WO2014066668A1

WO2014066668A1 - Method for rare earth and actinide element recovery, extraction and separations from natural and recycled resources

Info

Publication number: WO2014066668A1
Application number: PCT/US2013/066663
Authority: WO
Inventors: Joseph Brewer; Neil Lawrence
Original assignee: Rare Earth Salts Separations and Refining LLC
Current assignee: Rare Earth Salts Separations and Refining LLC
Priority date: 2012-10-24
Filing date: 2013-10-24
Publication date: 2014-05-01
Anticipated expiration: 2015-04-24

Abstract

Methods are described for the recovery and separation of the rare earth elements from ore, tailings, or any other solid source. The methods described utilize mechanochemical methods for creating chemical compounds and complexes which are suitable for separation from the original materials. The rare earth element compounds created from the solids are then able to be extracted from the remainder of the materials through the use of solvents. Finally utilizing selective titrations, counter current chromatography and reverse phase chromatography the elements are separated from each other and converted into oxides, hydroxides, salts and organometallic compounds.

Description

METHOD FOR RARE EARTH AND ACTINIDE ELEMENT RECOVERY, EXTRACTION AND SEPARATIONS FROM NATURAL AND RECYCLED RESOURCES

CLAIM OF PRIORITY

This application claims the benefit of priority to U.S. Patent Application No. 61/717,916, filed October 24, 2012, entitled "Method for Rare Earth and Actinide Element Recovery, Extraction and Separations from Natural and Recycled Resources", which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to the extraction and separation of the rare earth and actinide elements from ore, tailings, recycled electronic materials or any other solid source. The rare earth elements are defined as those elements having atomic numbers 57 to 71 inclusive and elements 21 and 39 which are commonly found with the rest of the rare earth elements and have similar chemical and physical properties. The Actinide elements are defined as elements having atomic numbers 89 to 103, however only elements 89 to 92 of the actinides are naturally occurring in significant amounts.

BACKGROUND

Rare earth elements (REE) are irreplaceable chemicals used in the fabrication of a wide range of modern energy -related products such as high energy magnets, catalysts, and laser-guided military weapons. However, little progress has been made in the last 20 years in the efficiency and environmental friendliness of their refining processes. Difficulties in REEs refining from ores lie in their similar chemical and physical properties and the requirements of concentrated acid or caustic fusion. Coupling recent increasing demand of REEs with an unstable supply, there is a pressing need for new REE refining methods.

The rare earth oxides are amongst the most difficult materials to refine due to their highly favorable free energies. With the exception of Sm, Eu and Yb, the rare earth metals are being conventionally refined by calciothermic reduction at temperatures exceeding 1000 °C and in an inert atmosphere. There are two major industrial processes for the extraction of rare earth ores. One of the processes involves the digestion of the concentrated ore in concentrated sulfuric acid. The other is the extraction of the rare earths utilizing caustic fusion. Caustic fusion is undertaken by dissolving the non-silicate minerals in concentrated solutions of sodium hydroxide at temperatures of up to 600 °C. Both complex processes only result in a cake of oxide or hydroxide material that is highly concentrated with all of the rare earths present in their relative concentrations. This cake still must be refined and the elements must be separated from each other. Each step in the extraction and purification results in the loss of yield, cost increase and waste chemical.

Accordingly, there is a need for a refining method for REEs that reduces waste. There is yet a further need for a refining method for REEs that produces a higher yield. There is yet a further need for a method of refining REEs that reduces temperatures and energy demands of the processes.

SUMMARY

One object of the method is the reduction in the number of steps and chemical usage in the preparation of REE oxides, hydroxides, salts and organometallic compounds.

A further object of the method is the extraction and separation of REE oxides, hydroxides, salts and organometallic compounds through the use of mechanochemistry. Mechanochemistry is the use of mechanical energy to overcome the energy of activation of a chemical reaction. This is in contrast to thermochemistry in which the energy to overcome the energy of activation of the reaction is provided by adding heat to the reaction.

Another objective of the method is to provide a method by which REE can be extracted from solid natural resources readily and economically.

Furthermore the objective of the separation of the REE one from another after extraction from the solid source is achieved through the use of selective titration and precipitation of either the REE or the containing matrix.

The objective of the separation of the REE one from another is also achieved through the use of various methods of chromatography including but not limited to ion exchange, counter current, normal phase and reverse phase.

Other objectives of this invention will become apparent and will in part appear herein. DESCRIPTION OF DRAWINGS

FIG. 1 is an overlay of x-ray powder diffraction (XRD) data of typical apatite ore before and after mechanochemical processing demonstrating some of the physical and chemical changes produced by the processing. The major differences are pointed out and lettered.

FIG. 2 is an offset of the same XRD data of typical apatite ore before and after mechanochemical processing which is displayed in Fig. 1. The offset makes some of the physical and chemical changes produced by the processing more apparent than the overlay. The major differences are pointed out and lettered.

FIG. 3 is a graph of the data from a typical titration separation of REE from an ore sample in which the 1 1 most abundant REE are separated from one another.

FIG. 4 is XRD data taken from the cerium oxide produced by this process demonstrating the relatively high purity which is achievable by this process directly from ore to useable product.

FIG. 5 is a schematic of A) a granule of ore with B,C) inclusions which represent one or more REE minerals demonstrating that the desired minerals are frequently included in very small grains in the main ore body. Also shown are d) schematic representations, not to scale, of one possible ligand molecule being brought into close contact with the ore so that the reaction can occur between it and the REE mineral removing the REE from the ore.

FIG. 6 is a schematic of various types of mills which are suitable for the disclosed methods. A) ball mill B) planetary mill C) vibratory mill D) stirring ball mill E) pin mill F) rolling mill.

FIG. 7 is a schematic representation of counter current chromatography as used in the method. A) is a piston driven pump that forces the B) REE compound laden mobile phase through a diffuser into C) a column containing the liquid stationary phase which is not miscible with the stationary phase finally leading to the D) extraction of the same or new REE compounds in turn from the eluent or retained in the stationary phase. DETAILED DESCRIPTION

The disclosed methods overcome the limitations of the current technology by not requiring the entire ore to be dissolved. Elements which are not dissolved remain in solid form, thus requiring a much smaller mass of chemical to be used overall. Additionally the separation of large volumes of REE concentrate has proven to yield the more pure salts compared to the same separation technique used on small volume samples. This is likely due to the longer time allowed for equilibrium to be reached as well as the simple fact that a larger total mass of the desired element is present allowing for all 15 elements to be eluted.

Mechanochemistry is a field of chemistry with a long history.

Mechanochemistry is the use of mechanical energy to overcome the energy of activation of a chemical reaction. This is in contrast to thermochemistry in which the energy to overcome the energy of activation of the reaction is provided by adding heat to the reaction. The earliest apparent reported use of mechanical energy to drive a chemical reaction was reported in a book by Theophrastus of Ephesus (371 - 286 B.C.) "De Lapidibus" translated to "on stones" in which the reaction of cinnabar (HgS) ground in a brass mortar with a brass pestle in the presence of vinegar produced metallic mercury. The reaction in modern terms would be expressed HgS + Cu ->Hg + CuS. From these beginnings

mechanochemistry has been utilized, sometimes without recognition, to drive many reactions. The chemical reactions are thought to occur due to the deformation and fracturing of solids which in turn leads to the reactants coming into contact one with another in the appropriate orientation and with the proper energy. The chemical reactions typically occur at very small sizes at the moment of impact. Typically the mechanical energy required for mechanochemistry is imparted to the reactants through the use of a mortar and pestle, or in a mill of some sort. A variety of mills which can be utilized in conjunction with the method are shown in figure 4.

The formation of REE compounds which are more soluble in a given solvent than the remainder of the material in the ore, or other resource can be accomplished by reacting the REE minerals within the solid with other molecules which form ligand complexes with the REE. Additionally it is possible to form covalent or ionic compounds with the REE by adding other reactants. The nature of the reacting compound whether ligand or not dictates the properties of the final REE compound; for example by reacting a REE with Ethylenediaminetetraacetic acid (EDTA) a compound is formed which is much more soluble in water than a typical REE oxide. Reacting a REE with a porphyrin molecule can form a metal organic framework which is very insoluble in water while becoming very soluble in dimethyl sulfoxide (DMSO).

Two major techniques are utilized after extracting the REE compounds from the solid mass; chromatography and titration. Chromatography is the selective separation of a mixture by passing a compound loaded mobile phase through a stationary phase which interacts with the compound in the mobile phase. Various forms of chromatography have proven useful in the method; ion exchange, counter current, normal phase and reverse phase. In particular counter current chromatography (CCC) has proven to be very useful as it allows nearly 100% recovery of the REE compounds, the selective change or REE compounds to new compounds during separation, and a system by which fouling of the stationary phase is almost unheard of. Titration is the stepwise addition of one chemical compound to a solution containing one or more chemical compounds to effect a change in the solution. In the case of the method titration is used by adding a solution stepwise which contains a precipitating compound such as sodium hydroxide, or oxalic acid to a solution containing REE compound. A variety of other acids may be used including nitric acid, hydrochloric acid, sufuric acid, trichloroacetic acid, phosphoric acid, formic acid, acetic acid, propionic acid, carbonic acid mixtures of these or other suitable acids. In some situations, base dissolution may be carried out to extract the REE. In such embodiments, the base may be selected from sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, sodium bicarbonate, calcium carbonate, ammonium hydroxide, potassium carbonate, lithium hydroxide, mixtures of these, or other suitable bases.

The addition of a precipitating agent to the REE containing solution causes the REE to come out of solution as a solid which is no longer soluble in the original solvent. In figure 3 we demonstrate that a solution containing 14 REE, from a typical ore sample which were selectively dissolved into solution after mechanochemical processing to produce ligand compounds, are capable of being selectively separated by carefully adjusting the pH of the solution. Of the 14 REE 1 1 were found in sufficient concentration and with sufficiently distinct solubility products (K_sp) that they could be separated as high purity hydroxides and oxides. In other examples utilizing 2 different precipitating compounds all 14 elements were precipitated in a nearly quantitative form.

The method comprises several parts which when combined allow for the extraction of well separated rare earth elements (REE) from a wide variety of solid sources including but not limited to ore, tailings, slag, sludge, recycled magnets, and or recycled electronics. This process is unique in that it combines mechanochemical synthesis of soluble REE compounds as a method of extracting the REE from the solid source with titrimetric and chromatographic techniques for the green separation of each of the elements into a highly pure useable REE compound, oxide, or salt without the need for the use of metallic calcium or heating to temperatures above 200 °C. This process utilizes ball-milling to impart the energy to induce a wide variety of solid-solid chemical reactions. The repeated welding together of particles and fracture accompanying ball/powder collisions enable the reacting surfaces to be dynamically regenerated during mechanical ore milling process. Consequently, the reaction kinetics during milling are greatly enhanced as reaction sites are brought together under favorable conditions with high local pressure leading to reactions which are thermodynamically favored at room temperature with reasonable reaction rates. By adding various salts, solvents, or organic compounds such as but not limited to β-ketoiminate, EDTA, DTPA, 2(trimethylsilylamino)-6-methylpyridine, ammonium oxalate, sodium nitrate, DMSO, 2-aminoterephthalic acid, 4,4- azobenzenedicarboxylic acid, 4-carboxylic benzaldehyde, 4,4- biphenyldicarbonitrile, ammonium acetate, benzene- 1,3,5-tricarboxyllic acid, benzoic acid, ferrocene, benzene, water, nitric acid, sulfuric acid,

iodobenzenediacetate, L-ascorbic acid, tetraethylammoniumiodide, sodium laureth sulfate, terephthalic acid, toluene or 2,2-bipyridine-4,4-dicarboxylic acid a wide variety of chemicals can be selectively formed during the mechanochemical processing of solid sources. Other potentially suitable ligands include those disclosed in U.S. Pat. No. 6,060,614, to Orvig, the disclosure of which is hereby incorporated herein by reference in its entirety, and which discusses various chelating ligands that may be useful in the process disclosed herein. These products can then be removed by solvation, leaving behind the undesired elements such as calcium and iron for further traditional processing.

Mechanochemical REE refinement process is unique and innovative over the present industrial processes because it combines four processes: acid or base dissolution of REE ore, refining, alloying, and powder manufacture, into a cost effective, low temperature process. Since the kinetics of such mechanically activated reactions depend on milling parameters such as collision energy and frequency, as well as the thermodynamic properties of the reaction, this allows mechanical activation via mechanical milling processes to induce a wide range of chemical reactions. The process has been shown to extract > 90% of the REE from both simulate and actual ore samples. The REE from the simulated and actual ore samples have been recovered as individual salts, oxides, hydroxides, and organometallic compounds with purity in excess of 95%. The separation of the most abundant 1 1 REE from an actual ore sample have been recovered in approximately relative concentrations, the other elements were not present in high enough concentrations to be detected using our equipment.

The process of this method allows for the use of a wide variety of aqueous (water) and non-aqueous solvents which are carefully selected to take advantage of the solubility of the products which are produced. For example in an acidic solution containing cerium chloride combined with praseodymium chloride the cerium will precipitate as a hydroxide when the solution is titrated with sodium hydroxide long before the praseodymium will. This is due to the difference in the solubility product (K_sp) of the different compounds. In equation 1.1 Ksp of cerium hydroxide is defined as the ratio of the products to reactants in this case the products are listed as the ions which are in solution and the reactants are the solid and liquid reactants.

_K um no- I

\H₂0 \[Ce(OH ), }

However the activity of solids and pure liquids is defined as 1 therefore the equation can be simplified to equation 1.2

So the difference in solubility constants of each compound is dependent upon the concentrations of each of the free ions. In the case of pH or pOH, the concentration of H⁺ and OH^", respectively, are logarithmically proportional to the pH or pOH value as seen in equation 1.3 and 1.4:

pH = - logfff ^÷!

pOH = - logoff-]

Therefore at a pH of 1 , the H⁺ concentration is 10 times more than at pH of 2. Conversely, using the relationship in equation 1.5, the OH- concentration at a pH of 1 is 10 less than at pH of 2:

,_T mo^{- 14}

The same principles apply in other aqueous and non-aqueous solution and allow us to create a system of solutions through which we can selectively precipitate out each of the REE. Additionally the same principle allows us to determine the best mobile and stationary phase for counter current chromatography. As long as there is a sufficient difference in the K_sp of the mobile and stationary phase and those phases are not miscible they can be utilized. By creating a series of columns with a variety of stationary phases this method creates solutions which are appropriate for selective titrations for the production of specific chemicals.

Examples

In the following examples, REE were extracted from a number of ore and tailing samples. In these examples, the ore or tailings samples were preground to 200 mesh size (-75 μτη) particle size. Stoichiometric amounts of ligands (i.e., EDTA and DTP A) were added to preground ore/tailings and 50 μΐ_^ of acid (i.e., nitric or sulfuric acid)/50 grams of preground ore/tailings. The mixture of ligands, acid and ore/tailings was then further ground to 2400 mesh particle size (6 μηι). The mixture of ground ligands, acid and ore/tailings was then washed with acid (i.e., 1M nitric acid) and filtered. Thet pH of filtered acid washed solution was adjusted to 1. The pH 1 adjusted solution was then titrated with a base (i.e., NaOH or KOH) to various pH end points. At those end points, specific materials precipitated and the solution was centrifuged to separate the precipitated solid material from the solution. At each endpoint, the solution was decanted from the solid precipitate and titrated to the next end point. Example 1

Synthetic ore was prepared having a combination of REE oxides in ratios approximately the same as those found in the elk creek deposit in southeaster Nebraska combined with calcite (calcium carbonate, CaCCb). This simulated ore was processed in a liquid assisted mechanochemical method in a vibratory mill with a combination of ligands a small amount of solvent (~\ μL/g mixture) for several hours. The resulting mixture was then mixed with water which had been pH adjusted to 1. The CaCCb from the original solid was filtered from the rest of the solution as it was not soluble under these conditions. The resulting aqueous solution was then titrated with ammonium hydroxide. As the pH of the solution increased each REE element precipitated selectively and was collected for further verification of the purity and identity of the REE present.

The resulting precipitates from each even were calcined at 400 °C and were then examined utilizing x-ray powder diffraction (XRD) to verify the identity of the oxide. The powders were also examined utilizing electron microscopy (SEM) with coupled with energy dispersive x-ray spectroscopy (EDX) and the crystallite were found to vary from between 100 nm to 1 mm with the average being about 300 μηι. The elemental composition and absence of grains of impurities was verified. Additionally the samples were digested in acid and were analyzed by inductively coupled argon plasma optical emission spectroscopy (ICP-OES) and the purity was verified.

Example 2

Apatite tailings from the pea ridge mine in central Missouri were processed using a liquid assisted mechanochemical method in a ball mill. The ore was mixed with a combination of salts, and organic solids with an organic solvent being used for the assist. The resulting mixture was ball milled for several hours and the powder was then mixed with n-butanol and filtered. The filtrate contained the original Cas(P04)3 from the ore. The remaining solution was then processed utilizing CCC and divided into 4 fractions which were individually titrated utilizing oxalic acid producing 10 clean precipitations of REE and a liquid solution containing a high concentration of iron and other transition metals.

The resulting precipitates from each even were calcined at 400 °C and were then examined utilizing XRD to verify the identity of the oxide. The powders were also examined utilizing SEM and EDX and the crystallite were found to vary from between 100 nm to 1 mm with the average being about 500 μηι. The elemental composition and absence of grains of impurities was verified. Additionally the samples were digested in acid and were analyzed by ICP-OES and the purity was verified.

Example 3

Apatite tailings the same as used in Example 2 were processed in the same manner as the simulated ore in Example 1. Most of the resulting precipitations were equally pure as those in Example 2 with the exception of the last to precipitate which was contaminated, co-precipitated, with iron hydroxide.

Comparative Example 1

A sample of the same simulated ore as used in Example 1 was processed in an identical manner but excluded the use of any ligands or other reacting materials. The resulting solution when titrated produced no detectable precipitation events. ICP analysis verified that only trace amounts of REE and Ca were present in the solution.

Although a few exemplary embodiments of the present invention have been shown and described, the present invention is not limited to the described exemplary embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the embodiments of the invention and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

It will be further understood that the terms "comprises" and/or

"comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

Moreover, it will be understood that although the terms first and second are used herein to describe various features, elements, regions, layers and/or sections, these features, elements, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one feature, element, region, layer or section from another feature, element, region, layer or section. Thus, a first feature, element, region, layer or section discussed below could be termed a second feature, element, region, layer or section, and similarly, a second without departing from the teachings of the present invention.

It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. Further, as used herein the term "plurality" refers to at least two elements. Additionally, like numbers refer to like elements throughout.

Claims

CLAIMS What is claimed is:

1. A method for the preparation of rare earth elements from a solid source for extraction by mixing the source with a chemical mixture and then activating the reaction through the use of mechanochemical means.

2. A method for the separation of rare earth elements from the solid source after having been processed by the method of Claim 1 through the use of solvents chosen to dissolve the newly formed compounds.

3. A method for the preparation of rare earth element compounds from the solutions produced by the method of Claim 2 through the use of either titration alone or in conjunction with chromatography.