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Publication numberUS3483968 A
Publication typeGrant
Publication dateDec 16, 1969
Filing dateJun 12, 1967
Priority dateJun 12, 1967
Publication numberUS 3483968 A, US 3483968A, US-A-3483968, US3483968 A, US3483968A
InventorsKaiser Robert
Original AssigneeAvco Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of separating materials of different density
US 3483968 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Dec. 16, 1969 METHOD OF SEPARATING MATERIALS OF DIFFERENT DENSITY Filed June 12, 19s? R. KAISER 3,483,968

2 Sheets-Sheet l GLASS v CERAMIC CORAL CLOSED M dH -XIO 3 dynes /cc IF m ROBERT KAISER INVENTOR.

ATTORNEYS R. KAISER Dec. 16, 1969 METHOD OF SEPARATING MATERIALS OF DIFFERENT DENSITY Filed June 12, 1967 2 Sheets-Sheet 2 zwmo JA E ommO a JA E QMmOJO JA E ROBERT KAISER INVENTOR.

ATTORNEYS 6 wumaowdz United States Patent US. Cl. 209-1 7 Claims ABSTRACT OF TI-IE DISCLOSURE Method of separating materials of different density by passing a controlled magnetic field through a ferrofluid and introducing the materials into the ferrofluid.

DEFINITIONS For the purposes of this discussion, a ferrofluid is defined as a material comprising a permanent colloidal suspension of ferromagnetic particles in a liquid carrier. The particles do not separate from the liquid carrier in the presence of a magnetic, gravitational, or acceleration field. The composite which is comprised of carrier fluid and particles appears to have the property of magnetic polarizability that is uniform Additional information relating to the subject matter of this invention may be found in the co-pending application entitled, Means For and Method of Moving Objects by Ferrohydrodynamics, Ser. No. 487,520, filed Sept. 15, 1965, to the same assignee as this application.

For the purposes of this discussion, levitation shall be understood to mean the effect of raising a body in contact with or submersed in ferrofluid in a direction opposite to gravity.

BACKGROUND OF THE iNVENTION In general, this invention is directed to a process of separating materials of different density and more particularly to accomplishing this objective through the use of magnetic fields and ferrofiuids.

OBJECTS It is an object of the invention to provide a novel method of separating materials according to differences in density.

It is another object of the invention to provide a method of separating materials of different density using the interaction of magnetic fields and ferrofiuids.

It is yet another object of the invention to achieve separation of materials of different density by differential levitation whereby materials of different density occur in different elevational strata.

It is still another object of the invention to achieve separation of materials by sequential levitation whereby materials of different density are levitated in sequence in accordance with their respective densities.

It is yet another object of the invention to achieve separation of materials of different density which is a function only of the density and independent of the shape and size of the material.

The invention, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a curve useful in describing the theory of operation.

FIGURE 2 is a schematic representation of process steps involved in separating materials of different density by sequential levitation.

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FIGURE 3 is a schematic representation of a process step useful in adapting a portion of FIGURE 2 to convert the FIGURE 2 process into a process for separating materials of different density by differential levitation.

THEORY OF OPERATION The purpose of this invention is to separate materials of different density using the principle of levitation in a ferrofluid. While the process and theory will be discussed in terms of solid particles, the process will work with immiscible liquids of different density.

The following equation was developed from the force equation presented in the co-pending patent application identified above. It described the equilibrium gravitational and magnetic forces acting on a non-magnetic object in a ferrofluid in the presence of a magnetic field having a vertical gradient.

Z7;d Z (Equation 1) In the above equation:

=density of the solid,

=density of the liquid,

gzacceleration of gravity=981 cm/sec.

M=average magnetization of liquid displaced by solid particle, gauss dH/dZ=gradient of magnetic field oersted/cm.

The gravitational term in Equation 1 (the left-hand term) is determined only by the difference in density of the solid object being levitated and density of ferrofluid used. For any given system both of these parameters are known. The magnetic (right-hand) term of Equation 1 is uniquely determined by the height, Z, above an arbitrary reference line. Since H is also a function of Z so is dH a function of Z. For a given ferrofluid, the magnetization of the liquid, M, is determined by the local field H, so it too, is solely a function of Z.

In practice, it is important to recognize that there are tWo specific requirements for the magnetic field. Frst, it must be strong enough to result in a noticeable magnetization of the fluid and secondly, the magnitude of this field must decrease in the upward direction so as to create a vertical gradient dH/dZ.

It would appear when a mixture of solid objects of different density is immersed in a ferrofluid and such a magnetic field applied, such of these solid objectsor non-magnetic immisible fluids-of different density can be selectively levitated. At least two situations have become clear. If dH/dZ is uniform throughout the ferrofluid, the levitation forces increase with an increase in MdH/dZ. If M is a saturation value as will most often be the case, the levitation force is purely a function of dH/dZ. Accordingly, as dH/dZ is increased, objects of lowest density will be levitated first to be followed in a sequence by objects of greater density in order of their relative densities.

On the other hand, if the magnetic field has a nonhomogeneous gradient, dH/dZ opposed to the direction of gravity, that is to say the magnitude of dH/dZ decreases in the Z direction opposite to the gravitational field, objects of different density will seek different levels in the fluid such that in each case Equation 1 is satisfied. Under these conditions, objects of lesser density will be elevated above objects of greater density. In other words, objects seek levels of elevation that are a function of their relative densities. There are two extreme cases where there can be no separation, namely when all the objects are levitated to the surface or when none of the objects are levitated at all.

A prepared mixture of solid objects of different specific gravities (densities) was immersed in a ferrofluid in the presence of a magnetic field gradient opposed to the direction of gravity. The objects immersed Were:

Material: S.g. Glass 2.35

Ceramic 2.72

Diamonds 3.40 Sapphire 3.96 Coral 5.46

These solid objects floated at different levels which allowed the objects to be easily separated. It should be noted that objects of different sizes and shapes in each of the materials were used in these experiments and that these parameters did not influence the results. The curve in FIGURE 1 summarizes the results demonstrated experimentally. The curve 11 in FIGURE 1 represents a theoretical prediction based on Equation 1. The discrete points taken with three different objects having three different densities is seen to correlate very closely with the prediction.

A magnetic levitation effect is most pronounced and most effective when performed with nonmagnetic materials. The magnetic levitation effect will be smaller with solid objects that are magnetically responsive than with magnetically non-responsive materials. Magnetically responsive solids will behave as non-magnetic objects of higher density. The magnetic lift term will be equal Where M is the volume average magnetization of the solid. When M =0, this reduces to Equation 1. When M M, there is no magnetic levitation effect possible. The presence of strongly magnetic substances (i.e., M M) in the batch of materials to be separated has very little deleterious effect on the process described since the material will be attracted to the magnetic field and made an inactive constituent.

GENERAL DISCUSSION While it was known previously that non-magnetic objects could be levitated, the unique developments embodied in the invention covered by this discussion was the realization that ferromagnetic levitation could be adapted to solve a problem of separating materials according to their density. Further contribution was the realization that this could be done through the manipulation of dH/dZ in particular and MdH/dZ in general. Both sequential levitation and differential leviation represents an important contribution to advancing the state of the art as it existed prior to the invention.

SEQUENTIAL LEVITATION Separation of objects of different density by means of sequential levitation is best described by reference to FIGURE 2. The common elements of FIGURE 2A through FIGURE 2E are a container 12 in which a quantity of ferrofluid 13 is inserted. Extending from one side of the container 12 is a pair of screens 14 and 16, respectively. These screens may be moved laterally, to the right in this particular configuration, to block the upward or downward movement of particles that may be placed Within the container 12. At the bottom of the container 12 is found a valve 17 which when open serves to drain the ferrofluid 13 from the container 12. A magnetic field source is shown schematically at 18.

In accordance with one aspect of the theory previously discused, the magnetic field source 18 when energized will provide a uniform dH/dZ within the ferrofluid 13. Finally, objects having different densities are immersed in the ferrofluid 13 as shown in particular in FIGURE 2A. These objects 19 are further assumed to have densities varying from very low to high. In this case since all of the objects 19 are found at the bottom of the container 12, the density of the least dense objects in this 4 case obviously is higher than the density of the ferrofluid 13.

In FIGURE 2A all of the objects 19 rest on the bottom of the container 12 and the magnetic field source is de-energized as indicated. In FIGURE 2B the magnetic field source has been turned on. There is created within the ferrofluid 13 a value of of sufficient magnitude to cause the low density particles 21 to float to the top of the ferrofluid 13. In this case, a uniform gradient dH/dZ is produced. This is symbolically shown at 20 in FIGURE 2B. It must be emphasized that the low density particles 21 need not necessarily be homogeneous in their composition, but their densities must be such that they all are less than or equal to the density of the densest particle floating in the ferrofluid. At this point, the screen 14 is moved to the right and placed in a position to prevent any further particles that may Want to rise from rising past the height of the screen 14.

Before proceeding, an assumption has been made that M does not vary. This will apply to most instances where an electromagnet is the magnetic field source and that the magnetic field generated results in saturation of the ferrofluid.

In FIGURE 2C the following conditions exist. The magnetic field source is turned on but its density is such that is higher than that which exists in connection with FIG- URE 2B. Under these conditions, the medium density particles 22 are levitated but for the presence of the screen 14 in this case, the medium density particle 22 noted will rise to the surface of the ferrofluid 13. Here again, the common element in the medium density particle 22 is that all of these are less dense than the densest particle levitated.

With the magnetic field source still on, the screen 16 is now moved to the right separating the medium density particles 22 from the heavy density particles 23, Finally, the magnetic field source is turned off. Clearly, in the absence of magnetic field, the levitated particles 21 and 22 tend to fall toward the bottom of the container 12 and are prevented from doing so by the screens 14 and 16. The valve 17 is now open draining the ferrofluid 13 from the container 12 and it is clear from FIGURE 2C that a complete separation has been achieved, in this case into three cuts, so to speak, of the original mixture of objects 19 (FIGURE 2A), according to the respective densities of the particles.

It is clear that by providing a larger number of screens and by more. accurate control of the magnetic field it would appear possible to separate the original mixture of the objects 19 into a greater number of cuts. Generally, however, as the process is conceived, three will be adequate. For example, if one wanted to recover a valuable component such as diamonds which exist as a trace commodity in the dirt better known as gangue, in which it exists in a material state, one would adjust the system shown schematically in FIGURE 2 such that light density gangue would float to the top, diamonds and those elements of gangue of the same density as diamonds in the center with the heavy gangue remaining on the bottom. The result is a mixture of diamonds and gangue in the center cut in which diamonds are found in a substantially larger concentration in the original gangue.

DIFFERENTIAL LEVITATION In the event the magnetic field generated by the magnetic field source is designed to have a non-homogeneous distribution of dH/dZ as more particularly shown in FIGURE 3 by a separation between the dotted lines 24. It is clear from Equation 1 that the objects of different density will be levitated within the fluid to difierent levels of elevation as shown in FIGURE 3. It is merely necessary now to insert the screens 14 and 16 as described previously, drain the ferrofluid 13 and remove the three cuts.

Summarizing the process briefly, a ferrofluid of known density and magnetization is provided. A magnetic field having a magnetic field gradient in the opposite direction to gravity is passed through the ferrofluid. A mixture of materials, preferably non-magnetic or less magnetic than the ferrofluid, of different density is placed in the ferrofluid.

All of the mixture may float in which case (lg dZ is high. All of the mixture may sink in which case (1H cZZ is small. It is quite clear that intermediate situations are easily achieved by adjusting M, dH/dZ or both.

This invention relates to a unique method of materials separation which is based on the ability to control and change the apparent density of the ferrofluid both in space (differential levitation) and time (sequential levitation) by application of a properly designed magnetic field whose intensity and space gradients can be varied at will in combination with the proper application in time and space of mechanical dividers.

It is to be emphasized that the proper sequence of events has to occur in the right order and the magnetic field has to be properly designed in order for the object of this invention which is the separation of materials of differing density to occur. For example, if a mixture of solid particles is placed in a bath of ferrofluid and a magnetic field gradient is applied which results in flotation of the densest particles to the surface of the bath, levitation will have occurred but separation will not have occurred.

What is claimed is:

1. A method of separating materials of different density comprising the steps of:

(a) providing a ferrofluid material comprising a permanent colloidal suspension of magnetic material in a liquid carrier, which colloidal suspension does not separate from the liquid carrier in the presence of magnetic, gravitational or an acceleration field, of known density and magnetization;

(b) passing a variable magnetic field through the ferrofiuid, said field having a magnetic field gradient dH/dZ in a vertical direction opposite to gravity;

(c) inserting in the ferrofluid a mixture of materials of diflerent density; and

(d) adjusting the magnitude of at least the magnetic field gredient dH/dZ for positioning at least two materials of different density at difierent elevations IVI in the ferrofluid with the lighter density material being above material of greater density.

2. A method of separating materials of diiferent density as described in claim 1 in which the magnetic field intensity as well as its gradient are varied.

3. A method of separating materials of different density as described in claim 1 in which the magnetic field gradient is uniform.

4. A method of separating materials of different density as described in claim 1 in which the magnetic field gradient is nonuniform.

5. A method of separating materials of different density comprising the steps of:

(a) providing a ferrofluid material comprising a permanent colloidal suspension of magnetic material in a liquid carrier, which colloidal suspension does not separate from the liquid carrier in the presence of magnetic, gravitational or an acceleration field, of known density and magnetization;

(b) passing a variable magnetic field through the ferrofluid, said fields having a magnetic field gradient dH/dZ in a direction opposite to gravity;

(c) inserting in the ferrofluid a mixture of materials of different density and adjusting the magnetic field intensity and gradient so that all of the mixture of materials is at one elevation; and

(d) adjusting the magnitude of at least the magnetic field gradient dH/dZ for positioning materials of different density at difierent elevations in the ferrofluid with the lighter density material being above material of greater density.

6. A method as described in claim 5 in which said adjustment comprise a sequence of changes for changing the elevation of constituents of said mixture in sequence in accordance with their relative density.

7. A method as described in claim 5 in which dH/dZ is non-uniform providing differential levitation and said adjustment sets the range of density which will be levitated.

References Cited UNITED STATES PATENTS 2,902,153 9/1959 Green 209208 3,065,640 11/1962 Langmuir 73-517 3,133,876 5/1964 Klass 209-1 3,206,987 9/1965 Cunningham 73517 OTHER REFERENCES American Journal of Physics, vol. 33, No. 5, May 1965, pp. 406, 407; Electrostatic Separation, by Lewis Epstein.

International Science and Technology, July 1966, Magnetic Fluids, pp. 4854 and 56, R. E. Rosensweig.

FRANK W. LUTTER, Primary Examiner US. Cl. X.R. 209-172.5; 210-

Patent Citations
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Referenced by
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US3788465 *Apr 28, 1972Jan 29, 1974Us InteriorDevice and process for magneto-gravimetric particle separation using non-vertical levitation forces
US3862029 *Oct 1, 1973Jan 21, 1975Joyce John EDensity gradient fractionator
US3951784 *Jan 29, 1975Apr 20, 1976Avco CorporationFine powder classification by ferrofluid density separation
US3951785 *Jan 29, 1975Apr 20, 1976Avco CorporationClassification by ferrofluid density separation
US4025448 *Dec 29, 1975May 24, 1977Union Carbide CorporationSuperparamagnetic wax compositions useful in magnetic levitation separations
US4052297 *May 30, 1973Oct 4, 1977Avco CorporationMaterials handling apparatus for a ferrofluid sink/float separator
US4062765 *Dec 29, 1975Dec 13, 1977Union Carbide CorporationApparatus and process for the separation of particles of different density with magnetic fluids
US4085037 *Dec 29, 1975Apr 18, 1978Union Carbide CorporationProcess for separation of non-magnetic particles with ferromagnetic media
US4526681 *Oct 31, 1983Jul 2, 1985Purdue Research FoundationIntroducing second particles having different magnetic susceptibility, establishing magnetic susceptibility gradient, causing particles to separate
US4594149 *May 21, 1982Jun 10, 1986Mag-Sep Corp.Apparatus and method employing magnetic fluids for separating particles
US4663029 *Apr 8, 1985May 5, 1987Massachusetts Institute Of TechnologyMethod and apparatus for continuous magnetic separation
US4819808 *Jun 2, 1986Apr 11, 1989Mag-Sep Corp.Apparatus and method employing magnetic fluids for separating particles
US4961841 *Apr 7, 1989Oct 9, 1990Mag-Sep CorporationApparatus and method employing magnetic fluids for separating particles
US6026966 *Oct 29, 1997Feb 22, 2000Svoboda; JanFerrohydrostatic separation method and apparatus
US6159271 *Sep 11, 1998Dec 12, 2000The Boeing CompanySeparation of gas and liquid, e.g. hydrazine, water, in an orbiting spacecraft by placing magnet(s) in a container opposite a desired location for the diamagnetic liquid; the diamagnetic force repels the liquid to where desired
US6851557Feb 15, 2000Feb 8, 2005Jan SvobodaFerrohydrostatic separation method and apparatus
US6994219Jan 26, 2004Feb 7, 2006General Electric CompanyMethod for magnetic/ferrofluid separation of particle fractions
US7753211Dec 21, 2006Jul 13, 2010Bakker Holding Son B.V.Method and device for separating solid particles on the basis of a difference in density
US8485363May 9, 2011Jul 16, 2013Bakker Holding Son B.V.Device for and method of separating solid materials on the basis of a mutual difference in density
EP0839577A1 *Oct 30, 1997May 6, 1998De Beers Consolidated Mines LimitedFerrohydrostatic separation method & apparatus
EP1800753A1 *Dec 12, 2006Jun 27, 2007Bakker Holding Son B.V.Method and device for separating solid particles on the basis of a difference in density
EP2386358A1May 10, 2011Nov 16, 2011Bakker Holding Son B.V.Device for and method of separating solid materials on the basis of a mutual difference in density
WO2000048740A1 *Feb 15, 2000Aug 24, 2000De Beers Cons Mines LtdFerrohydrostatic separation method and apparatus
WO2013037732A1 *Sep 10, 2012Mar 21, 2013Siemens AktiengesellschaftA method and a system for determining counts of a target cellular entity in a suspension using magnetic levitation
Classifications
U.S. Classification209/1, 209/172.5, 210/695, 210/222
International ClassificationB03C1/00, B03C1/32
Cooperative ClassificationB03C1/32
European ClassificationB03C1/32