scrubbing and attrition effects desirable for conditioning the pulp feed to the flotation apparatus and thereby enhances the conditioning action but it is not essential.

In a preferred embodiment, the restricted opening com prises a valve opening and the slurry under high pressure is directed against the valve to force it slightly away from its seat against the force of resilient means, such as a spring or the like, yieldably urging it toward its seat, whereby the slurry under pressure is forced in the form of a thin film edgewise at an extremely high velocity through the highly restricted opening between the valve and its seat and against the impact surface. The direction of flow of the slurry through the valve opening is at an angle to the direction of flow to the valve, and the opening is preferably annular in shape, i.e., it has the shape of a thin annular disc.

Preferably, the valve is rotated to prevent the slurry from wearing a channel in the valve seat and to cause the wear effects of the slurry on the valve and valve seat to be more uniform whereby the useful life of the valve and valve seat before overhaul and repair becomes necessary, is substantially increased.

The fluid pressure can be generated by a suitable pressure pump such as a piston pump operating on the slurry.

The valve, mounted on or near the pump discharge, can be any one of several designs such as that used for the high pressure homogenizing of milk and is commonly referred to as a homogenizing valve.

The impact surface can be provided by an impact ring around the annular valve opening and within a fraction of an inch therefrom, as is customary with valves of this design. The ring forms with the periphery of the valve a passage of restricted cross section extending at an angle to the valve opening and through which the slurry flows after impacting'against the ring.

A pump and valve assembly such as that known as a. Manton-Gaulin Single Stage Homogenizing Valve Assembly is suitable. Such assemblies have been known for many years but to our knowledge they have never been used in mineral flotation to condition the mineral pulp prior to flotation. Also, the apparatus described in our copending US. application Serial No. 197,813, of which this application is a continuation-in-part, and US. Patent No. 3,039,703 are suitable. However, valves of similar and modified design providing like action can be used within the scope of this invention.

This conditioning means is especially effective in concentrating laminar minerals, such as talc, by froth flotation because it selectively delaminates the laminar min-.

erals by basal cleavage to thereby eliminate or free from the laminar minerals, the interlayer occlusions. Consequently, it provides simultaneously both for conditioning the surfaces of the laminar mineral particles and liberating minerals one from another, i.e., the laminar mineral from the occlusions. Also, delamination exposes large areas of fresh uncontaminated surfaces of the laminar mineral previously forming the inner surfaces of the laminar mineral layers, for contact with the reagents and ultimately with the bubbles.

The details of the conditioning means are shown in FIGS. 2, 3, 4 and 5. Referring to these figures, mineralbearing ore to be subjected to flotation and water or a tailing from a subsequent flotation operation as described below, are added to pulp feed tank 13 equipped with an agitator 14 to produce a uniform slurry of the ore in water. This slurry is fed by gravity or pump (not shown) to the inlet 15 of a liquid piston pump 16 of the pressure pump and valve assembly 17. The slurry is sucked from inlet 15 through suction ball check valve 18 of pump 16 into the pump cylinder 19 by the suction stroke of piston 20 and is forced through discharge ball check 21 to and through the high pressure pump outlet 22 into the high pressure inlet passage or chamber 23 of the valve assembly 24 and against valve 25 which is urged toward the valve seat 27 by a heavy spring 28. The high pressure exerted on the valve 25 by the slurry in the confined passage 23 forces the valve slightly away (a fraction of an inch) from its seat 27, whereby the slurry under pressure flows in the form of a thin film edgewise and at an extremely high velocity through the highly restricted valve opening 29 against an annular impact ring 30 extending around the valve. The slurry then flows through the narrow passages 31 between the ring 30 and the adjacent outer peripheral walls of the valve 25 and valve seat member 23a. Scrubbing and attrition to remove slimes or flotation interfering components from the surfaces of the minerals in the ore are achieved by the shearing effect on the mineral particles of the closely spaced valve seat 27 and valve face 32 forming opening 29 and of the closely spaced impact ring 30 and outer peripheries of the valve and valve seat member forming passages 31, all of which are made of a very hard material such as tungsten carbide, by the turbulence and cavitation of the mineral particles as they flow through opening 29 against impact ring 30 and through passages 31 and by shattering and impact of the particles against the impact ring 30 and valve face 32. The various changes in direction of flow of the slurry from 23 to 29 and from 29 to 31 also contribute to the scrubbing and attrition phenomenon.

As pointed out in our copending application, Serial No. 197,813, it is believed that the restricted opening 29 also functions to flow orient laminar minerals in the direction of flow through the opening to achieve a selective delaminating effect, and, when an impact ring is used, to provide edgewise impact of the laminar minerals against the impact ring which causes further selective delamination.

This selective delamination of the laminar minerals frees them from the undesirable impurity occlusions between the laminar layers to thereby permit the laminar mineral to be separated from such occlusions during the subsequent flotation operation. Conventional grinding techniques, such as a ball mill, primarily grind the laminar particles into smaller laminar particles rather than primarily and selectively delaminating them as with applicants conditioning means. Consequently, the occlusions between the layers are not freed from the laminar minerals nearly as much. Furthermore, this selective delamination exposes large areas of fresh surface of the laminar mineral for exposure to the flotation reagents and ultimately the bubbles, as compared to conventional grinding techniques.

Conventional conditioning techniques involve violent agitation of the mineral slurry which does not provide selective delamination and hence does not free the laminar mineral from the interlayer occlusions or expose large areas of the laminar mineral.

It is for the above reasons that the conditioning means of the present invention is particularly advantageous in flotation of laminar minerals, such as talc, mica, etc. However, the improved scrubbing and attrition effects achieved by the conditioning means of the present invention, presumably by the above mentioned shearing, cavitation, impact and direction changing effects, provides improved conditioning of non-laminar minerals and mixtures of laminar and non-laminar minerals as well, so that higher yields of high purity mineral are obtained.

Referring to FIGURE 2, some or all of the conventional flotation reagents may be added to tank 13 so that as the mineral slurry passes through the conditioning assembly, i.e. pump and valve assembly 17, the reagents can attach or react with the fresh surfaces as they are formed or freed of interfering impurities.

An embodiment of the novel flotation machine arrangement of the present invention is depicted in FIG- URES 6 and 7. Mineral ore is pulped in a tank 13 fitted with an agitator 14. The ore pulp or slurry is passed through a conditioning unit 33 of either a conventional nature or that described above and depicted in FIGURES 2, 3, 4 and 5. Alternately, conditioning unit 33 can be dispensed with altogether and agitating in tank 13 relied on to provide conditioning, this being a conventional method of conditioning. The pulp then passes to one or more flotation machines called roughers, e.g. Denver Sub A Flotation Machines, arbitrarily chosen as two in number in FIGURE 6 and indicated as R1 and R2. Flotation reagents can be added at one or more of the following points: at tank 13, after the conditioning means 33 and before R1, in R1, in R2. The reagent system and flotation conditions are so adjusted as to maximize the recovery of desired mineral fraction reporting to the froth. The tailing from R1 is passed to the inlet of R2. The tailing 39 from the last rougher machine (from R2) can be discarded or subjected to one or more of the following treatments: additional delamination in the case of laminar minerals to liberate more of the desired fraction from the tailing followed by additional flotation, additional flotation to recover more of the same fraction without further delamination, a different flotation to recover a different mineral fraction.

The froths from the two or more rougher machines are combined and the combined froth is then passed to a series of cleaners, arbitrarily chosen as four in number in FIGURES 6 and 7 and indicated as C1, C2, C3 and C4, each of which may be a Denver Sub A Flotation Machine. The cleaner flow circuit configuration is termed by us, Counter-Current Flotation and provides for cleaning and recleaning of the concentrate reporting to the froth by redispersing it in pulp which carries successively lower and lower amounts down to zero of the mineral fraction being depressed or not desired in the concentrate reporting to the froth.

The flow circuit to, between and from C1, C2, C3 and C4, is shown in detail in FIG. 7. The combined froth from R1 and R2 is passed through line 33a to the inlet 1 of the froth flotation machine C1. The tailing overflow from the tailing outlet 8a of the succeeding froth flotation unit C2 is also passed through line 340 to the inlet 1 of C1 where it is admixed with the froth from line 33a to provide liquid for flotation in C1. The overflow tailing from tailing outlet 8a of C1 is passed through line 34d back to the tank 13 to provide the liquid for the pulping of ore feed to the tank. The froth from C1 is passed through line 33b to the inlet of C2. The overflow tailing from C3 is also passed through line 34b to the inlet of C2 where it is admixed with the froth from C1 to provide liquid for flotation in C2. The froth from C2 is passed through line 330 to the inlet of C3. The overflow tailing from C4 is also passed through line 34a to the inlet of C3 where it is admixed with the froth from C2 to provide liquid for flotation in C3. The froth from C3 is passed through line 33d to the inlet of C4. Water is added to such froth at 37 to provide liquid to flotation in C4. The froth from C4, rich in the desired mineral fractions, is collected from C4 through line 33e and the desired mineral fraction is recovered therefrom by conventional means. Thus, whereas the froth passes from C1 to C2 to C3 to C4, the tailing pass countercurrently from C4 to C3 to C2 to C1 to tank 13 and the conditioning means 33. The froth from each succeeding flotation machine from C1 to C4 contains less and less of the undesired mineral fraction and the desired mineral fraction therein is purer whereas the tailing from each successive flotation machine from C4 to C1 contains more and more of the undesired mineral fraction and less and less of the desired mineral fraction. In some cases the desired mineral fraction may be in the tailing and the undesired fraction in the froth in which case the final tailing is collected.

While a minor amount of water may be added in the form of a spray to the froths at

points

34, 35 and 36, suflicient only to transfer the froths to the inlets of C1, C2 and C3, respectively, the major amount of water to continuously maintain a predetermined water balance in the entire cleaner circuit and tank 13 shown in FIGURES 6 and 7, i.e., to provide tailing overflow in all of the cleaners C1, C2, C3 and C4 and maintain a predetermined slurry or pulp level in the tank 13, is added at point 37. Here, the water sweeps the froth from the next to last cleaner, C3, into the inlet of the last cleaner C4. If 12 cleaners were employed, the major quantity of water entering the circuit would be used to carry the froth from the 11th cleaner into the 12th cleaner. This water then flows backward in the circuit with the tailings, passing from the last cleaner to the next to the last cleaner, and so on, until it enters the first cleaner, C1, carrying each time the non-floating fraction in a direction counter-current to the movement of the froth. The water introduced at 37 provides the major portion of the liquid for flotation in all of the cleaners and for pulping ore feed to the tank, the amounts of water added at 34, 35 and 36 being only minor. The water added at 34, 35, 36 and 37 should be of good quality, i.e., it should not contain any substantial amount of slimes and other impurities. If desired, water can be added at 38 to dilute the pulp before it enters the first rougher but the bulk of this water is eliminated with the rougher tailing 39 so that it can be ignored with respect to water balance in the cleaner and tank circuit.

Although most efficient operation is achieved by adding the bulk of the water to maintain the desired water balance in the cleaner and tank circuit at 37, a substantial part of such water can be added at 34, 35 and 36 with resulting loss in efliciency due to the fact that such water is not being utilized in all the cleaners. For example, water added at 34 is not utilized in cleaning the froths in C2, C3 and C4, water added at 35 is not utilized in cleaning the froths in cleaners C3 and C4 and water added at 36 is not utilized in cleaning the froth in C4. on the other hand, water added at 37 is utilized in cleaning the froths in all the cleaners. In any event, suflicient Water must be added at 37 to provide tailing overflow from C4, i.e., to provide liquid for flotation in C4.

Although it is by far preferred to recycle all the tailing from C1 to tank 13 to achieve optimum yield, a part or all of such tailing may be removed. In such case, water must be added to tank 13 to replace the volume of tailing from C1 not recycled in order to pulp the ore feed to tank 13.

It has been stated above that a sufiicient amount of water is added at 37 to provide tailing overflow in all the cleaner units and to continuously maintain the desired slurry or pulp balance or level in tank or container 13 where the pulp is formed. The slurry in such tank may be considered as the slurry supply or reservoir. Where grinding or other equipment such as a ball mill is used to form the pulp, such ball mill may be used as the conmtainer for forming the slurry and the slurry therein becomes the slurry supply and the water from C1 is passed to such ball mill to maintain the desired slurry balance or level therein.

All the water in the system, except that present in the froth removed from C4, is removed from the system at 39.

Referring to FIGURES 6 and 7, each cleaner machine receives the pulp from the machine succeeding it and the froth from the machine preceding it, e.g. the inlet of C3 receives pulp from C4 and froth from C2.

The tailing discharged from the first cleaner, C1, contains that undesired mineral fraction which reported to the froth in the roughers but did not report to the first cleaner froth. As aforesaid, this stream, termed a middling, can be returned to tank 13 Where it is admixed with the incoming ore and is thereafter passed through the rougher floation circuit.

It should be noted that each rougher and cleaner machine as shown in FIGURES 6 and 7 can be an individual machine or a plurality of machines arranged in series. In the latter case, with respect to the cleaners, the froth from the plurality of machines would be collected as a single froth and passed forward to the next plurality of machines arranged in series. When it is stated that the plurality of machines is arranged in series it is meant that the tailing from each machine of the group or plurality is passed to the inlet of the next machine of the group with the froth from each machine being combined with the froths from the other machines of the group to form a single froth, which in the case of the cleaners, is passed to the inlet of the first machine of the next group of machines in series. Also, in the case of the cleaners, the final tailing from the next group would be passed to the inlet of the first machine of the first group. In the claims, the term flotation unit includes a single flotation machine as well as a plurality arranged in series.

The circuit described above and in FIGURES 6 and 7, by its design achieves both high concentrate purity and high recovery from the ore fed to the circuit.

In the beneficiation of talc by froth flotation, while the above described flotation circuit has distinct advantages with the use of conventional conditioning means, when the pump and homogenizing valve assembly of the present invention and shown in FIGS. 2 to 5 is used in conjunction-with it for conditioning the pulp exceedingly high purity concentrates can be obtainedat high yields.

Also, although the use of the pump and valve assembly described above with conventional flotation circuits provides improved flotation, even better results are achieved when such assembly is used with the above described improved flotation circuit of the present invention.

Tale is a naturally occurring hydrous magnesium silicate which co-occurs with silica, carbonates, iron compounds and lesser impurities. However, talc frequently occurs in a sufficiently high concentration or state of purity that selective mining methods augmented by dry grinding techniques provide this mineral as a cheap filler for industrial applications in rubber, roofing and a multi tude of other fields.

In cosmetics, paper and certain other talc consuming applications, the specifications placed on talc require beneficiation and concentration of the tale to a higher state of purity than that achieved by selective mining and grinding alone.

Talc responds to flotation and the flotation of talc to improve purity has been known and practiced for many years. However, insofar as we know, no flotation process has ever been developed or practiced which could yield, at high recovery, a tale equivalent in purity to the best grades of Italian Talc now widely used in the cosmetic industry. Moreover, talc has never to our knowledge been floated in accordance with the flotation machine arrangement herein described and claimed.

EXAMPLE 1 A talc ore containing approximately 50% talc was charged to the tank 13 of FIGURE 6 so that the pulp or slurry in the tank remained at approximately 30% solids. The ore fed was approximately 100% finer than 100 mesh and approximately 80% finer than 325 mesh. Pulp was withdrawn from tank 13 by a pump (not shown) at the rate of one gallon per minute (g.p.m.) and passed to the conditioning means 33 having the construction of FIGURES 2, 3, 4 and 5. The pressure drop across the valve assembly 24 was maintained at 1500 p.s.i., i.e., the pressure of pulp delivered to the valve was 1500 p.s.i. The pulp was diluted with water at 38 after passing through the conditioning means 33 so that the concentration of the pulp fed to the first rougher, R1, was 12%. A flotation reagent feeder (not shown) was placed so as to add Ultrawet DS (an alkyl aryl sulfonate surfactant manufactured by The Atlantic Refining Company, Philadelphia, Pa.) at the rate of 0.05 lb. per ton of raw ore fed, to tank 13.

Two roughers, R1 and R2, were used and consisted of two No. 7 Denver Sub-A laboratory flotation machines. The pulp overflow (tailing) from R1 was drawn into the inlet 1 of R2 (see FIGURES l and 6). The froths from R1 and R2 were joined and transferred to the inlet 1 of the first cleaner C1 with the aid of a small amount of spray water added at 34 (suflicient only to transfer the froth). The rougher tailing from R2 was discharged to waste.

Four cleaners were used in the Counter-Current Flotation cleaning circuit. These cleaners, C1, C2, C3 and C4 (see FIGURES 6 and 7) also were No. 7 Denver Sub-A laboratory flotation machines. The froth from C1 was transferred to the inlet of C2 using a small amount of spray water (sufficient only to transfer the froth) added at 35. The froth from C2 was transferred to the inlet of C3 using a small amount of spray water (sufficient only to transfer the froth) added at 36. The froth from C3 was transferred to the inlet of C4 by the addition of a substantial quantity of water at 37. The overflow tailing from C4 was passed to the inlet of C3, the overflow tailing from C3 was passed to the inlet of C2, the overflow tailing from C2 was passed to the inlet of C1, and finally the overflow tailing from C1 was passed to tank 13. When the operation was started up it was necessary to add water to tank 13 to provide 30% solids in the tank. However, after the operation was started addition of water to the tank was discontinued and all the water supplied to the system to replace that which was being lost or removed was added at 38, 34, 35, 36 and 37, suflicient water being added at 38 to keep the solids concentration entering the roughers at 12%, i.e., to dilute the pulp from conditioning means 33 from 30% to 12%. The'bulk of the rest of the water was added at 37. That is, while minor amounts of water were added as a spray to transfer the froth at 34, 35 and 36, special attention was given to the rate of water addition at 37 in order to provide tailing overflow in all the cleaners and to continuously maintain the desired water balance in the cleaner and tank 13 circuit, i.e., maintain a substantially constant slurry level in tank 13. Sutficient ore was continuously added to tank 13 to keep the solids concentration in the tank'at 30% solids.

The ore fed to the agitated tank 13 contained approximately 50% talc, 15% carbonates and silica and other impurities. The solids contained in the froth discharged from the final cleaner C4 were 99.0% talc. The yield of talc was 35% based on the total dry ore fed to tank 13 or 70% based upon the tale available in the ore. The tale had excellent slip and color. A wet screen test gave 90% finer than 325 mesh.

Another run (Run 2) was made using the same equipment, setup and feeds (ore, reagent and water) as above except that the pump and valve assembly 33 was omitted, the only conditioning being provided by agitation in tank 13, which is a conventional way of conditioning ore for flotation. The solids contained in the froth discharged from the final cleaner C4 were 98.5% tale. The yield of talc was 22% based on the total dry ore fed to tank 13 or 44% based upon the talc available in the ore. The talc had poorer slip and poorer color than the product of Run 1. Moreover, a wet screen analysis of the product gave only 70% finer than 325 mesh. Microscopic comparison of the talc products of Run 1 and Run 2 showed that whereas the talc of Run 1 was highly delaminated and hence contained relatively small amounts of occluded impurities (such impurities were set free by delamination in the homogenizing pump and valve assembly and reported to the tailings), the-talc of Run 2 was not nearly as highly delaminated and hence contained more occlusions so that it was not as pure as the talc of Run 1, the analytical tests for purity notwithstanding. In any event, the talc from Run 1 had superior slip and color properties quite startling to persons skilled in the cosmetic talc art. Thus, the con ditioning means of the present invention, i.e., the homogenizing pump and valve assembly, provides for a rapid, almost instantaneous method of conditioning and reduction in particle size to produce a better concentrate at a higher yield.

Another run (Run 3) was made using the same feeds, set up equipment as the first run except that (1) the units C1, C2, C3 and C4 were placed in series with each other and the roughers so that they acted as additional roughers, i.e., the tailing from rougher 2 was passed to the inlet of C1, the tailing from C1 to the inlet of C2 and so on and the froths were removed from each of R1, R2, C1, C2, C3 and C4 and were combined without passing through any succeeding units, the last tailing from C4 being discarded, and (2) the water was added directly to the tank 13 to maintain the solids concentration at 30% and to maintain the desired slurry level in the tank rather than at 34, 35, 36 and 37 as in Run 1. The amount of water added at 38 was the same. The results were as follows: the solids contained in the froth were 88% talc. The yield of talc was 28% based on the total dry ore fed to tank 13 or 56% based upon available taic in the ore. However, it is pointed out that this talc yield had admixed therewith 12% impurities so that the product recovered from the froth was of poor purity and thus of poor quality. The tale had substantially poorer slip and poorer color than

Runs

1 and 2. A wet screen analysis of the product gave finer than 325 mesh. Thus, the use of the novel flotation machine arrangement or circuit of the present invention gave markedly better results than conventional flotation.

Run 3 was repeated (Run 4) except for the omission of the pump and valve assembly 33, the slurry from tank 13 passing directly to the roughers and then to the four flotation machines in series as per Run 3. Thus, the only conditioning was agitation in the tank 13. This represents conventional practice, i.e., agitation to condition followed by conventional flotation techniques with a plurality of flotation units in series. The results were as follows: the solids contained in the froth were also 88% talc. The yield of talc was 15% based on the total dry ore fed to tank 13 or 30% based on available talc in the ore. The talc had very poor slip and very poor color. A wet screen analysis of the product gave 68% finer than 325 mesh.

The pressures used, the dimensions of the homogenizing valve, the size of the valve opening and the solids concentration and particle sizes of the slurry feed to the pump and homogenizing valve assembly may be the sameas those described in the above mentioned copending application and may vary over the same ranges. Thus, the pressure may in some cases be as low as 250 p.s.i.g. or even 100 p.s.i.g. or as high as 5000 p.s.i.g. and higher. The concentration of the slurry fed to the pump and homogenizing valve is not particularly critical so long as it is not too thick to be handled by the valve and so long as the concentration fed to the flotation units is adjusted so that selectivity of the flotation operation is not impaired to the point of becoming uneconomical. Also particle size is not particularly critical so long as the mineral particles in the slurry from tank 13 are not too large to be handled by the equipment.

An example of a non-laminar mineral which can be processed to advantage in accordance with the present invention is a magnesite bearing ore.

Although, as aforesaid, the method and apparatus of the present invention provide improved flotation of laminar and nonlaminar minerals, the best results at the present time, have been achieved with talc.

In some cases, where self floating minerals are treated, flotation reagents may not be required. In such cases, the conditioning means scrubs the mineral surfaces for better attachment to the bubbles.

As aforesaid, this application is a continuation-in-part of our copending application Serial No. 197,813, which in turn is a continuation of our application Serial No. 189,- 933, now abandoned, which in turn is a continuation of our application Serial No. 782,992, now abandoned, which in turn is a continuation-in-part of our application Serial No. 758,930, now abandoned.

We claim:

1. A method of mineral froth flotation comprising conditioning a liquid slur-ry feed of mineral particles by forcing it in the form of a thin film edgewise through a thin hard-surfaced gap under a high pressure and at a high velocity by virtue of reduction of said high pressure to a substantially lower pressure, flowing the conditioned mineral particles through at least one rougher froth flotation unit, flowing the froth from said unit to the first of at least two cleaner froth flotation units, the froth from each of said cleaner units being passed to the inlet of its succeeding unit, passing the tailin-g from each of said cleaner units to the inlet of its preceding unit, and adding suflicient water to the froth from the next to the last cleaning unit to provide tailing overflow in said last cleaning unit.

2. A method according to claim 1 for concentrating talc in a froth, said mineral particles comprising a talebearing ore.

3. A method according to claim 1 for concentrating clay, said mineral particles comprising a clay-bearing ore.

4. A method according to claim 1, the discharge of said slurry from said gap being directed against a hard impact surface.

5. A method of mineral beneficiation comprising forming a liquid slurry of mineral particles, forcing said slurry in the form of a thin film edgewise through a thin, hardsurfaced gap under a high pressure and at a high velocity by virtue of reduction of said high pressure to a substantially lower pressure, and subjecting the resulting slurry to froth flotation.

6. A method according to claim 5, for beneficiation of talc-bearing ore, said mineral particles comprising said talc-bearing ore.

7. A method according to claim 5 for beneficiation of clay-bearing ore, said mineral particles comprising said clay-bearing ore.

8. A method according to claim 5, the discharge of said slurry from said gap being directed against a hard impact surface.

9. A method according to claim 5, said froth flotation comprising flowing the discharge of slurry from said gap through at least one rougher froth flotation unit, flowing the froth from said unit to the first of at least two cleaner froth flotation units, the froth from each of said cleaner units being passed to the inlet of its succeeding unit, passing the tailing from each of said cleaner units to the inlet of its next preceding unit, whereby the tailings flow from unit to unit countercurrently with the froth.

10., A method according to claim 9 including adding suflicient water to at least one of the froths from said cleaner units to provide tailing overflow in all of said cleaner units.

11. A method according to claim 10, said liquid slurry being passed to said gap from a liquid container, the tailing of said first cleaner unit being recycled to said container and said added water being suflicient to maintain a substantially constant slurry level in said container.

12. A mineral froth flotation system comprising at least one rougher froth flotation unit, means for flowing a liquid slurry of mineral particles to said rougher unit, at least two cleaner froth flotation units, means for flowing the froth from said rougher unit to the first of said cleaner units, means for flowing the froth from each of the cleaner units to the inlet of its succeeding cleaner unit, means for flowing the tailing of each of said cleaner units to the inlet of its preceding unit, a container for said liquid slurry, said means for flowing said liquid slurry of mineral particles to said rougher unit comprising means for passing said slurry from said container to said rougher unit, means for passing the tailing from said first cleaner unit to said container, said means for flowing the froth from each of said cleaner units to its succeeding unit comprising means for spraying, with water froth from each of the cleaner units before the next to the last cleaner unit into the inlet of its next succeeding unit and means for adding suflicient water to the froth from the next to the last cleaner unit to provide said overflow in all of the cleaner units and to maintain said predetermined slurry level in said con-tainer.

13. A mineral froth flotation system comprising at least one rougher froth flotation unit, means for flowing a liquid slurry of mineral particles. to said rougher unit, at least two cleaner froth flotation units, means for flowing the froth from said rougher unit to the first of said cleaner units, means for flowing the froth from each of the cleaner units to the inlet of its succeeding cleaner unit, means for flowing the tailing of each of said cleaner units to the inlet of its preceding unit and means for adding suflicient water to at least one of the froths from said cleaner units to provide tailing overflow from all of said cleaner units, said system also including conditioning means for conditioning the slurry feed to said rougher unit, said conditioning means comprising means for forcing a slurry of said mineral particles in the form of a thin film edgewise through a thin hard-surfaced gap under a high pressure and a high velocity by virtue of reduction of said high pressure to a substantially lower pressure and means for feeding the discharge from said gap to said rougher unit.

14. A mineral froth flotation system comprising at least one rougher froth flotation unit, means for flowing a liquid slurry of mineral particles to said rougher unit, at least two cleaner froth flotation units, means for flowing the froth from said rougher unit to the first of said cleaner units, means for flowing the froth from each of the cleaner units to the inlet of its succeeding cleaner unit, means for flowing the tailing of each of said cleaner units to the inlet of its preceding unit and means for adding suflicient water to at least one of the froths from said cleaner units to provide tailing overflow from all of said cleaner units, said system also including conditioning means for conditioning the slurry feed to said rougher unit, said conditioning means comprising a spring loaded valve and valvev seat, a pump for pumping a slurry of said mineral particles against said valve under a pressure suflicient to force said spring loaded valve to open a fraction of an inch and force the slurry to flow edgewise in the form of a thin film through the valve opening at a high velocity, the shape of said valve and valve seat causing said slurry to flow through the valve opening formed thereby edgewise in the form of said thin film, and means for feeding the output from said valve to said rougher unit.

15 Apparatus according to claim 14, said conditioning means including an impact surface located at the exit of said valve opening and against which the discharge from said opening is directed.

16. Apparatus according to claim 15, said impact surface being ring-shaped and extending around and spaced slightly from said valve opening and forming with the periphery of said valve and valve seat a narrow annular passage which is at an angle to said gap.

17. Apparatus for beneficiating minerals, said apparatus comprising means for forcing a slurry of mineral particles in the form of a thin film edgewise through a thin hard-surfaced gap under a high pressure and ata high velocity by virtue of reduction of said high pressure to a substantially lower pressure, at least one froth flotation unit for concentrating a desired fraction of said minerals and means for flowing the discharge from said gap to said froth flotation unit.

18. Apparatus according to claim 17, the discharge from said gap being directed against a hard impact surface.

19. A mineral froth flotation system comprising a container for a liquid slurry of mineral particles, at least one rougher froth flotation unit, means for flowing said liquid slurry of mineral particles from said container to said rougher unit, at least two cleaner froth flotation units, means for flowing the froth from said rougher unit to the first of said cleaner units, means for flowing the froth from each'of the cleaner units to the inlet of its succeeding cleaner unit, means for flowing the tailing of each of said cleaner units to the inlet of its preceding unit, means for passing the tailing from said first cleaner unit to said container, said means for flowing the froth from each of said cleaner units to its succeeding unit comprising means for spraying, with water, froth from each of the cleaner units before the next to the last cleaner unit into the inlet of its next succeeding unit, and means for adding suflicien-t water to the froth from the next to the last cleaner unit to provide tailing overflow from all of said cleaner units.

References Cited by the Examiner UNITED STATES PATENTS 2,184,115 12/1939 Coke 209168 2,285,394 6/1942 Coke 209-166 2,569,680 11/1951 Leek 209-5 X WILLIAM W. DYER, JR., Primary Examiner.

H. F. PEPPER, Assistant Examiner.

Claims

5. A METHOD OF MINERAL BENEFICATION COMPRISING FORMING A LIQUID SLURRY OF MINERAL PARTICLES, FORCING SAID SLURRY IN THE FORM OF A THIN FILM EDGEWISE THROUGH A THIN, HARDSURFACED GAP UNDER A HIGH PRESSURE AND AT A HIGH VELOCITY BY VIRTUE OF REDUCTION OF SAID HIGH PRESSURE TO A SUBSTANTIALLY LOWER PRESSURE, AND SUBJECTING THE RESULTING SLURRY TO FROTH FLOTATION.