CN107614442B

CN107614442B - Water treatment and/or remediation process

Info

Publication number: CN107614442B
Application number: CN201580080445.8A
Authority: CN
Inventors: G·道格拉斯
Original assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Current assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Priority date: 2015-04-15
Filing date: 2015-04-15
Publication date: 2021-07-23
Anticipated expiration: 2035-04-15
Also published as: KR20170135959A; WO2016164958A1; JP6722693B2; AU2015391054A1; AU2015391054B2; CN107614442A; JP2018519148A

Abstract

A method for treating water containing one or more dissolved cationic species and/or one or more dissolved anionic species is described. The method comprises the following steps: adding a magnesium and/or aluminum containing silicate material to the water and dissolving at least a portion of the silicate material in the water thereby leaching at least a portion of the magnesium and/or aluminum from the silicate material into the water. The method further comprises controlling the reaction conditions to achieve a suitable Mg: an Al ratio, the layered double hydroxide containing Mg and Al as main substances in the lattice of the LDH; wherein at least one of the dissolved cationic and/or anionic species is incorporated into the LDH formed in situ. Furthermore, a Mg-containing compound or an Al-containing compound may optionally be added to achieve a suitable Mg: the Al ratio.

Description

Water treatment and/or remediation process

Technical Field

The present invention relates to methods of treating and/or remediating water, including but not limited to natural, waste and process waters.

The process of the invention relates to all water, other liquids or solutes or solvents or mixtures (whether miscible or immiscible) and solids, such as but not limited to natural water, waste water or mineral processing/metallurgical streams and electronic waste (e-waste) streams, derived from one or more processes including leaching or chemical extraction in acidic, neutral or alkaline reagents, which may typically contain a range of elements (as ions, molecules, complexes, micelles, aggregates, particles or colloids, etc.) and metals or metallic substances or other elements (e.g. and including metals, metalloids, lanthanides or rare earths (REEs), actinides, transuranics and radionuclides) that can all be considered as articles or contaminants.

Background

Layered Double Hydroxides (LDHs) are a class of both naturally occurring and synthetically produced materials characterized by positively charged mixed metal hydroxide layers separated by interlayers containing water molecules and various exchangeable anions. LDHs are most commonly produced by co-precipitation of divalent (e.g. Mg) species at moderate to high pH²⁺，Fe²⁺) And trivalent (e.g. Al)³⁺，Fe³⁺) Metal cation solutions (Taylor,1984, Vucel ic et al 1997, Shin et al 1996).

The LDH compound may be represented by general formula (1):

M_(1-x) ²⁺M_x ³⁺(OH)₂A^n-yH₂O (1)

wherein M is²⁺And M³⁺Are respectively divalent and trivalent metal ions, and A^n-Is an interlayer ion of valence n. x represents the ratio of trivalent metal ions to the total amount of metal ions, and y represents a variable amount of interlayer water.

Common forms of LDHs include Mg²⁺With Al³⁺(commonly known as hydrotalcite [ HT)]) And Mg²⁺With Fe³⁺(referred to as lepidocrocite), but other cations including Ni, Zn, Mn, Ca, Cr and La are known. The amount of surface positive charge generated depends on the molar ratio of the metal ions in the lattice structure and the preparation conditions, as they influence crystal formation.

The formation of HT (the most commonly synthesized LDH, often with carbonate as the major "exchangeable" anion) can be described most simply by the following reaction:

6MgCl₂+2AlCl₃+16NaOH+H₂CO₃→Mg₆Al₂(OH)₁₆CO₃.nH₂O+2HCl

typically, the ratio of divalent to trivalent cations in the hydrotalcite varies from 2:1 to 4: 1. Other synthetic pathways for HT (and other LDHs) formation include neutralization of acidic solutions from Mg (OH)₂Brucite and MgO (calcined magnesia) synthesis (e.g. Albiston et al, 1996). This can be described by the following reaction:

6Mg(OH)₂+2Al(OH)₃+2H₂SO₄→Mg₆Al₂(OH)₁₆SO₄.nH₂O+2H₂O

a range of metals at various concentrations can also be co-precipitated simultaneously, thus forming a multi-metallic LDH. HT or LDH was first described 60 years ago (Frondel,1941, Feitknecht, 1942). Sometimes they may also occur in nature as auxiliary minerals in soils and sediments (e.g. Taylor and McKenzie, 1980). Layered double hydroxides can also be synthesized from industrial waste by reacting bauxite slag (red mud) derived from alumina extraction with seawater (e.g. Thornber and Hughes,1987), as described in the following reaction:

6Mg(OH)₂+2Al(OH)₃+2Na₂CO₃→Mg₆Al₂(OH)₁₆CO₃.nH₂o +2NaOH or by reaction of lime with fly ash derived from fossil fuels (e.g., coal fired power stations) (rerdon and Della valley, 1997).

Within the LDH or HT structure, there are octahedral metal hydroxide sheets with a net positive charge due to the limited displacement of divalent cations by trivalent cations as described above. Thus, it is possible to displace a wide range of inorganic or organic anions into the LDH or HT structure. These anions are often referred to as "interlayer anions" because they fit between the hydroxide material layers. Layered double hydroxides are generally unstable at pH's below about 5 (Ookubu et al, 1993), but can act as buffers over a wide solution pH range (Seida and Nakano, 2002). Layered double hydroxides or HT, and in particular those containing carbonate as the major anion, have also proven to have a considerable ability to neutralize a range of inorganic acids by consuming both hydroxyl and carbonate anions contained within the LDH structure (e.g. Kameda et al, 2003).

Many studies have been carried out to investigate methods of exploiting the anion exchange properties of LDHs. These studies have focused on the removal of phosphate and other oxo-anions and humus from natural and waste waters (Miyata,1980, Misra and Perrotta,1992, Amin and Jayson,1996, Shin et al, 1996, Seida and Nakano, 2000). Phosphate is one of many anions that can be exchanged into the interlayer spaces of the LDH. Laboratory studies of phosphate uptake using synthetically prepared Mg-Al HT and a range of initial dissolved phosphate concentrations have shown that the uptake capacity to absorb from about 25-30Mg P/g (Miyata,1983, Shin et Al, 1996) to about 60Mg P/g is also influenced by initial phosphate concentration, pH (maximum phosphate uptake is close to pH 7), crystallinity and HT chemical composition (Ookubo et Al, 1993). The main obstacle to the use of HT for the removal of phosphate from natural and/or waste water is the selectivity of carbonate over phosphate, wherein the selective sequence is in general order CO₃ ^2->HPO₄ ^2->>SO₄ ^2-,OH^->F^->Cl^->NO₃ ^-(Miyata,1980,1983, Sato et al, 1986, Shin et al, 1986, Cavani et al, 1991). Many HT's are also synthesized with carbonate as the major anion, thus requiring anion exchange before they are exposed to phosphate. The reduction in phosphate absorption by HT is further reduced when carbonate is also combined with sulfate, nitrate and chloride (as can be common in natural or waste water) (Shin et al, 1996).

Much of the recent research has focused on the formation and study of synthetic LDHs or specific HT or analogues, and their subsequent reactivity towards a range of anions, particularly silicates (e.g. Depege et al, 1996), with the aim of forming polymetallic aluminosilicates which are considered as potential precursors for clay materials to limit metal mobility and bioavailability (e.g. Ford et al, 1999). The possibility of co-precipitation of silicate and aluminate anions, as another precursor of clay mineral analogues, also exists.

Thus, other structural elements or interlayer ions (both inorganic and organic) may be included to assist in displacement and/or inclusion of ions from solution, and/or to increase stability. Subsequently from pure Mg-Al or mainly Mg-Al HT, minerals of the chlorite or layered silicate type are formed, which may be isochemical in composition similar to or when compared to HT, or may have chemical properties similar to HT, wherein the displacement of some ions is determined by the properties of the added Mg and/or Al or the properties and chemical composition of the natural or waste water that may affect the final geochemical, crystallinity or mineralogy.

This increased stability of the LDH or HT or chlorite type minerals or other LDH or HT derivatives may also be achieved by partial or complete evaporation, calcination or vitrification (resulting in partial or complete dehydration and partial/total recrystallization) possibly in combination with the above chemical processes. The use of co-modifying or encapsulating LDH or HT with LDH or HT may also be an option to further increase physical or chemical stability.

The international atomic energy agency, which is an international collaboration center in the nuclear domain, working with multiple partners in member countries and around the world to promote safe, reliable and peaceful nuclear technology, published a report in 2004 summarizing the prior art in the field of processing effluents from uranium mines and plants. Importantly, the novelty of the invention described herein using the addition of chemical compounds to alter the solution chemistry to form LDH or HT is illustrated by the absence of any similar description or process (IAEA,2004) for treating the effluent from uranium ores.

It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in australia or any other country.

Disclosure of Invention

In one aspect, the present invention provides a method for treating water containing one or more dissolved cationic species and/or one or more dissolved anionic species, the method comprising the steps of:

(a) adding a magnesium and/or aluminum containing silicate material to water and dissolving at least a portion of the silicate material in the water, thereby leaching at least a portion of the magnesium and/or aluminum from the silicate material into the water; and

(b) controlling reaction conditions to achieve a suitable ratio of Mg to Al in water for the in situ formation/precipitation of a Layered Double Hydroxide (LDH) containing Mg and Al as the predominant species in the lattice of the LDH;

wherein at least one of the dissolved cationic and/or anionic species is incorporated into the LDH formed in situ.

The applicant has realised that the addition of magnesium and/or aluminium containing silicates, such as Mg containing sepiolite, vermiculite, attapulgite or talc or kaolinite or natural or synthetic minerals such as zeolites or other clay minerals, may produce magnesium and/or aluminium ions into the water when at least a portion of the silicate material is subjected to the dissolution step (step [ a ]) of the process of the invention. Without being bound by theory, it is theorized that leaching at least some of the magnesium and aluminium ions into the water results in the leached magnesium and/or aluminium ions being absorbed for use in forming the LDH material in situ.

The use of magnesium and/or aluminium containing silicate materials as a source of magnesium and/or aluminium ions for forming LDH materials has several advantages.

The applicant has appreciated that the addition of the silicate material to water followed by dissolution of at least a portion of the silicate results in leaching of at least some of the magnesium and/or aluminium ions originally present in the silicate material. However, the applicants have unexpectedly found that the remaining undissolved silicate material provides nucleation sites to promote the in situ formation or precipitation of LDH material, thereby increasing the production of LDH formed in water.

It is also understood that the undissolved silicate material also acts as a reagent to increase the density and/or aggregate particle size of the LDH formed in situ, thereby facilitating settling and/or dewatering or physical separation and recovery of the LDH in water.

Another advantage afforded by the process of the invention is that the undissolved silicate material can also be used as an additional cation or anion exchanger in water. This means that the undissolved silicate material can help act as an adsorbent for ionic species dissolved in the water, in addition to the LDH material.

The silicate materials described above may also include, but are not limited to, one or more of the following: attapulgite; clinoptilolite; sepiolite; talc; vermiculite, mineral aggregates or intergrowths in the form of rocks (e.g. ground granite, greenstone or serpentine), coatings, soils, sediments or waste materials (e.g. from alumina refining (red mud) or coal combustion (fly ash)).

In at least some embodiments, the undissolved silicate material from step (a) and the LDH formed in situ in step (b) form an insoluble clay material mixture, wherein the clay material mixture incorporates the at least one or more dissolved cationic species and/or one or more dissolved anionic species. Such mixtures may also be referred to as hybrid clay mixtures.

In one embodiment, the step of dissolving the magnesium and aluminium containing silicate material comprises leaching the magnesium and aluminium from the silicate material under acidic pH conditions. For example, the silicate material may be dissolved by introducing an acidic solution, such as a hydrochloric acid solution and/or a sulfuric acid solution. Applicants have recognized that acid treatment or acid leaching of silicate materials containing both aluminum and magnesium can result in leaching or release of aluminum and magnesium ions from the silicate material into the water. Thus, in at least some embodiments, performing the dissolution step under acidic conditions can result in leaching of magnesium and aluminum ions into the water. The leached ions can be used to adjust the Mg to Al ratio and use magnesium and aluminium ions as structural units of the LDH formed in situ.

In an alternative embodiment, the step of dissolving the magnesium and/or aluminium containing silicate material comprises leaching the magnesium and/or aluminium from the silicate material under alkaline conditions. Performing the dissolution step of the silicate material (containing both magnesium and aluminium) under alkaline conditions results in low dissolution of magnesium and relatively high dissolution of aluminium ions into the water. In at least some embodiments, performing the dissolution step under alkaline conditions can result in leaching of at least aluminum ions into the water, which can be used to adjust the Mg: Al ratio, and using the leached aluminum ions as structural units of the LDH formed in situ.

Furthermore, in at least some embodiments, Si may also leach into water as a result of the dissolution step of the present invention. Excessive leaching of the silica can potentially occupy interlayer anion exchange sites within the LDH during formation, or can combine with leached aluminum ions to form other compounds during LDH formation. In some embodiments, the method further comprises controlling leaching of the silica into the water.

In at least some embodiments, the dissolving step comprises agitating the silicate material in the water to leach the at least a portion of the magnesium and/or aluminum from the silicate material. Agitation may be by one or more methods, such as stirring and/or sonication and/or any other desired means of agitation. It is also contemplated that a series of agitation steps may be utilized to agitate the silicate material. Applicants have recognized that agitation of the silicate material results in increased leaching of magnesium and/or aluminum ions from the silicate material into the water.

In at least some embodiments, the step of adding comprises adding a mixture comprising the magnesium and/or aluminum containing silicate material and an additional silicate material. It is important to appreciate that the change in the divalent to trivalent ratio (Mg: Al) required for the formation of the LDH can be achieved by carefully combining one or more magnesium and/or aluminium containing silicate materials in the required proportions. As a result, the amount of additional Mg or Al required to be added is reduced, which can result in significant benefits.

In a further embodiment, the step of controlling the reaction conditions comprises adding at least one Mg-containing compound and/or at least one Al-containing compound to achieve a suitable Mg to Al ratio in water for forming the LDH in situ.

Mg or Al dissolved in water may comprise leached magnesium and/or aluminum ions derived from dissolved silicate material, and in at least some embodiments may also comprise magnesium and/or aluminum ions, which form part of the dissolved cations in the water being subjected to the process of the present invention.

This recognizes that many natural or, in particular, waste waters may include dissolved magnesium and/or aluminum ions. In the present invention, Mg ions and Al ions present in water are absorbed by forming LDH (including Mg and Al as main metal substances in the lattice structure of LDH). Advantageously, LDHs can also absorb other ions and strongly fix them into the interlayer spaces between the crystal lattices. Thus, other ions can also be removed from the water and largely fixed.

For example, the at least one aluminum-containing compound may comprise an aluminate (Al (OH)₄Or AlO₂-.2H₂O) or aluminum sulfate, aluminum hydroxide or aluminum-containing organometallic compounds.

Where a source of Al is desired, other inorganic compounds may also be used, such as aluminum sulfate (e.g., Al)₂(SO₄)S.18H₂O), aluminum hydroxide (A1(OH)₃) Or organometallic compounds (e.g. aluminium acetylacetonate C)₁₅H₂₁AlO₆). Preferably, these Al sources will be alkaline to raise the solution pH to a suitable level for LDH or HT formation, but may also be used where the final solution pH or a combination of these or other compounds is alkaline.

In some embodiments of the invention, it may also be necessary to add additional Mg to the water in order to adjust the ratio of Al to Mg in the water to the desired level, in order to obtain LDH or HT containing Mg and Al as the main metal species in the crystal lattice. This can be achieved, for example, by reacting MgO or Mg (OH)₂Adding into water. Advantageously MgO or Mg (OH)₂But also to achieve the desired pH characteristics suitable for forming LDHs (e.g. HT).

In some embodiments of the invention, it may be necessary or desirable to add additional alkali or acid neutralizing materials to the natural or wastewater in addition to the at least one Mg-containing compound or the at least one Al-containing compound. The additional alkali or acid neutralizing material may be selected from one or more alkali or acid neutralizing solutes, slurries or solid materials or mixtures thereof, such as lime, slaked lime, calcined magnesium oxide, sodium hydroxide, sodium carbonate, sodium bicarbonate or sodium silicate. This list is not exhaustive and other base or acid neutralizing materials may also be added. The additional base or acid neutralizing material may be added prior to or after the addition of the at least one Mg-containing compound or the at least one Al-containing compound to the natural objects or the wastewater.

In some embodiments of the invention, the order or sequence of adding the various base or acid neutralizing materials to the acidic water, wastewater, slurry or process water, as described elsewhere in this specification, may impart certain benefits. For example, the order of addition can impart geochemical and/or operational advantages to the neutralization process and the formation of Layered Double Hydroxides (LDHs) and other mineral precipitates.

Selective partial or total removal of Layered Double Hydroxides (LDHs) and/or other undissolved silicate materials and/or mineral precipitate or slurry components at various stages of the reaction, whether by addition of various base or acid neutralizing materials to acidic water, wastewater or process water, or by addition of acidic water, wastewater or process water to various base or acid neutralizing materials as described elsewhere in this specification, may also be considered advantageous.

Examples of such include the removal of precipitates or existing solids or aggregates, mixtures or co-precipitates thereof prior to the introduction of reverse osmosis to remove some or all of the remaining solutes or evaporation. This removal of Layered Double Hydroxide (LDH) and/or other mineral precipitates (including undissolved silicates) at various stages of the reaction, whether by the addition of various base or acid neutralizing materials to the acidic water, wastewater, or process water, or the addition of acidic water, wastewater, or process water to various base or acid neutralizing materials as described elsewhere in this specification, may be facilitated or enhanced by mechanical (e.g., centrifugation) or chemical (e.g., by the addition of flocculants) means, or combinations thereof.

In some embodiments of the invention, partial or total removal of water or other solvents or miscible or immiscible solutes (e.g. by partial or total evaporation or distillation) may be used to increase the concentration of one or more dissolved colloidal or particulate components or additional added components such as Mg and/or Al (e.g. for adjusting the appropriate Al to Mg ratio) to increase the concentration to a sufficient extent to initiate LDH formation.

The present invention, in at least some embodiments, also relates to water and water streams, including process water that may contain little or no Mg and/or Al or be dominated by other dissolved cations and/or anions. (e.g., those derived from some acid sulfate soils, industrial process or nuclear power plants, weapons, or research facilities). It is noted that not all water (e.g., process or wastewater) has a major ionic chemical composition suitable for forming LDHs or particular types of LDHs such as Mg-Al HT or similar compositions. Thus, it may be necessary to adjust this chemical composition to form LDH or more specific Mg-Al HT. The adjustment of the solution chemistry comprises the step of adding silicate material in the manner described in step (a) and may also comprise the addition of one or more reagents, for example reagents containing Mg and/or Al to achieve a suitable Mg to Al ratio to promote the formation of LDH in situ.

In some embodiments, the at least one dissolved anion in the water from a stream, e.g. a process stream, may comprise a complexing anion such that at least one of the complexing anions is intercalated into an interlayer of the LDH formed in situ, and wherein the one or more dissolved cations are incorporated into the LDH material's crystal structure or matrix. Preferably, the method may further comprise the step of controlling the pH level in the water, thereby controlling the morphology of the complexing anions.

It will be appreciated that cations, such as metal cations, may be incorporated into the metal oxide layer of the LDH forming the crystal structure or matrix. Applicants have also recognized that some metallic constituents, particularly metals such as uranium (or vanadium or chromium in other embodiments), are typically present as large-size oxygen-containing cations such as UO that cannot be accommodated in the crystal structure or matrix₂ ²⁺Are present. Applicants have found that such large size oxygen containing cations, such as UO, can be used by adjusting or controlling reaction conditions, such as pH conditions and/or adding reactants and the like₂ ²⁺Preferential formation of one or more complex anionic species, e.g. any UO₂(CO₃)₂ ^2-、UO₂(CO₃)₃ ^4-、CaUO₂(CO₃)₃ ^2-、UO₂ ²⁺-SO₄. For example, at lower pH, UO₂ ²⁺-SO₄Complexes (e.g. UO)₂(SO₄)₃ ^4-) Can predominate, while at moderate to high pH, UO₂ ²⁺-CO₃ ^2-Anionic complexes (e.g. UO)₂(CO₃)₂ ^2-、UO₂(CO₃)₃ ^4-、CaUO₂(CO₃)₃ ^2-) May predominate. In view of uranyl ion (UO)₂ ²⁺) As this morphology of anionic complexes, these preferentially partition into the anion interlayers of the LDH material. Thus, if the aqueous solution contains metals such as Cu, Mn, Ni, Pb, Zn and rare earth elements (REE; 15 metallic elements with atomic numbers from 57 to 71; REE is often described as part of the lanthanide series, and is often referred to as being part of the lanthanide series for convenienceLn³⁺) And uranium, the process of the invention separates the uranium from the remaining metals, metalloids and rare earth elements by preferentially forming uranyl complex anion complexes which will be intercalated in interlayers of the LDH and at least some of the metals and rare earth elements will be incorporated into the crystal structure of the LDH. E.g. predominantly Ln³⁺The REEs of the cations (Ce in +3 and +4 and Eu and +2 and +3 oxidation states) are strongly partitioned into the main metal hydroxide layer of the LDH material, replacing other +3 cations such as Al and Fe. As a result of the process of the invention, the REE is for example contained within the metal hydroxide layers of the LDH and the valuable uranium is contained as an anionic complex within the LDH interlayers.

The current embodiments also result in the formation of LDH materials that may typically contain more than 30% U and 0-50% REE. Such resulting amounts of uranium and rare earth metals are typically 100-fold 300 times the typical ore taste of these elements, thereby allowing for the bulk enrichment of valuable items. Another significant benefit provided by the present invention is that the process results in potentially problematic ions such as Na, Cl, and SO₄Or other additives or components from mineral processing or aqueous streams, thus potentially facilitating simpler processing, further enrichment, recovery, or purification). Yet another advantage of at least some embodiments of the present invention is that cleaner effluent is produced that can potentially be reused in mineral processing or other field applications or other operations without (or with minimal) additional treatment.

The present invention therefore also provides in at least some embodiments a method or process for treating process water for the recovery of selectively separated constituents in water provided in the form of an aqueous solution, wherein by subjecting the LDH from step (b) to a further recovery treatment step, different constituents have been absorbed by the LDH through different absorption mechanisms (e.g. uranium in the LDH interlayer, but REE in the LDH's crystal structure or metallic oxide layer). Various recycling process steps that may be used have been described in detail in the preceding paragraphs of the specification.

In some embodiments, the process comprises recovering the separated LDH from step (b) from the aqueous stream before subjecting the LDH to the recovery treatment step. This recovery of LDH may be carried out by recovery means such as settling, flocculation or filtration.

In one embodiment, the method further comprises the step of controlling the pH level of the aqueous solution to thereby control the morphology of the complexing anion. The applicants have found that the morphology of the anionic complex can be suitably adjusted or controlled by adjusting the pH conditions. For example, at lower pH, UO formation may be preferential₂ ²⁺-SO₄Complexes (e.g. UO)₂(SO₄)₃ ^4-) While at moderate to higher pH conditions UO may form predominantly₂ ²⁺-CO₃ ^2-Anionic complexes (e.g. UO)₂(CO₃)₂ ^2-、UO₂(CO₃)₃ ^4-、CaUO₂(CO₃)₃ ^2-)。

The separated LDH may be treated to recover components therefrom. In some further embodiments, the recovery treatment step may be performed by: the separated LDH is introduced into an ion exchange solution to cause ion exchange to occur whereby complex anions of the metallic constituent in the interlayer of the LDH are ion exchanged with anions in the ion exchange solution. In this way, by performing the ion exchange step, the complex anion of the metallic solution enters the solution. It will be appreciated that such an ion exchange step involves an ion exchange solution having at least one substituent anion such that the substituent ion displaces at least some of the intercalated or complexed anion by an ion exchange mechanism, thereby causing the anion or complexed anion to be released from the LDH interlayer into the ion exchange solution. At the same time, intercalated or complexed anions of the metallic constituents are released from the interlayer of the LDH and other metals present in the LDH's crystal structure or matrix (e.g. REE/metals) remain incorporated into the LDH material's crystal structure or matrix.

The applicant has found that recovery of LDH from step (b) followed by an ion exchange process is particularly beneficial when the initial aqueous solution in step (a) comprises a leach solution with a high salt concentration, such as that used in a leach process for uranium recovery, since it has been found difficult to achieve an optimum ion exchange efficiency in such leach solutions, such as mining effluents. Employing the steps described in some embodiments including separating the LDH from step (b) and the methods described above results in higher ion exchange efficiency, resulting in better separation of the intercalated metallic components from the LDH.

In further embodiments, the ion exchange step further comprises controlling pH conditions to promote displacement of anions or complexing anions from the intermediate layer and/or to promote species formation of a preferred type of anion or complexing anion relative to other anions or complexing anions. For example, a strong base may be added to replace UO with OH anion by increasing pH₂ ²⁺-SO₄Or UO₂ ²⁺-CO₃A complex compound. It will be appreciated that such a recovery treatment step involves the recovery of uranium (in the form of uranyl complex anions) back into aqueous solution, even if the REEs remain incorporated into the LDH crystal structure. Alternatively, a strong acid is added to lower the pH, resulting in charged or neutral UO₂ ²⁺It is also possible for the complex to be displaced from the interlayer of the LDH. Here, sustained acid addition can also sufficiently break down the LDH crystal structure to release REE or other metals or elements.

In some embodiments, the substituent reagent may comprise one or more of the following: nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA) or a range of other complexing agents such as crown ethers or other organic or (complexed) inorganic ligands, and/or wherein the substituent reagent has significantly more electronegativity relative to the complex anion inserted in the LDH material, thereby causing the substituent reagent such as EDTA and/or NTA to displace the complex anion from the interlayer.

In a further embodiment, the recovery step further comprises separating the LDH material after the ion exchange step is completed. It will be appreciated that separating the LDH material after the ion exchange step is completed results in obtaining a separated LDH material comprising incorporated metallic cations or REEs present in the crystal structure of the separated LDH material. The incorporated metallic cations or REEs from the separated LDHs can be recovered by methods such as heat treatment or thermal decomposition of the separated LDH material, resulting in the formation of collapsed (collapsed) or metastable material.

In a further embodiment, the process may comprise adding further additives (e.g. silica) to the LDH material before or during the heat treatment or thermal decomposition. Preferably, the method may comprise controlling the ratio of the further additive to the LDH material to selectively control the formation of the oxide material upon heat treatment or thermal decomposition.

Additives such as silica may also be added to the LDH before or during the heat treatment or thermal decomposition step, in a range of forms including crystalline silica (e.g. quartz), amorphous or chemically precipitated silica, silicic acid, organic forms including tetraethyl silicate (te) or silica added to the LDH interlayer.

It is important to recognise that in addition to recovering LDH material, LDH may also be used for recovery and that undissolved silicate material from step (a) may also be used. Controlling the ratio of silica to LDH and/or controlling the temperature of the heat treatment may result in a series of reactions between the added form of silica and LDH which results in the formation of a series of materials such as minerals e.g. (or in addition to spinel and periclase) pyroxenes such as enstatite, olivines including forsterite and other minerals including silica which convert to high temperature forms including cristobalite.

It will be appreciated that by varying the amount of silica or other element in one or more forms relative to the LDH (by controlling the ratio of silica to LDH material), different proportions or series of minerals may be formed as a result of the heat treatment step. This method comprising the additives as described above is particularly advantageous for two reasons. A first advantage is that secondary mineral oxides such as metallic silicates or pyroxenes can be formed, which can constitute suitable long-term storage of a range of contaminants including radionuclides. A second advantage is that a given selected element can be distributed into the material formed as a result of the heat treatment, which formed material (determined by the composition of the LDH and the type and proportion of additives) can contribute to the selective recovery of the particular element contained in the selected mineral. The silica may be replaced by other additives in further embodiments, and the above embodiments are in no way limited to the addition of silica.

Thus, the addition of silicate material in step (a) of the present invention may also assist in the recovery of one or more dissolved species (cationic or anionic) from the LDH material.

In some alternative embodiments, the isolated LDH may be subjected to a dissolution step in which the isolated LDH is dissolved in a dissolution solvent, such as an acid, which results in the release of the intercalated complex anion and metal cation from the crystal structure of the isolated LDH into the dissolution solvent. Capturing metallic species from an initial aqueous solution containing a low concentration of the metallic species in the LDH material according to step (b), separating the LDH material, and then re-dissolving the separated LDH in a dissolving solvent, results in a solvent having a relatively higher concentration level of the metallic species (compared to the low concentration level of the initial aqueous solution). It should be appreciated that recovery of metallic species from solutions containing relatively high concentration levels of metallic species is more desirable and cost effective, and thus provides the artisan with the opportunity to use conventional metallurgical recovery methods that would otherwise be ineffective in capturing trace amounts of metallic species present in aqueous solutions as used in step (a) in at least some embodiments of the present invention. Thus, this embodiment has significant commercial advantages by providing a viable method or process for recovering metallic species from aqueous solutions having low concentrations of metallic species.

In an alternative embodiment of the process, ion exchange of the intercalated complexing anion may not be performed. Instead, the LDH comprising intercalated complex anions and incorporated metal or metals and other materials obtained from step (b) may be separated and subsequently subjected to a heat treatment process as described above. Such a heat treatment process initially leads to collapse of the LDH material, resulting in a loss of the layered structure characteristics of the LDH material, and subsequently to recrystallisation of the LDH material. In particular, the heat treatment and recrystallization of the collapsed LDH results in the formation of a first oxide material comprising the metallic constituent and a second oxide material comprising one or more of the other metals. For example, the applicant has unexpectedly found that calcination of an LDH comprising intercalated uranyl complex cations and rare earth metals incorporated into the crystal structure produces a first crystalline oxide material in the form of periclase incorporating a proportion of uranium and a second crystalline oxide material in the form of spinel oxide incorporating other items such as REE.

In a further embodiment, the heat treatment may be carried out under substantially reducing conditions to reduce intercalated complex anions present within the interlayer of the LDH material obtained in step (b). For example, during heat treatment of LDHs comprising intercalated uranyl complex anions, the heat treatment may be under anoxic conditions (e.g. N)₂) Or reducing (e.g. CO or C) conditions to form reduced U minerals, e.g. to produce Uraninite (UO)₂). In some alternative embodiments, other agents may be added to form UF₆As a gas phase to aid in the separation and recovery of U or a particular U isotope.

In some further embodiments, the method may comprise optimising the crystal structure or matrix of the LDH material to selectively incorporate one or more of the other metals into the crystal structure or matrix of the LDH. For example, optimisation can be carried out by introducing an additive, such as a carbonate in an alkaline liquid, to the aqueous solution to adjust the crystal structure of the LDH or the absorption of selected or specific rare earth elements in the matrix. Without being bound by theory, it is theorized that the amount/morphology of bicarbonate/carbonate in aqueous solution can potentially confer a certain selectivity to LDH materials (e.g. hydrotalcite) in view of the increased affinity of medium to heavy REEs for carbonate or bicarbonate.

In one embodiment, the predetermined metallic composition comprises uranium or vanadium, and wherein the one or more other metals comprise REE. Complexing the anion [ anion ] as described previously]Uranyl complex anions may be included such as, but not limited to: UO₂(CO₃)₂ ^2-、UO₂(CO₃)₃ ^4-、CaUO₂(CO₃)₃ ^2-、UO₂(SO₄)₃ ^4-、VO₂(OH)^2-、VO₃OH^2-、V₁₀O₂₈ ^6-、Cr₂O₇ ^2-. In at least some embodiments, the pH of the solution determines the morphology of the uranyl complex anion.

In one embodiment, the intercalated uranyl complex may be displaced from the interlayer of the LDH by the addition of a substituent reagent such as EDTA, NTA, crown ethers, etc. by the ion exchange step described in the previous section.

In an alternative embodiment, the LDH material may be subjected to a heat treatment step, thus such that the heat treatment results in thermal decomposition of the LDH material to recrystallise into a first crystalline oxide and a second crystalline oxide, such that uranium is incorporated into the first metal oxide and one or more REEs are incorporated into the second crystalline oxide. Preferably, the heat treatment may be carried out under substantially reducing conditions for reducing the uranyl ions from the +6 to the +4 oxidation state or a mixture thereof.

In at least some embodiments, the method comprises the steps of: contacting the separated LDH material with an aqueous solution to dissolve at least a portion of the LDH material into the solution to obtain an LDH dissolved in the solution and then controlling the reaction conditions in the aqueous solution for in situ precipitation of the LDH material 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 other cations are incorporated into the crystal structure or matrix of the LDH material formed in situ. Preferably, the step of dissolving the LDH in the aqueous solution comprises controlling the pH of the aqueous solution at a pH level of preferably less than 7, and more preferably less than 5, and even more preferably less than 3. In situ precipitation of LDH from dissolved LDH components may be carried out by controlling the reaction conditions in aqueous solution, including controlling the pH of the aqueous solution at a pH level preferably above 8.

It is within the scope of the present invention that any feature described herein may be combined with any one or more other features described herein, in any combination.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that prior art forms part of the common general knowledge.

Drawings

Figure 1 depicts the molar ratios of Al/Si and Mg/Al produced by 1M HCl and 1M NaOH after agitation (1-4 hours) and sonication + agitation (1 hour) of the filtered clay and zeolite solutions according to an embodiment of the present disclosure. The red line indicates an Al/Si molar ratio of 0.5 and a Mg/Al molar ratio of 3 (see text).

Figure 2 depicts the X-ray diffraction (XRD) spectrum of sepiolite/white clinoptilolite-hydrotalcite nano-hybrids. Note that the peaks corresponding to sepiolite and clinoptilolite precursors and the characteristic hydrotalcite (light blue)/Mg-Al hydroxide (pink) are at

Peaks at theta of 13 and 26 degrees.

Figure 3 depicts the phosphorus uptake capacity of a series of clay/zeolite nanocomposite materials synthesized in this study.

FIG. 4 is a schematic flow diagram of a method of separating one or more metallic articles in an aqueous solution by employing a method in accordance with a preferred embodiment of the present invention.

FIG. 5 shows the system U-H from pH 2-10₂O-SO₄-CO₃A morphological map of equilibrium with the atmosphere.

Detailed Description

The following text describes one or more embodiments in terms of examples according to the invention.

Raw materials are obtained from industrial and commercial sources, mainly aluminosilicate clays (e.g. vermiculite, attapulgite, sepiolite, talc kaolinite) and zeolites (white and pink clinoptilolite) containing Mg-Al or Al. These clays and zeolites were used as a source of raw materials (mainly Al and Mg) during acid and base dissolution experiments enhanced with sonication.

The initial batch decomposition reaction in both acid and base and additionally using agitated aluminosilicate including sonication is completed. ICP analysis results are given in table 1 and fig. 1 to quantify the extent of dissolution due to acid or base combined with stirring (1-4 hours) or sonication + stirring (1 hour). These results show that the large amount of Mg and Al release required for hydrotalcite synthesis (preferably Mg/Al molar ratio > 3: 1) can be obtained from clay or zeolite during acid extraction. In addition, some clays such as sepiolite (table 1) produce high concentrations of Mg and Al and high Mg/Al molar ratios. Under acidic conditions, all clays and zeolites show inconsistent dissolution, with higher Mg/Al and Al/Si ratios in the solute than in the solid. In contrast, under alkaline conditions, any inconsistent dissolution is masked by the secondary precipitation reaction.

TABLE 1. geochemical composition of the filtered solution produced by digestion with 1M HCl or 1M NaOH after stirring (1-4 hours) and sonication + stirring (1 hour) of the clay and zeolite suspensions.

Importantly, the use of the combination of sonication + stirring significantly improved the dissolution of Mg and Al relative to stirring alone. During acid digestion, depending on the chemical composition and purity of the clay or zeolite, large amounts of Si and other elements such as Fe and Ca may also be released. This is undesirable because excess silica can potentially occupy interlayer anion exchange sites within the LDH or HT during formation, or can combine with Al during LDH or HT synthesis to form other compounds. In particular, as shown in fig. 1, it is desirable that the Al/Si molar ratio is < 0.5. In addition, large amounts of Fe can result in substitution of one or both of Mg and Al in the LDH or HT structure. If Fe is present in sufficient amounts, this can lead to the formation of unstable patina.

As expectedIn that way, alkaline dissolution using stirring or sonication + stirring results in a significantly different solution composition, where the dissolution of Si is increased compared to the dissolution of Al, while Mg is low, as it may be as brucite-Mg (OH)₂And precipitated. Although excess silica is generally undesirable in the formation of LDH or HT as described above, there is a possibility of using residual clay or zeolite as a substrate for LDH or HT nucleation after dissolution.

In the presence of high Si, this may occupy at least a portion of the anion interlayer of the LDH or HT structure. This property can be exploited if calcination is required to form other high temperature phases as described elsewhere.

Further clay dissolution for experiment H₂SO₄Instead of HCl, to investigate the effect of using different acids (if any). These results are given in Table 2 and are illustrated in H₂SO₄Relatively less dissolved Si is produced in the presence, resulting in a lower Al/Si ratio. As mentioned above, this is considered important when synthesizing LDH or HT from a solution resulting from clay or zeolite dissolution. In addition, use of H₂SO₄Instead of HCl, the Mg/Al ratio is generally increased.

TABLE 2 Clay and Zeolite suspensions were passed through 1M H using sonication + stirring (1 hour)₂SO₄And the concentration ratios of Al, Si and Mg/Al and Al/Si in the solution resulting from the 1M HCl digestion.

In the above dissolution experiment and using H₂SO₄On the basis of supplementary experiments instead of HCl, a series of clays and zeolites were used for the synthesis of nano-hybrid materials. In addition, aluminates are also used as a source of additional Al and as a neutralizing agent. Table 3 gives a list of the prepared nanocomposite and its P-absorption capacity.

Table 3. phosphorus uptake capacity of a series of clay/zeolite nanocomposite synthesized in this study.

The mixing ratio of the solution in both the presence and absence of residual clay or zeolite solids was determined using the following equation:

v₁/v₂＝(r[Mg]₂–[Al]₂)/([Al]₁–r[Mg]₁)

wherein v is₁And v₂Is the volume ratio of the two clay or zeolite solutions required to give r, which is the Mg required in the final solution; al ratio (3 in this case), and [ Mg]₁、[Mg]₂And [ Al]₁And [ Al]₂The concentrations of Mg and Al in

solutions

1 and 2, respectively. The target Mg/Al molar ratio was calculated to be 3 when aluminate was added.

A mineralogical (XRD) analysis of the nanocomposite is depicted in fig. 2, which shows the presence of hydrotalcite in addition to residual clay or zeolite minerals used as a scaffold (scaffold) for hydrotalcite nucleation and precipitation.

The significance of the examples presented here is that a new class of new materials is synthesized using a novel preparation method that utilizes the elements contained in commercial clays to prepare a nano-hybrid comprising LDH in the form of hydrotalcite grafted onto an original clay or zeolite substrate. The beneficiation process adds significant utility and value to commercially exploited clays and zeolites as evidenced by the high P absorption achieved (as phosphate). High P-absorption indicates that these materials can also be used to remove other simple or complex anions from solution, such as uranylcarbonate complexes.

Referring to the flow diagram shown in fig. 4, ore bodies containing various metallic constituents, such as uranium and REE, may be introduced into an aqueous leach solution to obtain a pregnant leach solution or aqueous stream. Some metallic constituents, such as uranium, may form complex anions in solution, such as uranyl anion complexes as described in the preceding section. Some other metallic constituents, particularly such as REE, may generally form cations in aqueous solutions. The liquid phase of the pregnant leach solution containing dissolved anions and cations may be separated from undissolved solids and directed to a reaction step. The reacting step may include steps such as controlling the pH to determine the morphology of the uranyl complex as shown in fig. 5. The reacting step may form a complex anion containing the metallic constituent (e.g., uranium). The reaction step may be after the LDH formation step or an alternative LDH addition step or LDH addition and pH cycling to initiate partial dissolution of LDH and subsequent reformation.

In the LDH-forming step, an additive, for example a divalent additive such as MgO, may be added in combination with a trivalent additive (e.g. a soluble alumina salt) in a particular ratio and at a suitable pH (alkaline pH) to promote the in situ formation of LDH material in solution. Such LDH formation steps also result in the intercalation of an interlayer of complex anions (e.g. uranyl complex anions) of the LDH material formed in situ. Metallic cations are also incorporated into the metal oxide layer of the LDH material formed in situ, thereby forming part of the LDH's crystal structure or matrix. This separation of metallic species is based on different absorption mechanisms of different ions provided by the LDH materials formed in situ.

As previously mentioned, the LDH formation step may be replaced or supplemented by an LDH addition step in which preformed LDH material may be added to a solution containing a complexing anion (uranyl complexing anion) and metallic cations. The step of adding the preformed LDH material also results in the intercalation of interlayers of complex anions of the LDH material, such as uranyl complex anions. This step may also include controlling the pH so that a portion of the LDH may be initially dissolved at a pH of less than 9 and as low as pH 1 for a specified period of time as required to produce a sufficient degree of LDH dissolution, followed by increasing the pH to promote the LDH material reformation in situ. During this reformation step, other cations, such as REE cations, can be incorporated into the metal hydroxide layer in place of the original cations in the initially added LDH. In this process, some anions, especially those consisting of uranyl anion 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 addition of other solvents or reagents as required.

LDH materials comprising intercalated complex anions and obtained from the LDH forming step or the LDH adding step may be separated by processes such as settling, 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 (uranyl complex anion), such as an ion exchange process, in accordance with the steps described in the preceding part of the specification. Alternative methods of recovering the inserted metallic constituents may also be used, according to the process steps detailed in the previous section. As previously mentioned, the recovery treatment step may not be limited to the recovery of intercalated metallic species such as uranyl complex anions, but may further comprise the recovery of metallic cations such as REE incorporated into the LDH matrix during the LDH-forming step.

The presently described invention utilizes different absorption mechanisms of different metallic ionic species as a way to separate the metallic species. In the present invention, the desired separation and recovery is achieved by inserting at least one metallic constituent into an interlayer (e.g. uranyl complex anion) of the LDH (formed in situ or added to the solution) and then recovering the metallic constituent from the LDH by a further recovery step.

Examples

Example 1

In a first exemplary embodiment (example 1), the method may be used to process uranium-bearing ores. It is common for uranium-bearing ores to have a range of other elements present in addition to uranium. Other elements may include elements such As As, Se, Cu, and rare earth elements (REE-Ln)³⁺Including La-Lu + Sc + Y). Extensive work undertaken by the Applicant has demonstrated that REE is predominantly Ln in the +3 oxidation state³⁺A cation is present. Cerium is present in the +3 and +4 oxidation states. Europium is present in the +2 and +3 oxidation states. In this exemplary process, a uranium-containing solution from leached uranium ore is contacted with LDH material.

Insertion of the uranyl complex anion can be achieved in two different ways. In a first possible approach, the uranyl complex anion will readily intercalate into the interlayer of the LDH material added to the solution. However, using such a method does not result in the absorption of REEs into the matrix or crystal structure of the LDH material added to the uranium.

In a more preferred manner, the LDH material added to the uranium containing solution is dissolved in the uranium containing solution by lowering the pH of the solution to less than 3. Lowering the pH level causes the LDH material to dissolve, resulting in the release of divalent and trivalent cations (forming metal oxide layers of the LDH material) into solution. After dissolution of the LDH material, the pH is increased to provide alkaline reaction conditions in solution. Providing such alkaline conditions results in the reformation of LDH material due to its precipitation in solution. During the reformation of the LDH material, divalent and trivalent cations dissolved into the solution (as a result of the initial dissolution step) precipitate to form a metal oxide layer of the reformed LDH material. During the reformation step, at least some of the REE cations are also incorporated into the crystal structure of the reformed LDH material. The anionic uranyl complex is also intercalated in the interlayer of the reformed LDH material. It is important to recognise that since the divalent to trivalent ratio of the metals in the major metal hydroxide layers of the LDH can typically vary between 2:1 and 4:1, this ratio change can occur in the reformed LDH as the inclusion of other cations from the solution still allows the formation of a stable LDH.

During this process, REEs are shown to be strongly partitioned into the predominantly metal hydroxide layer of the reformed LDH material, replacing other +3 cations such as Al and Fe present in the initially added LDH material. Unlike the REE cation, uranyl ion (uranium is known in solution as UO)₂ ²⁺Presence of oxygen-containing cations) are considered too large to replace the +2 cations such as Mg2+ alkaline earth metal and transition metals normally present in the metal hydroxide layer of the LDH material. As shown in FIG. 2, under low pH conditions, anionic uranyl complexes, especially UO, are formed₂ ²⁺-SO₄Complexes (e.g. UO)₂(SO₄)₃ ^4-). At moderate to higher pH, UO₂ ²⁺-CO₃ ^2-Anionic complexes (e.g. UO)₂(CO₃)₂ ^2-、UO₂(CO₃)₃ ^4-、CaUO₂(CO₃)₃ ^2-) May predominate. Given this morphology of UO22+ as an anion complex, these uranyl anion complexes partition preferentially into the anion interlayers of LDHs. As a result, the method of example 1 provides the following advantages:

the valuable REE is contained within the metal hydroxide layer of the LDH

Valuable U is contained as an anionic complex within the LDH interlayer. The two valuable items U and REE are not only separated from each other in terms of the way they are combined in the initial solution, but also from other components including some contaminants, salts or ions which might otherwise interfere with the U or REE recovery process, which is very advantageous for subsequent separation, recovery and purification.

Solid LDHs are produced, which may typically contain more than 30% U and 0-50% REE, typically 100-300 times the typical ore taste of these elements, allowing for a large enrichment of valuable items.

Efficient separation of potentially problematic ions such as Na, Cl and SO from mineral processing streams₄Or other additives (potentially making processing, further enrichment, or recovery simpler).

Production of cleaner effluent that can potentially be reused in a mineral processing or other site or other operation without (or with minimal) additional treatment.

In addition to the above, several methods may be used to recover the items of interest (as described above) based on the separation of the obtained items, taking into account the different distribution or separation of U and REE. The recycling of the one or more items may be effected by one or more further steps of:

addition of a strong base to replace UO by OH anion₂ ²⁺-SO₄Complex, or UO with reduced pH to make charge lower or neutral₂The complex is displaced from the LDH interlayer.

Other complexing ligands or other anions may be addedAddition of ions (e.g. NTA, EDTA) to LDH to displace UO₂-complexing and forming new NTA, EDTA complexes.

Addition of other chemical agents, such as phosphates, vanadates or inorganic or organic peroxides or combinations thereof, to initiate precipitation of uranium.

The LDH containing U, REE metal is partially or completely dissolved by adding acid and the constituents are recovered by conventional means.

Addition of a reducing agent, oxygen deficit or gas (e.g. CO) to reduce the uranyl complex (U +6 oxidation state) to U (+4 oxidation state), for example as UO₂Thereby charge-based elimination of uranyl complexes with carbonate and allowing U to be recovered in the +4 oxidation state. Such recovery methods may include physical (e.g. sonication) or additional chemical (solvent-based) stratification of the LDH to recover the reduced U or applying other physicochemical methods as required.

Other separation methods, which may include calcination, such that upon heating, typically in the range of 100-. These phases (due to their chemical composition and crystal structure) may accommodate one of a variety of elements of interest, or may provide increased recovery opportunities for a particular element given the different physicochemical properties of the mineral phases formed by calcination.

The stabilization methods described herein may also find application in the nuclear or weapons industry to assist in the containment of uranium containing materials or waste products including transuranics or daughter radionuclides.

Example 2

In a second exemplary embodiment (example 2), the method of the invention may be used to process uranium-bearing ores, wherein the LDH may be formed in situ in a mineral processing or metallurgical stream comprising the uranium-bearing ore. A stream of uranium containing ore is typically fed with one or both of Mg and Al containing compounds to achieve the desired Mg/Al ratio in the stream which results in precipitation of LDH (e.g. hydrotalcite). As explained in example 1, uranium-containing ores include a series of other elements present in addition to uranium, including heavy metalsMetals, metalloids and/or REEs. Formation of LDH materials in situ also leads to the incorporation of cations such as Ln³⁺Cations and/or Ce 3+ and Ce 4+ and/or Eu 2+ or Eu 3+ oxidation states. The in situ formation of the LDH also results in the REE cations showing strong partitioning into the main metal hydroxide layers of the LDH. As previously mentioned, uranium is commonly referred to as Uranyl (UO)₂ ²⁺) The oxygen-containing cation of the cation is present and therefore the uranyl ion is too large to displace a +2 cation, such as Mg2+, into the LDH. Alkaline earth and transition metals are typically present in the metal hydroxide layer of the LDH. Thirdly, under low pH conditions, anionic uranyl complexes, especially UO, are formed₂ ^2+-SO₄Complexes (e.g. UO)₂(SO₄)₃ ^4-). At moderate to higher pH, UO₂ ^2+-CO₃ ^2-Anionic complexes (e.g. UO)₂(CO₃)₂ ^2-、UO₂(CO₃)₃ ^4-、CaUO₂(CO₃)₃ ^2-) May predominate. Considering the UO₂ ²⁺As this form of anion complex, these uranyl anion complexes preferentially partition into the anion interlayers of the LDHs formed in situ. The method described in example 2 also provides one or more of the several advantages of the method of example 1 as outlined above. The item of interest may also be recovered by one or more further recovery steps as outlined in example 1.

Example 3

In a third exemplary embodiment (example 3), the method of the invention may be used to process uranium-bearing ores, wherein the LDH may be formed in situ in an alkaline mineral processing or metallurgical stream comprising the uranium-bearing ore.

A stream of uranium containing ore is typically fed with one or both of Mg and Al containing compounds to achieve the desired Mg/Al ratio in the stream which results in precipitation of LDH (e.g. hydrotalcite). Due to the pre-existing alkaline conditions (pH at least greater than 7 and preferably greater than 8) of the alkaline mineral processing or metallurgical stream, when the desired Mg/Al ratio is reached,the LDH is advantageously formed in situ. As explained in example 1, uranium-bearing ores include a range of other elements present in addition to uranium, including heavy metals, metalloids, and/or REEs. Formation of LDH materials in situ also leads to the incorporation of cations such as Ln³⁺Cation and/or Ce³⁺And Ce⁴⁺And/or Eu²⁺Or Eu³⁺An oxidation state, and a series of anions (including oxometallic anions or oxoanions). Laboratory tests have demonstrated that it is preferable to add the Al-containing compound first or together with any Mg-containing compound to prevent Mg from precipitating as a Mg carbonate compound, such as MgCO3, rather than for LDH formation.

The in situ formation of the LDH also results in the REE cations showing strong partitioning into the main metal hydroxide layers of the LDH. As previously mentioned, uranium is commonly referred to as Uranyl (UO)₂ ²⁺) The oxygen-containing cation of the cation is present and therefore the uranyl ion is too large to displace a +2 cation, such as Mg2+, into the LDH. Alkaline earth and transition metals are typically present in the metal hydroxide layer of the LDH. Again, under the alkaline conditions of the stream, an anionic uranyl complex is formed. At medium to higher pH conditions of the stream, UO₂ ²⁺-CO₃ ^2-Anionic complexes (e.g. UO)₂(CO₃)₂ ^2-、UO₂(CO₃)₃ ^4-、CaUO₂(CO₃)₃ ^2-) May predominate. Considering the UO₂ ²⁺As this selective form of anion complexes, these uranyl anion complexes preferentially partition into the anion interlayers of the LDHs formed in situ.

It is important to understand that under the reaction conditions of example 3, as explained above, only the carbonate complex will predominate, and some REEs, particularly the Medium (MREE) and Heavy REEs (HREEs), may preferentially remain in solution due to the known preferential complexation of MREE and HREE by the carbonate ligand. This preferential form under alkaline conditions can be advantageously used in view of the generally low abundance of MREE and HREE, which are generally considered to be the most valuable components of REE.

In this specification and in the claims, the word "comprise", and derivatives thereof, including "comprises" and "comprising", includes each of the stated integers but does not preclude the inclusion of one or more additional integers.

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 of the present invention. Thus, the appearances 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.

In compliance with the statute, the invention has been described in language more or less specific as to structural or methodical features. It is to be understood that the invention is not limited to the specific features shown or described, since the means herein described comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art, if any.

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Claims

1. A method for treating water containing one or more dissolved cationic species and/or one or more dissolved anionic species, the method comprising the steps of:

(b) controlling the reaction conditions to achieve a ratio of Mg to Al in water for the in situ formation of a layered double hydroxide containing Mg and Al as the predominant species in the lattice of the LDH;

2. A process in accordance with claim 1, wherein the step of dissolving the magnesium and aluminium containing silicate material comprises leaching the magnesium and aluminium from the silicate material under acidic pH conditions.

3. A process according to claim 1, wherein the step of dissolving the magnesium and/or aluminium containing silicate material comprises leaching aluminium from the silicate material under alkaline conditions.

4. A method according to any one of claims 1 to 3, wherein the step of dissolving the silicate material further comprises leaching at least a portion of the silica from the silicate material.

5. A method according to any one of claims 1 to 3, wherein the dissolving step comprises agitating the silicate material in water to leach said at least part of the magnesium and/or aluminium from the silicate material.

6. A process according to any one of claims 1 to 3, wherein the step of adding comprises adding a mixture comprising the magnesium and/or aluminium containing silicate material and a further silicate material.

7. A process in accordance with any one of claims 1 to 3 wherein the step of controlling the reaction conditions comprises adding at least one Mg-containing compound and/or at least one Al-containing compound to achieve a ratio of Mg to Al in water for the formation of LDH in situ.

8. The method according to claim 7, wherein the at least one Al-containing compound comprises an aluminate or an aluminum sulfate, an aluminum hydroxide, or an aluminum-containing organometallic compound.

9. According to the claimsThe method of claim 7, wherein the at least one Mg-containing compound comprises MgO or Mg (OH)₂Or mixtures thereof.

10. The method of claim 8, wherein the at least one Mg-containing compound comprises MgO or Mg (OH)₂Or mixtures thereof.

11. A process in accordance with any one of claims 1 to 3 wherein the step of controlling the reaction conditions further comprises providing reaction conditions for the alkalinity of the LDH to be formed in situ.

12. A process in accordance with any one of claims 1 to 3 wherein the step of controlling the reaction conditions further comprises adding a base or acid neutralising material to form the LDH in situ.

13. The method of claim 11, wherein the additional alkali or acid neutralizing material is selected from one or more alkali or acid neutralizing solutes, slurries or solid materials or mixtures thereof, including lime, slaked lime, calcined magnesium oxide, sodium hydroxide, sodium carbonate, sodium bicarbonate or sodium silicate.

14. A process according to any one of claims 1 to 3, further comprising the step of removing at least a portion of the hydrotalcite formed in situ, wherein at least one of the dissolved cationic and/or anionic species is incorporated into the hydrotalcite or LDH.

15. A process according to any one of claims 1 to 3, wherein the silicate material comprises one or more of: attapulgite; clinoptilolite; sepiolite; talc; vermiculite mineral aggregates or symbionts in the form of rocks.

16. A process in accordance with any one of claims 1 to 3 wherein at least a portion of the silicate material from step (a) and the LDH formed in situ in step (b) form an insoluble clay material mixture, wherein the clay material mixture incorporates the at least one or more dissolved cationic species and/or the one or more dissolved anionic species.

17. A process in accordance with any one of claims 1 to 3 wherein the undissolved clay material particles from step (a) provide nucleation sites for the formation of at least a portion of the LDH formed in situ in step (b).

18. A process in accordance with any one of claims 1 to 3 wherein the one or more dissolved cationic species in the water comprise magnesium and/or aluminium cations, such that at least a portion of the dissolved magnesium and/or aluminium is incorporated into the lattice of the LDH formed in situ.

19. A process in accordance with any one of claims 1 to 3 wherein at least one of the dissolved anions in the water is a complexing anion such that at least one of the complexing ions is intercalated into an interlayer of the LDH formed in situ.

20. A process in accordance with any one of claims 1 to 3 wherein the LDH formed in situ comprises hydrotalcite.

21. A process in accordance with any one of claims 1 to 3 for treating water containing dissolved metallic complex anion and one or more dissolved cations so that the metallic complex anion is intercalated within interlayers of the LDH material and wherein one or more other cations are incorporated into the LDH material's crystal structure or matrix.

22. The method of claim 21, further comprising the step of controlling the pH level in the water to control the formation of species that complex anions in the water.

23. A process in accordance with claim 21 further comprising separating the LDH from the water of step (b) and recovering the metallic constituent from the interlayer of the LDH by subjecting the separated LDH to a recovery treatment step.

24. A process in accordance with claim 23 wherein the recovery treatment step comprises an ion exchange step comprising adding at least one substituent anion to an ion exchange solution and introducing the separated LDH to the ion exchange solution such that the substituent anion displaces at least some of the intercalated complex anion by an ion exchange mechanism, thereby causing the complex anion to be released from the interlayer of the LDH into the ion exchange solution.

25. The method according to claim 24, wherein the ion exchange step further comprises controlling pH conditions to promote displacement of the complexing anion from the intermediate layer and/or to promote species formation of one type of complexing anion relative to other complexing anions.

26. A method according to claim 24 or claim 25 wherein the substituent reagent comprises one or more of: NTA, EDTA, and/or wherein the substituent reagent has substantially more electronegativity relative to the intercalated complex anion in the LDH material.

27. A process in accordance with claim 24 or claim 25 wherein the recovery treatment step further comprises separating the LDH material after the ion exchange step.

28. A process in accordance with claim 23 wherein the recovery treatment step comprises subjecting the LDH material to a heat treatment or thermal decomposition to form a collapsed or metastable material.

29. A process in accordance with claim 28 wherein the heat treatment step results in recrystallization of the LDH material after thermal decomposition resulting in formation of a first oxide material comprising the preselected metallic composition and a second oxide material comprising one or more other metals.

30. A method according to any one of claim 28 or claim 29, wherein the heat treatment is carried out under substantially reducing conditions.

31. A process in accordance with claim 28 or claim 29 further comprising adding additional additives to the LDH material before or during the heat treatment or thermal decomposition.

32. A process in accordance with claim 28 or claim 29 wherein the process further comprises controlling the ratio of additional additive to the LDH material to selectively control the formation of oxide material upon heat treatment or thermal decomposition.

33. A process in accordance with claim 23 wherein the recovery treatment step comprises optimising the crystal structure or matrix of the LDH material to selectively incorporate one or more other cations into the crystal structure or matrix of the LDH in step (b).

34. The method according to claim 29, wherein the metallic complexing anion comprises uranium or vanadium, and wherein the one or more other metals comprise rare earth metals.

35. A method in accordance with claim 21, wherein said metallic complexing anion comprises a uranyl complexing anion.

36. The method according to claim 35 wherein controlling the pH of the solution determines the species formation of the uranyl complex anion.

37. A process in accordance with claim 35 or claim 36 wherein the intercalated uranyl complex is displaced from the interlayer of the LDH by an ion exchange step which comprises adding at least one substituent anion to an ion exchange solution and introducing the separated LDH to the ion exchange solution such that the substituent anion displaces at least some of the intercalated complex anion by an ion exchange mechanism, thereby causing the complex anion to be released from the interlayer of the LDH into the ion exchange solution.

38. A process in accordance with claim 34 or claim 35 wherein the LDH material is subjected to a heat treatment step to form a collapsed or metastable material, such that the heat treatment is in use for reducing uranyl ions to U⁴⁺And/or U⁶⁺Under substantially reducing conditions.

39. The method of claim 23, further comprising the steps of: contacting the separated LDH material with an aqueous solution to dissolve at least a portion of the LDH material into the solution to obtain an LDH dissolved in the solution and then controlling the reaction conditions in the aqueous solution to precipitate LDH material 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 other cations are incorporated into the crystal structure or matrix of the LDH material formed in situ.

40. A process in accordance with claim 39 wherein the step of dissolving the LDH in the aqueous solution comprises controlling the pH of the aqueous solution at a pH level of less than 7.

41. The method according to claim 39, wherein the step of controlling the reaction conditions in the aqueous solution comprises controlling the pH of the aqueous solution at a pH level greater than 8.

42. A process in accordance with claim 35 wherein said uranyl complex anion is UO₂(CO₃)₂ ^2-、UO₂(CO₃)₃ ^4-、CaUO₂(CO₃)₃ ^2-Or UO₂(SO₄)₃ ^4-。