US2692677A

US2692677A - Process for classifying magnetized or magnetizable solids

Info

Publication number: US2692677A
Application number: US210252A
Authority: US
Inventors: Francis L Bosqui; Thomas D Heath
Original assignee: Dorr Co
Current assignee: Dorr Co
Priority date: 1951-02-09
Filing date: 1951-02-09
Publication date: 1954-10-26
Anticipated expiration: 1971-10-26

Description

Oct. 26, 1954 F. BOSQUI ETAL PROCESS FOR CLASSIFYING MAGNETIZED OR-MAGNETIZABLE SOLIDS 2 Sheets-Sheet 2 Filed Feb. 9, 1951 Annular Spray of Fines m m. m

FIG. 2.

d O O INVENTORSE Francis L, Bosqul a Thomas D. Heuih, By W Mulluw ATTORNEY Patented Oct. 26, 1954 UNITED STATES PATENT G'FFICE PROCESS FOR CLASSIFYING MAGNETIZED' OR MAGNETIZABLE SOLIDS Francis L. Bosqui and Thomas D. Heath, West-' port, Conn., assignors to-The Dorr Company,. Stamford, Conn., a corporation of Delaware Application February 9. 1951, Serial No. 210,252

4 Claims.

This invention relates to closed-circuit grinding of ores and other solids. In this type of grinding, the ore, usually found in the form of a solid mass'of a mixture of locked particles is supplied to a ball or other grinding mill the discharge of which is usually delivered to aclassifier where the finely divided solids are segregated into fractions of which fines go into one fraction while coarse particles go into another fraction. Thecoarse-particles so fractionated are returned to 1 the mill for regrinding Whereas the fines, being small enough, go tofurther treatment. This closed-circuit classifiication is quite satisfactory when the solids treated are not or do not become magnetically polarized, or, i. e. magnetized, But

to date, it has been impossible commercially without demagnetization to classify in closedcircuit grinding systems solids, of which magnetite ores are examples, that are magnetically susceptible, after said solids have become magin The desired function of the classifier in a closed-circuit grinding system, is to separate the suspended solids in the mill discharge so that the larger or coarser solid particles are passed from the classifier as one fraction returning to the mill,

It is a further object to classify while the finer solid particles, that are already ground fine enough, are passed from the classifier as another fraction that goes to further treatment. When the solids so treated have no constituent that is or can become magnetized the classification is satisfactory. But where the solids: have some constituent which is or becomes magnetized, such as certain iron fractions, it becomes highly unsatisfactory. The reason is that there is enough magnetic effect between 2- coarse-and fine particles so that their mutual magnetic attraction to each other is greater than the-classifying efiect of-the classifier, with the result that the fines cannot'be par-ted from the coarse in- 'the-classifi'er. This happens irrespective ofthe means by which the solids have become magnetized In any case, the suspended solids goingto' the classifier are said to be coherent, namely, particle'sthere'of arecoherent to each other with a magnetic force greater than the force available in the conventional gravity type classifier-s; so another object of this case is to devise ways and means-for effectively and satisfactorily cl'assifying or fractioning such solids into a coarse fraction and afines fraction in spite of such magneticmutualcoherence.

Some solids, either natural orartificial, that have some-magnetically susceptible constituent, are first given a roug-h concentrating step such as being passed through a magnetic separator or cobber,-.pri'or"to going to'the classifier in the closed-circuit grinding system. Such a separator acts to magnetite any solids present which are capableot being mag-netiz'edeven though they had not been previously magnetized, whereby the solids'magnetically cohere to one another. So it is anotherobject of thisinvention -to classify satisfactorily such cohering solids irrespective of whether they were naturally magnetized or became magnetized eitherin a magnetic separator or in any other way.-

In summary, the above, and possibly other objects, areattainedby passing the solids discharging fromthe grinding-mill, such as a ball or tubemilLto-a liquid-cyclone at such feed-pressure that sufi-lcient shearing forces are set up within the hydrocyclone so that the clusters or aggregates of magnetically cohered particles are broken up and simultaneously the coarse particles are hydraulically separated from the fine particles. The feedpressure must not be so great, however, that the shearingforces cause a substantial portion of the individual particles to be comminuted. The

coarse particles leave the hydrocyclone through its apex discharge, while fines leave it'from its base discharge. Any mutual coherent forces-between particles are overcome and contact between the particles is broken by the hydraulic shearing effects set up in such a hydrocyclone, with the result that the desired fractionation takes place.

A typical hydrocyclone so used comprises a conical section merging into a cylindrical section. The conical section has an outlet or discharge for coarse particles at its apex, while the cylindrical section has its top at what would be generally the base of the cone and in this base there is an outlet or discharge for fines. Suspension to be treated is fed to the hydrocyclone tangentially in the cylindrical section which normally has what is called a hollow vortex finder extending from the base that comprises the fines base discharge. The opening in the apex and in the base are co-axial through both of which extend an air-core around which fractionated fines fiow axially of the hydrocyclone to discharge through the vortex finder while the coarse solids are forced by centrifugal force toward the periphery of the conical section from whence the fraction of them discharges from the apex of the cone more or less annuarly around the air-core. The hydrocyclone comprises a swirling chamber, in which there is set up a differential velocity gradient of such magnitude that any given cluster of material will be subject to shearing forces which will tend to disintegrate the cluster into its component particles. This difierential velocity gradient is such that the liquid nearest the outer wall of the container is moving at the slowest velocity, whereas the material somewhere near to the center of the container is moving at the greatest velocity. When the difierential velocity gradient overcomes the magnetic coherence of the cluster, the particles therein act individually and then actin individually they are subjected to difierential settling rates because of the tangential velocity. This tangential velocity results in a centrifugal force which accomplishes the classification. It might be said that this invention first gives the particles a capacity for independent movement and then classifies them into a coarse fraction and a fine fraction while in this state of independent movement. The rate of classification will increase as the centrifugal force to which the particles are subjected increases.

Reference is now made to the drawings for a specific embodiment of this invention; however, it is to be realized that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive as the scope of the invention is defined by the appended claims and all changes that fall within the meaning and range of equivalents of the claims are therefore intended to be embraced thereby.

In the drawings, Fig. 1 represents a flowsheet showing the method of treating magnetized or magnetizable particles, so that they can be classified without demagnetization.

Fig. 2 is an idealistic drawing of the hydrocyclone showing the course taken by the particles in the apparatus.

More specifically, in the drawings magnetized or magnetizable natural or artificial solids are supplied to a ball mill II, in which they are ground to particles at least some of which are fine enough whereby magnetically suspectible solids are liberated. By way of example, a screen analysis of a typical embodiment of the material is presented later. From the ball mill the ground material is passed through line l2 to a magnetic separator l3, in which a primary separation is made to remove some of the nonmagnetic materials from the ore. The primary mag netic concentrate coming from the magnetic separator I3 contains both coarse and fine magnetized particles, and also contains a considerable amount of gangue material which is intimately associated with the particles, usually the larger particles. In this condition it is normally impossible commercially to classify the materials into a fine fraction and a coarse fraction, because the magnetic characteristics cause the particles to strongly cohere to one another. In general, at this point the fines comprise free gangue and liberated, relatively pure iron ore, whereas the coarse particles are solids with relatively pure iron ore particles still locked together with the gangue; therefore, it is desirable to separate the fines from the coarse so that the coarse may be recycled in closed-circuit to the ball mill II for further grinding.

The primary magnetics concentrate from the magnetic separator I3 is passed through pipe I 4 to pump I5, from which it is supplied under considerable pressure through pipe [6 to the hydrocyclone feed IT. This imparting of high pressure is essential for the next step which occurs. Suitable pressures are specifically disclosed later. The material enters the hydrocyclone l8 and is subjected to shearing forces which are so enormous that they cause the clusters of magnetically cohered particles to be broken up. This hydraulic disassociation is a temporary condition. While in this temporary condition of disassociation the hydrocyclone 18 causes the temporarily disassociated material to be hydraulically classified into a coarse fraction and a fine fraction. The fine fraction passes upwardly and out of the hydrocyclone through base discharge conduit IS. The coarse fraction passes downwardly and out of the hydrocyclone through apex outlet 20. After discharge from the hydrocyclone, the particles in each fraction will again cohere, but now they have been classified. It might be said that this step causes temporary disassociation simultaneously accompanied by permanent classification.

The fines passing upwardly out of the base discharge conduit IQ of the hydrocyclone l8 are carried through line 2| into magnetic separator 22 from whence they are subjected to the final finishing step and yield the finished magnetic concentrate through line 23. Any nonmagnetics which accompany the fines will be rejected through line 24.

The coarse material which is discharged through apex outlet 20 is passed through line 25, through which it is recycled to ball mill H; here it is reground and passed through the same steps as previously outlined. The result of this operation is a magnetic concentrate being produced through line 23, which magnetic concentrate is of extremely high purity. The data are presented later in table form showing the results of several runs.

Fig. 2 shows an idealistic view of the paths taken by the particles once they enter hydrocyclone l8. The materials enter the hydrocyclone feed II, which must be a tangential feed so as to create a swirling motion in cylindrical section 32. To assist this swirling motion and to prevent short-circuiting of the material upwardly through the upper end 34 of the cyclone, there is inserted a hollow vortex finder 35 which projects downwardly into the cyclone to such that its lower end 31 is at a point lower than that of the feed 11. After the material is swirling at great speed in cylindrical section 32, it then passes downwardl through conical section 33 and in so descending it swirls in ever decreasing circular paths. In these paths the shearing forces which are created temporarily overcome the magnetic coherence of the particles, thus causing disassociation without demagnetization. In this disassociated condition the centrifugal force thenfurther causes an internal classification within the cyclone such that the heavier and larger particles are thrown into a zone which will be located nearest the outermost shield of the hydrocyclone. The finer particles will be located in a zone which is concentric with that of the course particles but which is located nearer to the. center of the hydrocyclone. As these materials reach the apex outlet 20 the finer materials in the center of the hydrocyclone then turn upwardly and still in the directional swirling motion pass upwardly and out of the hydrocyclone through vortex finder 35. In the center of this ascending column of fines there will be located an air-core 33. The fines pass upwardly into hood 39, from whence they are discharged through pipe 21 to magnetic separator 22, as is shown in Fig. 1.

The coarse material is discharged through apex outlet 25 and passes from the apex outlet as an annular spray. This material is recirculated through pipe 25 back to the mill as shown in Fig. 1.

EXAMPLE 1 An iron ore, roasted to the magnetite state and magnetized b primary concentration in a magnetic-separater, was passed through a hydrocyclone having a 3 cylindrical diameter and having a 120 cone attached thereto. A /2" vortex finder was inserted through the uppermost portion of the cyclone. The cyclone apex measured Z-" A feed rate of solids of 3630 pounds per hour at an entrance pressure of 23 pounds per square inch was used. The solids in the feed pulp analyzed 39.3% by weight. After treatment in the hydrocyclone, the solids in the liquid coming from the vortex finder analyzed 15.2% by weight, whereas the solids coming from the apex analyzed 63.0% by weight. Not only was a disassociated classification effected, but these data show that the material was also thickened. The screen analysis of the iron ore used for this run was as shown in Table I:

Circulating l0ad=4.41

From an analysis of the information shown in TableI, it can be seen that although a feed was used containing 50% of the material of a size larger than 260 mesh (Tyler), nevertheless the cyclone was able to produce a vortex discharged material containing only 14% of a size larger than 200 mesh.

Four other runs using a cyclone whose characteristics were the same as previously described resulted in the information shown in Table II:

The screen analysis of the material produced from the runs shown in Table II is shown in Table III:

Table I I I Percent Cumulative Run Mesh Cyclone Cyclone Cyclone Feed pex Vortex 48 l. 51 l. 50 65 5. 65 10. 6 0. 46 3 100 15. 6 25.8 2. 77 150 31.8 40.0 11.0 200 45.1 55. 0 22.1 48 1. 4 l. 49 G5 4. 5 6. 25 0. 59 4 100 11.6 16.0 2.98 150 24. 2 29.8 9. 62

EXAMPLE 2 concentration of 35% was used for the feed. The.

vortex finder was 1.38" and the apex valve 1 The results of two runs made through a cycloneof these characteristics is shown below respectively in Tables IV and V:

Table IV RUN #6 Feed Per- Apex Per- Vortex Per- Mesh cent 0+ cent 0+ cent 0+ From the data which is here presented it can be seen that there is disclosed a method for classifying magnetized iron ore which was normally unclassifiable. There is also disclosed a method of controlling the mesh of separation of the material. If a coarse separation is desired, then a cyclone must be used which has a relatively large angled or flat conical section. If a finer mesh of separation is desired, then a steeper cyclone, such as a cone, may be used. A comparison of the data shown in Table I with that shown in Table IV reveals that the wide angled cyclone produced a vortex overflow containing particles 14% of which were larger than 200 mesh, whereas a small angled or steeper cyclone produced a vortex overflow containing only 2.54% particles with a size larger than 200 mesh. In general, in order to decrease the load on the closed-circuit grinding system the wider angled cyclones will be more desirable. Using the wide angled cyclone, resulting in the test data shown in Tables II and III, Cyclone Run 5, a magnetic concentrate was prepared which analyzed 51.7% Fe from a feed of crude ore which contained 36.8% Fe; the feed to the cyclone contained 43.5% Fe. However, if local conditions require a purer product of a finer particle size, this can be obtained from a cyclone with a steeper conical section than was used for the run resulting in Table I.

In this specification the separation has been indicated as occurring in an apparatus essentially containing a conical section. The desired result of this invention may also be attained according to the teachings herein by swirling the material in any sort of a space confined by a surface of revolution. It must be fed tangentially and the fines must discharge essentially axially at the feed end. The coarse material may discharge axially or peripherally at the opposite end of the enclosed space.

We claim:

1. The continuous process of hydraulically classifying magnetically cohered particles, which comprises the steps of temporarily hydraulically dissociating the particles; and, while they are temporarily so dissociated, by hydraulically segregating the particles into a fine particle fraction and a coarse particle fraction.

2. A continuous process of hydraulically classifying magnetically cohered particles, which comprises tangentially introducing a mixture of the particles and liquid into one end of a body of liquid enclosed in a space confined by a surface of revolution and having an axial outlet in the infeed end along with an outlet at the opposite end; temporarily hydraulically dissociating the magnetically cohered particles by swirling the liquid in the body at a pressure sufllcient to establish and maintain concentric swirls of liquid having difierent annular velocities whereby interfacial shearing forces are established and maintained of magnitude sufiicient to overcome magnetic coherence between the particles but insufficient to substantially comminute the particles; hydraulically segregating the particles while they are temporarily so dissociated into a fine particle fraction and a coarse particle fraction; withdrawing the fine particle fraction through the axial outlet at the infeed end of the body; and withdrawing the coarse particle fraction from the outlet at the opposite end of the body.

3. A continuous process of liberating and segregating magnetically susceptible solids from a solid mass of magnetically susceptible solids locked together with non-magnetically susceptible solids, which comprises the steps of grinding the massinto particles some of which are fine enough and others of which are not fine enough; temporarily hydraulically dissociating the magnetically cohered particles by establishing and maintaining a body of liquid enclosed in a space confined by a surface of revolution, tangentially introducing a suspension of the liquid and the cohered particles into an end section of the body at a pressure sufficient to swirl the body of liquid in concentric swirls having difierent annular velocities, establishing thereby interfacial shearing forces of sufiicient magnitude to overcome magnetic coherence between the particles but insufilcient to substantially comminute the particles; hydraulically segregating within the body the particles while they are temporarily so dissociated into a fine particle fraction and a coarse particle fraction; axially discharging the fine particle fraction from the infeed end of the body while discharging the coarse particle fraction from the opposite end of the body; recycling a quantity of the discharged coarse particles to the grinding step until the particles are ground fine enough; and subjecting the discharged fine particle fraction to magnetic separation to remove magnetically susceptible solids from the non-magnetically susceptible solids.

4. A continuous process of liberating and segregating magnetically susceptible solids from a solid mass of non-magnetically susceptible solids locked together with magnetically susceptible solids, which comprises the steps of grinding the mass into particles some of which are fine enough and others of which are not fine enough; magnetically removing magnetically susceptible particles from a substantial portion of the non-magnetically susceptible particles; temporarily hydraulically dissociating the magnetically cohered particles by establishing and maintaining a body of liquid enclosed in a space confined by a surface of revolution, tangentially introducing a suspension of the cohered particles into an end section of the body at a pressure sufiicient to swirl the body of liquid in concentric swirls having different annular velocities, establishing thereby interfacial shearing forces of sufiicient magnitude to overcome magnetic coherence between the particles but of insufficient magnitude to substantially comminute the particles; hydraulically segregating within the body the particles while they are temporarily so dissociated into a fine particle fraction and a coarse particle fraction; axially discharging the fine particle fraction from the infeed end of the body while discharging the coarse particle fraction from the opposite end of the body; recycling a quantity of the coarse particles to the grinding step until the particles are ground fine enough; and subjecting the discharged fine particle fraction to magnetic separation to remove magnetically susceptible solids from the non-magnetically susceptible solids.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,377,524 Samson June 5, 1945 2,388,471 De Vaney Nov, 6, 1945 2,468,586 Braund Apr. 26, 1949 2,543,689 Driessen Feb. 27, 1951 19 Number Name 1 Date 2,558,635 Vedensky June 26, 1951 2,573,192 Fontein Oct. 30, 1951 OTHER REFERENCES Number Country Date 627,423 Great Britain Aug. 9, 1949 FOREIGN PATENTS Canadian Mining Journal, vol. 71, No. 6, pages 68, 69, June 1950.

Engineering and Mining Journal, June 1950, vol. 151, issue No. 6, pages 71, 72, 73 (Erickson & Heckenoff) (Cyclone Separation May Be Solution for Fine Ore Problem).

Journal of the South African Chemical Institute, June 1949, vol. II, No. 1, pages 29-58.