**7.1 Lithium recovery by LMO type lithium-ion sieves**

## *7.1.1 Study of ternary phase diagram of Li-Mn-O*

With research [44], several LMO-type LISs have been well developed by many scientists [48]. As a rule, their precursors demonstrate a spinel structure. Because of multiple valence states of manganese, several lithium manganese oxides with different crystal structures can be formed. At 25°C, the phase diagram Li-Mn-O shows the isothermal cross-section **Figure 4** [139–143].

In the blue area in **Figure 4a**, the stoichiometric spinel phase defect is defined by the triangle Mn3O4·Li4Mn5O12·λ-MnO2. Using the general formula LixMn3−xO4 (0 ≤ x ≤ 1.33), one can imagine the stoichiometric spinel phases lying on the bond between Mn3O4 and Li4Mn5O12. According to the general formula Mn3−xO4 (0 ≤ x ≤ 1) defective spinels of manganese oxides located between Mn3O4 and λ-MnO2 are presented. In accordance with the general formula Li2O·yMnO2 (y > 2.5), the defect of lithium-manganese-oxide spinel is expressed and the communication line lies between Li4Mn5O12 and λ-MnO2. At this point, in LiMn2O4·Li2Mn4O9·Li4Mn5O12 the blue triangle in **Figure 4b** is the active area for preparing the precursors of LMO-type LISs. Therefore, it is possible to obtain high Li-Mn precursors such as Li5Mn4O9 and Li7Mn5O12 in principle, implying that high Li<sup>+</sup> capacity LISs may be obtained in the future.

Currently, only a few LMO-type LIS precursors with high Li<sup>+</sup> adsorption capacities such as λ-MnO2, MnO2·0.31H2O and MnO2·0.5H2O, which are derived from LiMn2O4, Li4Mn5O12 and Li1.6Mn1.6O4, respectively, were prepared. As shown in **Figure 5**, a phase diagram consisting of additional proton-type manganese oxides depending on the valence state of manganese, molar Li/Mn and H/Mn ratios constructed by Chitrakar et al. [47].

As shown in the figure, LIS precursors of the LMO-type can be classified into two types of reactions and are represented in two perpendicular planes: the vertical plane represents the redox reaction region, and the horizontal plane represents the ion exchange region. **Table 3** mainly summarizes their main properties for the absorption of lithium from aqueous solutions.

*(a) An isothermal cross section of the Li-Mn-O phase diagram at 25°C and (b) an expanded region of the Li-Mn-O phase diagram.*

**Figure 5.** *Phase diagram of LMO and their delithiated products [47]. Reproduced from Ref. [47].*

#### *7.1.2 The spinel structure of the precursors of LMO*

Inevitably, the chemical properties depend on the chemical structures to be determined, so the extraction of lithium by LMO precursors is explained by their peculiar chemical structure. Actually, all synthesized precursors of LMOs have spinel structures [144–152]. Among these, the LiMn2O4 structure is the most representative one, as shown in **Figure 6**.

Spinel LiMn2O4 has a cubic crystal structure that belongs to the spatial group *Fd3m*. The structure shows that the tetrahedron's 8a sites occupy lithium ions. At a molar ratio of 1:1, Mn3+ and Mn4+ ions are randomly distributed over 16d sites of octahedra, and oxygen anions occupy 32e sites of the face-centered cubes. Accordingly, the formula (Li)8a[Mn(III)Mn(IV)]16dO4 can be represented by spinels LiMn2O4, which can be described by the general spinel formula (AB2O4). From other side, the LiMn2O4 unit cell can be viewed as a complex cubic structure: oxygen atoms are 32 and 16 manganese atoms occupy half of the octahedral pore (16d), while the other half of the sections (16c) are free. Here are 8 of the lithium atoms occupy 1/8 of tetrahedral interstices plot (8a). Li+ can intercalate/deintercalate in three-dimensional networks of free octahedral and octahedral gaps along the

**205**

**Materials** **Precursors**

LiMn

O2 4 1D nano

1D nano λ-MnO2

LiMn

Li Mn 4 O5 12 Li Mn 4 O5 12

Li1.6Mn1.6

Li1.6Mn1.6

Li1.5Mn

Li1.51Mn1.63

Li1.57Mn1.65

**Table 3.** *Classification for some LMO type LISs.* 

O4

H1.39Li0.01Mn1.65

O4

ca. 37 mg g−1 (pH = 12)

O4

H1.36Li0.07Mn1.65

O4

34.07 mg g−1 (pH = 12.01)

—

—

O2 4

H1.5Mn

O2 4

ca. 15.3 mg g−1 (pH = 8.1)

O4

MnO2-0.5H

O2

40.9 mg g−1 (seawater)

O4

MnO2-0.5H

O2

42.1 mg g−1 (initial

Li+ concentration

10 mmol L−1, pH = 10.1)

H Mn 4 O5 12

49.6 mg g−1 (0.1 mol L−1

LiCl + LiOH solution)

MnO2–0.4H

O2

39.6 mg g−1 (10 mmol L−1

The Li+ adsorption capacity of the

The adsorption capacities of other ions were almost zero

[54]

except for Mg2+; the ratio of Mg/Li was reduced to less than 1

from 746

Kd: Li+ Kd: Li+

≫ Mg2+ > Na2+ > K+ > Ca+

[45]

≫ Mg2+ > Ca2+ > K+ > Na+

[142]

spherical ion sieve after 55 cycle's

adsorption-desorption was 0.4 mmol g−1

—

The Li+ adsorption capacity reduces

from 4.08 mmol g−1 to 3.62 mmol g−1

after six times

The Li+ adsorption capacity is

Kd: Li+

≫ Cg2+ > K+ > Mg2+ > Na+

[48]

35.4 mg g−1, and Li+ desorption rate

still reaches 96% at the second cycle

operation

—

400 times higher conc. of Li+ could be achieved while most of

[135]

Na+ remains in artificial seawater that contains 10 ppm of Li+

and 10,000 ppm of Na+ by chromatographic separation

—

—

[140]

[143]

LiCl solution, pH = 10.1)

O2 4

λ-MnO2

16.9 mg g−1 (LiCl

—

—

Equilibrium distribution (Kd): Li+

Kd: Li+

≫ Ca2+ > Mg2+ > Na+ > K+

≫ Ca2+ > Mg2+ > K+ > Na+

[140]

solution, pH = 9.19)

ca. 20 mg g−1

(10 mmol L−1 LiCl

solution, pH = 10.1)

**Ion sieves**

**Li+ uptake capacity**

**Regenerations**

**Li+**

**selectivity**

**Ref.**

*Lithium Recovery from Brines Including Seawater, Salt Lake Brine, Underground Water…*

*DOI: http://dx.doi.org/10.5772/intechopen.90371*

[141]


*Lithium Recovery from Brines Including Seawater, Salt Lake Brine, Underground Water… DOI: http://dx.doi.org/10.5772/intechopen.90371*

> **Table 3.**

*Classification for some LMO type LISs.* 

*Thermodynamics and Energy Engineering*

*7.1.2 The spinel structure of the precursors of LMO*

*Phase diagram of LMO and their delithiated products [47]. Reproduced from Ref. [47].*

occupy 1/8 of tetrahedral interstices plot (8a). Li+

representative one, as shown in **Figure 6**.

Inevitably, the chemical properties depend on the chemical structures to be determined, so the extraction of lithium by LMO precursors is explained by their peculiar chemical structure. Actually, all synthesized precursors of LMOs have spinel structures [144–152]. Among these, the LiMn2O4 structure is the most

*(a) An isothermal cross section of the Li-Mn-O phase diagram at 25°C and (b) an expanded region of the* 

Spinel LiMn2O4 has a cubic crystal structure that belongs to the spatial group *Fd3m*. The structure shows that the tetrahedron's 8a sites occupy lithium ions. At a molar ratio of 1:1, Mn3+ and Mn4+ ions are randomly distributed over 16d sites of octahedra, and oxygen anions occupy 32e sites of the face-centered cubes.

Accordingly, the formula (Li)8a[Mn(III)Mn(IV)]16dO4 can be represented by spinels LiMn2O4, which can be described by the general spinel formula (AB2O4). From other side, the LiMn2O4 unit cell can be viewed as a complex cubic structure: oxygen atoms are 32 and 16 manganese atoms occupy half of the octahedral pore (16d), while the other half of the sections (16c) are free. Here are 8 of the lithium atoms

in three-dimensional networks of free octahedral and octahedral gaps along the

can intercalate/deintercalate

**204**

**Figure 4.**

**Figure 5.**

*Li-Mn-O phase diagram.*

8a-16c-8a-16c channel, what is the structural basis of Li<sup>+</sup> intercalation/deintercalation in LiMn2O4 spinel [145].

The 1:2 ratio shows a spinel LiMn2O4 of the two metal cations Li and Mn; although the stoichiometric proportion may be somewhat weakened in some circumstances. For example, in **Figure 7** it is shown that manganese ions in 16d sites can be replaced by lithium ions without changing the entire crystal framework.

Since more lithium ions can be extracted or inserted, the corresponding LIS of the substituted precursor Li1.33Mn1.67O4 (or Li4Mn5O12) is theoretically a higher lithium capacity than λ-MnO2. Ammundsen et al. [148] the results of neutron diffraction studies of the lithium reinsertion process are given only for tetrahedral sites and not for octahedral sites, which indicates that the lithium extraction/insertion reaction can be expressed by the equation below:

$$\text{(Li)} \left[ \text{Li}\_{0:3} \text{Mn}\_{1:67} \right] \text{O}\_4 \text{+ H}^+ \leftrightarrow \text{(H)} \left[ \text{Li}\_{0:3} \text{Mn}\_{1:67} \right] \text{O}\_4 \text{+ Li}^+ \tag{1}$$

Another typical lithium-rich precursor to LMO is Li1.6Mn1.6O4 (or Li2Mn2O5), which are relevant LIS is MnO2·0.5H2O. Among all available manganese, LISs MnO2·0.5H2O has the highest theoretical lithium capacity (*ca*. 72.3 mg g<sup>−</sup><sup>1</sup> ). With this composition, the ratio of cations and anions (4:5) differs from that of typical spinel compounds (3:4), meaning that additional lithium ions are likely to be found in interstitial regions of the spinel structure with a single-digit arrangement [143]. Chitrakar et al. [47] proposed three hypothetical models through a preliminary Rietveld analysis, since there is still no published structural model for Li1.6Mn1.6O4: (1) (Li)8a[Li0.2]16c[Li0.4- Mn1.6]16dO4 site at the of 16c model with excess Li; (2) a (Li)8a[Li0.5Mn1.5]16dO3.75 model with oxygen deficiency and (3) a hexagonal lattice model with cation deficiency (Li0.8□0.2)3b(Mn0.8□0.2)3aO2 (the "□" are the free areas in the spinels). The modulation results showed that all models traced the X-ray peaks of the heat-treated sample, but the third model (a hexagonal lattice with a deficit of cations) accurately traced the relative intensity of the X-ray peaks. By Ariza et al. [147] showed that X-ray absorption spectroscopy of Li1.6Mn1.6O4 samples does not result in the complete displacement of the manganese absorption edge after lithium extraction/reintroduction. In addition, the structural arrangement and oxidation state of manganese remained unchanged during lithium extraction and re-administration, confirming the ion exchange mechanism for lithium extraction and re-administration. Thus, there is still some disagreement on the crystal structure of Li1.6Mn1.6O4. Possible future research by scientists should focus on this issue to link the development of LIS to the excellent absorption properties of lithium.

#### **Figure 6.**

*Promising type (a) cubic core in spinel unit cell LiMn2O4, (b) LiMn2O4 of extended three-dimensional frame structure and (c) λ-MnO2 with voids after Li ions removal. Green, pink and red represent Li, Mn and O atoms, respectively [146].*

**207**

*Lithium Recovery from Brines Including Seawater, Salt Lake Brine, Underground Water…*

Because of the specific configuration of the 3d electron orbit, Mn3+ can cause the Jahn-teller effect, which can cause severe distortions in the octahedral structure of MnO6. This distortion will be accompanied by a decrease in LMO stability and a decrease in the efficiency of the intercalation/deintercalation process

*(a) Cubic spinel lithium manganese oxide quadrants were comparison and (b) recorded under the 8.6 GPa. C, cubic spinel phase (spatial group Fd3m); W, tungsten strip model of polyhedral structure and structure* 

*refinement by Rietveld X-ray diffraction powder sample for Li1.33Mn1.67O4 (or Li4Mn5O12).*

 [153–157]. Much more seriously in industrial operations dissolving large amounts of manganese in water can lead to water contamination. Consequently, some alloying modifications have been proposed to replace Mn3+ with other metal

In the field of lithium-ion batteries, a wide variety of cation substitution (including Co2+, Ni2+, Cr3+, Mg2+, Al3+, Fe3+ and ions of rare earth element) has been applied to inhibit capacity fading and improve electrochemical performance [158–183]. Analogously, modifications of LIS by doping with metal ions to improve the absorption properties of lithium in aqueous solutions are proposed. The effect of LimMgxMn(III)yMn(IV)zO4 (0 ≤ x ≤ 0.5) on the dissolution of manganese within acid treatment, the results showed that the adsorption capacity of lithium and the chemical stability of protonated samples increased with the mg/MN ratio studied by Chitrakar et al. [181]. Mild chemical method of Mg2+ doped lithiummanganese spinel synthesized by Tian et al. [36]. During the periodic experiment,

of the initial concentration. In addition, kinetic experiments have shown that

by Feng et al. [182, 183]. Discovered that the extraction and insertion of Li<sup>+</sup>

topotaxically through ion exchange mechanisms. In addition, with LiAlMnO4

also follow the ion exchange mechanisms tested by Liu et al. [184]. LiMxMn2-xO4 spinel series (M = Ni, Al, Ti; 0 ≤ x ≤ 1) and comparison of their lithium reduction properties in aqueous solutions prepared by Ma et al. [185]. Studies have shown that LiAl0.5Mn1.5O4 spinels exhibit relatively high Li extraction coefficient and relatively low Mn and Al extraction coefficients when treated with acid, and

process in both compound LiMg0.5Mn1.5O4 spinel and LiZn0.5Mn1.5O4 spinel studied

the adsorption process followed by a pseudo-second-order model. Li<sup>+</sup>

showed a high pH and a dependence profile

extraction/insertion reactions in the aqueous phase,

extraction

are

*DOI: http://dx.doi.org/10.5772/intechopen.90371*

*7.1.3 The doping modification*

ions, which is more efficient.

it was found that the sorption of Li<sup>+</sup>

and LiFeMnO4 spinel Li<sup>+</sup>

of Li<sup>+</sup>

**Figure 7.**

*Lithium Recovery from Brines Including Seawater, Salt Lake Brine, Underground Water… DOI: http://dx.doi.org/10.5772/intechopen.90371*

#### **Figure 7.**

*Thermodynamics and Energy Engineering*

tion in LiMn2O4 spinel [145].

8a-16c-8a-16c channel, what is the structural basis of Li<sup>+</sup>

reaction can be expressed by the equation below:

has the highest theoretical lithium capacity (*ca*. 72.3 mg g<sup>−</sup><sup>1</sup>

The 1:2 ratio shows a spinel LiMn2O4 of the two metal cations Li and Mn; although the stoichiometric proportion may be somewhat weakened in some circumstances. For example, in **Figure 7** it is shown that manganese ions in 16d sites can be replaced by lithium ions without changing the entire crystal framework. Since more lithium ions can be extracted or inserted, the corresponding LIS of the substituted precursor Li1.33Mn1.67O4 (or Li4Mn5O12) is theoretically a higher lithium capacity than λ-MnO2. Ammundsen et al. [148] the results of neutron diffraction studies of the lithium reinsertion process are given only for tetrahedral sites and not for octahedral sites, which indicates that the lithium extraction/insertion

(Li)[Li0:33 Mn1:67] O4 + H<sup>+</sup> ↔ (H)[Li0:33 Mn1:67] O4 + Li<sup>+</sup> (1)

the ratio of cations and anions (4:5) differs from that of typical spinel compounds (3:4), meaning that additional lithium ions are likely to be found in interstitial regions of the spinel structure with a single-digit arrangement [143]. Chitrakar et al. [47] proposed three hypothetical models through a preliminary Rietveld analysis, since there is still no published structural model for Li1.6Mn1.6O4: (1) (Li)8a[Li0.2]16c[Li0.4- Mn1.6]16dO4 site at the of 16c model with excess Li; (2) a (Li)8a[Li0.5Mn1.5]16dO3.75 model with oxygen deficiency and (3) a hexagonal lattice model with cation deficiency (Li0.8□0.2)3b(Mn0.8□0.2)3aO2 (the "□" are the free areas in the spinels). The modulation results showed that all models traced the X-ray peaks of the heat-treated sample, but the third model (a hexagonal lattice with a deficit of cations) accurately traced the relative intensity of the X-ray peaks. By Ariza et al. [147] showed that X-ray absorption spectroscopy of Li1.6Mn1.6O4 samples does not result in the complete displacement of the manganese absorption edge after lithium extraction/reintroduction. In addition, the structural arrangement and oxidation state of manganese remained unchanged during lithium extraction and re-administration, confirming the ion exchange mechanism for lithium extraction and re-administration. Thus, there is still some disagreement on the crystal structure of Li1.6Mn1.6O4. Possible future research by scientists should focus on this issue to link the development of LIS to the excellent absorption

*Promising type (a) cubic core in spinel unit cell LiMn2O4, (b) LiMn2O4 of extended three-dimensional frame structure and (c) λ-MnO2 with voids after Li ions removal. Green, pink and red represent Li, Mn and O* 

Another typical lithium-rich precursor to LMO is Li1.6Mn1.6O4 (or Li2Mn2O5), which are relevant LIS is MnO2·0.5H2O. Among all available manganese, LISs MnO2·0.5H2O

intercalation/deintercala-

). With this composition,

**206**

**Figure 6.**

*atoms, respectively [146].*

properties of lithium.

*(a) Cubic spinel lithium manganese oxide quadrants were comparison and (b) recorded under the 8.6 GPa. C, cubic spinel phase (spatial group Fd3m); W, tungsten strip model of polyhedral structure and structure refinement by Rietveld X-ray diffraction powder sample for Li1.33Mn1.67O4 (or Li4Mn5O12).*

#### *7.1.3 The doping modification*

Because of the specific configuration of the 3d electron orbit, Mn3+ can cause the Jahn-teller effect, which can cause severe distortions in the octahedral structure of MnO6. This distortion will be accompanied by a decrease in LMO stability and a decrease in the efficiency of the intercalation/deintercalation process of Li<sup>+</sup> [153–157]. Much more seriously in industrial operations dissolving large amounts of manganese in water can lead to water contamination. Consequently, some alloying modifications have been proposed to replace Mn3+ with other metal ions, which is more efficient.

In the field of lithium-ion batteries, a wide variety of cation substitution (including Co2+, Ni2+, Cr3+, Mg2+, Al3+, Fe3+ and ions of rare earth element) has been applied to inhibit capacity fading and improve electrochemical performance [158–183]. Analogously, modifications of LIS by doping with metal ions to improve the absorption properties of lithium in aqueous solutions are proposed. The effect of LimMgxMn(III)yMn(IV)zO4 (0 ≤ x ≤ 0.5) on the dissolution of manganese within acid treatment, the results showed that the adsorption capacity of lithium and the chemical stability of protonated samples increased with the mg/MN ratio studied by Chitrakar et al. [181]. Mild chemical method of Mg2+ doped lithiummanganese spinel synthesized by Tian et al. [36]. During the periodic experiment, it was found that the sorption of Li<sup>+</sup> showed a high pH and a dependence profile of the initial concentration. In addition, kinetic experiments have shown that the adsorption process followed by a pseudo-second-order model. Li<sup>+</sup> extraction process in both compound LiMg0.5Mn1.5O4 spinel and LiZn0.5Mn1.5O4 spinel studied by Feng et al. [182, 183]. Discovered that the extraction and insertion of Li<sup>+</sup> are topotaxically through ion exchange mechanisms. In addition, with LiAlMnO4 and LiFeMnO4 spinel Li<sup>+</sup> extraction/insertion reactions in the aqueous phase, also follow the ion exchange mechanisms tested by Liu et al. [184]. LiMxMn2-xO4 spinel series (M = Ni, Al, Ti; 0 ≤ x ≤ 1) and comparison of their lithium reduction properties in aqueous solutions prepared by Ma et al. [185]. Studies have shown that LiAl0.5Mn1.5O4 spinels exhibit relatively high Li extraction coefficient and relatively low Mn and Al extraction coefficients when treated with acid, and

LiNi0.5Mn1.5O4 and LiTi0.5Mn1.5O4 spinels do not exhibit satisfactory Li<sup>+</sup> extraction and adsorption properties because of substantial cell contraction or expansion. By Chitrakar et al. Sb-doped LMO spinel was synthesized for the first time [186]. Samples received Li1.16Sb(V)0.29Mn(III)0.77Mn(IV)0.77O4 was a well-crystallized spinel-type structure, in the following order of affinity K < Na ≪ Li and exchange capacity reaching 5.6 mmol g<sup>−</sup><sup>1</sup> for Li<sup>+</sup> . In a subsequent study, a series of Li-Sb-Mn composite oxides with various Sb/Mn molar ratios by solid-state reactions obtained by Ma et al. [187]. Studies have shown that the molar ratio Sb/Mn of composite oxides Li-Sb-Mn is a decisive factor in the identification of their structure and extraction-adsorption properties Li<sup>+</sup> . Hereinafter, the acid-treated composite spinel oxide Li-Sb-Mn with a molar ratio Sb/Mn of 0.05 showed in lithium solution a high adsorption capacity of Li<sup>+</sup> 33.23 mg g<sup>−</sup><sup>1</sup> . By Chitrakar et al. the ion-exchange property of iron-doped lithium manganese oxides Li1.33FexMn1.67-xO4 (x = 0.15, 0.30 and 0.40) in Bolivian brine was studied [38]. Studies have shown that the adsorbent with a Fe/Mn ratio of 0.1, obtained by calcining the precursor at 450°C, has the highest extractability of lithium with HCl solution. Finally, from crude brine at a final pH of 2.0, the adsorbent showed lithium absorption of 18.1 mg g<sup>−</sup><sup>1</sup> with an increase in absorption to 28 mg g<sup>−</sup><sup>1</sup> at a final pH of 7.2 after adding 1 mol L<sup>−</sup><sup>1</sup> NaOH l-1 solution to the crude brine.

Study of the description of the LMO-doped spinels, it is obvious that doping modifications can effectively improve the adsorption properties of lithium. Nevertheless, little attention has been paid to refining LIS compared with the great progress of ion-doped manganese oxide spinels in the field of electrochemistry. At present, just several studies of LISs doped with a single metal have been studied. Lithium adsorption property of multicharged ions doped LISs, including several cation-doped, several anion-doped and cation-anion-doped LISs in aqueous solution, still an untouched area for research. Early research of numerous ion-doped LiMn2O4 showed high capacity retention, high discharge capacity, and lithium ion batteries good cycling performance. This is due to the fact that multiple ions doped LiMn2O4, have increased structural stability [188–197]. Besides, as cathodes, co-doping has a synergistic effect on increasing the cyclic durability of materials, which can for single ion-doped LiMn2O4 discourage all factors responsible for capacity loss [198–201]. Similarly, it has been convincingly shown that multiple ion doping has a beneficial effect on improving the regeneration efficiency and absorption capacity of lithium LISs in aqueous solutions. Prospective studies should focus on the synergistic effects of different ions on the reductive properties of lithium.
