Preparation and adsorption performance of multi-morphology H1.6Mn1.6O4 for lithium extraction

Xiulei Li,Baifu Tao,Qingyuan Jia,Ruili Guo

Chemistry and Chemical Engineering,Key Laboratory for Green Process of Chemical Engineering of Xinjiang Bingtuan,Shihezi University,Shihezi 832003,China

Keywords: Lithium-ion sieve Morphologies Lithium extraction Brine Adsorbent

ABSTRACT In this paper,a lithium-ion sieve(LIS)with different morphologies,such as rod-like(LIS-R),spherical(LIS-S),flower-like(LIS-F),and three-dimensional macroporous-mesoporous(LIS-3D),was prepared by hydrothermal synthesis,solid reaction,and hard-template synthesis.The results showed that the LIS with different morphologies presented great differences in specific surface area,pore volume,adsorption selectivity,and structure stability.LIS-3D with highest specific surface area and pore volume displayed the maximum adsorption capacity and adsorption rate,but the stability of LIS-3D was poor because of the manganese dissolution.By comparison,LIS-S has the best structural stability while maintaining a satisfactory adsorption capacity(35.02 mg·g?1)and adsorption rate.The LIS-S remained about 90%of the original adsorption capacity after five cycles of adsorption–desorption process.In addition,in the simulated brine system (the magnesium to lithium ratio of 400),the LIS-S exhibited the highest selectivity()of 425.14.In sum,the LIS-S with good morphology is a potential adsorbent for lithium extraction from brine.

1.Introduction

As a significant alkali metal and a strategic resource for the 21st century,lithium and its compounds have been widely used in nuclear energy,rechargeable batteries,medical drugs,lubricant greases,ceramic glasses,and so on [1–3].With the increase in the market demand for lithium and rapid exhaustion of its minerals,lithium extraction from the lithium-water resources has become increasingly important.Thus,it is essential to develop rapid and low-cost methods for separation of lithium from liquid lithium resources including brine and seawater.

For separation of Li+,a number of methods have been explored in recent years for the extraction of Li+from seawater,such as electrodialysis,co-precipitation,solvent extraction,membrane separation,and adsorption.Among these methods[4–8],the adsorption method is considered as one of the most promising lithium extraction methods.Currently,the developed adsorbents include lithium-ion sieves(LIS),ion-exchange resins and layered hydroxide.Manganese series spinel ion sieves and titanium series ion sieves,such as λ-MnO2[9],MnO2·0.3H2O [10],MnO2·0.5H2O [11],H2TiO3[12],and H4Ti5O12[13],are widely used in lithium-ion adsorption because of their special memory screening for Li+.There are many studies about the synthesis methods,adsorption capacity,and adsorption–desorption mechanism of LIS.For example,Yu et al.[14,15]found the adsorption capacity of LIS was affected by the content of spinel,surface area,and the valency of Mn.Recently,Chen et al.[16]suggested that the adsorbent with a smaller crystal size displays the higher absorption capacity and adsorption rate,because smaller size with larger specific surface area can consequently facilitate Li motion more easily.In addition,Cui et al.[17]reported that the adsorption equilibrium constant K?and the adsorption kinetic rate constant k increase with the decreasing particle size of adsorbent;meanwhile,the thermodynamic parameters,such as,all decrease.Yu et al.[18,19]prepared 1D MnO2nanorod ion-sieves,the results indicated that there are remarkable improvements of the ion-sieve selectivity by the well-maintained nanorod structure.The relatively high selectivity for Li+was attributed to the ion-sieve effect of the spinel lattice with a 3D (1×3) tunnel suitable in size for fixing lithium ions in cubic phase MnO2nanocrystal.Cao et al.[20]prepared flower-like α-Fe2O3and used it to remove As5+and Cr4+from the water; the flower-like structure was beneficial as it increased the adsorption capacity with the maximum adsorption capacity for As5+(51 mg·g?1)and Cr4+(30 mg·g?1).Among the above studies,it is obvious that the adsorbent morphology is an important factor that affects adsorption performance.Therefore,it is necessary to further improve the comprehensive performance by controlling the morphology of LIS.

In this study,Li1.6Mn1.6O4(LMO)with the highest theoretical Li+adsorption capacity and low manganese dissolution loss was selected.Li1.6Mn1.6O4with different morphologies,such as rod-like LMO,spherical LMO,flower-like LMO,and 3D microporous-mesoporous LMO,were synthesized by controlling manganese source,lithium source,and synthesis method.The crystallization phase,chemical phase,and morphology characteristic of LMO with different morphologies were investigated.In addition,the effect of LIS morphology on its adsorption capacity,adsorption selectivity,adsorption rate and cyclic adsorption performance was investigated.

2.Experimental

2.1.Materials

Potassium permanganate (KMnO4,≥99.5% pure),lithium nitrate(LiNO3,≥95%),and hydrochloric acid(HCl,36%–38%)were purchased from the Chengdu Kelong Chemical Reagent Factory.Lithium hydroxide monohydrate(LiOH·H2O,≥98%)was purchased from Aladdin.Manganese sulfate monohydrate(MnSO4·H2O,≥99%),manganese nitrate(Mn(NO3)2,50%,mass fraction,AR)was purchased from Macklin.Lithium chloride monohydrate(LiCl·H2O,≥99.5%)was purchased from Tianjin Shengao Chemical Reagent Co.,Ltd.Ammonium hydroxide(NH3·H2O,25%–28%)and manganese acetate (C4H6MnO4·4H2O,≥99.0%) were purchased from Tianjin Beilian Reagent Co.,Ltd.Citric acid(C6H8O7·H2O,≥99.5%)was purchased from Tianjin Fuchen Chemical Reagents Factory.

2.2.Preparation of the different morphologies of lithium-ion sieves

Generally,the procedures for the synthesis of LIS consisted of two successive steps.First,the lithium manganese oxide precursors were prepared by different methods and raw materials.Then,the precursors were transformed into LIS by acid treatment.The specific experimental steps are as follows.

The rod-like LMO(LMO-R)was prepared by hydrothermal reaction,and the molar ratio of Li to Mn was 4:1,in which the lithium source was LiOH·H2O,and the manganese source was 1D nanorodshaped γ-MnOOH (synthesized according to the literature [11]).First,8.0 g γ-MnOOH was put into a 160 ml 2 mol·L?1LiOH·H2O solution,and the solution was stirred at room temperature for 2 h to form a uniform suspension.Then,the suspension was transferred into a Teflon-lined autoclave and reacted for 12 h at 150 °C.After that,the precipitate obtained from the reactor was filtered and washed with deionized water and dried at 60 °C for 12 h.Subsequently,LMO-R was obtained by calcining at a rate of 5 °C min?1from room temperature to 350°C in air for 12 h.

The spherical LMO (LMO-S) was prepared by the solid-reaction method[21,22],and the molar ratio of Li to Mn was 1:1,in which the lithium source was LiNO3,and the manganese source was MnCO3[23].First,LiNO3and MnCO3with the molar ratio of 1:1 reacted at 270°C for 3 h.Then,the obtained reactants were calcined at the same rate of 5°C·min?1from 270°C to 350°C in air for 12 h.

The flower-like LMO (LMO-F) was prepared by a hydrothermal reaction,and the molar ratio of Li to Mn was 10:1,in which the lithium source was MnO,and the manganese source was LiOH·H2O.In the first step,36 mg KMnO4and 4.0 mg NaOH were added to 120 ml deionized water and continuously stirred for 30 min;the obtained mixture was transferred into a Teflon-lined stainless steel autoclave,and a hydrothermal reaction was carried out for 24 h at 140°C.The obtained precipitate MnO was filtered,washed with deionized water,and dried at 60°C for 12 h.In the second step,MnO was put into LiOH·H2O solution with a Li:Mn mole ratio of 10:1 to form a uniform suspension.Then,the suspension was transferred into a Teflon-lined autoclave and a reactor for 12 h at 210°C;the obtained reactants were calcined under the same conditions as those for LIS-R.

The 3D macroporous-mesoporous LMO(LMO-3D)was prepared based on a hard template.First,the polymethyl methacrylate(PMMA) hard template was prepared according to the literature[24].The molar ratio of reacting materials with C4H6MnO4·4H2O:LiNO3:C4H6MnO4·4H2O=1:1:1 was put into deionized water with magnetic stirring at room temperature to form a transparent solution; then,5 ml NH3·H2O was added to the above solution and stirred for 10 min,resulting in a yellow solution.Afterward,the solution was immersed in a PMMA microarray.After total immersion,vacuum filtration caused the lithium manganese precursor solution to fill the cracks of the crystals.Then,the mixtures were solidified in a 70°C oven for 24 h,and the sample was calcined in air to remove the PMMA template at 300 °C for 3 h at a rate of 1 °C·min?1.Next,LMO-3D was obtained by calcining at 600°C for 6 h at a rate of 2°C·min?1.

LMO with different morphologies(LMO-R,LMO-S,LMO-F,and LMO-3D)was placed in 0.5 mol·L?1HCl solution with a solid–liquid ratio of 1:500(g:mL)and treated for 12 h.Then,the treated LMO was washed with deionized water and dried at 60°C for 12 h to obtain LIS with different morphologies,which were named LIS-R,LIS-S,LIS-F,and LIS-3D.

2.3.Characterization

The crystalline structure of LMO and LIS was characterized by X-ray diffraction(XRD,D8 ADVANCE,Cu-Kα,40 kV,40 mA)with the range of 10°–90°at a scan speed of 2(°)·min?1.The surface images of LIS were analyzed by scanning electron microscopy (SEM,JSM-6490LV).The specific surface area and pore size of LMO and LIS were analyzed using a BET analyzer.The valence of Mn of LIS was analyzed by X-ray photoelectron spectroscopy.

2.4.Li+adsorption performance of lithium-ion sieves

LIS(0.1 g)was dispersed in a LiCl-NH4Cl-NH3·H2O buffer solution(100 ml,pH=10.1,Li+concentration=50 mg·L?1) at 30 °C and stirred(100 r·min?1)for 12 h.The adsorption capacity of Li+(Q)was calculated by the following equation:

where Q is the adsorption capacity,mg·g?1;C0is the initial concentration of lithium in the solution,mg·L?1;C is the lithium concentration after the adsorption,mg·L?1;V is the volume of the solution,L;and m is the mass of the LIS,g.

2.5.Adsorption kinetics studies

LIS(0.1 g)was dispersed in a LiCl-NH4Cl-NH3·H2O buffer solution(100 ml,pH=10.1,Li+concentration=50 mg·L?1)at 30°C for 12 h.The experimental data were fitted with a pseudo-first-order kinetics model(Eq.(2))and a pseudo-second-order kinetics model(Eq.(3)):

where Qeis the equilibrium adsorption capacity of LIS,mg·g?1;Qtis the adsorption capacity of LIS at a certain time,mg·g?1;k1is the rate constant for the pseudo-first-order model,h?1;and k2is the rate constant for the pseudo-second-order model,g·mg?1·h?1.

2.6.Adsorption isotherm studies

LIS(0.1 g)was dispersed in a LiCl-NH4Cl-NH3·H2O buffer solution(100 mL,pH=10.1)at 30°C for 12 h.The initial concentration was adjusted from 25 mg·L?1to 200 mg·L?1.The results were fitted by the Langmuir model(Eq.(4))and the Freundlich model(Eq.(5)):

where Qeis the equilibrium adsorption capacity of LIS,mg·g?1;Ceis the equilibrium concentration,mg·L?1;Qmis the maximum adsorption capacity of LIS,mg·g?1;KLis the Langmuir isotherm constant,L·mg?1;and n and KFare Freundlich constants,indicating the relative adsorption capacity and adsorption intensity,respectively.

2.7.Adsorption selectivity studies

LIS(0.1 g)was dispersed in simulation brine(100 ml,pH=8)at 30°C for 12 h.The distribution concentration,Kd;separation coefficient,αLiMe;and concentration factor,CFwere calculated using the following equations:

where Qeis the equilibrium adsorption capacity of LIS,mg·g?1;Ceis the equilibrium concentration,mg·L?1;Cois the initial concentration of metal ions in simulation brine,mg·L?1;V is the volume of the solution,ml;and m is the LIS mass,g.

3.Results and Discussion

3.1.Characterization of LIS structure and morphology

Fig.1 shows the SEM images of LIS with different morphologies.LIS-R(Fig.1a)had a straight rod-like shape with diameters around 250 nm and lengths of 3–6 μm.LIS-S(Fig.1b)had a uniform granulation with a diameter of approximately 500 nm,and its samples had good dispersion.LIS-F (Fig.1c) had flower-like particles composed of hundreds of small petals.The diameter of flower-like particles was in the range of 200 nm to ~300 nm.LIS-3D (Fig.1d)presented an interconnected porous structure with a diameter of 200 nm and a wall thickness of 50 nm.

Fig.2 shows XRD diffraction patterns of LMO(LMO-R,LMO-S,LMOF,and LMO-3D)and LIS(LIS-R,LIS-S,LIS-F,and LIS-3D)with different morphologies.All LMO and LIS presented the characteristic peaks at 18.8°,36.5°,44.5°,58.9°,and 64.7°,which corresponded to (111),(311),(400),(511),and (440) crystalline planes of spinel(Li1.6Mn1.6O4).In addition,the results indicated that the spinel crystal structure of LIS was well maintained after acid treatment.Compared with the XRD peaks of LMO,LIS characteristic peaks shifted by 2°to a higher angle.The reason was that the lattice constant decreased slightly because of the replacement of Li+with H+[25].

Fig.1.The SEM images of LIS with different morphologies:(a)LIS-R,(b)LIS-S,(c)LIS-F,and(d)LIS-3D.

Fig.2.The XRD patterns of different morphologies of lithium-ion-sieve precursors and lithium-ion sieves.

The specific surface area and pore size distribution of LMO with different morphologies and the corresponding LIS were analyzed by N2adsorption–desorption(Fig.3),and the structure parameter is shown in Table 1.All samples showed irreversible type IV adsorption isotherm with a type H-3 hysteresis loop as defined by IUPAC.As shown in Table 1,the surface roughness(Ds)and specific surface area of LIS increased after Li+was replaced by H+from the corresponding LMO.The pore size of all LIS samples was bigger than that of LMO,which indicated that the microstructure became loose after Li+displacement.The probable pore sizes of LIS-R,LIS-S,and LIS-3D were almost the same(~20 nm).However,the pore size of LIS-F was 11.1 nm,because the flower-shaped structure was formed by the accumulation of hundreds of petal-like sheets.

It can be confirmed from Table 1 that the pore volume and specific surface area of LIS were affected by the morphology.The pore volume order was LIS-3D(0.5987 cm3·g?1)>LIS-S(0.1578 cm3·g?1)>LIS-R(0.0844 cm3·g?1)>LIS-F(0.0617 cm3·g?1),meaning that LIS-3D and LIS-S can provide a larger pore passage for Li+-H+exchange.The specific surface area order was LIS-3D (104.82 m2·g?1) > LIS-S(34.61 m2·g?1) > LIS-F (33.21 m2·g?1) > LIS-R (17.29 m2·g?1).LIS-3D had a high specific surface area and exposed more adsorption sites,which was favorable for contact with Li+in the solution during the adsorption process.

Table 1The structural properties of LMO and LIS with different morphologies

3.2.The valence of Mn

The valency of Mn in different morphologies of LIS was carried out by chemical titration analysis and XPS characterization.Fig.4 presents XPS full spectra of LIS;in the figure,all LIS samples were composed of Mn,O,and Li elements,which indicated that LIS with different morphologies has the same chemical composition.

As shown in Fig.5,all samples presented two main contributions from spectra of Mn 2p,where the binding energy of the Mn 2p3/2peak is at~642 eV,and the Mn 2p1/2peak is at~652 eV.The binding energies of electrons of Mn4+2p3/2were about 642.9 eV and 643.76 eV,and the Mn3+2p3/2peak was recorded at 641.9 eV[16].The results showed that the valency of Mn of LIS-R,LIS-S,and LIS-F were almost close to Mn4+.However,the binding energy of Mn3+at 641.3 eV indicated that there was small content of Mn3+in LIS with different morphologies.

In addition,the average valency of Mn obtained by XPS and the chemical titration method (evaluated by the standard oxalic acid method) are listed in Table 2.It can be seen that the Mn valency of LIS-R,LIS-S,and LIS-F obtained by the two methods was consistent and very close to+4.However,the Mn valency of LIS-3D was lower than the theoretical valency (+4).The reason was that the hard-templated method may lead to low purity of the product during high-temperature calcination to remove the template.In addition,the manganese content of LIS-R,LIS-S,and LIS-F was 54.26%,53.16%,and 53.58%,respectively,which was very close to theoretical manganese content (53.93%).By contrast,the manganese content of LIS-3D was only 51.3%,indicating that the product was of low purity.

Table 2The valency of Mn and elemental content analysis for lithium-ion sieve precursors

Fig.3.(a)Nitrogen adsorption–desorption isotherms of LMO and LIS with different morphologies(b)Pore size distribution of LMO and LIS with different morphologies by the BJH model.

Fig.4.XPS spectra of LIS survey;(a)LIS-R,(b)LIS-S,(c)LIS-F,and(d)LIS-3D.

Fig.5.Mn2p core level;(a)LIS-R,(b)LIS-S,(c)LIS-F,and(d)LIS-3D.

3.3.The adsorption performance of lithium-ion sieves

The Li+adsorption capacities of all LIS samples were investigated on the condition of 50 mg·L?1Li+solutions at 30°C and pH=10.1.In Fig.6,all LIS samples reached the adsorption equilibrium after 12 h adsorption.The order of lithium equilibrium adsorption capacity was LIS-3D(48.76 mg·g?1)>LIS-S(35.02 mg·g?1)>LIS-F(33.21 mg·g?1)>LIS-R(30.60 mg·g?1).In addition,the adsorption rates of LIS-3D and LIS-S were significantly higher than those of LIS-R and LIS-F during the initial 2 h adsorption process.The first reason was that the high specific surface area had high contact area and adsorption site exposure for Li+when the adsorbents were dispersed into the solution.Hence,LIS-3D(104.82 m2·g?1)had the highest lithium equilibrium adsorption capacity than those of LIS-R,LIS-S,and LIS-F.The second reason was that the high pore volume and proper pore size provide a convenientand rapid diffusion path for Li+.LIS-S and LIS-F had similar specific surface areas,but LIS-S with larger pore volume and appropriate pore size (20.9 nm) had a higher adsorption rate during the initial 2 h adsorption process.So,the LIS with high specific surface area,large pore volume,and appropriate pore size presented satisfactory adsorption capacity and adsorption rate for Li+in solution.

Fig.6.The adsorption curves of different lithium-ion sieves.

The Li+adsorption data of LIS with different morphologies were fitted to the pseudo-first-order and pseudo-second-order models.As seen in Fig.7 and Table 3,all samples followed the pseudosecond-order model(R2> 0.99).The results indicated that the adsorption process of LIS with different morphologies is primarily chemical adsorption[26].In addition,the adsorption rate constant of LIS-3D (0.0153 g·mg?1·h?1) was the lowest among all adsorbents,suggesting a relatively high adsorption rate for Li+.Both LIS-3D and LIS-S showed excellent adsorption capacity and adsorption rate before 2 h,but the adsorption capacity of LIS-S was lower than that of LIS-3D after 2 h,because the three-dimensional network structure of LIS-3D promoted the transfer of Li+inside the adsorbent.

As shown in Fig.8 and Table 4,the Langmuir model and the Freundlich model were adopted to fit the experimental data; theresult showed that the Langmuir isotherm (R2> 0.99) provided a better fit to the experimental data than did the Freundlich isotherm.The estimated Qmvalue was in good agreement with the experimental maximum Li+adsorption capacity (LIS-R: 30.60 mg·g?1,LIS-S: 35.02 mg·g?1,LIS-F: 33.21 mg·g?1,and LIS-3D:48.76 mg·g?1).The Langmuir adsorption isotherm is based on the assumption that adsorption takes place at specific homogeneous sites on the adsorbent.This result consist with the Li+-H+exchange mechanism [27].

Table 3Parameters of pseudo-first-order and pseudo-second-order equations for LIS-R,LIS-S,LISF,and LIS-3D

A good adsorbent should be able to be regenerated and its adsorption sites renewed for many cycles [12].LIS with different morphologies recyclability was investigated by adsorption and desorption experiment,and the results are shown in Fig.9.It can be observed that the lithium desorption amount of all LIS was slightly lower than the lithium adsorption capacity.In addition,the adsorption capacity of all adsorbents decreased,and was 25 mg·g?1—37 mg·g?1after five cycles,among which the adsorption capacity of LIS-S remained at 90%of the initial adsorption capacity and that of LIS-3D only remained at 74%of the initial adsorption capacity.This can be attributed to the loss of manganese in the LIS framework.The dissolved manganese ions in the adsorption–desorption process of LIS-S were monitored for 10 cycles.The manganese mass loss in the first three cycles was 1.614%,1.096% and 0.582% respectively.After 4 cycles,manganese mass loss was maintained at 0.3%-0.5%,showing good adsorbent stability for the testing conditions.However,the average valency of Mn of LIS-3D deviated from 4.0,was 3.82,which led to the increase of manganese dissolution (3.5%),the collapse of the structure,and the decrease of LIS reusability [16,28,29].Therefore,it is necessary to change manganese valence close to 4.0 during synthesis of ion-sieve spinel-type adsorbents.

Fig.7.Adsorption kinetic models.(a)Pseudo-first-order.(b)Pseudo-second-order.

Fig.8.Adsorption isotherms:(a)Langmuir and(b)Freundlich.

3.4.The adsorption selectivity of lithium-ion sieves

The selectivity experiments were carried out in simulated brine containing different cations (Li+,Na+,K+,Ca2+,and Mg2+).In Tables 5–8,the Li+adsorption capacities of LIS-R,LIS-S,LIS-F,and LIS-3D in simulated brine were lower than those of the pure Li+solution because of the existence of competitive adsorption of ions.LIS is known for its high selectivity toward Li+based on the ionic size exclusion mechanism[30].In addition,the different cation distribution coefficient (Kd) of Li+?Ca2+> Mg2+> Na+> K+and the different hydrated ionic radii of K+(0.138 nm) > Na+(0.102 nm) > Ca2+(0.100 nm) > Mg2+(0.072 nm) > Li+(0.059 nm),which lead to the high selectivity of LISs for Li+.However,the ratio of magnesium to lithium in brine is higher than 400,and the hydrate ionic radii of Mg2+was close to that of Li+,which had a great influence on the adsorption of Li+.The separation factor(αLiMg)of LIS-R,LIS-S,LIS-F,and LIS-3D was 426.76,425.14,386.01,and 395.42,respectively.LIS-S presented the highest separation factor due to its suitable specific surface area and pore volume.LIS-3D with the maximum specific surface area(104.82 m2·g?1)had adsorption capacities for all ions,which led to the reduction of selectivity.

3.5.Comparison of Li+ uptakes of Li1.6Mn1.6O4 prepared by different methods

A comparison was made of lithium recovery from seawater/salt lake/brine with H1.6Mn1.6O4adsorbents(Table 9).Considering that lithium uptake by the adsorbent is strongly influenced by solution pH and lithium concentration in the solution.References[31]and[32]had similar investigation conditions with this study,and the results showed that H1.6Mn1.6O4prepared by R.Chitrakar had a maximum uptake of lithiumof 37 mg·g?1and 1.5%-2.5%of first cycle manganese mass loss[31,32].In this work,LIS-3D showed a maximum uptake of lithium of 42.15 mg·g?1with a maximum first cycle manganese mass loss of 3.5%.While LIS-R,LIS-S and LIS-F showed the similar adsorption capacity with other H1.6Mn1.6O4adsorbents.It can be concluded that the effect of LIS morphology on adsorption capacity was not significant,but more uniform sorption sites are contained in the LIS with appropriate pore size(20 nm)and high pore volume[19,29,35],which lead to the increase of the adsorption capacity and adsorption rate.In addition,the valence of manganese must be close to 4.0 when controlling the morphology and structure of LISs.

Table 4Derived Langmuir and Freundlich adsorption isotherm constants

Table 5The Li+selective adsorption of the LIS-R ion sieve

Table 6The Li+selective adsorption of the LIS-S ion sieve

Table 7The Li+selective adsorption of the LIS-F ion sieve

Table 8The Li+selective adsorption of the LIS-3D ion sieve

Table 9Comparison of Li+uptakes of Li1.6Mn1.6O4 prepared by different methods

4.Conclusions

The H1.6Mn1.6O4with different morphologies,such as rod-like,spherical,flower-like,and 3D microporous–mesoporous,was prepared by hydrothermal synthesis,solid-phase reaction,and hardtemplate synthesis methods.Characterization and adsorption results revealed that LIS-3D has relatively high adsorption capacity and adsorption rate,but its adsorption stability was poor because of the presence of manganese dissolution.LIS-S with the uniform particle size,uniform dispersion properties and the valence of manganese as+4 exhibited excellent adsorption performance for Li+in brine.The adsorption capacity of LIS-S remained at approximately 90%after five cycles of adsorption–desorption process.In addition,LIS-S exhibited the highest selectivity () of 425.14 and Kd=206.84 ml·g?1in simulated brine with magnesium-to-lithium ratio of 400.Therefore,the development of LIS having a specific surface area and a high pore structure is necessary for improving the adsorption performance of the LIS.

Declaration of Competing Interest

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work,there is no professional or other personal interest of any nature or kind in any product,service and/or company that could be construed as influencing the position presented in,or the review of,the manuscript entitled.

Acknowledgements

The authors gratefully acknowledge the National Natural Science Foundation of China,(Grant No.21868031).

Fig.9.The recyclability of(a)LIS-R,(b)LIS-S,(c)LIS-F,and(d)LIS-3D.