Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B59/00—Obtaining rare earth metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/02—Roasting processes
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
  • C22B7/006—Wet processes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the method includes mixing an ammonium sulfate powder and a powder containing the oxide waste material; firing the mixture at a temperature sufficient to decompose the waste into a residue, which is, to a large degree, soluble in aqueous solution; dissolving the residue in water to obtain a solution, which comprises rare earth constituents in salt form; separating rare earth constituents from the solution using at least one separation method; and subsequently using the separated rare earth constituent (salt or solution) as a raw material.
• Rare earth and zirconium oxide materials are critical for a broad range of technologies. Important industrial sectors such as defense, manufacturing, energy, transportation, optics and electronics all utilize rare earth materials in abundance. Rare earths exist as integral components in many technologies, including navigation / guidance systems, petroleum refining catalysts, advanced vehicle batteries, wind turbine motors, jet engines, miniature disk drives, speakers, televisions and monitors, compact fluorescent light bulbs and optical cables. Additionally, there are currently a limited number of economically viable sources of rare earths, making the recycling of rare earths an invaluable practice to industry. However, only a small percent of all rare earth minerals are recycled. The disclosed embodiments provide a simple method for the recycling of oxide materials that is especially suited for rare earth containing materials and zirconia containing materials.
• waste materials containing rare earth minerals and zirconia may be produced by a number of industrial processes, including thermal spray coating, electron beam vapor deposition, green machining of dental materials, and cubic zirconium gem production.
• the basics of this method consist of the following: a) mixing an ammonium sulfate powder and a powder containing oxide waste material; b) firing the mixture at a temperature sufficient to decompose a waste residue, which is, to a large degree, soluble in aqueous solution; c) dissolving the residue in water to obtain a solution that includes rare earth constituents in salt form; d) separating rare earth constituents from the solution using at least one separation method; and e) subsequently using the separated rare earth constituent (salt or solution) as a raw material.
• the coatings are removed by treating the material in a concentrated ammonium sulfate solution to cover the surface, and then heating the coated part to allow the ammonium sulfate to preferentially digest and disrupt the coating.
• the zirconia may be further recovered from the waste filtrate in (d) via precipitation or other separation methods.
• the reactants used in the recovery may also be recovered by appropriate precipitation and concentration of the filtrate produced in (d).
• a method for recovery, in reusable form, of rare earth minerals from waste materials containing rare earth minerals but no zirconia Such waste materials are produced by compact fluorescent light bulbs, rare earth containing catalysts, rare earth-iron alloy magnets, lanthanum manganate fuel cell electrodes, and NiMH batteries. If such materials occur in coatings, a method is also disclosed for removal of the coatings containing these wastes. The steps involved are the same as above pertaining to the reactions to which the materials are subjected, except that an oxalate precipitation agent is used to precipitate the rare earth minerals in (d) in the absence of zirconia.
• the rare earth waste materials are non-oxides, the materials must be oxidized prior to reaction with ammonium sulfate. If such materials occur in coatings, the materials are treated in a saturated ammonium sulfate solution to coat the surface with ammonium sulfate, which allows for a preferential chemical attack on the coated surface to effect removal of the materials.
• Also disclosed herein is a method for the recovery of zirconia from zircon, which is a typical waste produced by metal casting operations.
• FIG. 1 is a flow diagram representing an exemplary process as disclosed herein.
• FIGS. 2 - 6 depict X-ray diffraction plots of recovered rare earth oxides as disclosed in several of the examples.
• a method for recovering rare earth materials and zirconia from waste materials.
• the rare earths and zirconia recovered are directly reusable as raw materials.
• the processes producing these wastes include thermal spray coating, electron beam vapor deposition, green machining of dental wastes, and cubic zirconium gem production.
• These waste materials are characterized by compounds such as yttria-zirconia and Gd 2 0 3 -Zr0 2 . In some cases these wastes require cleaning by one or a combination of cleaning methods, including magnetic removal of tramp iron materials, acid leaching, and water rinsing to remove water-soluble materials.
• Materials which are not oxides require heating in oxidizing conditions to convert them to oxides.
• various heating times and temperatures are employed in the heating operations and it should be appreciated that while a particular time and temperature combination may be disclosed, heating may also be accomplished under equivalent conditions. For example, heating at a lower temperature for a longer time period or at a higher temperature for a shorter time period. It should be noted, however, that heating at temperatures far exceeding the noted temperature may result in undesirable changes that preclude decomposition of the waste material.
• the oxide materials and ammonium sulfate are then individually pulverized before mixing or pelletized and mixed in proportion of approximately 1 to 6 moles of ammonium sulfate to mole of waste oxide, more preferably in proportion of about 1 .5 to 3.5 moles of ammonium sulfate to mole of waste oxide.
• the mixture is then fired in boats, which may be open or closed.
• the boats may be composed of Pyrex, alumina, graphite, or stainless steel, and are placed in heating devices such as continuous kilns, periodic kilns, and autoclaves at temperatures from about 150 to 700 °C, more preferably 300 to 600 °C, and most preferably 350 to 500 °C.
• the mixtures may be fired in rotating kilns, in which case they may be fired without boats.
• the mixtures may also be fired in microwave ovens wherein either a microwave susceptible material such as carbon black is added to the mixture if the waste material is not itself microwave susceptible, or the mixture may be fired in a microwave susceptible container. In some cases the firing of the rare earth wastes and ammonium sulfate is repeated, as many as three times.
• the residue which is, to a large degree, soluble in aqueous solution is dissolved in water to obtain a solution containing salts of the rare earth minerals and zirconium.
• the rare earth constituents are separated from the solution using methods such as ion-exchange, solvent extraction, fractional crystallization, and/or precipitation.
• precipitation with an oxalate precipitation agent such as excess oxalic acid or ammonium oxalate, is suitable.
• the rare earth oxalate precipitate is washed one or more times with about a 2% oxalic acid solution.
• the rare earth precipitate is calcined at about 1000 °C to form the rare earth oxide.
• the zirconia is recovered by treating the filtrate generated by the oxalate precipitation with ammonium hydroxide to form a hydrous zirconia precipitate. This precipitate is subsequently washed and calcined at about 1000 °C to form zirconium oxide.
• the ammonium sulfate may be recovered by reacting the rare earth solution (e.g. , a solution containing salts of the rare earth minerals and zirconium) with ammonium hydroxide to precipitate all rare earth minerals and zirconium as hydroxides prior to the oxalic precipitation.
• the filtrate produced is then collected and dried at approximately 60 - 100 °C to form ammonium sulfate.
• the precipitant is then reacted with excess oxalic acid to put the zirconium into solution and leave the rare earth as an oxalate precipitant.
• the zirconia is recovered by treating the filtrate generated by the oxalate precipitation with ammonium hydroxide to form a hydrous zirconia precipitate. This precipitate is subsequently washed and calcined at 1000 °C to form zirconium oxide. The filtrate produced is then collected and dried at approximately 60 - 100 °C to form ammonium oxalate.
• a method for recovering rare earth minerals which are directly reusable as raw materials from waste materials where zirconia is not present.
• the processes or products producing these wastes include, for example, phosphors from the recycling of compact fluorescent light bulbs and other phosphor- containing products, electroceramics such as barium neodymium titanate, rare earth-iron alloy magnets, lanthanum manganate fuel cell electrodes, and NiMH batteries.
• waste materials are characterized by compounds of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, promethium, europium, gadolinium, terbium, dysprosium, erbium, thulium, ytterbium, and lutetium.
• this embodiment may also require grinding of the waste material.
• the conversion of materials to oxides may also be required, particularly for rare earth-iron magnets, in order to generate a form that is amenable to further processing by this method. The method of recovering these rare earth materials is comparable to the first embodiment.
• the material may be cut, ground or crushed into smaller sections and dipped into a saturated ammonium sulfate solution and reacted at about 425 °C for approximately 60 minutes to effect the sulfation of the rare earth minerals. The material is then rinsed with water to remove and collect the outer layer containing the rare earth minerals.
• zirconia is recovered from zircon, a typical waste from metal casting.
• the powdered casting waste is mixed with ammonium sulfate in the ratio of 2 moles ammonium sulfate to 1 mole zircon and 7% water is added to form a paste.
• the mixture is reacted for about 60 minutes at approximately 425 °C.
• the resultant materials are soaked in water and filtered to separate the amorphous Si0 2 .
• the filtrate of zirconium sulfate is reacted with ammonium hydroxide to yield a precipitate of hydrous zirconia, which is subsequently washed and calcined at about 1000 °C to form zirconium oxide.
• the zirconium can also be separated prior to precipitation of a yttrium compound.
• One method consists of autoclaving the salt solutions produced from reacting zirconia alloys with ammonium sulfate. Autoclave temperatures of 120 °C cause the formation of a zirconium-containing precipitant, which is washed and calcined to form zirconium oxide. The remaining filtrate is treated with oxalic acid or ammonium oxalate to form rare earth oxalate; the resulting precipitate is washed from one to three times with a 2% oxalic acid solution. Finally, the rare earth precipitate is calcined at 1000 °C to form the rare earth oxide.
• step 614 can include grinding, rinsing, acid leaching, magnetic particle removal and/or milling.
• step 618 the waste material sample is consolidated and prepared for reaction in either a powder slug, pelletized form, or disk form, although there may be other forms and consolidation techniques that are suitable depending upon the nature of the waste product.
• the oxide material and ammonium sulfate may be consolidated by pressing the combined materials into slugs, pellets, disks, etc.
• ammonium sulfate is added to the prepared material and the combination is then heated for at least a period of time to enable the reaction.
• the reacted material is then removed from the heat, cooled and rinsed with water at step 626 to form a salt.
• Optional step 630 may be carried out, introducing ammonium hydroxide, in order to enable the recovery of ammonium sulfate, for use in subsequent processing of more waste.
• a separation operation such as precipitation is carried out.
• an oxalate precipitation agent e.g., excess oxalic acid or ammonium oxalate
• zirconium rich filtrate can be precipitated with ammonium hydroxide, primarily forming zirconium hydroxide, where the hydroxide can then be filtered, washed and calcined to form zirconium oxide.
• Step 642 represents heating where, for example, the separated materials undergo a calcination operation to produce an oxide.
• an operation by which ammonium oxalate may be recovered for subsequent use in the process steps described above.
• ammonium sulfate may be recovered by, prior to oxalic precipitation, reaction of the rare earth solution with ammonium hydroxide to precipitate all rare earth minerals as hydroxides, followed by filtrating, collecting and drying to form ammonium sulfate.
• the ammonium oxalate may be recovered by collecting and drying the filtrate from the hydroxide precipitation after, of course, the completion of the process; because the separation of the zirconium and rare earth hydroxides from the ammonium sulfate must precede the oxalate reactions with the zirconium and rare earth - which yield a rare earth- oxalate precipitate, along with a zirconium oxalate in solution.
• a waste material containing 20 weight percent Y2O3 stabilized ZrC>2 was obtained from cubic zirconium gem manufacturing.
• the material was comprised of ball milled powder and mixed with 3 parts ammonium sulfate to one part Y 2 0 3 -Zr0 2 .
• the particle size may vary, use of a mesh in the range of 20 to 325 (U.S. Mesh), yielding particles in the range of 841 microns to 44 microns, and in particular a 100 mesh (149 microns or less) provided appropriate particles for further processing.
• the materials were fired in an aluminum crucible at 500 °C for 4 hours.
• the materials were pressed into a slug and fired in an aluminum crucible for 1 hour at 450 °C. Approximately 99% of the residue produced was water soluble, indicating that consolidation enhances the recovery of rare earth minerals from a fused material.
• the materials were pressed into an approximately 0.25 inch thick disk and transferred to an alumina crucible that was preheated to 450 °C and reacted for only 5 minutes. In this case approximately 78% of the residue produced was water soluble, indicating that only a short reaction time is required for substantial reaction.
• the characterization of the reaction time as "short" is intended to refer to the reaction being mostly completed over a range of only minutes, given the proper consolidation and heating conditions, so that the reaction period need not extend over the range of an hour or more as described in other examples herein. In other words, under proper conditions the reaction can be very efficient with regard to time.
• ammonium hydroxide was added to the solution of the sulfated Y 2 0 3 - stabilized Zr0 2 waste material to form a mixed yttrium-zirconium hydroxide via precipitation.
• the remaining filtrate was collected and dried at 60 °C to form ammonium sulfate.
• the mixed yttrium-zirconium hydroxide was further mixed with an excess of oxalic acid in solution so as to allow precipitation of yttrium oxalate while preventing precipitation of zirconium oxalate.
• the yttrium oxalate was filtered from solution, rinsed with an oxalic acid solution, then dried and calcined at 1000 °C to yield yttrium oxide.
• the zirconium rich filtrate was then precipitated with ammonium hydroxide, primarily forming zirconium hydroxide.
• the hydroxide was filtered, washed and calcined at 1000 °C to form zirconium oxide with reduced yttrium content.
• the filtrate from the zirconium hydroxide precipitation was collected and dried at 60 °C to form ammonium oxalate.
• the sulfated Y 2 0 3 -stabilized Zr0 2 waste material was autoclaved at temperatures of 200 °C to 250 °C, at equilibrium pressure in a digestion bomb. In all cases a precipitant was formed; the precipitant was subsequently filtered out, washed and calcined at 1000 °C. The resultant oxide was determined by x-ray diffraction (X D) (See FIG.
• EXAMPLE II Coarse Grade Gd 2 Zr 2 0 7 Electron Beam Physical Vapor Deposition Waste
• a coarse grade electron beam physical vapor deposition waste was milled to 20 mesh and mixed with ammonium sulfate in the proportion of 1.25 parts ammonium sulfate to 1 part Gd 2 Zr 2 0 7 .
• the materials were transferred to an alumina crucible and fired at 450 °C for 1 hour.
• Subsequent solution of the residue revealed that approximately 32% was soluble.
• the unreacted residue was mixed with ammonium sulfate in the proportion of 1.5 parts ammonium sulfate to 1 part Gd 2 Zr 2 0 7 and fired in an alumina crucible at 450 °C for 1 hour. In this case 41 % of the residue was soluble.
• the unreacted residue was mixed with ammonium sulfate in the ratio of 2.5 parts ammonium sulfate to 1 part Gd 2 Zr 2 0 7 and fired in an alumina crucible at 450 °C for 1 hour. In this case 90% of the residue was soluble.
• 96% of the waste material was solubilized and the presence of Gd 2 C>3 was confirmed by XRD as illustrated by the peaks of FIG. 4. This demonstrates the use of repeated treatments of this process to recover rare earth minerals from coarse waste materials such as those produced by electron beam physical vapor deposition and thermal barrier coatings.
• EXAMPLE III Perovskite Fuel Cell Electrode Material (La 2 0 3 -Ce0 2 -Mn0 2 )
• Perovskite fuel cell electrode material (La 2 0 3 -Ce0 2 -Mn0 2 ) was mixed with ammonium sulfate in proportion of 1 part perovskite powder to 3 parts ammonium sulfate and pressed into a slug. The slug was fired at 450 °C for 1 hour and the resultant product was readily dissolved in deionized water, indicating complete reaction. The rare earth minerals were separated using oxalate precipitation.
• EXAMPLE IV Ce0 2 -doped Y 2 0 3 -Al 2 0 3 (YAG) Phosphor
• YAG phosphor waste was mixed with ammonium sulfate in the proportion of 3 parts ammonium sulfate to 1 part phosphor powder and pressed into a slug. The mixture was fired at 475 °C for 1 hour and the resultant residue was readily dissolved in deionized water, indicating complete reaction. The Y2O3 rare earth mineral was separated from the residue by oxalate precipitation. This demonstrates the utility of the process on difficult to recycle YAG phosphors.
• EXAMPLE VI Rare Earth Minerals from Compact NiMH Batteries.
• Typical NiMH batteries contain about 7% rare earth elements including cerium, lanthanum, neodymium and praseodymium.
• the NiMH filling was removed from the spent battery and fired at 1000 °C to oxidize it, converting it to NiO and a rare earth oxide-nickel oxide compound.
• This oxidized waste material was mixed with ammonium sulfate in the ratio of 3 parts ammonium sulfate to 1 part waste material and pressed into a slug.
• the slug was fired at 450 °C for 1 hour and the residue was dissolved in deionized water. The result was that the bulk of the rare earth material was reacted and dissolved, while most of the NiO was left unreacted. This demonstrates the processing of NiMH battery waste to extract rare earth minerals into solution.
• Rare earth magnet alloys contain several percent of rare earth elements including neodymium, samarium, cerium, lanthanum, praseodymium, and ytterbium.
• the magnet waste is first crushed and fired at 1000 °C to oxidize it.
• the oxidized material is then easily pulverized to a powder.
• This oxide powder is then mixed with ammonium sulfate in the ratio of 3 parts ammonium sulfate to 1 part oxide powder and pressed into a slug.
• the mixture was fired at 400 °C for 1 hour and then dissolved in deionized water.
• the bulk of the rare earth material was reacted and dissolved.
• the rare earths were then separated from the solution by oxalate precipitation.
• Electron beam physical vapor deposition and thermal barrier coatings contain a super alloy with 7 weight percent Y2O3 and 93 weight percent Zr0 2 .
• the coatings In order to recover these materials, the coatings must first be stripped off their respective parts. The coated parts are heated to 400 °C in a crucible and sufficient ammonium sulfate is sprinkled on top of the component surfaces to melt the coating and form a liquid layer, completely covering the component. The temperature is held for at least 10 minutes and the coatings are removed, cooled and rinsed. The process is repeated five times to remove all of the coating.
• the automotive catalyst honeycomb material is cut into sections and dipped into a saturated ammonium sulfate solution and reacted for 60 minutes at 425 °C.
• the catalyst material is then rinsed with water and exhibits a reduction in mass of approximately 22% as the result of the removal of the outer catalyst layer.
• the removed material is approximately 6.8% particulate by mass, while the remainder consists of dissolved salts.
• the solids are separated from the solution by filtration and the cerium is separated from the filtrate by precipitation via oxalic acid.
• the precipitate of cerium oxalate is collected and calcined at 1000 °C to form cerium oxide, as demonstrated by the peaks detected in in the x-ray diffraction of FIG. 5. Approximately 5.3% of the total substrate mass is recovered as cerium oxide, based on the original substrate mass.
• a woodstove combustion catalyst honeycomb material is broken into large chunks and mixed with 2 parts ammonium sulfate to one part catalyst material.
• the mixture is reacted for about 60 minutes at 425 °C in a pyrex beaker.
• the catalyst material is then rinsed with water and exhibits a reduction in mass of approximately 4% from the original mass, resulting from the removal of the outer catalyst layer.
• the removed material is comprised of fine particulate and dissolved salts.
• the solids are separated from the solution and are determined using XRD to contain the catalyst palladium, a platinum group metal (i.e., ruthenium, rhodium, palladium, osmium, iridium, and platinum). Referring to FIG.
• the presence of palladium is confirmed by, for example, the signature peaks as detected using x- ray diffraction.
• the palladium was further separated by dissolving it in fresh Aqua Regia; the solution was filtered, evaporated and fired at 900 °C to form palladium metal.
• BaNd 2 Ti 4 0 12 waste material is a byproduct of the production of electronic tape cast material.
• the material once milled, is a fine grain tape cast waste material. It was mixed with 3 parts ammonium sulfate to one part waste materials and 10% water was added to form a paste. The paste was reacted for 60 minutes at 425 °C in a pyrex pan. The reacted material was treated with water and filtered. The solid that was filtered was determined by XRD to be BaS0 4 . The filtrate was treated with excess oxalic acid and the resulting precipitant that formed was filtered, dried and calcined at 1000 °C.
• the resultant material was determined by x-ray diffraction to be Nd 2 0 3 .
• the filtrate was treated with ammonium hydroxide and the resulting precipitant that formed was filtered, dried and calcined at 1000 °C.
• the resultant material was determined by x-ray diffraction to be Ti0 2 . This demonstrates the recycling of rare earth electroceramic materials which contain barium and/or titanium. A similar result would be possible with rare earth modified lead-zirconia-titanate.
• Zircon (a typical waste from metal casting) is ground and thermally decomposed before being passed through a -325 mesh. More specifically, ground Zircon and a coarser fused/thermally decomposed Zircon (beads of Zr0 2 and Si0 2 from a plasma prepared powder) were processed with 3 parts ammonium sulfate to one part Y 2 0 3 -Zr0 2 . The materials were mixed and approximately 7% water was added to form a paste that was further mixed in a Pyrex beaker. The paste was then reacted for about 60 min at 425 °C. The reacted material was then soaked in water and the solids were separated by filtration.

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• 2012
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