# Shaping layered double hydroxides in geopolymer for selective lithium extraction in fixed-bed process

Maël Ferrand, Yves Barre, Roua Benrhouma, Guillaume Munier-Gondiant, Thomas David, Maxime Duchateau, Alban Gossard, Agnes Grandjean

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Maël Ferrand, Yves Barre, Roua Benrhouma, Guillaume Munier-Gondiant, Thomas David, et al. Shaping layered double hydroxides in geopolymer for selective lithium extraction in fixed-bed process. Materials Letters, 2026, 408, pp.140148. 10.1016/j.matlet.2026.140148. cea-05504199

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# Shaping layered double hydroxides in geopolymer for selective lithium extraction in fixed-bed process

Maël Ferrand<sup>a</sup>, Yves Barré<sup>a</sup>, Roua Benrhouma<sup>a</sup>, Guillaume Munier-Gondiant<sup>b</sup>, Thomas David<sup>b</sup>, Maxime Duchateau<sup>a</sup>, Alban Gossard<sup>a,*</sup>, Agnès Grandjean<sup>c</sup>

## ARTICLE INFO

### Keywords:

- Direct lithium extraction
- Layered double hydroxide
- Geopolymer
- Adsorbent
- Fixed-bed process

## ABSTRACT

This study presents a method to shape Li/Al layered double hydroxides (Li/Al LDHs) adsorbent in a mesoporous potassium-based geopolymer binder, for the selective extraction of lithium in a fixed-bed process. After synthesis, the Li/Al LDHs powder is well dispersed into the binder, favorable for lithium adsorption kinetics. Batch and column extraction experiments in a brine with high magnesium content demonstrate effective lithium extraction with high selectivity. The geopolymer matrix traps $Mg^{2+}$ via cation exchange with $K^{+}$ improving lithium purity in the eluate. Overall, this composite is a promising material for scalable and selective direct lithium extraction from saline effluents.

## 1. Introduction

Given its extensive use in the context of the energy transition, global demand for lithium is steadily increasing. Among the various lithium deposits, highly saline sources—such as salars and geothermal brines—offer a promising alternative [1]. Accordingly, extraction processes on solid supports are currently under investigation, but require the development of specific materials [2]. Li/Al layered double hydroxides (LDHs) have attracted significant attention due to their remarkable selectivity for lithium and durability [3–5]. However, since this adsorbent is generally produced as a powder, a shaping step is essential to enable its use in columns, preventing clogging and ensuring proper flow through the system.

Geopolymer are amorphous materials consisting in a 3D arrangement of $SiO_4$ and $[AlO_4]^{-}$ tetrahedral synthesized from dissolved aluminosilicate precursors, following successive reactions comparable to a sol-gel reaction [6]. If well formulated, they present a mechanically robust structure as well as a significant mesoporous network. These properties make them efficient as a binder for powder to be used in fixed-bed processes [7]. This article presents a shaping methodology of Li/Al LDHs using geopolymer as a binder, and demonstrates its efficiency for lithium extraction both in static and dynamic processes.

## 2. Experimental

The Li/Al LDHs (BH1) was synthesized via a hydrothermal route according to [8]. The shaping was performed via a dispersion/grinding route using a potassium-based geopolymer (GP) as binder to obtain a composite sample GPBH1. BH1 powder is dispersed during the geopolymer sol-gel synthesis. For obtaining this material, KOH pellets were dissolved in a silicate solution (Bétol 5020 T, Wöllner GmbH) and ultrapure water. Metakaolin and BH1 was then added under stirring to ensure homogeneous dispersion. The reaction mixture was then placed for 2 weeks at 100% relative humidity and room temperature. Finally, the resulting sample (GPBH1) was crushed and sieved ranging from 300 to 1000 µm. The BH1 content was calculated to obtain 20 wt% in the final composite because higher amounts lead to crumbled materials. The geopolymer formulation (Table S1) was selected due to its large porous network. The different materials were analyzed by X-ray tomography, Scanning Electron Microscopy (SEM), $N_2$ adsorption-desorption, X-ray diffraction and Energy Dispersive X-ray Spectroscopy (EDS). More details are given in the Supplementary Materials.

Lithium sorption performances in batch and dynamic process were evaluated in a synthetic brine containing $0.06 \text{ mol.L}^{-1}$ of LiCl and $1.7 \text{ mol.L}^{-1}$ of $MgCl_2$. Kinetics were performed in batch mode at 80 °C with solid to liquid ratio of 100 $\text{g.L}^{-1}$. The suspensions were stirred during

<footnote><sup>a</sup> Univ. Montpellier, CEA, DES, ISEC, DMRC, Marcoule, France</footnote>

<footnote><sup>b</sup> Univ. Grenoble Alpes, CEA, DES, LITEN, DTNM, Grenoble, France</footnote>

<footnote><sup>c</sup> Univ. Montpellier, CEA, DES, ISEC, DPME, Marcoule, France</footnote>

<footnote>* Corresponding author.
E-mail address: alban.gossard@cea.fr (A. Gossard).</footnote>
different times, and filtered before solution analysis by Inductively
Coupled Plasma - Atomic Emission Spectrometry (ICP-AES).

Dynamic extraction and elution of Li⁺ were performed at 80 °C with 25 g of GPBH1 packed in a bed volume of 44 cm³. First, the column was conditioned using a 1.7 mol.L⁻¹ MgCl₂ solution. Then, the brine was pumped through the column from top at a flow rate of 2.25 mL.min⁻¹ for lithium extraction. Finally, deionized water was flowed through the column for a washing and desorption process. Samples were collected from the outlet flow at different time intervals before analysis. The sorption capacity and the separation factor were then calculated using Eq. (S1), (S2) and (S4).

**3. Results and discussion**

GPBH1 exhibits mechanical robustness and uniform texture (Fig. S1). BH1 presents a Li/Al LDHs hexagonal phase, with a low proportion of gibbsite (Fig. 1d). GP displays a broad hump at around 10–30°, typical of an amorphous aluminosilicate network, along with distinct peaks corresponding to residual quartz, anatase and illite coming from the metakaolin precursor. GPBH1 pattern shows identical reflections to BH1 and GP, highlighting the preservation of the BH crystalline structure. GPBH1 2D representation using X-ray tomography is represented in Fig. 1a. Li/Al LDHs phases were segmented from GP with Illastik software. Li/Al LDHs phases are homogeneously dispersed all over the volume, without agglomerates in specific regions, as

demonstrated using a Voronoï diagram (Fig. S4–6). SEM image of GPBH1 displayed in Fig. 1b shows the Li/Al LDHs particles embedded within the geopolymer, exhibiting a layered morphology and particles dimensions comparable to BH1 (Fig. S2).

As shown in Fig. 1c, BH1 are non-mesoporous particles. GPBH1 and GP exhibit a type IV isotherm, which is characteristic of mesoporous materials [9]. Li/Al LDHs embedding within geopolymer decreases the specific surface area and the total pore volume. Furthermore, GPBH1 pore size distribution shifts toward larger diameters, with an average pore size of about 13 nm compared to 8 nm for GP (Fig. S3). Nevertheless, GPBH1 granules remain mesoporous which is beneficial for a fixed-bed extraction process [2]. Overall, the physicochemical features of GPBH1 (mesoporosity, mechanically robustness, preservation of crystallinity) are suitable for the lithium extraction in batch and column process.

GP, GPBH1 and BH1 lithium extraction kinetics are represented
Fig. 2a. The kinetic of BH1 is extracted from our previous work [8]. GP
doesn't extract lithium. GPBH1 reaches thermodynamic equilibrium
within 24 h, significantly faster than BH1, which required approxi-
mately one week. Indeed, in saline effluent, BH1 particles may tend to
agglomerate [10], leading to a reduced mass transfer and a slower
adsorption kinetic compared to the well-dispersed adsorbent embedded
within the geopolymer. Under these experimental conditions, GPBH1
exhibits a Li⁺ sorption capacity of 0.18 mmol.g⁻¹, corresponding to
approximately 20% of the extraction capacity of BH1 [8], in accordance

<figure><img src="image_3.png" /><figcaption>**Fig. 1.** (a) and (b) X-ray tomography segmented slice (Li/Al LDHs in white) and SEM image of GPBH1; (c) and (d) N₂ adsorption-desorption isotherms and X-ray diffractograms of BH1, GP and GPBH1.</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>Fig. 2. (a) Li⁺ adsorption kinetics of BH1 (from [8]), GP, and GPBH1 and (b) Breakthrough curve of GPBH1 granules.</figcaption></figure>

with the 20 wt% of BH1 incorporated in the GP matrix, meaning that the mesoporous geopolymer allows the well accessibility of the adsorbent and does not interfere with the extraction process.

The Li⁺ adsorption breakthrough curve given Fig. 2b was plotted as [Li]t/[Li]₀ as a function of the number of bed volume (BV). The bed volume corresponds to the volume occupied by the material in the column, as defined by Eq. (S3). The first part shows the decrease of [Li]t/[Li]₀ between 0 and 0.8 BV, resulting from residual lithium coming from the elution of GPBH1 by the solution (1.7 mol.L⁻¹ MgCl₂, Li-free) used for column conditioning. Then, [Li]t/[Li]₀ increases up to 1 reached at 9.3 BV corresponding to the lithium adsorption phase until the bed reaches saturation. The total amount of extracted lithium was estimated to 31 mg, corresponding to a capacity of 0.17 mmol.g⁻¹. This capacity is equivalent to those obtained in kinetic experiment, which validates the appropriate condition of the dynamic tests and the accessibility of the BH1 sorption sites.

The elution phase was performed using ultrapure water. Lithium and magnesium concentrations are shown in Fig. 3a as a function of the BV of water passed through the column. The first eluted fractions, up to 0.5 BV, correspond to the rinsing of the solution remaining in the bed porosity. Thus, magnesium concentration gradually decreases, while lithium concentration remains very close to those of the initial solution composition. Then, a sharp drop in magnesium concentration and a slight increase in lithium concentration are observed, leading to lithium concentrations higher than those of magnesium in the eluate (Fig. 3b).

For BV between 0.5 and 1.3, the average [Mg²⁺] and [Li⁺] were 35.5 mmol.L⁻¹ and 168 mmol.L⁻¹, respectively, giving a Li/Mg separation factor (SF, Eq. (S4)) of 680 [11]. GPBH1 thus demonstrates a high selectivity for lithium in a fixed-bed process.

The magnesium still present during the elution may originate from the geopolymer, which is able to trap Mg²⁺ [12], and subsequently releasing a part back in solution upon contact with water. EDS elemental mapping have been realized before and after the extraction process to confirm this hypothesis (Fig. 4b and c).

Potassium, initially localized in the geopolymer, was largely replaced by magnesium following extraction. During the adsorption column tests, the geopolymer captured Mg²⁺ through a cation exchange mechanism with two K⁺. This result indicates that the geopolymer retains the major part of Mg²⁺ trap during adsorption process and thus enhances the eluate lithium purity and SF.

It is noteworthy the lithium recovery at 1.3 BV was determined to be 8.5 mmol, exceeding the extracted amount of 4.4 mmol. To investigate this discrepancy, the grains were characterized after extraction. X-ray diffraction analysis were performed on materials collected at different column heights (every 4 cm) (Figure 3Figure 4a). From 0 (top) to approximately 16 cm of the column, the X-ray diffractograms reveal a gibbsite phase only. Then, the Li/Al LDHs structure is partially retained. This results suggest that elution induced excessive lithium desorption, collapsing the Li/Al LDH structure [13], and explain the excessive lithium recovery. This desorption step will be then crucial to be better

<figure><img src="image_5.png" /><figcaption>Fig. 3. Evolution of (a) [Li⁺] and [Mg²⁺] and (b) the molar ratios during the elution phase.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Fig. 4. GPBH1 characterization before and after continuous column test: (a) X-ray diffractograms, Q = Quartz; (b, c) SEM images and EDS mapping.</figcaption></figure>

controlled in case of recycling materials and performing successive cycle of adsorption/elution. Indeed, after elution, GPH1 globally maintains a satisfying mesoporous structure, making this material promising for successive uses (Fig. S8).

## 4. Conclusion

Incorporation of 20 wt% of Li/Al LDHs in a geopolymer results in a homogeneous, mechanically stable, and mesoporous composite, able to extract lithium in a fixed-bed process. The mesoporous geopolymer facilitates rapid lithium adsorption kinetics in batch experiments, while maintaining its sorption capacity. Column tests confirmed effective lithium extraction, with a Li/Mg separation factor of 680, demonstrating excellent selectivity for lithium. The geopolymer phase plays a key role in trapping Mg²⁺ via cation exchange with K⁺, minimizing the presence of magnesium in the eluate and enhancing lithium purity. The LiCl-selective structure is preserved along the column, although excessive elution can induce LiCl desorption and structural collapse. These results highlight the potential of geopolymer-supported Li/Al LDHs for scalable, high-purity lithium recovery from geothermal brines.

### CRediT authorship contribution statement

**Maël Ferrand:** Writing – original draft, Methodology, Investigation, Formal analysis, Data curation. **Yves Barré:** Writing – review & editing, Validation, Methodology, Formal analysis. **Roua Benrhouma:** Formal analysis, Data curation. **Guillaume Munier-Gondiant:** Writing – original draft, Formal analysis, Data curation. **Thomas David:** Formal analysis, Data curation. **Maxime Duchateau:** Writing – original draft, Validation, Methodology, Formal analysis. **Alban Gossard:** Writing – review & editing, Validation, Supervision, Methodology, Conceptualization. **Agnès Grandjean:** Writing – review & editing, Supervision, Funding acquisition, Conceptualization.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgment

The authors warmly thanks Lithium de France for their financial supports. We would like to express our gratitude to Benoît Meilleray and Lise Barnouin for their technical support throughout this work.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2026.140148.

### Data availability

Data will be made available on request.

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