BR112014027848B1 - METHODS FOR OBTAINING COMPOSITIONS COMPRISING KAOLINITE - Google Patents

Abstract

COMPOSITIONS OF RARE EARTH ELEMENTS OBTAINED FROM PARTICULATE MATERIAL COMPRISING KAOLINITE, AND METHODS FOR OBTAINING THESE COMPOSITIONS COMPRISING KAOLINITE. A method for obtaining compositions of rare earth elements is described. The method includes providing a dispersed aqueous suspension of a particulate material including at least one compound of rare earth elements and kaolinite. The method further includes adding to the suspension a selective flocculating polymer which facilitates the separation of at least a portion of the at least one rare earth element compound from kaolinite by flocculation thereof, and allows particles of the rare earth element compound to be or remain unflocculated. The method further includes allowing the polymer-containing suspension to separate, in a selective flocculation separator, into layers including a flocculated product layer and a deflocculated layer containing part of the at least one rare earth element compound. The method further includes extracting each of the separate layers from the separator. Composite rare earth elements include La2O3, CeO2, Nd2O3, or Y2O3.

Description

[0001] This international PCT application claims priority benefits for, and incorporates by reference herein in its entirety, the U.S. Provisional Patent Application. At the. 61/645,237, filed on May 10, 2012.

DESCRIPTION FIELD

[0002] This description relates to rare earth element compositions obtained from particulate compositions comprising kaolinite and methods for obtaining rare earth element compositions from particulate materials comprising kaolinite.

FUNDAMENTALS OF THE INVENTION

[0003] Kaolin or kaolinite clay is a clay containing rock comprised of kaolin minerals that are white or almost white, or can be processed to become white or almost white. Such clays were formed by weathering or hydrothermal alteration of feldspar and mica mineral components contained in feldspar rocks such as granite and gneiss. Primary kaolin clays are those found in deposits at the site where they were formed, and they usually contain, with the kaolin minerals, some unaltered mica and possibly feldspar, and stable minerals such as quartz, which must be separated from the clay. during the refining process of clay products. For example, primary kaolin deposits are mined and processed in places such as southwest England, France, Germany, Spain, and the Czech Republic. Sedimentary kaolin, which is alternatively known as secondary kaolin, is that which contains sediments eroded from a feldspathic source rock and deposited in fluvial or marginal marine environments, such as those associated with deltas. For example, kaolin clays mined and processed from deposits in Georgia, South Carolina, and Alabama in the United States, and from deposits in the state of Pará in Brazil, are generally of the sedimentary type. Sedimentary clays deposited in different geological eras can also be used, such as Tertiary or Cretaceous clays.

[0004] Rare earth elements include the fifteen lanthanides, scandium, and yttrium (ie, correspond to elements associated with atomic numbers 57-71, 21, and 39, respectively). Rare earth elements, although relatively abundant in the Earth's crust, are typically dispersed and not found in concentrated amounts or economically exploitable forms in most crustal rocks. Exceptions include igneous rocks such as the carbonatites located in Mountain Pass, California; peralkaline syenites and granites located in Pajarito Mountain, New Mexico; and veins of monazite-apatite lodged in granite near Crescent Peak, Nevada. The largest rare earth deposit in the world is at Bayan Obo in Inner Mongolia, China. Rare earth at Bayan Obo is recovered as a by-product of iron production from a variety of rock types containing magnetite. Rare earth elements are concentrated in specific accessory minerals associated with the ore. Some of the minerals that may contain rare earth elements are apatite, bastnasite, florencite, monazite, xenothymium. Bastnasite is a lanthanide carbonate. Apatite, monazite, and xenothymium are phosphates. Florencita and a variety of lesser known rare earth containing minerals are hydrated aluminum phosphates. Phosphate-containing minerals resist the chemical attack of weathering and can be found in sedimentary deposits. Some marine heavy mineral sand deposits, which contain monazite and xenothymium that can be economically separated, are at Eneabba, Australia; and other heavy mineral beach sand deposits mined and processed as by-products in Brazil, India, Malaysia, Thailand, China, Taiwan, United States, New Zealand, Sri Lanka, Indonesia, Zaire, and Korea. Some kaolinite claystone (sedimentary kaolin) deposits contain trace concentrations of hydrated aluminum phosphates, but non-commercially developed sedimentary kaolin deposits are known to produce rare earth concentrates.

[0005] The processes used for separating minerals containing rare earth elements from deposits are specific to each occurrence. Surface or underground mining of a hard rock rare earth ore, such as carbonatite or granite, typically requires liberation of mineral by crushing and grinding the ore prior to beneficiation. Flotation is used at Mountain Pass, California, to concentrate bastnasite particles released from an ore containing about 5% by weight REO (rare earth oxide) to a form of a concentrate containing about 60% by weight REO. Gold alluvial sand deposits containing monazite and xenothymium grains can employ gravity separation equipment, such as jigs, spiral classifiers, and hydrocyclones, to separate different sand particles of heavy minerals from light minerals based on their different specific gravity. The heavy gravity separator minerals are then fed to a magnetic separator to remove magnetic minerals, an electrostatic separator to remove titania minerals, and a final magnetic separation stage to separate zirconium. Rare earth mineral concentrate produced from a variety of geological environments is then fed to a process that extracts the REE (rare earth elements) by dissolution in hot concentrated acid or alkaline leaching. Another chemical fractionation to separate specific rare earth elements takes place after the leaching step.

[0006] Rare earth elements are an affordable commodity due to their numerous uses in modern devices and processes. For example, rare earth elements are often used in batteries, compact fluorescent lights, aerospace components, flat panel displays, high-temperature superconductors, lasers, polishing compounds, catalysts, water purification devices, compact speakers, and electronic devices, among other devices and methods. So, although concentrated deposits of rare earth elements are rare, the demand for rare earth elements is increasing. As a result, it would be desirable to identify new economically viable ways to concentrate useful amounts of rare earth elements from sources where rare earth elements are disseminated in REO-containing minerals having a low mass concentration in the rock. For example, because rare earth elements can be found as a component in minerals disseminated at low mass concentrations in rocks having high kaolinite concentrations, it would be desirable to develop an economically viable way to separate compositions of rare earth elements from material containing kaolinite, such as kaolin.

[0007] In addition to rare earth compositions, kaolin also often includes a number of substances considered to be impurities, particularly when kaolin is refined for use as an ingredient, pigment, or filler material in a variety of application compositions, such as , for example, loading and coating of paper, cardboard, and similar products. For example, kaolinite is a white mineral and is often used in such application compositions to impart, among other things, whiteness and shine. However, one or more desirable properties of kaolin can be adversely affected by the presence of impurities. Typical impurities may include, but are not limited to, minerals containing titania, such as anatase and rutile, quartz, mica, phosphates, smectite, and other silicate, oxide and hydroxide compounds containing transition elements, such as iron and chromium, and heavy metals such as lead and thorium. Thus, it would be desirable to develop a method of treating kaolin or other kaolinite-containing compositions such that not only rare earth element compositions are separated from the kaolinite-containing material, but other impurities are also separated from the kaolin or kaolinite-containing compositions.

SUMMARY OF THE INVENTION

[0008] According to a first aspect, a method for obtaining compositions of rare earth elements can include providing a dispersed aqueous suspension of a particulate material, including at least one compound of rare earth element and kaolinite. The method may further include adding to the suspension a selective flocculation polymer which facilitates the separation of at least a portion of the at least one rare earth element compound from the kaolinite by flocculation thereof, and allows particles of the rare earth element compound to are or remain deflocculated. The method may also include allowing the polymer-containing suspension to separate into layers in a selective flocculation separator, including a layer of flocculated product and a deflocculated layer containing part of the at least one rare earth element compound. The method may further include extracting each of the separate layers from the separator.

[0009] According to another aspect, the deflocculated layer may be an overflow layer. In accordance with another aspect, part of the at least one composite of rare earth elements may include particles having an equivalent spherical diameter of less than 325 microns. For example, the rare earth element composite particles may be a part of the deflocculated layer, and the rare earth element composite particles may float in the upper layer of the separate layers. In accordance with yet another aspect, the density of the deflocculated layer containing part of the at least one compound of rare earth elements can range from about 1.0005 to about 1.03. According to another aspect, the kaolinite can be included in the flocculated layer, and the flocculated layer can be in the bottom layer of the separated layers.

[0010] According to yet another aspect, the selective flocculation polymer may include a high molecular weight polymer. For example, the selectively flocculating polymer can include a weakly anionic organic polymer having a molecular weight greater than about 100,000. For example, the selectively flocculating polymer can include acrylamide-containing anionic units, the anionic units including not more than about 15% by weight of polymer. In another aspect, the total amount of selectively flocculating polymer added can range from about 0.01% to about 0.5% dry weight based on the dry weight of the particulate material.

[0011] According to yet another aspect, the particulate material can be obtained from kaolin. For example, the particulate material can be obtained from primary kaolin and/or secondary kaolin. According to another aspect, providing the dispersed aqueous suspension of the particulate material may include adding water and dispersing agent into inherently wet raw kaolin.

[0012] According to another aspect, the compound of rare earth elements may include compounds containing particles of rare earth elements. The at least one compound of rare earth elements can include particles having an equivalent spherical diameter of less than about 325 microns.

[0013] According to another aspect, the compound of rare earth elements can include La2O3 from more than 0% by weight to about 8.0% by weight, from about 0.1% by weight to about 5.0% by weight, or from 0.2% by weight to about 4.0% by weight. The compound of rare earth elements can include CeO2 from greater than 0% by weight to about 5.0% by weight, from about 0.1% by weight to about 4.5% by weight, or from 0 .3% by weight to about 4.0% by weight. The compound of rare earth elements can include Nd2O3 from greater than 0% by weight to about 2.0% by weight, from about 0.1% by weight to about 1.5% by weight, or from 0 .2% by weight to about 1.0% by weight. The compound of rare earth elements can include Y2O3 from greater than 0% by weight to about 0.2% by weight, from about 0.001% by weight to about 0.2% by weight, or from 0.01 % by weight to about 0.2% by weight.

[0014] According to another aspect, the deflocculated layer can include up to about 8.0% by weight La2O3, up to about 4.0% by weight CeO2, up to about 1.0% by weight Nd2O3, and up to about 0.2% by weight Y2O3. According to another aspect, the deflocculated layer can include up to about 4.0% by weight La2O3 to about 4.0% by weight CeO2, up to about 1.0% by weight Nd2O3, and up to about 0.1% by weight of Y2O3.

[0015] In accordance with yet another aspect, the method may further include conditioning the suspension before adding the selective flocculation polymer thereto, allowing the suspension to age for a period of at least thirty minutes. In another aspect, the method can include adjusting the pH of the suspension to be at least about 6.5 before allowing the suspension to age. In yet another aspect, the method may further include adding a conditioning chemical prior to or during aging.

[0016] According to another aspect, the method further includes adding sodium salt to the suspension after providing the dispersed aqueous suspension. In another aspect, the method can further include mechanically stirring the suspension during aging.

[0017] According to yet another aspect, the method may further include adjusting the pH of the suspension to be at least about 8, before adding the selective flocculation polymer. For example, the method can include adjusting the pH of the suspension to be at least about 9.8, to at least about 10.2, for example, so that the pH varies between about 10.2 and about 12. .5 before adding the selective flocculation polymer.

[0018] According to yet another aspect, the method may further include deagglomerating the dispersed aqueous suspension by a mechanical working process. For example, deagglomeration may include amalgamation or some type of high shear liquid working.

[0019] According to yet another aspect, the dispersed aqueous suspension may have a solids content of at least about 30% by weight. According to another aspect, the method can further include adding water to the separated layers before extracting the separated layers from the separator, so that the solids contents of the layers range from about 5% to about 15% by weight.

[0020] According to another aspect, the method may further include heating the dispersed aqueous suspension before adding the selective flocculation polymer.

[0021] Additional objects and advantages of the invention will be provided in part of the description that follows, and may be learned by practice of the invention. The objects and advantages of the invention will be realized and achieved by means of the particular elements and combinations indicated in the appended claims.

[0022] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.

[0023] The accompanying drawing, which is incorporated into and forms a part of this report, illustrates an exemplary embodiment of the invention and, together with the description, serves to explain principles of the invention.

[0024] BRIEF DESCRIPTION OF THE DESIGN

[0025] Fig. 1 is a diagrammatic flowchart showing an exemplary method of obtaining rare earth element compounds.

[0026] DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0027] Surprisingly and beneficially we find that compositions of rare earth elements can be obtained from particulate material containing kaolinite by the exemplary methods described here. For example, rare earth element compositions can be obtained from kaolin by the exemplary methods described herein.

[0028] According to some embodiments, a method of obtaining rare earth element compositions includes providing a dispersed aqueous suspension of a particulate material including at least one compound of rare earth elements and kaolinite. The exemplary method further includes adding to the suspension a selective flocculation polymer which facilitates the separation of at least a portion of the at least one rare earth element compound from the kaolinite by flocculation thereof and allows particles of the earth element compound to rare are or remain deflocculated.

[0029] The exemplary method also includes allowing the polymer-containing suspension to separate, in a selective flocculation separator, into layers, including a flocculated product layer and a deflocculated layer containing part of the at least one composite of elements of rare Lands. The exemplary method further includes extracting each separate layer from the separator.

[0030] According to some embodiments, the deflocculated layer is an overflow layer, in particular an upper layer of the separated layers. For example, particles of the composite of rare earth elements are a part of the deflocculated layer, and the particles of the composite of rare earth elements surprisingly float in the upper layer of the separated layers. In some embodiments, the kaolinite can be included in the flocculated layer, and the flocculated layer can be in the bottom layer of the separate layers.

[0031] According to some embodiments, the particulate material can be obtained from kaolin. For example, the particulate material can be obtained from primary kaolin and/or secondary kaolin. According to some embodiments, providing the dispersed aqueous suspension of the particulate material can include adding water and dispersing agent into an inherently wet raw kaolin.

[0032] According to some embodiments, the method includes conditioning the aqueous suspension by aging, for example, together with the addition of a conditioning chemical, which may be present during part or all of the aging, before raising the pH , for example, to a pH of at least 9.5, during selective flocculation, which may occur following addition of the selective flocculation polymer.

[0033] According to some embodiments, adjusting the pH to a value of at least about 8, for example, from about 10.5 to about 12.5, is carried out before adding the flocculating polymer selective. For example, the pH can be adjusted to be at least about 9.5, for example, from about 10.5 to about 12.5, for example, from about 10.5 to about 11.5 before, during, and/or after conditioning the aqueous suspension. According to some embodiments, the pH during conditioning of the aqueous suspension can be in the range from about 6 to about 9.5, for example from about 6.5 to about 7. The inventors believe that the benefit of raising the pH, for example, in combination with conditioning, for selective flocculation of particulate matter including rare earth element compounds and kaolinite, especially for the purpose of separating and removing, in a deflocculated form, rare earths, has not previously been recognized.

[0034] According to some embodiments, undesirable impurities such as, for example, one or more of titania, mica, feldspar, silicates such as quartz, clay mineral impurities such as smectites and other candites, phosphates, and metal oxides of, for example, iron and other transition metals, can be separated from kaolinite by embodiments of the methods described herein. Such methods can be used alone or in combination with one or more other known beneficiation processes.

[0035] According to some embodiments, the amount of undesirable impurities, especially fine impurities having an average particle size, for example, of less than about 1 micron or, in many cases, less than about 0 .5 microns, if present in treated particulate matter (eg kaolin clay), can be significantly reduced. Another potential advantage of some embodiments of the method described here is that it can allow the avoidance of costly foam flotation purification processes often employed in the beneficiation of, for example, kaolin.

[0036] Another possible advantage of some embodiments of the method described here is that it may allow the reduction of undesirable titania-containing impurities and fines in the particulate material (e.g., kaolin clay) to levels such that other treatment processes Conventional materials, which can beneficially be used in the treatment of particulate matter, can be applied more effectively. A further possible advantage of some embodiments of the method is that the method can be applied in one of several steps of a multi-step beneficiation process. For example, some embodiments of the method may be applied prior to other beneficiation steps, such as one or more oxidation, comminution (e.g. milling), particle size grading (e.g. centrifugation) , magnetic separation, and bleaching. As a result, the particulate matter (e.g. containing kaolinite) employed in some embodiments of the method, may include raw kaolin, which, apart from a dehulling step applied before or during the method, need not be subjected to any other particle separation or beneficiation steps until after treatment by the treatment method, for example after extracting the separated layers from the separator.

[0037] Another possible advantage is that the fineness and purity of the particulate material treated by the method are not critical, which can further distinguish embodiments of the described method from other treatment methods. For example, a kaolin treated by the method may include a raw kaolin ore having a kaolinite content greater than 5%, such as greater than 10%, greater than 20%, greater than 30%, greater than 40 %, greater than 50%, greater than 60%, greater than 70%, greater than 80%, or even greater than 90%. In another example, a kaolin treated by the method can include a raw kaolin ore having a kaolinite content of less than 90% by weight (e.g., in the range of 5% by weight to 90% by weight, of 5 % to 70%, or 50% to 90%), although kaolin ore and descaled sludge, having a kaolinite content greater than 70% by weight, may also be more favorably treated by the method.

[0038] According to some embodiments, the method described here can be operated as a batch, semi-continuous or continuous process.

[0039] According to some embodiments, the starting material for the method may include substantially dry kaolin clay. The starting material can be treated by adding water and dispersant thereto to produce the dispersed aqueous suspension of particulate material. According to some embodiments, mechanical working (e.g., by amalgamation) is applied to the aqueous suspension of particulate material, whereby agglomerates present in the particulate material are broken down by the working process. The working process can be carried out before a conditioning step and can be applied during the treatment of the starting material with water and dispersant. Dispersant addition and job application can be applied together, for example in a batch, semi-continuous, or continuous process.

[0040] Suitable dispersants for suspension particles include anionic dispersants employed in a deflocculation/selective flocculation separation process. For example, the dispersant may include an inorganic agent, such as, for example, an alkali metal silicate (e.g., sodium silicate or potassium silicate), or a condensed phosphate salt, such as, for example, sodium hexametaphosphate or sodium pyrophosphate. Alternatively, or in addition, the dispersant may include an organic agent, such as, for example, a lignosulfonate (e.g., sodium lignosulfonate) or a polycarboxylate (e.g., a polyacrylate, such as sodium polyacrylate). ).

[0041] According to some embodiments, a dispersant composition suitable for addition to the aqueous suspension during treatment of the aqueous suspension with water and dispersant includes an inorganic agent (e.g., condensed phosphate salt) and a polycarboxylate (e.g., a low molecular weight polyacrylate (e.g., a weight average molecular weight of less than 20,000)) added during water and dispersant treatment or later (e.g., when the product conditioning chemical is added next to mechanical work). The term "polyacrylate" in this specification includes copolymers of acrylic acid with other monomers (eg, maleic acid or methacrylic acid). In such copolymers, the acrylic acid units can provide at least 50% by weight of polymer. In such a dispersant composition, the weight ratio (on a dry or "active" weight basis) of inorganic agent to polycarboxylate may, for example, be x:1, where x is greater than 1. In such a ratio, x may be at least 2.0 (eg, 2.0 to 5.0). According to some embodiments, the inorganic agent of the dispersing composition can include sodium hexametaphosphate and the polycarboxylate can include sodium polyacrylate.

[0042] According to some embodiments, the dispersed aqueous suspension is treated by the mechanical working process at a particle solids concentration of at least about 30%, at least about 40%, at least about 50%, at least about 60%, or about 70% or more by weight. A work input of at least about 5 kJ/kg, for example, at least about 15 kJ/kg (e.g., from about 20 kJ/kg to about 400 kJ/kg), can be applied during the process of mechanical work.

[0043] According to some embodiments, after providing the dispersed aqueous suspension of particulate matter, including any applied mechanical work, the suspension may be diluted and/or descaled to remove large particles that may still be present in the aqueous suspension.

[0044] According to some embodiments, the pH of the aqueous suspension can be adjusted prior to conditioning. For example, the pH of the aqueous suspension can be adjusted to be about 6 or greater (e.g., from about 6.5 to about 9.5, e.g., from about 6.5 to about 7.5). According to some embodiments, the pH can be adjusted before conditioning the suspension and again following conditioning to an even higher value. Any pH adjustment can be carried out by adding one or more suitable basic substances, for example selected from alkali metal hydroxides and carbonates, and ammonium hydroxides and carbonates, such as, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, or ammonium hydroxide.

[0045] According to some embodiments, exemplary aging conditioning of the method may be carried out for a period of at least about 30 minutes, for example, at least about two hours, prior to addition of the flocculating polymer selective. According to some embodiments, aging is carried out for a period of at least about five hours (e.g., from at least about eight to about 24 hours, e.g., for a period of about one hour). to seven days) before addition of the selective flocculation polymer.

[0046] According to some embodiments, conditioning may include aging and adding a conditioning chemical, and the conditioning chemical may be added prior to aging. According to some embodiments, the conditioning chemical can be added after some or all of the aging. The conditioning chemical can include, for example, one or more salts of a monovalent ion metal (e.g., one or more sodium salts). The sodium salt(s) includes an organic salt, such as, for example, a polycarboxylate salt, or a halide, such as sodium chloride. The polycarboxylate may be sodium polyacrylate. Sodium polyacrylate, where used, may be one of the commercially available products employed as mineral dispersants. The optionally added conditioning chemical(s) may be delivered to the aqueous suspension via one or more static in-line mixers. Alternatively, the conditioning chemical(s) may be added to the aqueous suspension in one or more conventional mixers, employing mechanical agitation means to promote thorough mixing.

[0047] According to some embodiments, during aging conditioning, if the suspension contains one or more conditioning chemicals, the suspension may be mechanically agitated, for example by movement or recirculation. Such agitation can be relatively light and can be applied continuously, semi-continuously, or intermittently.

[0048] According to some embodiments, the selective flocculation polymer can be mixed with the aqueous suspension before supplying the mixture to the selective flocculation separator. For example, these two ingredients can be thoroughly mixed together before being fed into the separator. The selectively flocculated polymer can be added via one or more static in-line mixers. Alternatively, the selectively flocculating polymer can be added to the aqueous suspension in one or more conventional mixers, employing conventional mechanical agitation means to promote good mixing. According to some embodiments, the selectively flocculating polymer can be added in one or more doses at one or more addition points prior to supplying the suspension to the separator.

[0049] According to some embodiments, the feeder aqueous suspension to be supplied to the selective flocculation separator may have a specific gravity in the range of about 1.03 to about 1.15. The solids content of the suspension can range from about 5% to about 21% by weight (e.g., from about 10% to about 15% by weight). Dilution with water can be carried out before supplying to the separator, for example before adding the selective flocculation polymer.

[0050] According to some embodiments, the aqueous feeder suspension to be supplied to the selective flocculation separator can be heated, for example, by using hot water in a water dilution step and/or by passing the suspension through an external heater (e.g., a heating jacket of a heat exchanger) to raise the temperature by at least about 10 °C, for example, from about 15 to 20 °C to about 30 to 35 °C or more.

[0051] The selective flocculation polymer may be one of the selective flocculation polymers previously known or used in the art. For example, organic polymers useful as the selective flocculation polymer include water-soluble weakly anionic organic polyelectrolytes having an average molecular weight greater than about 10,000, greater than about 100,000, or greater than about 1,000,000 . Weakly anionic polymers can contain both anionic and non-ionic groups. Anionic properties can be imparted to synthetic non-ionic organic polymers, for example, by the presence of side chains of anionic groups, such as carboxylic acid, carboxylic anhydride, and carboxylic acid salt groups. Non-ionic groups on a polymer side chain may also be present, resulting from the presence of certain hydrophilic groups, for example, one or more of the following hydrophilic groups: carboxylic acid amide, carboxy alkyl ester, pyrrolidone, hydroxy, hydroxy alkyl ether, and alkoxy. High molecular weight weakly anionic synthetic polymers, such as polyacrylamides containing some replacement of amide groups by carboxyl groups, are suitable (e.g., about 1% to about 20% by weight replacement of amide groups, from about 1% to about 15% by weight of amide groups, or from about 1% to about 10% by weight of amide groups). Such polyelectrolytes can be prepared by copolymerizing the nonionic monomer(s) (e.g. acrylamide) and one or more suitable carboxylic acids (e.g. acrylic acid), or by the partial hydrolysis of non-ionic polymer(s) (eg, polyacrylamide). According to some embodiments, the concentration of the selective flocculation polymer in the separation of layers in the selective flocculation separator can range from about 0.001% to about 0.5%, for example, from about 0.05% to about 0.5% by weight, based on the dry weight of particulate material present.

[0052] According to some embodiments, the specific weight of the deflocculated aqueous layer (e.g., an overflow layer containing compound(s) of rare earth elements and/or impurities) resulting from the method embodiments it can be at least about 1.0005, for example, ranging from about 1.0005 to about 1.02. In other embodiments, the deflocculated aqueous layer can have a specific gravity ranging from about 1.001 to about 1.01. In yet other embodiments, the deflocculated aqueous layer can have a specific gravity ranging from about 1.001 to about 1.003. Adjustment of specific gravity can be done by adjusting the dose of selective flocculation polymer added to the suspension being treated.

[0053] According to some embodiments, following formation of the layers, the layer of deflocculated rare earth element compound(s) and/or impurities may be separated from the layer of flocculated particles (e.g., particles of kaolinite) by conventional means, for example by elutriation, decanting, and/or siphoning batch operation or via a continuous separator. The extracted flocculated suspension may be further treated in a known manner, for example by optional high shear pumping or mixing to dissolve the flocs, followed by one or more beneficiation processes, such as, for example, one or more oxidation, comminution (eg, milling), particle size classification (eg, sieving and/or centrifugation), magnetic separation, bleaching, washing, and dehydration (eg, spray drying).

[0054] According to some embodiments of the method, before or during further processing, the extracted non-flocculated suspension (overflow) may be further treated in an additional selective flocculation step to provide further separation of the compound(s) of rare earth elements from kaolinite. For example, the extracted non-flocculated suspension obtained can be treated by repeating one or more of the previously applied steps prior to the addition of the selective flocculation polymer. According to some embodiments, the selective flocculation polymer, which may be the same as or different from the selective flocculation polymer used in the initial selective flocculation process, can be added in an appropriate step. Thereafter, the extracted flocculated suspension is again allowed to separate in a selective flocculation separator, and the respective formed layers are subsequently extracted as in the previous selective flocculation and extraction steps.

[0055] According to some embodiments, the flocculated suspension (e.g., containing kaolinite) may be treated to decompose the flocs therein, and then may be treated with an oxidizing agent to oxidize residual polymers and other impurities oxidizable elements present in the flocculated suspension following the selective flocculation process(es). The oxidizing agent may include, for example, ozone applied to the kaolin product suspension separated in a conventional ozonator (eg, in gaseous form bubbled into the suspension).

[0056] According to some embodiments, the separated and extracted deflocculated layer (e.g., containing compound(s) of rare earth elements and/or impurities) can be further treated to recover, purify, and/or use ingredients there. Furthermore, the water in the material can be separated by dehydration and can be purified and recycled for reuse in other processes, such as those described here or others.

[0057] According to certain embodiments, the compounds of rare earth elements, obtained from the method described above, may comprise constituents of, or isomorphic substitutions within, anatase, augelite, berlinite, berylonite, boehmite, brukite, cacoxenite, crandalite, diasporium, ernstite, eylettersite, ferrisicklerite, florencite, fourmarierite, gibbsite, gorceishite, goyazite, graftonite, hinsdalite, jagowerite, litiophyllite, olymphate, orpheite, monetite, monazite, muscovite, parsonite, phosphophyllite, plumbogummite, pseudomalachite, pseudorutile, pyromorphite, rutile, saleeite, serrabrancaite, siclerite, synferite, smrkovecite, svanbergite, uranphyte, viseite, vavelite, vailandite, weinebeneite, woodhouseite, zairite, compounds containing lanthanum, compounds containing cerium, compounds containing yttrium, compounds containing prasiodymium, compounds containing neodymium, compounds containing chromium, zirconium-containing compounds, niobium-containing compounds, lead-containing compounds, thorium-containing compounds, strontium-containing compounds, rare earth-containing compounds, or combinations thereof.

[0058] According to some embodiments, the at least one composite of rare earth elements includes particles having an equivalent spherical diameter of less than about 325 microns. In other embodiments, the at least one composite of rare earth elements includes particles having an equivalent spherical diameter of less than about 5 microns. In yet other embodiments, the at least one composite of rare earth elements includes particles having an equivalent spherical diameter of less than about 1 micron. In yet other embodiments, the at least one compound of rare earth elements includes particles having an equivalent spherical diameter ranging from about 1 micron to about 0.05 microns.

[0059] According to some embodiments, the rare earth element compound is a rare earth element oxide. For example, the compound of rare earth elements can include at least one of La2O3, CeO2, Nd2O3, and/or Y2O3. The compound of rare earth elements can include La2O3 from greater than 0% by weight to about 8.0% by weight, for example, from about 0.1% by weight to about 5.0% by weight, or from 0.2% by weight to about 4.0% by weight. The compound of rare earth elements can include CeO2 from greater than 0% by weight to about 5.0% by weight, for example from about 0.1% by weight to about 4.5% by weight, or from 0.3% by weight to about 4.0% by weight. The compound of rare earth elements can include Nd2O3 from greater than 0% by weight to about 2.0% by weight, for example from about 0.1% by weight to about 1.5% by weight, or from 0.2% by weight to about 1.0% by weight. The compound of rare earth elements can include Y2O3 from greater than 0% by weight to about 0.2% by weight, for example, from about 0.001% by weight to about 0.2% by weight, or from 0.01% by weight to about 0.2% by weight.

[0060] According to some embodiments, the deflocculated layer can include up to about 8.0% by weight of La2O3, up to about 4.0% by weight of CeO2, up to about 1.0% by weight of Nd2O3, and up to about 0.2% by weight Y2O3. For example, the deflocculated layer can include up to about 4.0% by weight La2O3, up to about 4.0% by weight CeO2, up to about 1.0% by weight Nd2O3, and up to about 0. 1% by weight of Y2O3. The deflocculated layer can be processed to remove kaolin and/or chemical salts.

[0061] According to some embodiments, the kaolinite sub-extravasation product obtained by the method described herein may have the following product properties: the percent residual TiO2 may be less than about 0.7% by weight ( based on the dry weight of the kaolinite product). According to some embodiments, the described method can be effective in treating kaolinite-containing inorganic particulate materials having a wide range of particle size properties. It may be particularly suited to producing thin materials suitable for use, for example, as pigments in paper products. For example, the product produced can have the following properties: average particle size from about 0.2 microns to about 5 microns (e.g., from about 0.2 microns to about 1.5 microns); percentage (by weight) of particles having a size less than 2 microns, of at least about 60% (e.g., at least about 80% by weight or at least about less than 90% by weight) . For purposes of this application, chemical analyzes were performed using a SIEMENS SRS3000 wavelength dispersive X-ray Fluorescence Spectrometer (XRF) and results are reported as elemental oxide in percent by weight (% by weight). Samples for XRF analysis containing particles larger than 200 mesh (74 microns) are ground using a SpectroMill Ball Pestle Impact Grinder or other suitable mill. The dry powder is weighed and precisely mixed with Chemplex X-Ray Mix Powder (binding aid) to form a dry blend containing 90% sample powder and 10% binding aid. The mixture is blended for five minutes using a SpectroMill Ball Pestle Impact Grinder and then pressed into pellets using a Spex 3624B Hydraulic Press set to twenty ton pressure.

[0062] For purposes of this application, measurements of particle size distribution (equivalent spherical diameter) and reported measurements of average size are as measured in a well-known manner by sedimentation of a fully dispersed suspension of the particles diluted in 10% solids in a standard aqueous medium of deionized water, and assayed using a SEDIGRAPH®5100 machine supplied by Micromeritics Corporation. The sample submitted for particle size analysis has already been sieved through a 325 mesh to remove grains and waste particles larger than about 44 µm particles. The SediGraph results report the PSD of the residue-free debarked sample.

[0063] In the following description with reference to Fig. 1, weight percent values given for additives are, unless otherwise noted, percentages by weight of dry or active amounts of the additives based on the dry weight of inorganic particulate material present in the treated suspension.

[0064] In the exemplary embodiment shown in Fig. 1, particulate material containing kaolinite and rare earth element compounds, for example, raw particulate kaolin obtained near the Capim River (Rio Capim) in Brazil, is supplied as a substantially dry solid material from a source 1, together with water from a source 2, to a mixer 3. An aqueous suspension having a solids content of at least about 30% (e.g., from about 40% to about 70% or more by weight) is formed in the mixer 3 One or more of the following materials are also added to the suspension being treated in mixer 3: (a) inorganic dispersant (e.g. sodium hexametaphosphate) from source 4: (b) alkali (e.g. sodium hydroxide) sodium or sodium carbonate) from a source 5; and (c) organic polyelectrolyte dispersant (e.g., sodium polyacrylate) from a source 6.

[0065] The materials from sources 1, 2, 4, 5 and 6 are carefully mixed and worked together in the mixer 3. The mechanical work of the aqueous suspension of kaolin in the mixer 3 is applied to decompose agglomerates of solid particles. The resulting dispersed suspension has a pH of about 6.5 to about 7. An output stream 7, including the dispersed suspension after treatment in the mixer 3, can be supplied (e.g. after dilution with water) from a source 8 to a descaler 9, where large particles are separated and removed.

[0066] The conditioning chemical (eg, a sodium halide and/or a sodium polyacrylate) can be added from a source 10. The dehulled kaolin suspension is then supplied to a conditioning tank 11 , where the suspension is allowed to stand with gentle mechanical agitation for an aging period (eg, for at least 30 minutes, or for several hours or days).

[0067] After aging conditioning, another optional conditioning chemical can be added (ie, in addition to or instead of the one applied before aging) from chemical additive source 10. Thereafter, the suspension is supplied to a mixer 12. The suspension can be diluted by adding water from a fountain 13 to adjust the specific gravity of the suspension. The pH of the suspension is adjusted to be at least about 9.5 by adding alkali, such as, for example, sodium hydroxide or sodium carbonate, from a 14 source.

[0068] An output stream from the mixer 12 includes the particulate suspension and additives having a low solids concentration of, for example, about 10% to about 15% by weight, and a pH of at least about 9.5 . The suspension may be passed through a heater 15 (e.g., a heat exchanger), which heats the suspension to a temperature ranging from about 30°C to about 40°C.

[0069] Next, a stream of the suspension is supplied to a mixer 17, where the selectively flocculating polymer, consisting of a high molecular weight polyacrylamide having less than about 15% by weight of anionic groups, is added in a source 16. The output of mixer 17 is a stream 18 of the suspension, which is supplied as a feed to a separator 19, in which separation of kaolinite from rare earth element compounds and/or impurities takes place by selective flocculation. Following this separation, a flocculated sub-extravasation layer 20 and a deflocculated extravasation layer 21 are formed. A kaolinite-containing product stream 23 from the sub-extravasation layer 20, including beneficiated kaolinite flakes, is collected from the separator 19 at its base 22. 24 including the deflocculated layer, which includes rare earth element compounds and/or impurities, separated by the selective flocculation process in the overflow layer 21, is extracted from an upper region of the separator 19, when the deflocculated layer, containing the deflocculated rare earth elements and impurities, rises to the top of the separate layers.

[0070] The stream 23 containing the flocculated suspension containing kaolinite is passed (e.g. after shearing the flakes therein by a shearing device 25) through an ozonator 27, in which ozone gas is applied thereto. The applied ozone concentration can range from, for example, about 0.01% to about 0.05% by weight. Ozone decomposes residual polymer and other oxidizable impurities (eg organic color contaminants) present in the suspension. An output stream 28 from the ozonator 27 is supplied to a plant 29, where the beneficiated kaolinite-containing suspension may be further treated by conventional processing steps as described above, to produce a commercially acceptable pigment product 30 available in dry form or in powder form. mud when desired (e.g., having the properties described above).

[0071] The deflocculated layer (overflow) can optionally be further processed or dehydrated. Further processing may include (a) returning a portion of the overflow layer to dilute the incoming feed in place of a portion of the source water 13: (b) adding additional high molecular weight polymer to flocculate kaolinite and separate the kaolinite layer flocculated to further concentrate the rare earth-containing compounds in the deflocculated suspension (overflow); (c) perform flotation using a variety of reagents to create a foam with air bubbles, collect phosphate-containing and/or rare earth-containing particles on top of the bubbles, and suppress collection of silicate and/or kaolinite-containing particles on top of the bubbles, and remove foam containing phosphate and/or rare earths; or (d) perform flotation, using a variety of reagents to create a foam with air bubbles, collect particles containing silicate, containing titania, and/or kaolinite on the bubbles, suppress the collection of particles containing phosphate or rare earths on the bubbles , and separating the foam from the pulp containing phosphate and/or rare earths.

[0072] According to some embodiments, the compound of rare earth elements may be an oxide of rare earth elements. For example, the compound of rare earth elements can be at least one of La2O3, CeO2, Nd2O3, and/or Y2O3. For example, the compound of rare earth elements can include La2O3 from greater than 0% by weight to about 8.0% by weight, for example from about 0.1% by weight to about 5.0% by weight, or from 0.2% by weight to about 4.0% by weight. The compound of rare earth elements can include CeO2 from greater than 0% by weight to about 5.0% by weight, for example from about 0.1% by weight to about 4.5% by weight, or from 0.3% by weight to about 4.0% by weight. The compound of rare earth elements can include Nd2O3 from greater than 0% by weight to about 2.0% by weight, for example from about 0.1% by weight to about 1.5% by weight, or from 0.2% by weight to about 1.0% by weight. The compound of rare earth elements can include Y2O3 from greater than 0% by weight to about 0.2% by weight, for example, from about 0.001% by weight to about 0.2% by weight, or from 0.01% by weight to about 0.2% by weight.

[0073] According to some embodiments, the deflocculated layer can include up to about 8.0% by weight of La2O3, up to about 4.0% by weight of CeO2, up to about 1.0% by weight of Nd2O3, and up to about 0.2% by weight Y2O3.

[0074] According to some embodiments, the deflocculated layer can include up to about 4.0% by weight La2O3 to about 4.0% by weight CeO2 to about 1.0% by weight Nd2O3 , and up to about 0.1% by weight of Y2O3.

[0075] The rare earth oxides in the deflocculated layer can be further concentrated and recovered using such rare earth concentration and recovery methods as would be well known to a person of ordinary skill in the art. For example, the deflocculated layer may be subjected to solvent extraction, acid extraction, or supercritical fluid extraction. The deflocculated layer can also be processed to remove kaolin and/or chemical salts.

[0076] The process of floating off particles containing phosphates and rare earths can be an effective way to increase the concentration of compound containing phosphate mineral and rare earths from a range of about 1% by weight to 10% to a range of about 20% by weight to 90% by weight, and solids increase from less than about 1% to less than about 10%.

[0077] Following the optional processing of the non-flocculated suspension (overflow), the minerals and/or compounds containing phosphate and/or rare earths need to be dehydrated to increase the solids concentration. Various processes could be used to concentrate solids, such as the use of membrane filters, polishing filters, disk nozzle centrifuges. The addition of chemicals to coagulate and flocculate the minerals and/or compounds containing phosphate and/or rare earths will improve the performance of some of these dewatering technologies and will enable other filter systems such as rotary vacuum filters and thickeners to be used to increase pulp solids and form a cake that can be more easily handled and transported than low solids pulp.

[0078] Three examples of treatment fields for suspensions or slurries of particulate matter containing kaolinite and rare earth element compounds are provided below, with the fields being obtained by exemplary embodiments of the method described herein. In each of these examples, a percentage value of the listed materials obtained is quoted as a percentage by weight on a dry or active basis, based on the dry weight of particulate material present in the slurry.

EXAMPLE 1

[0079] In Example 1, the feed material was a cream-colored raw kaolin particulate material containing kaolinite, rare earth element compounds, and impurities such as anatase. An exemplary embodiment of the method described above was carried out as follows:

[0080] The crude was mixed using sodium polyacrylate 3 #/dst (dry short ton) (Acumer 9400) and the pH was adjusted to between 6 and 6.5 using sodium hydroxide. The resulting mineral water liquid clay was dehusked through a 325 mesh screen to produce on a dry basis 4.0 kg of dehusked clay, which was used as the feed material. The feed material was then diluted to 10% solids with 0.73 kg/ton (short active-dry) 0.075% high molecular weight polymer solution (HYPERFLOC AF359), pH adjusted to 11.5 with NaOH , shaken 30 seconds, and allowed to precipitate into a 12” diameter x 12” tall cylinder, resulting in a floc precipitation rate of 0.6”/sec and non-flocculated supernatant having a specific weight of 1.002 measured by hydrometer.

[0081] The non-flocculated supernatant (overflow) is less than about 1% solids and needs to be dehydrated for further processing into rare earth metals and/or for ease of handling. The supernatant is purified using about 15 #/dst alum ("as received" dry basis) and sufficient sulfuric acid to lower the pH of the supernatant to about 3. The purification is completed with the addition of 210 ppm of high molecular weight (dry-dry) (HYPERFLOC AF 359) is allowed to precipitate overnight. The resulting precipitated solids are then dried and measured for elemental content.

[0082] Table 1 below shows the materials obtained by performing the method described above for the feed of Example 1. The obtained rare earth element compounds (i.e. oxides of rare earth elements) were present in the overflow layer deflocculated (i.e. the top layer of the separated layers).

EXAMPLE 2

[0083] In Example 2, the feed material was a kaolinite containing kaolinite sand, rare earth element compounds, and impurities. The exemplary method described above with respect to Example 1 was carried out to treat the feedstock material of Example 2. Table 1 below shows the materials obtained by performing the method described above for the feedstock material of Example 2. obtained rare earths were present in the deflocculated extravasation layer.

EXAMPLE 3

[0084] In Example 3, feed material was a crude composite particulate material containing kaolinite, rare earth element compounds, and impurities. The exemplary method described above with respect to Example 1 was carried out to treat the feedstock material of Example 3. Table 1 shows the materials obtained by performing the method described above for the feedstock material of Example 3. The rare earth element compounds obtained were present in the deflocculated extravasation layer.

EXAMPLE 4

[0085] In Example 4, the feed material was a soft clay particulate material containing kaolinite, rare earth element compounds, and impurities such as Anastasium. An exemplary embodiment of the method described above was carried out as follows:

[0086] The crude was blended using 3#dst (dry short ton) sodium polyacrylate (Acumer 9400) and the pH was adjusted to between 6 and 6.5 using sodium hydroxide. The resulting mineral water liquid clay was dehusked through a 325 mesh screen. The dehusked mud material was then diluted to 10% solids with 0.82 kg/ton (short active-dry) 0.075% solution high molecular weight polymer (HYPERFLOC AF359), pH adjusted to 11.5 with NaOH, shaken 30 seconds, and allowed to precipitate into a cylinder 12" diameter x 12" high, resulting in a precipitation rate of 0.4”/sec and non-flocculated supernatant having a specific weight of 1.002 measured by hydrometer. This separation resulted in 4.8% of the dry solids collected in the non-flocculated spillover and 95.2% of the dry solids being discarded in the flocculated underspill.

[0087] The non-flocculated supernatant (overflow) is less than about 1% solids and needs to be dehydrated for further processing into rare earth metals and/or for ease of handling. The supernatant is purified using about 15 #/dst alum ("as received" dry basis) and sufficient sulfuric acid to lower the pH of the supernatant to about 3. Purification is completed with the addition of 10 #/dst of high molecular weight (dried-dried) polymer (HYPERFLOC AF 359) and allowed to precipitate overnight. The resulting precipitated solids are then dried and measured for elemental content.

[0088] Table 2 shows the processed materials obtained by performing the method described above for the feed of Example 4 compared to the values of the unprocessed mixed feed. The obtained rare earth element compounds (i.e., the rare earth element oxides) were present in the deflocculated spillover layer (i.e., the top layer of the separated layers).

EXAMPLE 5

[0089] In Example 5, the feed material was a “hard clay” particulate material containing kaolinite, rare earth element compounds, and impurities such as Anastasium. An exemplary embodiment of the method described above was carried out as follows:

[0090] The crude was mixed using sodium polyacrylate 4# dst (dry short ton) (Kemira, C211) and sodium hexametaphosphate 8#/dst, pH was adjusted to between 6.5 and 7.5 using if sodium hydroxide. The resulting mineral water liquid clay was dehusked through a 325 mesh sieve and sorted to 95% less than 2 microns in a laboratory scale centrifuge. The sorted material was then diluted to 10% solids with 0.73 kg/ton (short active-dry) 0.075% high molecular weight polymer solution (HYPERFLOC AF359), pH adjusted to 11.5 with NaOH , shaken 30 seconds, and allowed to precipitate into a 12” diameter x 12” tall cylinder, resulting in a floc precipitation rate of 0.6”/sec and non-flocculated supernatant having a specific weight of 1.002 measured by hydrometer.

[0091] The non-flocculated supernatant (overflow) is less than about 1% solids and needs to be dehydrated for further processing into rare earth metals and/or for ease of handling. The supernatant is purified using about 15 #/dst alum ("as received" dry basis) and sufficient sulfuric acid to lower the pH of the supernatant to about 3. The purification is completed with the addition of 210 ppm of high molecular weight (dried-dried) (HYPERFLOC AF 359) and allowed to precipitate overnight. The resulting precipitated solids are then dried and measured for elemental content.

[0092] Table 2 shows the processed materials obtained by performing the method described above for the feed of Example 5, compared to the values of the unprocessed mixed feed. The obtained rare earth element compounds (i.e., the rare earth element oxides) were present in the deflocculated spillover layer (i.e., the top layer of the separated layers). Table 1

[0093] Table 1 shows that significant amounts of rare earth element compounds can be obtained in accordance with the above-referenced exemplary embodiment of the method described herein for obtaining rare earth element compositions from a kaolinite-containing particulate material and compounds of rare earth elements. Furthermore, the inventors have surprisingly found that rare earth element compounds separate from the flocculated kaolinite layer as part of the deflocculated overflow layer (i.e., top layer) of the layers in the selective flocculation separator. The inventors have also surprisingly found that rare earth element compounds take the form of particles having an equivalent spherical diameter of less than about 325 microns. Furthermore, impurities were also separated from the flocculated kaolinite layer and were present in the deflocculated layer. Table 2

[0094] Table 2 shows that the low levels of rare earth element compounds in the feedstock can be greatly enriched by employing the above-referenced exemplary embodiments of the method described herein to obtain rare earth element compositions. rare earths from a particulate material containing kaolinite and compounds of rare earth elements.

[0095] Furthermore, the inventors have surprisingly found that rare earth element compounds separate from the flocculated kaolinite layer as part of the deflocculated overflow layer (i.e. top layer) of the layers in the selective flocculation separator. The inventors have also surprisingly found that compounds of rare earth elements take the form of particles having an equivalent spherical diameter of less than about 325 microns. Furthermore, impurities were also separated from the flocculated kaolinite layer and were present in the deflocculated layer. Other embodiments of the invention will be apparent to those of skill in the art from consideration of the report and practice of the invention described herein. It is intended that the report and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

Claims (17)

1. Method, characterized by the fact that it comprises: - providing a dispersed aqueous suspension of a particulate material comprising at least one compound of rare earth elements and kaolinite; - adding to the suspension a selective flocculation polymer that facilitates the separation of at least a part of the at least one compound of rare earth elements from the kaolinite by flocculation of the kaolinite, and allows particles of the compound of rare earth elements to be or remain deflocculated and wherein the selectively flocculating polymer is a polyacrylamide containing 1% to 20% by weight replacement of amide groups by carboxylic groups; - allowing the suspension containing the polymer to separate in a selective flocculation separator, into layers comprising a layer of flocculated product and a deflocculated layer containing part of the at least one compound of rare earth elements; and - extracting each separate layer from the separator. 2. Method according to claim 1, characterized in that the deflocculated layer is an overflow layer. 3. Method according to claim 1, characterized in that part of the at least one compound of rare earth elements comprises particles having an equivalent spherical diameter of less than 325 microns. 4. Method according to claim 1, characterized in that part of the at least one compound of rare earth elements comprises particles having an equivalent spherical diameter of less than 1 micron. 5. Method according to claim 1, characterized in that the particulate material is obtained from kaolin. 6. Method according to claim 1, characterized in that the particulate material is obtained from sedimentary kaolin. 7. Method according to claim 1, characterized in that providing the dispersed aqueous suspension of the particulate material comprises adding water and dispersing agent to a dry crude kaolin. 8. Method according to claim 1, characterized in that the compound of rare earth elements comprises compounds containing particles of rare earth elements. 9. Method according to claim 1, characterized in that the specific weight of the deflocculated layer, containing part of the at least one compound of rare earth elements, is greater than 1.0005. 10. Method according to claim 1, characterized in that the specific weight of the deflocculated layer containing part of the at least one compound of rare earth elements ranges from 1.0005 to 1.02. 11. Method according to claim 1, characterized in that the specific weight of the deflocculated layer containing part of the at least one compound of rare earth elements ranges from 1.001 to 1.003. 12. Method according to claim 1, characterized in that the selective flocculation polymer comprises a polymer having a molecular weight greater than one million. 13. Method according to claim 1, characterized in that the selective flocculation polymer comprises a weakly anionic organic polymer having a molecular weight greater than 100,000. 14. Method according to claim 1, characterized in that it further comprises recovering part of the rare earth oxides in the deflocculated layer. 15. Method according to claim 14, characterized in that the recovery further includes concentrating the rare earth oxides in the deflocculated layer by solvent extraction. 16. Method according to claim 14, characterized in that the recovery further includes concentrating the rare earths in the layer deflocculated by acid extraction. 17. Method according to claim 14, characterized in that the recovery further includes concentrating the rare earths in the deflocculated layer by supercritical fluid extraction.

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