Selective separation of elements or commodities of interest in aqueous streams

Abstract

A process for selectively separating a metallic constituent from other metals and other materials accompanying the metallic constituent in a mixture is described. The process comprises the step of providing the mixture in an aqueous solution such that the metallic constituent forms a complex anion in the solution. One or more of the other metals forms a cation or a complex cation in the solution. Another step includes contacting the solution with one or more additives to form layered double hydroxide (LDH) material in situ such that the complex anion is intercalated within interlayers of the LDH material and wherein one or more of the other metals are incorporated into the LDH material's crystal structure or matrix. Another step involves the addition of an LDH to an aqueous solution. The process involves selectively recovering the metallic constituent from the interlayer of the LDH by subjecting the LDH to a recovery treatment step(s) and as required, methods to modify the LDH to facilitate metal separation and recovery or contaminant stabilisation.

Claims

1. A process for selectively separating a metallic constituent from one or more other elements and other materials accompanying the metallic constituent in a mixture, the process comprising: (a) providing the mixture in an aqueous solution such that the metallic constituent forms a complex anion selected from the group consisting of a uranyl complex anion, a vanadyl complex anion, a chromium complex anion, a transuranic complex anion, and a radionuclide complex anion in the aqueous solution and wherein the one or more other elements forms a cation or a complex cation in the aqueous solution; (b) contacting the aqueous solution with one or more additives to form layered double hydroxide (LDH) material in situ such that the complex anion is intercalated within interlayers of the LDH material to form an intercalated complex anion, and introducing additional additives comprising bicarbonates or carbonates into the aqueous solution to optimize a crystal structure or matrix of the LDH material, wherein the one or more other elements are selectively incorporated into the crystal structure or matrix of the LDH material; (c) after (b), separating the LDH material from the aqueous solution; and (d) after (c), selectively recovering the metallic constituents from the interlayers of the LDH material by subjecting the LDH material obtained from step (c) to a recovery treatment step; wherein the selectively recovering comprises: (I) subjecting the LDH material to heat treatment or thermal decomposition in an anoxic, reducing, inert or oxidizing gas, thereby forming a collapsed or metastable LDH material and resulting in formation of a first oxide material comprising the metallic constituent, a second oxide material comprising the one or more other elements, or a third material comprising the metallic constituent and the one or more other elements; or (II) subjecting the LDH material to ion exchange by adding the LDH material and at least one substituent agent to an ion-exchanging solution such that the at least one substituent agent displaces at least some of the intercalated complex anion by an ion exchange mechanism thereby resulting in the intercalated complex anion being released from the interlayers into the ion-exchanging solution, wherein the ion exchange comprises controlling pH conditions of the ion-exchanging solution.

2. A process in accordance with claim 1 wherein the metallic constituent comprises uranium, vanadium, chromium or a transuranic element or radionuclide capable of forming the complex anion in the aqueous solution and wherein the one or more other elements comprises one or more metals selected from the group consisting of Cu, Mn, Ni, Pb, Zn and rare earth metals.

3. A process in accordance with claim 1 wherein the step of contacting the solution with one or more additives to form layered double hydroxide (LDH) material in situ further comprises: (i) adding a magnesium and/or aluminium containing silicate material to the aqueous solution and dissolving at least a part of the silicate material in the solution thereby leaching at least a part of the magnesium and/or aluminium from the silicate material into the solution; and (ii) controlling reaction conditions for achieving an appropriate Mg:Al ratio in the solution for formation of the layered double hydroxide (LDH) material in situ.

4. A process in accordance with claim 3 wherein the step of controlling the reaction conditions comprises addition of at least one Mg-containing compound and/or at least one Al-containing compound for achieving the appropriate Mg:Al ratio in the solution for formation of the LDH material in situ.

5. A process in accordance with claim 4 further comprising the step of removing at least a part of the LDH material formed in situ, wherein the at least one of the said dissolved cation and/or anion species comprising magnesium and/or aluminium is incorporated in the LDH material.

6. A process in accordance with claim 3 wherein the step of controlling the reaction conditions further comprises providing substantially alkaline reaction conditions for formation of the LDH material in situ.

7. A process in accordance with claim 3 wherein the step of controlling the reaction conditions further comprises addition of alkaline or acid-neutralising material for formation of the LDH material in situ.

8. A process in accordance with claim 3 wherein the silicate material is one or more of: Attapulgite; Clinoptilolite; Sepiolite; Talc; or Vermiculite.

9. A process in accordance with claim 3 wherein at least a part of the silicate material from step (i) and the LDH material formed in situ in step (ii) form an insoluble clay material mixture wherein the insoluble clay material mixture incorporates said cation or complex cation in the solution and/or complex anion in the solution.

10. A process in accordance with claim 3 wherein undissolved parts of the silicate material comprise undissolved clay material particles from step (i) and provide nucleation sites for formation of at least a part of the LDH material formed in situ in step (ii).

11. A process in accordance with claim 3 wherein the cation or complex cation in the solution comprises magnesium and/or aluminium cations such that the magnesium and/or aluminium is incorporated into the interlayers of the LDH material formed in situ.

12. A process in accordance with claim 3 wherein step (i) further comprises adding an additional material to a mixture comprising the silicate material.

13. A process in accordance with claim 1 wherein the LDH material formed in situ comprises hydrotalcite.

14. A process in accordance with claim 1 wherein the substituent agent is selected from the group consisting of: nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), a crown ether or other organic or (complex) inorganic ligand.

15. A process in accordance with claim 1 wherein the substituent agent is more electronegative relative to the complex anion intercalated in the LDH material.

16. A process in accordance with claim 1, further comprising, after (II), separating the LDH material to obtain a separated LDH material comprising the one or more other elements incorporated into the crystal structure or matrix of the separated LDH material; and subjecting the separated LDH material to heat treatment or thermal decomposition to recover the one or more other elements.

17. A process in accordance with claim 16, further comprising, prior to or during the heat treatment or thermal decomposition of the separated LDH material, adding a further additive to the separated LDH material.

18. A process in accordance with claim 17, further comprising controlling a ratio of the further additive to the separated LDH material.

19. A process in accordance with claim 17, wherein the further additive comprises crystalline silica, amorphous or chemically-precipitated silica, silicic acid, tetra-ethylsilica(te), or silica added to the LDH interlayers.

20. A process for selectively separating a metallic constituent from one or more other elements and other materials accompanying metallic constituent in a mixture, the process comprising: (a) providing the mixture in an aqueous solution such that the metallic constituent forms a complex anion selected from the group consisting of a uranyl complex anion, a vanadyl complex anion, a chromium complex anion, a transuranic complex anion, and a radionuclide complex anion in the aqueous solution and wherein the one or more other elements forms a cation or a complex cation in the aqueous solution; (b) contacting the aqueous solution with a layered double hydroxide (LDH) material such that the complex anion is intercalated within interlayers of the LDH material, and introducing additives comprising bicarbonates or carbonates into the aqueous solution to optimize a crystal structure or matrix of the LDH material, wherein the one or more other elements are selectively incorporated into the crystal structure or matrix; (c) after (b), separating the LDH material from the aqueous solution; and (d) after (c), selectively recovering the metallic constituent from the interlayer of the LDH material by subjecting the LDH material from step (b) to a recovery treatment step; wherein the selectively recovering step comprises: (I) subjecting the LDH material to heat treatment or thermal decomposition in an anoxic, reducing, inert or oxidizing gas, thereby forming a collapsed or metastable LDH material and resulting in formation of a first oxide material comprising the metallic constituent, a second oxide material comprising the one or more other elements, and a third material, or further mineral phases, comprising the metallic constituent and the one or more other elements; or (II) subjecting the LDH material to ion exchange by adding the LDH material and one or more substituent agents to an ion-exchanging solution such that the one or more substituent agents displaces at least some of the intercalated complex anion by an ion exchange mechanism, thereby resulting in the intercalated complex anion being released from the interlayers into the ion-exchanging solution, wherein the ion-exchange comprises controlling pH conditions of the ion-exchanging solution.

21. A process in accordance with claim 20 wherein the step of contacting the LDH material with the aqueous solution comprises dissolving at least a part of the LDH material into the solution thereby obtaining dissolved LDH material in the solution followed by controlling the reaction conditions in the aqueous solution for in situ precipitation of LDH material formed in situ from the dissolved LDH material such that the complex anion is intercalated within interlayers of the LDH material formed in situ and wherein one or more of the other elements are incorporated into a crystal structure or matrix of the LDH material formed in situ.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is schematic flowchart of a process for separating one or more metallic commodities in an aqueous solution by adopting a process in accordance with a preferred embodiment.

(2) FIG. 2 represents a speciation diagram for the system U—H.sub.2O—SO.sub.4—CO.sub.3 from pH 2-10 in equilibrium with the atmosphere.

(3) FIG. 3 depicts Molar ratios of Al/Si and Mg/Al produced by 1 M HCl and 1 M NaOH after stirring (1-4 hours) and ultrasonication+stirring (1 hour) of filtered clay and zeolite solutions in accordance with an embodiment of the present disclosure. Crossed lines mark Al/Si molar ratio of 0.5 and Mg/Al molar ratio of 3 (see text).

(4) FIG. 4 depicts X-ray diffraction (XRD) spectrum of sepiolite/white clinoptilolite-hydrotalcite nanohybrid. Note peaks corresponding to sepiolite and clinoptilolite precursors and characteristic hydrotalcite (pale blue)/Mg—Al hydroxide (pink) peaks at ˜13 and 26 degrees, 2 Theta.

(5) FIG. 5 depicts phosphorus uptake capacity of a range of clay/zeolite nano-hybrid materials synthesised in this study.

(6) FIG. 6 depicts an integrated, grey-scale diffractogram of approximately 500 X-ray diffraction (XRD) traces collected during calcination of a hydrotalcite sample heated up to 1350° C. using a Pt strip heater;

(7) FIG. 7 depicts an integrated, grey-scale diffractogram of approximately 500 X-ray diffraction (XRD) traces collected during calcination of a hydrotalcite sample heated up to 1350° C. using a Pt strip heater in the presence of quartz;

(8) FIG. 8 depicts an integrated, grey-scale diffractogram of approximately 500 X-ray diffraction (XRD) traces collected during calcination of a hydrotalcite sample heated up to 1350° C. using a Pt strip heater in the presence of amorphous silica;

(9) FIG. 9 depicts an integrated, grey-scale diffractogram of approximately 500 X-ray diffraction (XRD) traces collected during calcination of a hydrotalcite sample heated up to 1350° C. using a Pt strip heater in the presence of interlayer silica;

(10) FIG. 10 is a graphical representation of the quantitative extent of hydrotalcite decomposition relative to formation of other mineral phases as a function of temperature in the presence of quartz at a silica:hydrotalcite ratio of 1:1;

(11) FIG. 11 is a graphical representation of the quantitative extent of hydrotalcite decomposition relative to formation of other mineral phases as a function of temperature in the presence of quartz at a silica:hydrotalcite ratio of 3:1; and,

(12) FIG. 12 is a back scattered SEM image of a calcined hydrotalcite showing a bright (high atomic mass) discrete U-bearing grain occurring discretely along with spinel and periclase grains.

DETAILED DESCRIPTION

(13) Referring to the flow diagram illustrated in FIG. 1, an ore body containing a plurality of metallic constituents such as uranium and REE may be introduced to an aqueous leaching solution to obtain a pregnant leaching solution or aqueous stream. Some of the metallic constituents such as uranium may form complex anions in the solution, such as uranyl anionic complexes, as described in previous sections. Some of the other metallic constituents particularly constituents such as the REE may typically form cations in the aqueous solutions. The liquid phase of the pregnant leach solution containing the dissolved anions and cations may be separated from the undissolved solids and directed to a reaction step. The reaction step may comprise steps such as controlling the pH to determine the speciation of the uranyl complexes as illustrated in FIG. 2. The reaction step may form complex anions containing the metallic constituent (e.g. uranium). The reaction step may be followed by an LDH formation step or alternatively an LDH addition step or LDH addition and cycling of the pH to induce partial dissolution and then reformation of the LDH.

(14) In the LDH formation step, additives such as divalent additives such as MgO may be added in combination with trivalent additives such as soluble alumina salts in specific ratios and under suitable pH (alkaline pH) to promote the in-situ formation of LDH material in the solution. Such an LDH formation step also results in intercalation of the complex anion (such as the uranyl complex anion) interlayers of the LDH material formed in-situ. The metallic cations are also incorporated into the metal oxide layers of the LDH material formed in situ thereby forming a part of the crystal structure or matrix of the LDH. Such separation of the metallic species is based upon the differing uptake mechanisms for different ions provided by the LDH material formed in situ.

(15) As described earlier, the LDH formation step may be substituted or complemented by an LDH addition step in which pre-formed LDH material may be added to the solution containing the complex anions (uranyl complex anion) and the metallic cations. The step of adding pre-formed LDH material also results in intercalation of the complex anion (such as the uranyl complex anion) interlayers of the LDH material. This step may also include controlling pH so that part of the LDH may be initially dissolved at a pH of less than 9 and as low as pH 1, for specified time intervals as required to yield a sufficient degree of LDH dissolution, followed by an increase in the pH to promote reformation of the LDH material in situ. During this reformation step, other cations such as REE cations may be incorporated into the metal hydroxide layer substituting for the original cations in the initially added LDH. During this process, some anions, in particular those comprised of uranyl anionic complexes may also be substituted into the interlayer of the LDH material. Note that other techniques may also be used in the dissolution or reformation steps including (ultra) sonication or the addition of other solvents or reagents as required.

(16) The LDH material containing the intercalated complex anion and obtained from the LDH formation step or the LDH addition step may be separated by processes such as sedimentation, flocculation, filtration, cyclonic separation or other known separation methods. The separated LDH material may then be subjected to a further process for recovering the intercalated complex anion (e.g. the uranyl complex anion) such as an ion exchange process in accordance with the steps described in the preceding sections of the specification. Alternative methods of recovering the intercalated metallic constituent may also be employed in accordance with the process step detailed in the preceding sections. As discussed earlier, the recovery treatment step may not be limited to recovery of the intercalated metallic constituent such as the uranyl complex anion but may further include recovery of the metallic cations such as REE incorporated in the LDH matrix in the LDH formation step.

(17) The process described herein utilises the differing uptake mechanisms for different metallic ionic species as a way of separating the metallic species. In some embodiments, desirable separation and recovery is achieved by intercalating at least one metallic constituent in the interlayer (such as the uranyl complex anion) of the LDH (formed in-situ or added to the solution) and subsequently recovering the metallic constituent from the LDH by a further recovery step.

EXAMPLES

Example 1

(18) In a first exemplary embodiment (example 1) the process may be utilised for the processing of uranium-bearing ores. It is common in uranium bearing ores that a range of other elements are present in addition to uranium. The other elements may include elements such as As, Se, Cu and the rare earth elements (REE— Ln.sup.3+ comprising La—Lu+Sc+Y). The inventor has found that REE predominantly exist as Ln.sup.3+ cations in a +3 oxidation state. Cerium exists in +3 and +4 oxidation states. Europium exists in +2 and +3 oxidation states. In the exemplary process, a uranium bearing solution derived from leaching of a uranium ore was contacted with LDH material.

(19) There are two different ways in which intercalation of the uranyl complex anion may be achieved. In a first possible way, the uranyl complex anion would readily intercalate into the interlayer of the LDH material added to the solution. However, utilising such a method does not result in uptake of the REE into the matrix or crystal structure of the LDH material added to the uranium.

(20) In a more preferred way, the LDH material added to the uranium bearing solution was dissolved in the uranium bearing solution by reducing the pH of the solution to less than 3. Reducing the pH level resulted in dissolution of the LDH material thereby resulting in the release of divalent and trivalent cations (that form the metal oxide layers of the LDH material) into the solution. After dissolving the LDH material, the pH was increased to provide alkaline reaction conditions in the solution. Providing such alkaline conditions resulted in reformation of the LDH material as a result of precipitation of the LDH material in the solution. During the reformation of the LDH material the divalent and trivalent cations that were dissolved into the solution (as a result of the initial dissolving step) precipitated to form the metal oxide layer of the reformed LDH material. During the reformation step at least some of the REE cations were also incorporated into the crystal structure of the reformed LDH material. Anionic uranyl complexes were also intercalated into the interlayer of the reformed LDH material. Importantly it has been recognised that as the divalent to trivalent ratio of metals in the primary metal hydroxide layer of the LDH may typically vary between 2:1 and 4:1, changes in this ratio may occur in the reformed LDH due to incorporation of other cations from solution that still allow a stable LDH to form.

(21) During the course of the process, the REE were shown to be strongly partitioned into the primary metal hydroxide layer of the reformed LDH material substituting for other +3 cations such as Al and Fe that were present in the initially added LDH material. Unlike the REE cations, the uranyl ion (uranium is known to exist as a UO.sub.2.sup.2+ oxy-cation in solution) is considered too large to substitute for the +2 cations such as Mg.sup.2+ Alkaline earth and transition metals generally present in the metal hydroxide layers of LDH material. As shown in FIG. 2, under low pH conditions, anionic uranyl complexes are formed especially UO.sub.2.sup.2+−SO.sub.4 complexes (e.g. UO.sub.2(SO.sub.4).sub.3.sup.4−). Under intermediate to higher pH UO.sub.2.sup.2+−CO.sub.3.sup.2− anionic complexes (e.g. UO.sub.2(CO.sub.3).sub.2.sup.2−, UO.sub.2(CO.sub.3).sub.3.sup.4−, CaUO.sub.2(CO.sub.3).sub.3.sup.2−) may predominate. Given this speciation of the UO.sub.2.sup.2+ as anionic complexes, these uranyl anionic complexes preferentially partition into the anionic interlayers of LDH. As a result, the process of example 1 provides the following advantages: Valuable REE are contained within the metal hydroxide layers of the LDH Valuable U is contained as anionic complexes within the LDH interlayers. Separation of these two valuable commodities U and REE, not only from each other in terms of the way they are bound in the initial solution, but also from other components including some contaminants, salts or ions etc. that may otherwise interfere in the U or REE recovery process is highly beneficial for later separation, recovery and purification. A solid LDH is produced that typically may contain in excess of 30% U and 0-50% REE, typically 100-300 times typical ore grades of these elements thus allowing substantial enrichment of the commodities of value. Effective separation of potentially problematic ions such as Na.sup.+, Cl.sup.− and SO.sub.4.sup.2− or other additives from the mineral processing stream (with the potential to make for simpler processing, further enrichment or recovery). Production of a cleaner effluent that may potentially be reused in mineral processing or other site or other operations without (or minimal) additional treatment.

(22) In addition to the above, given the different partitioning or separation of U from REE, several methods may be utilised for recovering a commodity of interest based upon the separation of commodities achieved, as elucidated above. Recovery of one or more commodities may be carried out effectively by one or more of the following further steps: the addition of a strong alkali to displace UO.sub.2.sup.2+−SO.sub.4 complexes by OH.sup.− anions, or reducing the pH such that less charged or neutral UO.sub.2 complexes are displaced from the LDH interlayers. other complexing ligands or other anions (e.g. NTA, EDTA) may be added to the LDH to displace the UO.sub.2-complexes and form new NTA, EDTA complexes. addition of other chemical reagents such as phosphates, vanadates or inorganic or organic peroxides, or combinations thereof, to induce uranium precipitation. partial or complete dissolution of a U-, REE-metal-containing LDH by the addition of acid and recovery of the constituents by conventional means. addition of reducing agents, anoxia or gases (e.g. CO) to reduce uranyl complexes (U +6 oxidation state) to U (+4 oxidation state) for example as UO.sub.2 to eliminate the uranyl complexation with carbonate on the basis of charge and allow recovery of U in the +4 oxidation state. Such recovery methods may include physical (e.g. ultrasonication) or otherwise chemical (solvent-based) delamination of the LDH to recover the reduced U or the application of other physicochemical methods as required. other methods of separation that may include calcination such that with heating, typically in the range 100-1200° C., there will be layer collapse and re-crystallisation of the LDH leading to the formation of discrete or intimately associated mineral phases such as spinel and periclase. These phases, by virtue of their chemistry and crystal structure, may accommodate one of more elements of interest or may provide enhanced opportunities for recovery of particular elements given the different physicochemical properties of the mineral phases formed from calcination.

(23) The methods of stabilisation described here may also find applications in the nuclear energy or weapons industries to assist in the containment of Uranium bearing materials or wastes including transuranics or daughter radionuclides.

Example 2

(24) In a second exemplary embodiment (example 2) the process may be utilised for the processing of uranium-bearing ores, in which LDH can be formed in situ within a mineral processing or metallurgical stream that includes the uranium bearing ores. The uranium ore containing stream was dosed, typically with one of or both of Mg and Al containing compounds, to achieve a desired ratio of Mg/Al in the stream which results in precipitation of LDH such as hydrotalcites. As explained in example 1, uranium bearing ores include a range of other elements that are present in addition to uranium which includes heavy metals, metalloids and/or REE. Forming the LDH material in situ also results in incorporation of the cations such as Ln.sup.3+ cations and/or Ce.sup.3+ and Ce.sup.4+ and/or Eu.sup.2+ or Eu.sup.3+ oxidation states. In situ formation of the LDH also results in REE cations being shown to be strongly partitioned into the primary metal hydroxide layer of LDH. As discussed earlier, since uranium exists as an oxy-cation commonly known as a uranyl (UO.sub.2.sup.2+) cation, the uranyl ion is too large to be substituted for +2 cations such as Mg.sup.2+ into the LDH. Alkaline earth and transition metals generally present in the metal hydroxide layers of the LDH. Once again, under low pH conditions, anionic uranyl complexes are formed, especially UO.sub.2.sup.2+−SO.sub.4 complexes (e.g. UO.sub.2(SO.sub.4).sub.3.sup.4−). Under intermediate to higher pH UO.sub.2.sup.2+−CO.sub.3.sup.2− anionic complexes (e.g. UO.sub.2(CO.sub.3).sub.2.sup.2−, UO.sub.2(CO.sub.3).sub.3.sup.4−, CaUO.sub.2(CO.sub.3).sub.3.sup.2−) may predominate. Given this speciation of the UO.sub.2.sup.2+ as anionic complexes, these uranyl anionic complexes preferentially partition into the anionic interlayers of LDH formed in situ. The process described in example 2 also provides one or more of the several advantages of the process of Example 1 as summarised above. The commodities of interest may also be recovered by one or more of the further recovery steps listed under Example 1.

Example 3

(25) In a third exemplary embodiment (Example 3) the process may be utilised for the processing of uranium-bearing ores, in which LDH can be formed in situ within an alkaline mineral processing or metallurgical stream that includes the uranium bearing ores.

(26) The uranium ore containing stream was dosed, typically with one of both of Mg and Al containing compounds, to achieve a desired ratio of Mg/Al in the stream which results in precipitation of LDH such as hydrotalcites. Due to the pre-existing alkaline conditions (pH of at least greater than 7 and preferably greater than 8) of the alkaline mineral processing or metallurgical stream, in situ formation of LDH is favourable when the desired ratio of Mg/Al is achieved. As explained in Example 1, uranium bearing ores include a range of other elements that are present in addition to uranium which includes heavy metals, metalloids and/or REE. Forming the LDH material in situ also results in incorporation of the cations such as Ln.sup.3+ cations and/or Ce.sup.3+ and Ce.sup.4+ and/or Eu.sup.2+ or Eu.sup.3+ oxidation states and a range of anions including oxo-metallic anions or oxyanions. Laboratory trials have demonstrated that the Al containing compound is preferably to be added first or in conjunction with any Mg containing compound to prevent the precipitation of the Mg as Mg carbonate compounds such as MgCO.sub.3 rather than it being utilised in the formation of the LDH

(27) In situ formation of the LDH also results in REE cations being shown to be strongly partitioned into the primary metal hydroxide layer of LDH. As discussed earlier, since uranium exists as an oxy-cation commonly known as a uranyl (UO.sub.2.sup.2+) cation, the uranyl ion is too large to be substituted for +2 cations such as Mg.sup.2+ into the LDH. Alkaline earth and transition metals generally present in the metal hydroxide layers of the LDH. Once again, under the alkaline conditions of the stream, anionic uranyl complexes are formed. Under the intermediate to higher pH conditions of the stream, UO.sub.2.sup.2+−CO.sub.3.sup.2− anionic complexes (e.g. UO.sub.2(CO.sub.3).sub.2.sup.2−, UO.sub.2(CO.sub.3).sub.3.sup.4−, CaUO.sub.2(CO.sub.3).sub.3.sup.2−) may predominate. Given this selective speciation of the UO.sub.2.sup.2+ as anionic complexes, these uranyl anionic complexes preferentially partition into the anionic interlayers of LDH formed in situ.

(28) It is important to appreciate that under the reaction conditions of example 3, as explained above only carbonate complexes will predominate and some REE, particularly the mid (MREE) to heavy REE (HREE) may be preferentially retained in the solution due to the known preferential complexation of MREE and HREE by carbonate ligands. This preferential speciation under alkaline conditions may be used advantageously given that the MREE and HREE are generally considered the most valuable components of the REE due to their often low abundance.

(29) In another exemplary embodiment, the step of contacting the solution with one or more additives to form layered double hydroxide (LDH) material was carried out by adding a magnesium and aluminium containing silicate material in the aqueous solution and dissolving at least a part of the silicate material in the solution thereby leaching at least a part of the magnesium and/or aluminium from the silicate material into the water; and controlling reaction conditions for achieving an appropriate Mg:Al ratio in the solution for formation of the layered double hydroxide (LDH) in situ.

(30) Raw materials, primarily Mg—Al or Al-bearing aluminosilicate clays (vermiculite, attapulgite, sepiolite, talc kaolinite) and zeolites (white and pink clinoptilolite), were procured from industrial and commercial sources. These clays and zeolites were used as sources of raw materials, principally Al and Mg, during acid and alkali dissolution experiments enhanced by the use of ultrasonication.

(31) Initial batch decomposition reactions of the aluminosilicates in both acid and alkali and with the additional use of agitation including ultrasonication were completed. Results of ICP analyses to quantify the extent of dissolution due to acid or alkali in combination with stirring (1-4 hours) or ultrasonication+stirring (1 hour) are presented in Table 1 and FIG. 3. These results indicate that substantial Mg and Al release (preferably >3:1 Mg/Al molar ratio) as required for hydrotalcite synthesis can be achieved from clays or zeolites during acid extraction. In addition, some clays such as sepiolite (Table 1) yielded both high concentrations of Mg and Al and high Mg/Al molar ratios. Under acidic conditions, all clays and zeolites demonstrated incongruent dissolution with Mg/Al and Al/Si ratios higher in the solute than the solid. In contrast, under alkali conditions any incongruent dissolution was obscured by secondary precipitation reactions.

(32) TABLE-US-00001 TABLE 1 Geochemistry of filtered solutions produced by 1M HCl or 1M NaOH digestion after stirring (1-4 hours) and ultrasonication + stirring (1 hour) of clay and zeolite suspensions. Mg Al Si Mg/ Clay/zeolite Al Si Mg Ca Fe K Na mM mM mM Al Al/Si Attapulgite sonicated 88 172 183 206 52 61 143 8 3 6 2.3 0.5 1 hr in 1M HCl Attapulgite sonicated 31 176 0 3 0 34 24202 0 1 6 0.0 0.2 1 hr in 1M NaOH Attapulgite stirred 1 27 25 113 172 10 28 384 5 1 1 4.6 1.1 hr in 1M HCl Attapulgite stirred 1 7 70 0 6 0 31 22591 0 0 3 0.0 0.1 hr in 1M NaOH Attapulgite stirred 2 29 34 117 173 12 28 82 5 1 1 4.5 0.9 hr in 1M HCl Attapulgite stirred 2 8 81 0 6 0 32 22620 0 0 3 0.0 0.1 hr in 1M NaOH Attapulgite stirred 4 38 63 125 170 17 31 90 5 1 2 3.6 0.6 hr in 1M HCl Attapulgite stirred 4 10 103 0 5 0 32 21519 0 0 4 0.0 0.1 hr in 1M NaOH Clinoptilolite (pink) 192 74 35 139 32 17 114 1 7 3 0.2 2.7 sonicated 1 hr in 1M HCl Clinoptilolite (pink) 54 158 0 2 1 13 25419 0 2 6 0.0 0.4 sonicated 1 hr in 1M NaOH Clinoptilolite (pink) 85 16 18 90 11 9 49 1 3 1 0.2 5.4 stirred 1 hr in 1M HCl Clinoptilolite (pink) 10 32 0 19 0 7 23071 0 0 1 0.0 0.3 stirred 1 hr in 1M NaOH Clinoptilolite (pink) 85 18 17 89 11 8 51 1 3 1 0.2 4.9 stirred 2 hr in 1M HCl Clinoptilolite (pink) 10 35 0 17 0 17 23211 0 0 1 0.0 0.3 stirred 2 hr in 1M NaOH Clinoptilolite (pink) 107 28 21 99 14 9 63 1 4 1 0.2 4.0 stirred 4 hr in 1M HCl Clinoptilolite (pink) 13 41 0 11 0 10 22719 0 0 1 0.0 0.3 stirred 4 hr in 1M NaOH Clinoptilolite (white) 347 67 45 146 13 198 76 2 13 2 0.1 5.4 sonicated 1 hr in 1M HCl Clinoptilolite (white) 160 777 0 1 0 160 24486 0 6 28 0.0 0.2 sonicated 1 hr in 1M NaOH Clinoptilolite (white) 151 18 21 75 4 157 49 1 6 1 0.2 9.0 stirred 1 hr in 1M HCl Clinoptilolite (white) 13 98 0 3 0 120 22080 0 0 3 0.0 0.1 stirred 1 hr in 1M NaOH Clinoptilolite (white) 152 20 22 78 4 162 49 1 6 1 0.2 7.9 stirred 2 hr in 1M HCl Clinoptilolite (white) 22 130 0 2 0 119 22496 0 1 5 0.0 0.2 stirred 2 hr in 1M NaOH Clinoptilolite (white) 178 28 24 85 5 163 49 1 7 1 0.2 6.5 stirred 4 hr in 1M HCl Clinoptilolite (white) 31 182 0 2 0 120 23054 0 1 6 0.0 0.2 stirred 4 hr in 1M NaOH Sepiolite sonicated 1 18 75 326 22 6 7 5 13 1 3 19.8 0.3 hr in 1M HCl Sepiolite stirred 1 h 20 105 357 22 7 10 5 15 1 4 19.9 0.2 in 1M HCl Sepiolite stirred 2 h 23 125 374 22 16 13 4 15 1 4 18.4 0.2 in 1M HCl Sepiolite stirred 4 h 76 406 1312 26 50 19 8 54 3 14 19.1 0.2 in 1M HCl Talc sonicated 1 hr in 10 53 71 11 4 6 57 3 0 2 8.1 0.2 1M HCl Talc stirred 1 h in 1M 1 5 16 9 1 3 7 1 0 0 17.3 0.2 HCl Talc stirred 2 h in 1M 1 8 18 9 1 3 6 1 0 0 16.9 0.2 HCl Talc stirred 4 h in 1M 4 30 40 9 2 2 7 2 0 1 11.4 0.1 HCl Vermiculite sonicated 538 784 1605 19 570 532 28 66 20 28 3.3 0.7 1 hr in 1M HCl Vermiculite sonicated 2 15 0 1 1 59 25733 0 0 1 0.1 0.1 1 hr in 1M NaOH Vermiculite stirred 1 28 13 71 47 30 139 7 3 1 0 2.9 2.1 hr in 1M HCl Vermiculite stirred 1 1 3 1 3 1 37 22442 0 0 0 1.3 0.3 hr in 1M NaOH Vermiculite stirred 2 84 85 234 48 90 170 10 10 3 3 3.1 1.0 hr in 1M HCl Vermiculite stirred 2 1 3 0 3 0 46 22636 0 0 0 0.1 0.2 hr in 1M NaOH Vermiculite stirred 4 127 169 359 49 136 193 6 15 5 6 3.1 0.8 hr in 1M HCl Vermiculite stirred 4 0 4 0 4 0 55 22335 0 0 0 1.1 0.1 hr in 1M NaOH

(33) Importantly, the dissolution of Mg and Al is substantially enhanced using the combination of ultrasonication+stirring relative to stirring alone. During an acid digest, substantial Si and other elements such as Fe and Ca may also be released depending on the chemistry and purity of the clay or zeolite. This is undesirable as excess silica can potentially occupy the interlayer anion exchange site within the LDH or HT during formation or may combine with Al to form other compounds during LDH or HT synthesis. In particular, it is desirable that the Al/Sl molar ratio is <0.5 as depicted in FIG. 3. In addition, abundant Fe may result in substitution for one or both of Mg and Al in the LDH or HT structure. If Fe is present in sufficient quantities this may lead to the formation of unstable green rusts.

(34) Alkali dissolution using either stirring or ultrasonication+stirring, as expected, yielded a substantially different solution composition with enhanced dissolution of Si over that of Al, while Mg was low as it is likely to have precipitated as brucite —Mg(OH).sub.2. Whilst excess silica is generally undesirable in the formation of LDH or HT as described above, potential exists to use the remnant clay or zeolite after dissolution as substrates for LDH or HT nucleation.

(35) In cases where high Si is present, this may occupy at least part of the anionic interlayers of the LDH or HT structure. This property may be exploited if calcination is required to form other high temperature phases as described elsewhere.

(36) Further clay dissolution experiments were undertaken with H2SO4 in place of HCl to investigate the effects, if any, of using a different acid. These results are presented in Table 2 and illustrate that relatively less dissolved Si is produced in the presence of H2SO4 yielding lower Al/Si ratios. As outlined above, this is considered important in the synthesis of LDH or HT from solutions produced by clay or zeolite dissolution. In addition, Mg/Al ratios generally increased using H.sub.2SO.sub.4 in place of HCl.

(37) TABLE-US-00002 TABLE 2 Ratios of concentrations of Al, Si and Mg and Mg/Al and Al/Si in solutions produced by 1M H.sub.2SO.sub.4 and 1M HCl digestion using ultrasonication + stirring (1 hour) of clay and zeolite suspensions. Clay/ Al Si Mg Mg/Al Al/Si zeolite (H.sub.2SO.sub.4/HCl) (H.sub.2SO.sub.4/HCl) (H.sub.2SO.sub.4/HCl) (H.sub.2SO.sub.4/HCl) (H.sub.2SO.sub.4/HCl) Vermiculite sonicated 1 hr in 1M 0.7 0.5 0.7 1.0 1.4 HCl or H.sub.2SO.sub.4 Sepiolite sonicated 1 hr in 1M 2.7 0.7 3.1 1.2 3.8 HCl or H.sub.2SO.sub.4 Attapulgite sonicated 1 hr in 1M 0.6 0.6 0.8 1.3 1.0 HCl or H.sub.2SO.sub.4 Kaolinite sonicated 1 hr in 1M 1.5 1.4 5.0 3.3 1.1 HCl or H.sub.2SO.sub.4 Pink clinopt sonicated 1 hr in 1M 0.4 0.2 0.4 1.1 1.9 HCl or H.sub.2SO.sub.4 White clinop sonicated 1 hr in 0.7 0.6 0.7 1.0 1.1 1M HCl or H.sub.2SO.sub.4

(38) On the basis of the above dissolution experiments and supplementary experiments using H.sub.2SO.sub.4 in place of HCl, synthesis of the nano-hybrid materials was undertaken using a range of clay and zeolite. In addition, aluminate was also used as both a source of additional Al and as a neutralising agent. A list of the nano-hybrid material produced and their P-uptake capacity is given in Table 3.

(39) TABLE-US-00003 TABLE 3 Phosphorus uptake capacity of a range of clay/zeolite nano-hybrid materials synthesised in this study. P-uptake Clay/zeolite mg/g Unground vermiculite + white clinoptilolite 4.6 ALL SOLIDS Unground Vermiculite + aluminate ALL 5.4 SOLIDS Sepiolite + aluminate ALL SOLIDS 9.0 Unground vermiculite/white clinoptilolite 11.7 NO SOLIDS Sepiolite/white clinoptilolite ALL SOLIDS 13.2 Sepiolite + white clinoptilolite ALL 13.5 SOLIDS Vermiculite + white clinoptilolite ALL 13.7 SOLIDS Vermiculite + aluminate ALL SOLIDS 14.1 Unground vermiculite/white clinoptilolite 14.3 ALL SOLIDS Vermiculite/white clinoptilolite ALL 14.5 SOLIDS Unground vermiculite + aluminate NO 15.4 SOLIDS Vermiculite/white clinoptilolite NO 17.5 SOLIDS Vermiculite + aluminate NO SOLIDS 19.8 Sepiolite/white clinoptilolite NO SOLIDS 28.4 Sepiolite + aluminate NO SOLIDS 41.7

(40) Mixing ratios of solutions both with and without residual clay or zeolite solids present were determined using the equation:
v.sub.1/v.sub.2=(r[Mg].sub.2−[Al].sub.2)/([Al].sub.1−r[Mg].sub.1)
where v.sub.1 and v.sub.2 are the volume ratio of the two clay or zeolite solutions required to give r which is the required Mg:Al ratio in the final solution (in this case 3), and [Mg].sub.1, [Mg].sub.2 and [Al].sub.1 and [Al].sub.2 are the concentrations of Mg and Al in solutions 1 and 2, respectively. Where aluminate was added, target Mg/Al molar ratios of 3 were calculated.

(41) Mineralogical (XRD) analysis of the nano-hybrid materials indicated the presence of hydrotalcite in addition to the residual clay or zeolite mineral which acted as a scaffold for hydrotalcite nucleation and precipitation is depicted in FIG. 4.

(42) The significance of the examples presented here is that a new class of material has been synthesised using a novel preparation method utilising elements contained within commercial clays to produce nano-hybrids which contain LDH in the form of HT grafted onto the original clay or zeolite substrate. The beneficiation process adds significant utility and value to commercially-mined clays and zeolites as demonstrated by the high P-uptake (as phosphate) achieved as depicted in FIG. 5. The high P-uptake demonstrates that other simple or complex anions, for instance uranyl-carbonate complexes, may also be removed from solution using these materials.

Example 4

(43) Four samples of hydrotalcite were calcined by heating the sample up to 1350° C. with a Pt strip heater. FIGS. 6-7 depict the decomposition of the hydrotalcite samples as they undergo calcination alone or in the presence of crystalline silica (quartz), amorphous silica, and with interlayer silica, and the progressive formation of spinel (Al silicate) and periclase (Mg silicate) phases with increasing temperature.

(44) FIG. 6 shows that hydrotalcite decomposes to a dehydrated hydrotalcite form between 330-350° C. A periclase phase begins to form between about 450-550° C. with spinel forming at around 850° C.

(45) FIG. 7 shows that hydrotalcite in the presence of quartz decomposes to a dehydrated hydrotalcite form between 310-355° C. Quartz alpha to beta phase transformation is indicated as forming at about 550° C.; a periclase phase begins to form between about 750-800° C. with spinel forming at around 1200° C. Forsterite forms at about 1300° C. corresponding to the disappearance of quartz.

(46) FIG. 8 shows that hydrotalcite in the presence of amorphous silica decomposes to a dehydrated hydrotalcite form between 375-425° C. A periclase phase begins to form between about 800-850° C. with spinel forming at around 1100° C. Forsterite forms at about 1210° C.

(47) FIG. 9 shows that hydrotalcite in the presence of interlayer silica decomposes to a dehydrated hydrotalcite form between 310-340° C. A periclase phase begins to form between about 400° C. with spinel and forsterite forming at around 495° C.

(48) The quantitative extent of decomposition of hydrotalcite and formation of other minerals as a function of temperature in the presence of quartz for different quartz: hydrotalcite ratios were also examined by heating the sample up to 1350° C. with a Pt strip heater. FIG. 10 shows the decomposition of hydrotalcite with quartz:hydrotalcite ratio of 1:1 and FIG. 11 shows the decomposition of hydrotalcite with quartz:hydrotalcite ratio of 3:1.

(49) Calcination of hydrotalcite results in the mineral formation of spinel and periclase as well as element segregation. The back scatter SEM image of the bright (high atomic mass) discrete U-bearing grain is shown in FIG. 12 indicating that there is migration of U and some other elements into discrete phases during calcination.

(50) In view of the mineral/elemental segregation, it may be possible to selectively leach the calcined hydrotalcite to remove U or, alternatively, to crush the calcined hydrotalcite and employ flotation or heavy mineral separation techniques to remove and recover U.

Example 5

(51) The type of ambient atmosphere used to form the hydrotalcite also has an effect on the elemental uptake of U and REE in the hydrotalcite, as well as mineral segregation post-calcination. In Table 4 below is an example of the elemental uptake when the hydrotalcite was formed under an inert (e.g. nitrogen (N.sub.2)) or a reducing (e.g. carbon dioxide (CO.sub.2)) atmosphere.

(52) TABLE-US-00004 TABLE 4 Element Mean N.sub.2 Mean CO.sub.2 Al 1.68 10.10 Mg 7.56 20.34 U 18.28 7.73 Fe 2.31 8.07 Th 16.85 1.09 Si 0.51 3.22 Y 2.75 0.46 Ca 0.29 9.49 Ce 32.75 5.42 O 18.76 34.39 Total 101.56 100.31

Example 6

(53) Table 5 below shows the selective separation of U from a synthetic raffinate containing uranium, and two rare earth elements, lanthanide and yttrium by formation of a Fe(II)/Fe(III) LDH material. The concentration of Al, Mg, Fe, U, La and Y in the synthetic raffinate is shown in the second column of Table 5. The concentration of Al, Mg, Fe, U, La and Y remaining in the solution following formation of the Fe(II)/Fe(III) LDH material is shown in the third column of Table 5.

(54) Additional Mg(II) in the form of MgCl.sub.2.6H.sub.2O was added to adjust the M.sup.2+:M.sup.3+ cation ratio to about 2.5 so as to cause formation of Fe(II)/Fe(III) LDH material. The precipitate so formed was a blue-green colour which is characteristic of Fe(II)/Fe(III) LDH material containing mixed Fe valency.

(55) Formation of the Fe(II)/Fe(III) LDH material results in uptake of substantially all of the uranium, lanthanide and yttrium from the synthetic raffinate.

(56) TABLE-US-00005 TABLE 5 Sample Synthetic raffinate Fe(II)/Fe(III) LDH Al 3183 <0.1 Mg 919 1.7 Fe 15499 1.7 U 183 <0.5 La 73.7 0.1 Y 25.9 <0.1

(57) In the present specification and claims (if any), the word ‘comprising’ and its derivatives including ‘comprises’ and ‘comprise’ include each of the stated integers but does not exclude the inclusion of one or more further integers.

(58) Reference throughout this specification to ‘one embodiment’ or ‘an embodiment’ means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

(59) It is to be understood that the embodiments are not limited to specific features shown or described since the means herein described comprises preferred forms of putting the embodiments into effect. The embodiments are, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.