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Publication numberUS3463310 A
Publication typeGrant
Publication dateAug 26, 1969
Filing dateFeb 27, 1968
Priority dateFeb 27, 1968
Also published asDE1758135A1, DE1758135B2
Publication numberUS 3463310 A, US 3463310A, US-A-3463310, US3463310 A, US3463310A
InventorsBerman Martin, Ergun Sabri
Original AssigneeUs Interior
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Separation method
US 3463310 A
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Description  (OCR text may contain errors)

SEPARATION METHOD Filed Feb. 27, 1968 wtmll mw /NvE/vrons SABR/ E RGU N MART /N HERMAN s lulllllll'lll'dll HHH HHHIHIIH HHUII'IH UVHHIIIIIHUH HIIH HIIIIH H H... |||||I|IY kum United States Patent O 3,463,310 SEPARATION METHOD Sabri Ergun and Martin Berman, Pittsburgh, Pa., assignors to the United States of America as represented by the Secretary of the Interior Filed Feb. 27, 1968, Ser. No. 708,627 Int. Cl. B03c 1/16, 1/00 U.S. Cl. 209-8 14 Claims ABSTRACT OF THE DISCLOSURE This invention resulted from work done by the Bureau of Mines of the Department of the Interior, and the domestic title to the invention is in the government.

BACKGROUND OF INVENTION It is known that the magnetic properties of many minerals can be altered by subjecting them to a heat treatment. This is the simplest and probably the only practical method for altering magnetic properties. The process may be a simple heating, an oxidizing roast as for many sultides, a reducing roast as for hematite and other iron oxides or a combination of several treatments. After such heat treatment, the mineral being procesed is conventionally subjected to a magnetic separation step.

Some of the minerals which are known to display increased magnetic activity after heat treatment include pyrite, hematite, marcasite, siderite, chalcopyrite, arsenopyrite, bornite, pyrolusite and many others. Temperatures used in the heat treatment generally range from about 300 to 1000 C. for a contact time of few seconds to an hour or more. Treatment conditions used include oxidizing, inert and reducing atmospheres depending upon the mineral. Heat treatment followed by magnetic separation now finds its greatest use in ore concentration.

It has been proposed to use this same process for the removal of pyrite from coal. Sulfur content of bituminous coals mined in the United States ranges from less than 1% to as much as 6% or more. Pyritic sulfur generally makes up from about 40 to 80% of the total sulfur present. Recent emphasis on the reduction of sulfur dioxide emissions from coal burning processes is forcing utilities and other coal users to rely either on scarce, naturally occurring low sulfur coals or on coals which have been processed to lower their sulfur content.

Finely divided coal can be subjected t a thermal treatment, usually in the presence of steam and air, to effect at least a partial conversion of the contained pyrite particles to pyrrhotite, magnetite and gamma-hematite. Because these minerals are all ferromagnetic while the original pyrite is paramagnetic, the treatment allows an elficient magnetic separation of the altered pyrite from the coal.

The pyrite-pyrrhotite transition takes place very rapidly at temperatures on the order of 600 C. and the pyrite to magnetite or hematite oxidation reaction also requires relatively high temperatures. Coal treatment temperatures as high as 360 C. have been used and alteration of the surfaces of pyrite grains to magnetic forms has been reported at these conditions.

In spite of the apparent attractiveness of this process for the removal of pyrite from coal, it has two major 3,463,310 Patented Aug. 26, 1969 ICC drawbacks which seriously limit its applicability. First, the cost of heating the coal makes the process economically unattractive. Secondly, and most important, heating coal above about 200 C. starts to drive ott the coal volatiles. Besides changing the burning characteristics 0f coal, volatiles lost from the coal represent a significant portion of its calorific value.

The process of this invention takes advantage of the conductivity differences to electromagnetic radiation between pyrite and coal in order to selectively heat the surface of pyrite particles contained within the coal. C011- version of at least the surface of pyrite particles to ferromagnetic forms is accomplished without substantial heating of the coal.

It is an object of this invention to selectively alter the properties of one member in a physical mixture by subjecting the mixture to electromagnetic radiation.

Another object of this invention is to alter at least the surface of a diamagnetic or paramagnetic mineral to ferromagnetic forms by selectively heating that mineral while it is in physical admixture with other components.

A specific object of this invention is to remove pyrite from coal.

DESCRIPTION OF THE INVENTION The invention will be more clearly understood from the following description of a preferred embodiment wherein reference is made to the accompanying drawing.

The figure is a schematic flow diagram of a preferred embodiment of the separation process.

Referring now to the figure, there is shown an arrangement particularly adapted for the treatment of coal to remove the contained pyrite. Finely-divided coal from feeding hopper 11 is deposited upon moving conveyor belt 12 by means of feeding device 13 and distributor 14. The particle size range of coal fed t0 the process should conform as nearly as is conveniently possible to the size range producing maximum pyrite availability, or substantial physical release of pyrite crystals from the coal matrix. Since the size of pyrite particles is known to vary widely between different types of coals, the preferred size range is dependent between different types of coals, the preferred size range is dependent primarily upon the particular coal being processed. Particle size range producing maximum pyrite availability will vary generally in the broad range of about 40 to 400 mesh. `In Pittsburg seam coal for example, maximum pyrite availability occurs in the range of 200 to 400 mesh.

Tunnel irratiator 15 is of rectangular cross-section with electrically conducting walls. End sections 16 and 17 terminate the tunnel section and function to suppress the escape of electromagnetic energy. Coal is carried through tunnel 15 by continuous belt conveyor 12 formed of a dielectric material such as a reinforced Teflon. Conveyor 12 may be mounted on rotating drums 18 and 19 disposed one at each end of the tunnel as is conventional in the art. A driving force is applied to at least one of the drums in the direction indicated by arrow 20.

Electromagnetic energy, produced by a suitable conventional source 21, is introduced into tunnel 15 by means of energy conduit 22. At microwave frequencies, conduit 22 comprises a waveguide of rectangular cross section having a series of openings spaced along the wall facing the interior of tunnel 15. Microwave energy is thus directed downwardly into the interior of the tunnel where it interacts with the pyrite and coal. Depending upon the frequency of electromagnetic radiation utilized, coaxial cables, striplines and the like may be utilized as the energy conduit rather than the waveguide.

Treatment time of the coal within the irradiating cavity or tunnel 15 is dependent upon the moisture content of the coal, the frequency of the electromagnetic radiation and the effective voltage gradient within the tunnel. Treatment times in the range of 1 to about 100 seconds are satisfactory for most coals over the frequency range investigated. At 10 ghz, exposure times of about 2 to 10 seconds were found satisfactory.

While preferential heating of pyrite dispersed in coal occurs over a wide range of the electromagnetic spectrum, it is preferred to operate at frequencies above 106 cycles per second or 1 mhz. In a most preferred embodiment, frequencies used are above 109 cycles per second or 1 ghz.

Optimum process efliicenies are obtained when only surface modilication of the individual pyrite particels to ferromagnetic forms has been achieved. Continued exposure results in more complete reaction of the pyrite but also results in undue heating of the coal. It is preferred that exposure time be limited to a pyrite conversion level of less than 10% and most preferably to a pyrite conversion level of less than 5%.

In some instance, it is desirable to provide a controlled' ow of treating gas through the tunnel 1S. Gas may be introduced via conduit 23 at one end of tunnel 15 and removed via conduit 24. In processing coal for the removal of pyrite, the treating gas preferably is air. Use of air as the treating gas performs two functions; it sweeps out water vapor released from the coal and it provides a EXAMPLE Samples of finely divided coal containing pyrite were subjected to electromagnetic radiation at frequencies ranging from 400 khz to ghz. Throughout this frequency range, preferential heating of the contained pyrite was observed. As the frequency increased, the preferential heating of pyrite relative to coal become more pronounced. Pyrite in the mixture thus treated was strongly attracted to a magnet and no losses of coal volatiles were observed.

Good conversion of the pyrite particles to ferromagnetic forms was observed at 10 ghz without noticable heating of the coal. The trend of the data indicated that even higher frequencies would increase the selectivity of the heating process.

While the process has been illustrated using a conveyor-tunnel type of apparatus, the electromagnetic treatment may be performed using any other applicable type of high frequency heating equipment. For example, a coaxial tube arrangement having an annular treatment chamber with the electromagnetic radiation facilities arranged within the inner tube may also be used to advantage The process has been illustrated as being particularly applicable to the removal of pyrite from coal. By appropriate choice of radiation frequency, separations may be performed on other mineral mixtures. Generally, any mineral mixture having at least one member which is susceptible to being altered to a more highly magnetic form upon heating can be treated by this process. One example of such a mixture is a pyrite-chalcopyrite-silicate ore which may be treated to produce a copper concentrate.

What is claimed is:

1. A process for the separation of a mixture of particulate materials, at least one of said materials being susceptible to a change in its magnetic properties upon heating, which comprises subjecting said mixture to electromagnetic radiation having a frequency whereat said material susceptible to a change in magnetic properties absorbs electromagnetic energy `more strongly than does the other components in said mixture and is thereby preferentially heated, continuing the irradiation for a time sufficient t0 cause conversion of at least a surface layer of said particulate material being susceptible to such a change to a more highly magnetic form, terminating the irradiation before substantial heating of the other components of the mixture occurs, subjecting said irradiated mixture to a magnetic separation step and recovering a portion enriched in said magnetically altered material.

2. The process of claim 1 wherein the conversion of said magnetically alterable material is less than 10%.

3. The process of claim 1 wherein said frequency is greater than 1 mHz.

4. The process of claim 1 wherein said mixture is contacted with a How of treating gas during said irridation step.

5. The process of claim 1 wherein said mixture comprises coal and said material susceptible to a change in magnetic properties upon heating is pyrite.

6. The process of claim 5 wherein said more highly magnetic form comprises pyrrhotite.

7. The process of claim 5 wherein said frequency is greater than 1 mHz.

8. The process of claim 7 wherein said frequency is greater than 1 gHz.

9. The process of claim 5 wherein said mixture is contacted with a ow of treating gas during said irridation step. y

10. The process of claim 9 wherein said treating gas comprises air.

11. The process of claim 5 wherein the conversion of said pyrite is less than 10%.

l2. The process of claim 11 wherein the conversion of said pyrite is less than 5%.

13. The process of claim 5 wherein the particle size of said coal is less than about 40 mesh.

14. The process of claim 13 wherein the particle size range of said coal is less than about 200 mesh.

References Cited UNITED STATES PATENTS 1,478,295 12/1923 Perkins 209-11 1,512,870 10/1924 Ullrich 209-214 2,907,456 10/ 1959 Brison 209-11 3,097,160 7/1963 Rich 20'9-11 X FOREIGN PATENTS 67,456 5/ 1927 Sweden.

OTHER REFERENCES Aronov et al., Coke Production, Heating Coals with High Frequency Currents, Stal. 15, 771-776, 1955.

Kester, Magnetic Demineralization of Pulverized Coal, Mining Eng., May 1965, pp. 72-76.

HARRY B. THORNTON, Primary Examiner R. HALPER, Assistant Examiner U.S. Cl. X.R. 209-214, 11

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1478295 *Oct 6, 1920Dec 18, 1923Metals Production Company Of NTreatment of complex sulphide ores
US1512870 *Sep 2, 1920Oct 21, 1924Krupp Ag GrusonwerkMethod of recovering fuel from residues
US2907456 *May 21, 1957Oct 6, 1959Int Salt CoSeparation of materials
US3097160 *Nov 30, 1959Jul 9, 1963Robert E CohnMethod of separating differentially heated particles
SE67456A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3969225 *Aug 28, 1975Jul 13, 1976I. Jordan KunikDifferential separation of particulates by combined electro-static and radio frequency means
US3976557 *Nov 29, 1974Aug 24, 1976Hydrocarbon Research, Inc.Hydrogen, hydrogen sulfide
US4052170 *Jul 9, 1976Oct 4, 1977Mobil Oil CorporationMagnetic desulfurization of airborne pulverized coal
US4077871 *Apr 14, 1975Mar 7, 1978Occidental Petroleum CorporationDifferential heating
US4193767 *Oct 26, 1978Mar 18, 1980Fipke Charles EParticulate mineral separation process
US4252638 *Dec 6, 1978Feb 24, 1981Klockner-Humboldt-Deutz AgMethod for the desulfurization of coal
US4259560 *Sep 21, 1977Mar 31, 1981Rhodes George WProcess for drying coal and other conductive materials using microwaves
US4342640 *Nov 24, 1980Aug 3, 1982Chevron Research CompanyMagnetic separation of mineral particles from shale oil
US4359379 *Dec 16, 1980Nov 16, 1982Nippon Oil Company, Ltd.Process for fluid catalytic cracking of distillation residual oils
US4388179 *Nov 24, 1980Jun 14, 1983Chevron Research CompanyMagnetic separation of mineral particles from shale oil
US4406773 *May 13, 1981Sep 27, 1983Ashland Oil, Inc.Magnetic separation of high activity catalyst from low activity catalyst
US4466362 *Mar 3, 1982Aug 21, 1984Massachusetts Institute Of TechnologyHeating, magnetic separation
US4661118 *Apr 15, 1985Apr 28, 1987The United States Of America, As Represented By The Secretary Of The InteriorMethod for oxidation of pyrite in coal to magnetite and low field magnetic separation thereof
US5096066 *Mar 6, 1990Mar 17, 1992Genesis Research CorporationBeneficiating coal fines
US5153838 *Aug 6, 1991Oct 6, 1992Genesis Research CorporationProcess for beneficiating particulate solids
US5161695 *Apr 13, 1992Nov 10, 1992Roos Edwin HMethod and apparatus for separating particulate material according to conductivity
US5171424 *Oct 22, 1990Dec 15, 1992Ashland Oil, Inc.Magnetic separation of old from new cracking catalyst by means of heavy rare earth "magnetic hooks"
US5190635 *Oct 17, 1991Mar 2, 1993Ashland Oil, Inc.Magnetic separation of deactivated catalyst from more active particles
US5262962 *Aug 9, 1991Nov 16, 1993Genesis Research CorporationProcess for beneficiating particulate solids
US5280836 *Mar 12, 1992Jan 25, 1994Genesis Research CorporationProcess for beneficiating particulate solids
US5538624 *Oct 21, 1994Jul 23, 1996Ashland Inc.Process, apparatus and compositions for recycle of cracking catalyst additives
US6923328Feb 22, 2002Aug 2, 2005Wave Separation Technologies Llcheating ores using microwaves or sound waves to increasing magnetic sensitivity, then diving into magnetic or nonmagnetic particles
US7318528 *Jul 26, 2004Jan 15, 2008Iradj HessabiPrecious metal recovery
US7571814Sep 28, 2004Aug 11, 2009Wave Separation Technologies LlcMethod for separating metal values by exposing to microwave/millimeter wave energy
US8197678Mar 23, 2011Jun 12, 2012MR & E, Ltd.Refining coal-derived liquid from coal gasification, coking and other coal processing operations
US8366882Sep 10, 2009Feb 5, 2013C20 Technologies, LlcProcess for treating agglomerating coal by removing volatile components
US8394240Sep 10, 2009Mar 12, 2013C2O Technologies, LlcProcess for treating bituminous coal by removing volatile components
US8469196Jul 9, 2009Jun 25, 2013Wave Separation Technologies, LlcMethod and apparatus for separating metal values
US8470134Sep 10, 2009Jun 25, 2013C2O Technologies, LlcProcess for treating coal by removing volatile components
CN100532592CFeb 19, 2003Aug 26, 2009波分离技术有限责任公司Method and apparatus for separating metal values
EP0431965A2 *Dec 7, 1990Jun 12, 1991De Beers Industrial Diamond Division (Proprietary) LimitedMagnetic separation of material using eddy currents
WO1980002220A1 *Apr 9, 1980Oct 16, 1980D BrandonAn apparatus and method for thawing materials stored in gondola-type containers
WO2003072835A1 *Feb 19, 2003Sep 4, 2003Stephen BirkenMethod and apparatus for separating metal values
U.S. Classification209/8, 209/11, 209/214, 208/426, 208/402
International ClassificationB03C1/015, B03C1/005, C10B57/00, C10B57/08
Cooperative ClassificationC10B57/08, B03C1/015
European ClassificationC10B57/08, B03C1/015