阅读说明：本技术 镧系元素掺杂的层状双氢氧化物及其生产方法 (Lanthanide-doped layered double hydroxide and method for producing the same ) 是由 埃琳娜·米哈埃拉·塞夫特尔 巴尔特·米希尔森 史蒂文·马伦斯 佩吉·库尔 薇拉·迈嫩 于 2018-12-21 设计创作，主要内容包括：本发明涉及一种用于生产镧系元素掺杂的层状双氢氧化物(Ln掺杂的LDH)的方法,所述方法包括以下步骤：制备不含碳酸盐的碱性溶液；制备包含镧系元素的盐的金属盐溶液；将该碱性溶液和该金属盐溶液共沉淀以形成混合物和Ln掺杂的LDH沉淀物,其中该混合物的pH保持在恒定值；老化该沉淀物；并且从该溶液中分离出该沉淀物。该碱性溶液是氨水溶液。本发明还涉及通过此种方法可获得的镧系元素掺杂的层状双氢氧化物(La掺杂的LDH),以及通过此种方法可获得的镧系元素掺杂的层状双氢氧化物的用途。(The present invention relates to a process for the production of a lanthanide-doped layered double hydroxide (Ln-doped LDH), the process comprising the steps of: preparing an alkaline solution free of carbonate; preparing a metal salt solution comprising a salt of a lanthanide; co-precipitating the alkaline solution and the metal salt solution to form a mixture and Ln-doped LDH precipitates, wherein the pH of the mixture is maintained at a constant value; aging the precipitate; and separating the precipitate from the solution. The alkaline solution is an aqueous ammonia solution. The invention also relates to a lanthanide-doped layered double hydroxide (La-doped LDH) obtainable by such a method, and to the use of a lanthanide-doped layered double hydroxide obtainable by such a method.)

1.A method for producing a lanthanide-doped layered double hydroxide (Ln-doped LDH), the method comprising the steps of:

a) preparing an alkaline solution free of carbonate;

b) preparing a metal salt solution comprising a lanthanide salt;

c) adding the alkaline solution and the metal salt solution to form a mixture, wherein the pH of the mixture is maintained at a constant value, so as to form Ln-doped LDH precipitates;

d) aging the precipitate; and

e) separating the precipitate from the mixture

Characterized in that the carbonate-free alkaline solution is an aqueous ammonia solution.

2. The method of claim 1, wherein the NH of the aqueous ammonia solution₃The concentration is between 20% w/w and 30% w/w.

3. The method of claim 1 or 2, wherein in step (c), the adding of the basic solution and the metal salt solution is performed by adding the basic solution to the metal salt solution at a rate of 5 to 10 mL/min/liter of metal salt solution.

4. The process of any one of the preceding claims, wherein in step (c) the pH of the formed mixture is comprised between 9 and 13, preferably between 10 and 12, more preferably between 10 and 11.

5. The process of any one of the preceding claims, wherein step (c) is carried out at a temperature comprised between 1 ℃ and 65 ℃; preferably between room temperature and 65 c, preferably at room temperature.

6. The method of any one of the preceding claims, wherein the metal salt solution comprises a salt of a lanthanide and a salt of one or more of a divalent, trivalent, or tetravalent metal cation.

7. The process of claim 6, wherein the cation ratio of Me2+/(Me3+ and/or Me4+)/Ln3+ in the metal salt solution is 2-4/0.8-0.95/0.05-0.2; in particular Me2+/Me3+/Ln3 +: 4-5/0.95/0.05, wherein Me refers to a metal element.

8. The method of claim 6, wherein the metal salt solution comprises a salt of a lanthanide, an aluminum salt, and a salt of one or more of calcium, magnesium, and zinc; salts of lanthanum, aluminum and calcium, magnesium or zinc are preferred.

9. The process of claim 8, wherein in the metal salt solution the molar ratio of Ca/Al/Ln is from 2 to 4/0.5 to 0.95/0.05 to 0.5, or the molar ratio of Mg/Al/Ln is from 2 to 4/0.5 to 0.95/0.05 to 0.5, or the molar ratio of Zn/Al/Ln is from 2 to 4/0.5 to 0.95/0.05 to 0.5.

10. The method of claim 8 or 9, wherein the metal salt solution comprises salts of lanthanides, aluminum, and magnesium.

11. The method of claim 10, wherein in the metal salt solution, between Mg, Al and LnIn a molar ratio of Mg_xAl_yLn_zWherein x is between 2 and 4, y is between 0.9 and 0.95, and z is between 0.05 and 0.1.

12. The method of any one of the preceding claims, wherein the metal salt solution comprises CaCl₂.2H₂O、AlCl₃.6H₂O and LaCl₃.7H₂O; or Mg (NO)₃)₂.6H₂O、Al(NO₃)₃.9H₂O and La (NO)₃)₃.6H₂O; or Zn (NO)₃)₂.6H₂O、Al(NO₃)₃.9H₂O and La (NO)₃)₃.6H₂O。

13. The process of any one of the preceding claims, wherein step (d) is carried out at a temperature comprised between 1 ℃ and 150 ℃ for a time of at least 1 hour.

14. The method of claim 13, wherein step (d) comprises contacting the precipitate and the mixture with each other at a temperature between 1 ℃ and 65 ℃, preferably between 10 ℃ and 65 ℃.

15. A lanthanide-doped layered double hydroxide obtainable by the process as claimed in any one of claims 1 to 14, wherein the lattice parameter a of the unit cell of the crystal structure of the LDH material₁₁₀Lattice parameter a of the unit cell of the crystal structure of the undoped LDH material₁₁₀At least 1.6% greater.

16. The lanthanide-doped layered double hydroxide of claim 15, comprising brucite-like layers and interlaminar portions between the brucite-like layers, wherein at least 90% of the anions in the interlaminar portions are nitrate anions.

17. The lanthanide-doped layered double hydroxide as claimed in claim 15 or 16, wherein the lanthanide is doped into the brucite-like layers of the layered double hydroxides.

18. The lanthanide-doped layered double hydroxide of claim 17, wherein doping the lanthanide into the brucite-like layer produces a non-segregated lanthanide phase in said layered double hydroxide.

19. The lanthanide-doped layered double hydroxide of any one of claims 15-18, wherein the lanthanide is La, Eu, or Tb.

20. Use of a lanthanide-doped layered double hydroxide obtainable by a process as defined in any one of claims 1 to 14 or a lanthanide-doped layered double hydroxide as defined in any one of claims 15 to 19 as an adsorbent or catalyst, preferably as an adsorbent for anions, preferably as an adsorbent for inorganic or organic anions, preferably as an adsorbent for heavy metal anions and oxyanions.

21. Use of a lanthanide-doped layered double hydroxide as claimed in claim 20 as an adsorbent or catalyst at a pH comprised between 7 and 14, preferably between 8 and 13, more preferably between 10 and 12, even more preferably between 11 and 12.

22. Use of a lanthanide-doped layered double hydroxide obtainable by the process as defined in any one of claims 1 to 14 or a lanthanide-doped layered double hydroxide as defined in any one of claims 15 to 19, wherein the lanthanide is Eu or Tb, as a fluorescent material.

Technical Field

The present invention relates to a process for producing a lanthanide-doped layered double hydroxide (Ln-doped LDH). The invention also relates to a lanthanide-doped layered double hydroxide (La-doped LDH) obtainable by such a method, and to the use of a lanthanide-doped layered double hydroxide obtainable by such a method.

Background

Heavy metals such as Cr, Mo, W, Mn, V, Nb, Sb, and the like are found in low grade industrial waste streams such as hydrometallurgical slags. These industrial waste streams are complex mixtures in which the amount of by-product metals present is typically as low as very low compared to the associated primary metals. In the art, the liberation of metals is typically carried out by alkali leaching on the waste stream, thereby producing a complex leachate mixture containing valuable metals having a high pH value (e.g., from 12 to 14). Further processing of these leach liquor mixtures is then necessary in order to separate, recover or remove metals therefrom. However, due to the high pH of the leach liquor mixtures, any conventional recovery or removal treatment requires that the pH of these mixtures be first lowered to the acidic range (e.g. to a pH below 5, typically about 2 to 3), and then that further separation, recovery or removal of these metals is actually carried out. This reduction in pH is often a challenging and expensive operation.

The prior art on oxygen anion absorption includes adsorbents of different nature or origin, such as activated carbon, anion exchange resins, biological materials, waste products or minerals, most of which have low stability and/or low performance (i.e. limited adsorption capacity) in alkaline environments (i.e. at pH higher than 7). For example, anion exchange resins (e.g. anion exchange resinsA830、MP 62、

M 610、

MP 64) only works effectively at pH below 7 (typically in the pH range of 1 to 4). Furthermore, the adsorption equilibrium of such resins is reached only after about 2 hours, so that the absorption of heavy metal oxyanions is very slow. Moreover, even under acidic conditions (pH below 7), the maximum adsorption capacity of many anion exchange resins known in the art is about 40mg of heavy metal oxyanion per gram of adsorbent, which is relatively low.

Recently, there has been an increasing interest in using a class of anionic clays known as Layered Double Hydroxides (LDHs) or hydrotalcite-like compounds (htlcs) to remove inorganic contaminants, such as oxyanions and monoatomic anions, such as fluoride, chloride, bromide, and iodide, from aqueous solutions by adsorption and/or ion exchange processes. Goh et al, in Water Res [ Water research ]2008,42(6-7),1343-68, for example, provide an overview of LDH synthesis methods, LDH characterization techniques, and the use of LDHs for removing oxyanions, as is generally known in the art so far.

LDHs are mineral materials with a layered clay-type structure. The structure of the LDH material comes from that of brucite, which is of the formula Mg (OH)₂In the form of a mineral of magnesium hydroxide, wherein the divalent metal cation M²⁺(the metal cation is octahedrally coordinated by a hydroxyl group) by a higher valence cation M³⁺(e.g., Al)³⁺) Isomorphous substitution. This substitution produces positively charged brucite-type layers that are electrically neutralized by anions that are located in the interlayer region along with the crystalline water molecules.

The structures of typical octahedral units and LDHs are shown in fig. 1 and 2, respectively. The basal plane spacing (c') depicted by reference numeral (1) in fig. 2 is the total thickness of the LDH-structured brucite-like sheets (3) and the interlayer region (2). M²⁺Or M³⁺Octahedral units (with OH)^-Six coordinates) share edges to form an infinite sheet. The sheets are stacked on top of each other and bonded together by hydrogen bonds.

LDH is represented by the general formula [ M ]²⁺ _1-xM³⁺ _x(OH)₂]^x+(A^n- _x/n)·mH₂O represents, wherein M²⁺Is a divalent cation (e.g. Mg)²⁺、Zn²⁺、Ca²⁺Etc.), M)³⁺Is a trivalent cation (e.g. Al)³⁺、Fe³⁺、Mn³⁺Etc.), the value of x is equal to M³⁺/(M²⁺+M³⁺) In a molar ratio of A and A^n-Is an interlayer anion (or intercalation anion) having a valence of n (e.g. CO)₃ ^2-、NO₃ ^-Etc.). The parent material of these anionic clays is a hydrotalcite of naturally occurring minerals having the formula Mg₆Al₂(OH)₁₆CO₃.4H₂O。

As is well known, LDH materials have excellent anion exchange capacity for a large number of inorganic anions (e.g. nitrate, sulphate, chromate, etc.) and organic anions (e.g. acetate, tartrate, carboxylate, etc.). Furthermore, LDHs are known in the art to be thermally stable, have a relatively high surface area, be easily and economically viable to produce, and have low toxicity. This versatility of LDH-type materials has led to its application in many fields, for example as adsorbents of (oxygen) anions, as catalysts, catalyst precursors or catalytic supports, as nanofillers for polymer nanocomposites, as sensors, or medically as drug carriers. However, the main concern of using LDHs as adsorbents for (oxy) anions in the art is still related to their low stability in alkaline environments.

It is therefore desirable to provide LDHs that are stable at high pH (e.g. ranging from 10 to 13) while maintaining maximum adsorption capacity.

Poernomo guard et al, "Lanthanide-Doped Double hydroxide intercalated with sensing equations, effective Energy Transfer between Hostand guards Layers [ Lanthanide Doped Layered Double hydroxide intercalated with Sensitizing anion: effective energy transfer between host layer and guest layer ] ", Journal of Physical Chemistry C, Vol.113, No. 39, pp.17206-17214, describes a process for preparing terbium (Tb) -doped layered double hydroxides, which comprises the following steps: a mixed solution of salts of Mg, Al and Tb was added dropwise to an aqueous NaOH solution, aged and the precipitate was separated.

The inventors of the present invention have found that Ln-doped LDHs obtained by the above-described approach suffer from a decrease in crystallinity with increasing degree of Ln doping.

Disclosure of Invention

It is an object of aspects of the present invention to provide at least one alternative route for the preparation of lanthanide-doped Layered Double Hydroxides (LDHs), in particular to provide an alternative route which does not have the above-mentioned disadvantages and/or is more robust and/or leads to an improvement of the lanthanide-doped LDHs. It is an object of various aspects of the present invention to produce layered double hydroxide type anionic clays and to use the produced materials as adsorbents.

Thus, according to a first aspect of the present invention, there is provided a method for producing a lanthanide-doped Layered Double Hydroxide (LDH) as set forth in the appended claims. The method comprises the following steps: preparing an alkaline solution, wherein the alkaline solution does not comprise a carbonate; preparing a metal salt solution comprising a lanthanide salt; combining the alkaline solution and the metal salt solution to form a mixture and Ln-doped LDH precipitates, wherein the pH of the mixture is maintained at a constant value; aging the precipitate; and separating the precipitate from the solution. The method is performed without carbonate. According to the invention, the alkaline solution is an aqueous ammonia solution.

By performing the method of the invention, the LDH material is doped with a lanthanide in the brucite-like sheets (rather than by incorporating a lanthanide in the interlayer region between two brucite-like sheets, as is the case using methods known in the art). Furthermore, the preparation route according to the invention allows to reduce or even completely prevent the segregation of lanthanides. Thus providing alkaline stability to the Ln doped LDH obtainable by the process of the invention, allowing the doped LDH to be used directly as an adsorbent to recover (oxygen) anions in a highly alkaline environment, i.e. at a pH of 10 up to about 13.5.

Further advantageous aspects of the invention are set out in the dependent claims.

According to a second aspect of the present invention, there is provided a lanthanide-doped layered double hydroxide, as obtainable or obtained by the method according to the present invention, as set forth in the appended claims. In lanthanide-doped LDHs, the lattice parameter a of the unit cell of the crystal structure of the LDH material₁₁₀Lattice parameter a of the unit cell of the crystal structure of the LDH material, advantageously being greater than that of the undoped LDH material₁₁₀An increase of at least 1.6%. a is₁₁₀The increase in (a) demonstrates that the lanthanide is incorporated directly into the lattice layers of the LDH material (rather than into the interlaminar region between the two brucite-like sheets, as is the case with doped LDHs produced using methods known in the art).

According to yet other aspects of the present invention there is provided the use of a lanthanide-doped layered double hydroxide obtainable by a method according to the first aspect or a lanthanide-doped LDH according to the second aspect, as set forth in the appended claims. Described herein is the use as an adsorbent, as a catalyst or as a fluorescent material.

Drawings

Aspects of the present invention will now be described in more detail, with reference to the appended drawings, wherein like reference numerals represent like features, and wherein:

FIG. 1 schematically shows a polymer having a functional group of OH^-Anionic octahedral coordination, M²⁺Or M³⁺Octahedral units of metal cations;

FIG. 2 schematically represents a Layered Double Hydroxide (LDH) structure having (1) basal plane spacing (c'), (2) interlaminar regions, and (3) brucite-like sheets;

fig. 3 depicts XRD patterns (left) and SEM images (right) of Ca2Al hydrocalumite-type structures obtained in example 1.a (non-La doped HC-type material);

fig. 4 depicts XRD patterns of (a) Ca2Al, (b) Ca3Al, and (c) Ca4Al hydrocalumite-type materials obtained in example 1.a (non-La-doped HC-type material);

FIG. 5 depicts (a) Ca2Al, (b) Ca2Al0.9La0.1(3.3 m% La), (c) Ca2Al0.8La0.2(6.6 m% La), (d) Ca2Al0.5La0.5(16.5 m% La) and (e) La (OH)₃XRD pattern of reference material (example 1.B, La doped HC type material);

FIG. 6 depicts (a) Ca2Al0.9La0.1(3.3 m% La) aged at room temperature, (b) at 65 ℃, (c) at 110 ℃ and (d) La (OH)₃XRD pattern of reference material (example 1.B, La doped HC type material);

FIG. 7 depicts the XRD patterns of (a) Mg3Al (example 1.C, non-La doped HT type material), (b) Mg3Al0.95La0.05(1.65 m% La), and (C) Mg3Al0.9La0.1(3.3 m% La) (example 1.D, La doped HT type material);

FIG. 8 shows the amount of adsorbed chromate (q) over time for conventional non-La doped hydrotalcite-type (LDH) materials with different intercalating anions at pH 8_e，mgCr⁶⁺(iv)/g): ZnAl type (left), and MgAl type (right) (andMG 63HT comparison);

fig. 9 shows chromate adsorption efficiency and material stability during adsorption for ZnAl (left) and MgAl (right) type conventional hydrotalcites at different pH values;

FIG. 10 is a Bolbex (Pourbaix) diagram (E)_hpH diagram) depicts the cation morphology as a function of pH;

figure 11 shows the adsorption efficiency during adsorption tests at different pH (left) and the measured value of metal release during adsorption tests as a function of pH (right);

fig. 12 depicts XRD patterns of La doped MgAl HT type material before and after chromate adsorption in different pH media: (a) such as synthetic mg3al0.9la0.1(3.3 m% La) (see example 1.D, La doped HT type material), (b) mg3al0.9la0.1(3.3 m% La) after adsorption at pH 8 and (c) mg3al0.9la0.1(3.3 m% La) after adsorption at pH 13;

FIG. 13 shows the volumes of ammonia solution required to achieve the pH of different co-precipitation steps during synthesis at different temperatures;

FIG. 14 shows XRD patterns of (a) Mg3Al0.95La0.05(1.65 m% La), (b) Mg3Al0.95Ce0.05(1.65 m% Ce), (c) Mg3Al0.95Eu0.05(1.65 m% Eu), (d) Mg3Al0.95Tb0.05(1.65 m% Tb), (e) Mg3Al0.95Gd0.05(1.65 m% Gd), and (f) Mg3Al0.95Yb0.05(1.65 m% Yb);

FIG. 15 shows the Raman spectrum of Mg3Al0.95Eu0.05(1.65 m% Eu) and the inset is at less than 1200cm^-1An enlarged view in the spectral range of (a);

FIG. 16 shows the catalytic results of the conversion of 1-octanol to methyl and dioctyl carbonates by MK8-14, MK51-35C, hydrotalcite, toluene sulfonic acid, and sulfuric acid after 2, 4, 5.5, and 22 hours of reaction, expressed as area percent of the peaks in GC-MS.

Detailed Description

A method for producing a lanthanide-doped layered double hydroxide (Ln-doped LDH) according to aspects of the invention comprises the steps of:

(a) preparing an alkaline solution (as a co-precipitant), wherein the alkaline solution does not comprise a carbonate;

(b) preparing a metal salt (aqueous) solution comprising a salt of a lanthanide (as a precipitation solution);

(c) combining the alkaline solution and the metal salt solution to form (by co-precipitation) a mixture of Ln-doped LDH precipitates and solution, thereby maintaining the pH of the formed solution at a constant value;

(d) aging the precipitate; and

(e) and separating the precipitate from the solution.

The synthesis according to the process of the invention is carbonate free. More particularly, the co-precipitation of aspects of the invention is in the absence of a carbonate (e.g., Na) as a co-precipitating agent in an alkaline environment₂CO₃) In the case of (i.e. the alkaline solution does not contain carbonate, or in other words, the alkaline solution does not contain carbonate). Furthermore, methods used in the art for producing Ln-doped LDHs cannot convert Ln³⁺The cation is incorporated into the brucite-like sheet, which is a necessary condition for maintaining the ion-exchange properties and is critical for providing alkaline stability of the doped structure (see further below).

Indeed, for example, Wang et al in Chemical Engineering Journal]2017,309,445-453 reports the synthesis of a structure containing MgAl and CaAl, which contains La³⁺The metal acts as a dopant and the structure can act as a coagulant for graphene oxide. The structural synthesis reported by Wang et al was performed in NaOH and Na₂CO₃Co-precipitation of metal nitrates in the presence of the mixture is carried out, which facilitates the formation of carbonate species very early in the co-precipitation, thus preventing isomorphous substitution into the crystal lattice. Indeed, the structure of the MgAlLa material reported by Wang et al reveals a La phase separated from the LDH phase₂O₃Combined (the latter phase being the predominant phase due to the high La content relative to Al) and thus a composite LDH/La material₂O₃Rather than a La-doped MgAl structure. Furthermore, Wang reports a structure comprising carbonate anions in the interlayer. As will be further demonstrated in the examples below, by the method of the present inventionThe Ln-doped LDH material obtainable by the process consists only of the LDH structure therein, in which Ln³⁺Cation (advantageously La)³⁺Cations) are incorporated or doped (by isomorphous displacement) into the lattice layer (as can be seen from the XRD patterns of fig. 7 and 12 and the data in tables 1A to 1D, see examples below). In contrast, in the methods described in the art, La-doped LDHs are obtained only by inserting lanthanide anion complexes into the interlayer regions of the LDH.

According to aspects of the invention, the alkaline solution is an ammonia solution. Advantageously, the concentration of the ammonia solution is comprised between 20 and 30% (w/w) NH₃Advantageously, the concentration of the solution is 25% (w/w) NH₃。

In the context of the present invention, ammonia solution refers to a solution of ammonia in water, by NH₃(aqueous) representation.

Advantageously, the (aqueous) solution of metal salt comprises or consists of: salts of lanthanides, aluminum (salts) and one or more of calcium, magnesium and zinc.

In the context of the present invention, a salt of a lanthanide refers to a salt comprising one of the elements of the lanthanide as a cation.

Advantageously, the lanthanide in the metal salt solution is lanthanum (La), (or in other words, the metal salt solution comprises a salt of lanthanum, europium (Eu) or terbium (Tb).

Advantageously, the metal salt solution does not contain carbonates, or in other words, the metal salt solution does not contain carbonates.

More advantageously, the metal salt solution comprises, or consists of: lanthanum salts, aluminum (salts) and one or more of calcium, magnesium and zinc (salts).

More advantageously, the metal salt solution comprises, or consists of: salts of lanthanides, aluminum (salts) and calcium, magnesium or zinc. Even more advantageously, the metal salt solution comprises, or consists of: lanthanum salts, aluminium salts and salts of calcium, magnesium or zinc.

More advantageously, in the solution of the metal salts, the molar ratio Ca/Al/Ln (advantageously Ca/Al/La) is comprised between 2 and 4/0.5 and 0.95/0.05 and 0.5, or the molar ratio Mg/Al/Ln (advantageously Mg/Al/La) is comprised between 2 and 4/0.5 and 0.95/0.05 and 0.5, or the molar ratio Zn/Al/Ln is comprised between 2 and 4/0.5 and 0.95/0.05 and 0.5. Advantageously, the molar ratio Mg/Al/Ln (advantageously Mg/Al/La) ranges from 2 to 4/0.9 to 0.95/0.05 to 0.1. Even more advantageously, in the solution of the metal salts, the molar ratio Ca/Al/Ln (advantageously Ca/Al/La) is comprised between 2/0.5 and 0.9/0.1 and 0.5, or the molar ratio Mg/Al/Ln (advantageously Mg/Al/La) is comprised between 3/0.9 and 0.95/0.05 and 0.1, or the molar ratio Zn/Al/Ln (advantageously Zn/Al/La) is comprised between 2/0.5 and 0.95/0.05 and 0.5.

Advantageously, the anion present in the (aqueous) solution of the metal salt is hydroxide (OH)^-) And Nitrate (NO)^3-) Bromine ion (Br)^-) Chloride ion (Cl)^-) Or fluoride ion (F)^-) (ii) a Advantageously, the anion present in the metal salt solution is hydroxide, nitrate or chloride. In the process of the invention, the anions present in the metal salt solution form interlayer anions in the interlayer regions between the brucite-like sheets of the Ln-doped LDH material. Advantageously, at least 70% of the anions, advantageously at least 80%, advantageously at least 90%, are nitrates.

More advantageously, the metal salt solution comprises, or consists of: CaCl₂.2H₂O (calcium chloride dihydrate), AlCl₃.6H₂O (aluminum chloride hexahydrate) and LaCl₃.7H₂O (lanthanum (III) chloride heptahydrate). Alternatively, the metal salt solution comprises, or consists of: mg (NO)₃)₂.6H₂O (magnesium nitrate hexahydrate), Al (NO)₃)₃.9H₂O (aluminum nitrate nonahydrate) and La (NO)₃)₃.6H₂O (lanthanum (III) nitrate hexahydrate). In another alternative, the metal salt solution comprises, or consists of: zn (NO)₃)₂.6H₂O (Zinc nitrate hexahydrate), Al (NO)₃)₃.9H₂O (aluminum nitrate nonahydrate) and La (NO)₃)₃.6H₂O (lanthanum (III) nitrate hexahydrate).

More advantageously, the incorporation of Ln is obtained by the process of the inventionMiscellaneous Ca²⁺The LDH material of (i.e. Ln-doped hydrocalumite) comprises chloride ions (i.e. chloride ions originally present in the metal salt solution) as interlayer anions in the interlayer regions between these brucite-like sheets. Alternatively, Ln-containing doped Mg obtainable by the process of the invention²⁺The LDH material of (i.e. Ln-doped hydrotalcite) contains nitrate as interlayer anions (i.e. nitrate originally present in the metal salt solution) in the interlayer regions between these brucite-like sheets. Nitrate advantageously forms at least 90% of the anions in the interlayer region. In another alternative, Zn containing Ln doping obtainable by the process of the invention²⁺The LDH material of (i.e. Ln-doped zinc zircon) contains nitrate as an interlayer anion (i.e. nitrate originally present in the metal salt solution) in the interlayer region between these brucite-like sheets.

Even more advantageously, the concentration of the metal salt solution is comprised between 0.5M and 2M, advantageously 1M.

Even more advantageously, in the presence of CaCl₂.2H₂O、AlCl₃.6H₂O and LaCl₃.7H₂The molar percentage (or molar percentage or molar proportion, mol%) of La in the solution of the metal salt of O is comprised between 1 and 17.5, advantageously between 3.3 and 16.5. Alternatively, in the presence of Mg (NO)₃)₂.6H₂O、Al(NO₃)₃.9H₂O and La (NO)₃)₃.6H₂The molar percentage of La in the metal salt solution of O is comprised between 1 and 17.5, advantageously between 1.65 and 3.3. In yet another alternative, in the presence of Zn (NO)₃)₂.6H₂O、Al(NO₃)₃.9H₂O and La (NO)₃)₃.6H₂The molar percentage of La in the metal salt solution of O is comprised between 1 and 17.5, advantageously between 1.65 and 17.5.

The metal salt in the precipitation solution (i.e. in the metal salt solution) is a precursor for forming a precipitate in step (c) by co-precipitation with a basic solution. More particularly, by subjecting in step (c) toThe alkaline solution and the metal salt solution are combined to form a mixture of Ln doped LDH precipitates and the solution by co-precipitation (more specifically, Ln doped LDH precipitates (solid phase) are formed in the solution). The alkaline solution and the metal salt solution are combined in such a way that the pH of the solution formed in said step is maintained at a constant value. In this way, the LDH material is treated with a lanthanide, more particularly Ln³⁺Cation (advantageously lanthanum, more particularly La)³⁺Cation) doping is performed by using (or by) Ln³⁺Cation (advantageously La)³⁺Cation) isomorphous replacement of trivalent metal cation M³⁺Initially present in octahedral units of brucite-like sheets of the LDH material. In aspects of the invention, the chemical composition of the LDH material is thus achieved by doping Ln in brucite-like sheets³⁺Cation (advantageously La)³⁺Cations) in the sheet (rather than by incorporating cations in the interlaminar region between two such brucite sheets). Doping can be done at various cation ratios. This manner of doping provides alkaline stability to the Ln-doped LDH (advantageously La-doped LDH) produced by the process of the invention, allowing the Ln-doped LDH to be used directly as an adsorbent under harsh conditions, for example for adsorbing valuable metals from industrially complex highly alkaline leach liquor mixtures having a pH of up to 10 to about 13.5.

Combining the alkaline solution and the metal salt solution in step (c) is performed by adding the alkaline solution to the metal salt solution or by adding the metal salt solution to the alkaline solution. Advantageously, an alkaline solution is added to the metal salt solution.

The alkaline solution (or the solution of the metal salt) is added in such a manner that the pH of the solution formed in said step is maintained at a constant value. More advantageously, the rate of addition of the alkaline solution to the metal salt solution (or of the metal salt solution to the alkaline solution) is set so as to keep the pH of the solution formed in said step constant (i.e. at a constant value). The addition may be performed dropwise. Advantageously, the rate of addition is from 5 to 10 mL/min/liter of metal salt solution (or from 5 to 10 mL/min/liter of alkaline solution when metal salt solution is added to alkaline solution).

Advantageously, the pH of the forming solution in the coprecipitation step is comprised between 9 and 13, advantageously between 10 and 12, advantageously between 10 and 11.

More advantageously, in the coprecipitation step, the rate of addition of the basic solution to the metal salt solution (or of the metal salt solution to the basic solution) is from 5 to 10 mL/min/litre of metal salt solution (or/litre of basic solution) so as to maintain the pH of the solution formed (by coprecipitation) at a constant value comprised between 9 and 13, advantageously between 10 and 12, advantageously between 10 and 11.

Advantageously, the coprecipitation step is carried out at a temperature of up to 65 ℃, advantageously up to 50 ℃, advantageously up to 40 ℃, advantageously up to 30 ℃. The coprecipitation step is advantageously carried out at a temperature comprised between 1 ℃ and 65 ℃; advantageously between room temperature and 65 ℃, or alternatively between 1 ℃ and 50 ℃, advantageously between 1 ℃ and 40 ℃, advantageously between 1 ℃ and 30 ℃, advantageously between 1 ℃ and room temperature (20 ℃).

The process of the invention is carried out in the absence of carbonates (e.g. Na)₂CO₃) Is carried out in the case of (1). More particularly, in the process of the invention, the co-precipitation is carried out in an alkaline environment (i.e. by alkaline co-precipitation) in the absence of carbonate. According to the invention, the coprecipitation is carried out in an ammonia solution.

After the co-precipitation step is performed, the formed precipitate is aged. More particularly, the precipitate and the solution formed in step (c) are kept in contact with each other for a period of time during the aging step. Advantageously, the step of ageing the precipitate (step (d)) is carried out for a period of at least 1 hour, advantageously between 1 hour and 24 hours, advantageously from 6 hours to 24 hours. The step (d) of ageing the precipitate is advantageously carried out at a temperature comprised between 10 ℃ and 150 ℃, advantageously between 10 ℃ and 65 ℃. Alternatively, step (d) of aging the precipitate is advantageously carried out at a temperature of up to 65 ℃ (for example between 1 ℃ and 65 ℃), advantageously up to 50 ℃, advantageously up to 40 ℃.

Advantageously, step (d) is carried out at a temperature comprised between 10 ℃ and 65 ℃, advantageously between room temperature and 65 ℃, advantageously at 65 ℃, for a time comprised between 1 hour and 24 hours. Alternatively, step (d) is carried out by carrying out the hydrothermal treatment at a temperature comprised between 80 ℃ and 150 ℃, advantageously at 110 ℃, for a time such as from 1 hour to 24 hours. Advantageously, the hydrothermal treatment is carried out in an autoclave.

After performing the aging step, the Ln doped LDH precipitates are separated from the solution. Advantageously, the precipitate comprising (or consisting of) Ln-doped LDH material is separated from the solution by filtration or centrifugation.

Advantageously, after the separation step, the precipitate is washed (one or more times with distilled water) and optionally dried to obtain the Ln-doped LDH material in powder form. The (optional) drying of the precipitate can be carried out at a temperature comprised between 10 ℃ and 150 ℃, advantageously between room temperature and 80 ℃, for 1 to 48 hours. More advantageously, the drying of the precipitate is carried out between room temperature and 60 ℃ for 6 to 24 hours.

Advantageously, the method according to the invention may comprise one or a combination of the following aspects:

-the alkaline solution comprises 25% (w/w) ammonia solution;

metal salt solutions from 1M Mg (NO)₃)₂.6H₂O (magnesium nitrate hexahydrate), Al (NO)₃)₃.9H₂O (aluminum nitrate hexahydrate) and La (NO)₃)₃.6H₂O (lanthanum (III) nitrate hexahydrate) with a Mg/Al/La molar ratio ranging from 3/0.9 to 0.95/0.05 to 0.1;

-step (c) is carried out at room temperature at a pH comprised between 10 and 12;

step (d) is carried out at a temperature comprised between 10 ℃ and 150 ℃ for a time comprised between 1 hour and 24 hours (advantageously at 65 ℃ for 24 hours).

Advantageously, after step (d) (the ageing step), the precipitate comprising (or consisting of) the La doped LDH material is separated from the solution by filtration or centrifugation. After the separation step, the precipitate is washed (one or more times with distilled water) and optionally dried to obtain a powdered La-doped LDH material. The dried precipitate may be maintained at 60 ℃ for 24 hours.

Advantageously, by performing the method of the invention, the unit cell parameter a of the unit cell of the crystal structure of the (powdered) Ln-doped LDH material (advantageously La-doped LDH material) formed is₁₁₀Lattice parameter a of the unit cell compared to the crystal structure of the non-Ln-doped powdered LDH material (i.e. the same non-Ln-doped LDH material)₁₁₀An increase of at least 1.6%. Increased lattice parameter a₁₁₀Lanthanide cation (Ln) was confirmed³⁺) (advantageously lanthanum cation, La)³⁺) Indeed incorporated into the lattice layer of the LDH material.

According to a further aspect, the invention relates to the use of a lanthanide-doped layered double hydroxide, advantageously a lanthanum-, europium-or terbium-doped layered double hydroxide, obtainable by the process according to the invention, as an adsorbent (or absorber) or catalyst. Advantageously, the Ln-doped LDH (advantageously the La-doped LDH) is used as an adsorbent for anions, such as organic or inorganic anions, in particular heavy metal anions, advantageously as an adsorbent for heavy metal oxyanions.

In the context of the present application, the term oxyanion is intended to have the general formula A_xO_y ^z-Wherein a represents a chemical element, and O represents an oxygen atom. Examples of oxyanions are arsenite, arsenate, chromate, phosphate, selenite, selenate, vanadate, molybdate, manganate, borate, nitrate, and the like.

The term (heavy) metal oxyanion means having the general formula A_xO_y ^z-Wherein the element a represents a (heavy) metal chemical element, and O represents an oxygen atom.

The Ln-doped LDH (advantageously La-doped LDH) obtainable by the process according to the invention may for example be used as an adsorbent for wastewater treatment (wastewater containing heavy metals, such as wastewater from hydrometallurgical processes) or for treating alkaline leachate containing metal oxyanions. Alternatively, the Ln-doped LDH (or calcined form thereof, advantageously the La-doped LDH or calcined form thereof) may be used as a catalyst in reactions under high pH environments, such as photocatalysis, or as a basic catalyst in, for example, aldol condensation reactions. Ln-doped LDHs (advantageously La-doped LDHs) can also be used for treating wastes of toxic effluents produced in the electroplating industry, the coal industry, refining, pesticides, fungicides and the steel production industry.

Advantageously, the Ln-doped LDH (advantageously La-doped LDH) obtainable by the process according to the invention is ecologically friendly (non-toxic).

The Ln-doped LDH (advantageously La-doped LDH) obtainable by the process according to the invention can be directly applied in highly alkaline streams without the need to lower the pH beforehand.

Advantageously, the Ln-doped LDH (advantageously La-doped LDH) obtainable by the process according to the invention is used as adsorbent at a pH comprised between 7 and 14, advantageously between 8 and 13, advantageously between 10 and 12, advantageously between 11 and 12, for example at a pH of 11.5.

In other aspects, the invention relates to a lanthanide-doped layered double hydroxide (Ln-doped LDH) obtainable by the method according to the invention. More particularly, the invention relates to lanthanide-doped layered double hydroxides (in particular La-doped LDHs) obtainable by the process according to the invention, wherein the LDH material has a crystal structure with a unit cell lattice parameter a₁₁₀Lattice parameter a of the unit cell compared to the crystal structure of a non-La doped LDH material (i.e., the same non-La doped LDH material)₁₁₀An increase of at least 1.6%. Increased lattice parameter a₁₁₀Lanthanum (more particularly, La) was confirmed³⁺Cations) are indeed incorporated into the lattice layers of the LDH material.

The Ln-doped LDH obtainable by the process according to the invention may be used as an adsorbent (advantageously as an adsorbent for heavy metal anions, more advantageously as an adsorbent for heavy metal oxyanions), or the Ln-doped LDH (or a calcined form thereof) may be used as a catalyst. More particularly, the Ln-doped LDH can be used as adsorbent in a highly alkaline environment, i.e. at a pH comprised between 7 and 14, advantageously between 8 and 13, advantageously between 10 and 12, advantageously between 11 and 12 (for example at a pH of 11.5).

Advantageously, the Ln-doped LDH obtainable by the process according to the invention is ecologically friendly (non-toxic).