PHOSPHOR RECOVERY METHOD BACKGROUND

[0001] The invention relates generally to phosphor recovery processes, and,
in particular, to methods of chemical separation of phosphors from a retorted fluorescent powder mixture.

[0002] A phosphor is a substance that exhibits the phenomenon of
luminescence. Phosphors often include various types of rare earth compounds. Resources of concentrated deposits of rare earth compounds are limited in the earth leading to scarcity and high cost for the compounds. Therefore, there is a need for recycling and reusing spent or rejected phosphor materials.

[0003] Current methods of separating and recycling the spent or rejected
phosphor blends are selective to particular phosphors, involve elaborate chemical changes, or require expensive multiple processing steps that increase the processing costs of the phosphors. Therefore, there is a need for a simple, cost-effective method for recovering and recycling pure individual phosphors from spent or rejected phosphor materials.

BRIEF DESCRIPTION

[0004] Various embodiments of separating a phosphor material are disclosed herein. In
one embodiment, separating a phosphor material from a starting mixture is disclosed. The separating includes dispersing the starting mixture in an aqueous medium; dispersing an anionic surfactant in an organic medium; mixing the aqueous and organic mediums; separating the aqueous and organic mediums, and recovering the phosphor material from the organic medium.

[0005] In one embodiment, a method is disclosed. The method includes separating a barium magnesium aluminate (BAM) phosphor from a starting mixture, wherein the separating includes ultrasonically dispersing the starting mixture in an aqueous medium, dispersing at least about 2 Wt% of a surfactant that includes TOAB, CTAB, or a combination in the aqueous medium, dispersing at least about 2 Wt% of a surfactant that includes SDS, AOT, or a combination in an organic medium, mixing the aqueous and organic mediums, and recovering the BAM phosphor from the organic medium.

DETAILED DESCRIPTION

[0006] Embodiments of the present invention include the methods for
recovering a phosphor material from starting mixture that includes retorted fluorescent phosphor.

[0007] Approximating language, as used herein throughout the specification
and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about," is not limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value.

[0008] In the following specification and the claims that follow, the singular
forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

[0009] A phosphor is a luminescent material that absorbs radiation energy in
a portion of the electromagnetic spectrum and emits energy in another portion of the electromagnetic spectrum. In one embodiment, phosphors convert radiation, such as for example, ultraviolet radiation (UV) to visible light. Different combinations of phosphors provide different colored light emissions. A phosphor material may
convert UV or blue radiation to a lower energy visible light. The color of the generated visible light is dependent on the particular components of the phosphor material.

[0010] The phosphor material described above may be used in many different
applications. For example, the material may be used as a phosphor in lamp, in a cathode ray tube (CRT), in a plasma display device, or in a liquid crystal display. The material may also be used as a scintillator in an electromagnetic calorimeter, in a gamma ray camera, in a computed tomography scanner, or in a laser. These uses are meant to be merely exemplary and not exhaustive. The most common uses of phosphors are in CRT displays and fluorescent lights. Different embodiments of the present invention are described using the example of fluorescent lamps. However, the various methods disclosed here are not limited to fluorescent lamps but may be adapted to different applications.

[0011] One embodiment of the invention relates to a method of separating a
phosphor material from a starting mixture. The starting mixture, in one embodiment, includes retorted fluorescent powder (henceforward referred as "RFP"). RFP is a crushed powder made from used phosphor-containing equipment, such as used fluorescent lamps. The RFP may have phosphor material along with impurities associated with the recovery process. In one embodiment, the RFP includes a phosphor blend along with impurities such as metals, crushed glass powder, basing cement, crushed electrode, and alumina. A phosphor blend used in a fluorescent lamp normally includes one or more high-purity green, blue, and red phosphors. Table 1 shows typical examples and compositions of phosphors.

[0012] In some embodiments, a mixture or a blend of two or more types of
phosphors are present in RFP. For example, a phosphor blend may contain red, blue and green phosphors. The phosphor material is typically a multi-element complex compound, which normally decomposes into a mixture of different oxides or carbonates on different heat or chemical treatment.

[0013] One embodiment of the invention relates to a method of separating a
phosphor material from starting mixture that includes RFP. The "phosphor material" as used herein is in the context of a single phosphor compound having a particular composition. As used herein, the "composition" of the phosphor material is the chemical composition with particular identities, and relative numbers, of the constituent elements that make up the compound. Two phosphor materials having the same chemical composition may or may not have all the corresponding atoms in similar electronic charge states. For example, a first lanthanum phosphate (LAP) phosphor may have the composition LaP04: Ce3+, Tb3+, with a definite number of lanthanum, phosphorous, oxygen, cerium, and terbium elements in a first lattice with a first lattice structure. As used herein, a second LAP phosphor is said to have the same composition as the first LAP phosphor, if the number of lanthanum, phosphorous, oxygen, cerium, and terbium elements present in a second lattice is same as in the first LAP phosphor, regardless of the charge of each element, and lattice structure of the second lattice being similar to the first LAP phosphor. In one embodiment, the separated phosphor material is in the same electronic charge state as that of the phosphor material in the RFP, and the final phosphor material that is used for a visible light producing application.

[0014] As used herein, "separating" a phosphor material means that the
phosphor material during separation does not undergo decomposition from the initial phosphor material and after isolation is substantially the same as the initial phosphor material. In other words, the phosphor material present in an RFP is "separated" from the RFP into the substantially same phosphor material, without significant decomposition of the phosphor material. As used herein "substantially" is a qualifier term used to accommodate any small incidental variations in the chemical composition of the phosphor material that does not alter the visible light emission of the phosphor material more than 5%. As used herein "decomposition" is any kind of alteration of the phosphor material compound wherein the number of elements present in an unit cell of the phosphor material is reduced from the original phosphor material. Thus, the "separation" of the phosphor material may include separating a complex of the phosphor material from rest of the material, and then decomposing the complex to isolate the phosphor material, without decomposing the phosphor material itself in any stages of separation. In one embodiment, the complex of the phosphor material is a surface activated or surfactant attached phosphor material.

[0015] In one embodiment, the phosphor material separated from an RFP has
less than or equal to 10% variation in its quantum efficiency from the standard phosphor material of the substantially same chemical composition, as measured on
the powder in a spectrometer. In one embodiment, the quantum efficiency variation between the standard phosphor material and the separated phosphor material is less than about 5%. As used herein, the "quantum efficiency" is defined as the ratio of visible light emission of the phosphor material with respect to the absorbed ultraviolet energy.

[0016] In one embodiment, a phosphor material is separated from the RFP by
the use of a liquid-liquid extraction technique. Typically, liquid-liquid extraction is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent. It is an extraction of a substance from one liquid phase into another liquid phase. Liquid-liquid extraction of a biphasic mixture deals with two immiscible phases, such as for example, oil and water. In one embodiment, the biphasic extraction is carried out using immiscible combinations of inorganic and organic phases. In one embodiment, a material that is suspended in an inorganic liquid may be separated at the interface of inorganic and organic liquids by bringing it into contact with an immiscible liquid.

[0017] Some of the key parameters that determine the extraction efficiency
or yield of materials from a biphasic mixture are solubility, partition energy, and hydrophobicity. In one embodiment, the material that is separated using the liquid-liquid extraction process is a phosphor material. The phosphor materials such as that listed in Table 1, for example, are not soluble in water or organic liquids, and hence solubility and partition energy values of these phosphor materials are irrelevant in determining the partition of the phosphor materials in aqueous or organic phases. Further, these phosphor materials do not show strong hydrophilic or hydrophobic interactions in aqueous medium. Therefore, it is desirable to explore other routes of separation of phosphor materials through liquid-liquid extraction from a biphasic mixture. In one embodiment, a suspended mixture of RFP is formed by suspending the RFP in a liquid medium. In one embodiment, the liquid that is used for the suspension of RFP is inorganic. In one embodiment, RFP is suspended in water and dispersed.

[0018] The suspension and dispersion of RFP may be aided by the use of
dispersants, stirring, ultrasonication, or a combination of these techniques. A dispersant is a dispersing agent that may be a surface-active substance, or a non-surface active polymer added to a suspension, to improve the separation of particles in the suspension and to prevent settling or clumping. A dispersant may or may not attach to the surface of the suspended particles. In one embodiment, the dispersant that is used to disperse the suspended mixture includes sodium hexametaphosphate, ammonium salts of acrylic polymer, or combinations thereof.

[0019] In one embodiment, an organic liquid medium including a surfactant
material is used along with the phosphor material suspended in the inorganic liquid medium. Examples of the organic medium include, without limitation, acetonitrile, methanol, dichloromethane, chloroform, toluene, hexane, heptane, chloroform, pentane, acetone, isopropyl alcohol, ethanol, or any combination of the foregoing. Typically surfactants are surface active substances that lower surface tension of a liquid, the interfacial tension between two liquids, or the interfacial tension between a liquid and a solid. Depending on the nature, the surfactants are classified as an-ionic, non-ionic, cat-ionic, or amphoteric. As used herein a "surfactant" is a surface active agent that specifically attaches to the phosphor material surfaces. As used herein, a surfactant may also act as a dispersant, but the dispersant does not act as a surfactant.

[0020] In one embodiment, a liquid-liquid extraction process is employed to
separate and recover high-purity lanthanum phosphate (LAP), barium magnesium aluminate (BAM), or yttrium europium oxide (YEO) phosphors from a spent phosphor blend that includes all three phosphors (green, blue, red). In one embodiment, BAM is separated from LAP or YEO.

[0021] The surfactant that is used in the organic medium for the recovery of
phosphor blend of the RFP herein may include 2-thenoyl trifluoro acetone (TTA), ethylenediamine tetra acetic acid (EDTA), sodium dodecyl sulfate (SDS), dodecyl ammonium acetate (DAA), cetrimonium bromide (CTAB), ammonium lauryl sulfate (ALS), dioctyl sulfosuccinate sodium salt (AOT), hexadecyl (2-hydroxyethyl) dimethyl ammonium dihydrogen phosphate, 3- (N,N-dimethyl octadecyl ammonio) propane sulfonate, sodium oleate, oleic acid, Bis (2-ethylhexyl) phosphate, tetraoctyl ammonium bromide (TOAB), or a combination thereof.

[0022] In one embodiment, the surfactant that is used in the organic medium
is dispersed in the organic medium. The suspension and dispersion of surfactant may be aided by the use of dispersants, stirring, ultrasonication, or a combination of these techniques. In one embodiment, the dispersant that is used to disperse the surfactant includes sodium hexametaphosphate, ammonium salts of acrylic polymer, or combinations thereof.

[0023] In one embodiment, the surfactant that is dispersed in the organic
medium is an anionic surfactant. In one embodiment, the anionic surfactant dispersed in the organic medium does not dissolve in the organic medium. Examples of anionic surfactant includes sodium dodecyl sulfate (SDS), sodiumdodecyl benzene sulfonate (SDBS), dioctyl sulfosuccinate sodium salt (AOT), or a combinations of the foregoing. In one embodiment, a surfactant that is dispersed in the organic medium is soluble in the aqueous medium. For example, SDS is readily soluble in the aqueous medium while does not dissolve in many of the organic mediums.

[0024] In one embodiment, the aqueous medium including the dispersed and
suspended phosphor material and the organic medium including the dispersed anionic surfactant is mixed together. The mixing of the two mediums may be facilitated by mechanical or thermal agitation. The thoroughly mixed aqueous and organic mediums may be separated again and the phosphors in the starting mixture may be separated in the organic mediums and aqueous medium. In one embodiment, after mixing and separating the aqueous and organic mediums, a first phosphor is separated from the aqueous medium, and a second phosphor is recovered from the organic medium.

[0025] In one embodiment, the starting mixture in the aqueous medium
interacts with the anionic surfactant in the organic medium and forms a phosphor material-surfactant complex. This phosphor material-surfactant complex may include the phosphor material and at least a part of at least one of the surfactant that is present in the organic medium. In one embodiment, the phosphor material-surfactant complex forms at the interface of the aqueous and organic mediums. In one embodiment, the amount of surfactant in the organic medium is in a range from about 1 Wt% to about 5 Wt%. In one embodiment, the amount of surfactant in the organic medium is in a range from about 2 Wt% to about 4 Wt%.

[0026] In one embodiment, the aqueous medium includes a surfactant along with the starting mixture having the phosphor material. In one embodiment, the surfactant that is in the aqueous medium is a cationic surfactant. Examples of the cationic surfactant include cetrimonium bromide (CTAB), tetraoctylammonium bromide (TOAB), octadecylamine (ODA), dodecylamine (DDA), or a combination of the foregoing. In one embodiment, a cationic surfactant that is dispersed in the aqueous medium is soluble in the organic medium. For example, TOAB is readily soluble in the organic medium but does not dissolve in water. In one embodiment, the cationic surfactant dispersed in water is a phosphor specific surfactant for a phosphor material to be recovered from the aqueous medium.

[0027] In one embodiment, a starting mixture including a first phosphor material and a second phosphor material may be separated and recovered by using the biphasic separation method. The starting mixture may be dispersed in water along with a second phosphor-specific cationic surfactant. As used herein a "second phosphor-specific" surfactant is a surfactant that preferentially forms a complex with the second phosphor in the mixture. A first phosphor-specific anionic surfactant may be added to an organic medium, and the two mediums may be mixed and allowed to settle down. The anionic surfactant may form a first complex by attaching to the first phosphor material and be recovered from the organic medium. The cationic surfactant may form a second complex by attaching to the second phosphor material and be recovered from the aqueous medium.

[0028] In one embodiment, the phosphor material-surfactant complex recovered from the biphasic mixture is heat-treated to form a heat-treated mixture. Without being bound by any particular theory, the heat-treatment is considered to aid in the removal of some of the organic impurities, such as for example surfactant that may still be present in the separated mixture. Depending on the surfactant and any other impurities that are present in the phosphor material-surfactant complex, the heat-treatment of the complex may be conducted in oxidizing, neutral, or reducing atmosphere. In one embodiment, the heat-treatment is conducted in an oxidizing atmosphere or neutral atmosphere. In one embodiment, the heat-treatment is conducted in air. In one embodiment, the temperature of the heat-treatment varies from about 200°C to about 1000°C. In one embodiment, the heat-treatment temperature is in a range from about 400°C to about 500°C.

[0029] In one embodiment, the RFP considered for the separation of the
phosphor material has fine sized materials. In one embodiment, a median particle size of the RFP is less than about 5 microns. In one embodiment, the median particle size of the RFP is in a range from about 2 microns to 4 microns. A smaller size of the RFP powder helps in suspension and electrostatic separation of the phosphor material.

[0030] The RFP present in the starting mixture may include different metallic
non-metallic, and ceramic impurities along with a phosphor blend. These impurities, if present, may reduce the quantum efficiency of the recovered phosphor material. Therefore, it is desirable to remove these impurities from the RFP before or after the separation of individual phosphors from the phosphor blend. The separation of the impurities from the RFP may include, among other things, leaching with an acid solution, dissolving in suitable solvents, or dispersing the impurities and phosphor materials in different solvent mediums in a biphasic solution.
EXAMPLE

[0031] The following example illustrates methods, materials, and results, in
accordance with specific embodiments, and as such should not be construed as imposing limitations upon the claims. All components are commercially available, unless otherwise indicated.

[0032] A process is disclosed herein to separate and recover BAM from a
BAM and LAP mixture using a liquid-liquid extraction method. In one example, a phosphor blend including BAM and LAP was milled to reduce the particle size of the phosphor powders to approximately 3.5 microns. The mixture was mixed with water with about 15-40 grams per liter solid loading. The phosphor blend was dispersed and suspended in the water using dispersants and ultrasonication. The dispersants used included Calgon®, Darvan® 821a, or Dispex® A40 at a concentration of about 2-40 grams per liter of water. SDS surfactant was added to hexane and dispersed using a ultrasonication. The aqueous medium including the mixture and the hexane including the dispersed SDS were thoroughly mixed and then allowed to settle for about 12 hours.

[0033] The SDS surfactant is highly soluble in water. Further, the SDS
surfactant was found to have a strong affinity to Ba2+ ion. The affinity to Ba2+ ion helps in forming a BAM -SDS complex by attachment of SDS to the Ba2+ part of the BAM. Without being bound by any particular theory, it is envisaged that the high solubility of SDS in water hinders the effective formation of the BAM-SDS complex in aqueous medium. By dispersing in hexane, the SDS does not dissociate and the vigorous mixing with the aqueous medium facilitates an effective interaction between BAM and SDS. After strong agitation of the liquid phases, the phosphor settles mostly at the interface of organic (hexane) and aqueous media. SDS (that is dispersed in hexane) comes into contact with BAM at the interface where there is an enrichment of BAM, and attaches to BAM at the barium sites. The BAM -SDS complex has a hydrophobic surface. The resulting BAM-SDS complexes are then repelled to the hexane phase resulting in an efficient separation of BAM to the organic phase.

[0034] In another example, a LAP and BAM mixture blend with
approximately 3.5 microns average particle size was taken for BAM separation. The LAP+BAM blend was mixed with water with about 15-40 grams per liter solid loading and dispersed in the water using dispersants and ultrasonication. The dispersants used included Calgon®, Darvan® 821a, or Dispex® A40 at a concentration of about 2-40 grams per liter of water. The dispersion in water was treated with a LAP specific surfactant such as TOAB to form a LAP-TOAB complex and dispersed further using ultrasonication. In one example, SDS surfactant was added to hexane and dispersed using ultrasonication. The aqueous medium including the LAP-TOAB complex and BAM was mixed thoroughly with the hexane including the dispersed SDS and then allowed to settle for about 12 hours. The BAM phosphor complex was separated from the hexane and the LAP was separated from the aqueous part. The separated LAP and BAM phosphors were further heat-treated in air at a temperature range of about 350°C to about 500°C.

[0035] An experiment was conducted by dissolving the SDS surfactant in the
aqueous medium along with the starting mixture; dissolving the TOAB in hexane; mixing the two mediums and allowing for settling down. There were no segregation of any phosphor complexes in the organic phase and all the phosphor materials were observed to be settled down in the aqueous medium.

[0036] While only certain features of the invention have been illustrated and
described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

CLAIMS:

1. A method, comprising:
separating a phosphor material from a starting mixture, wherein the separating comprises dispersing the starting mixture in an aqueous medium;
dispersing an anionic surfactant in an organic medium; mixing the aqueous and organic mediums; and separating the aqueous and organic mediums, and recovering the phosphor material from the organic medium.

2. The method of claim 1, wherein the anionic surfactant comprises sodium dodecyl sulfate (SDS), sodiumdodecyl benzene sulfonate (SDBS), dioctyl sulfosuccinate sodium salt (AOT), or a combinations thereof.

3. The method of claim 1, wherein the aqueous medium further comprises a cationic surfactant.

4. The method of claim 3, wherein the cationic surfactant comprises cetrimonium bromide (CTAB), tetraoctylammonium bromide (TOAB), Octadecylamine (ODA), Dodecylamine (DDA), or a combination thereof.

5. The method of claim 3, wherein the amount of surfactant in the organic medium is in a range from about 1 Wt% to about 5 Wt%.

6. The method of claim 1, wherein the organic medium comprises acetonitrile, methanol, dichloromethane, chloroform, toluene, hexane, heptane, chloroform, pentane, acetone, isopropyl alcohol, ethanol, or a combination thereof.

7. The method of claim 1, wherein the amount of anionic surfactant in the organic medium is in a range from about 1 Wt% to about 5 Wt%.

8. The method of claim 1, wherein a median particle size of the starting mixture is less than about 5 microns.

9. The method of claim 8, wherein the median particle size of the starting mixture is in a range from about 2 microns to about 4 microns.
10. The method of claim 1, wherein the aqueous or organic medium further comprises a dispersant.

11. The method of claim 1, wherein the first phosphor comprises lanthanum phosphate (LAP), yttrium europium oxide (YEO), or a combination of LAP and YEO, and the second phosphor comprises barium magnesium aluminate (BAM).

12. A method, comprising:

separating a barium magnesium aluminate (BAM) phosphor from a starting mixture, wherein the separating comprises

ultrasonically dispersing the starting mixture in an aqueous medium;
dispersing at least about 2 Wt% of a surfactant comprising TOAB, CTAB, or a combinations thereof in the aqueous medium;

dispersing at least about 2 Wt% of a surfactant comprising SDS, AOT, or a combinations thereof in an organic medium;

mixing the aqueous and organic mediums; and
recovering the BAM phosphor from the organic medium.