SURFACE MODIFICATION COATING FOR LITHIUM EXTRACTION FROM FIELD COLLECTED LITHIUM BEARING WATERS

Description

RELATED APPLICATIONS

This application claims priority benefit of U.S. Provisional Application Ser. No. 63/709,596 filed Oct. 21, 2024, the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to lithium extraction from lithium bearing water, and more particularly to a lithium manganese oxide adsorbent coated with a ceramic, such as zirconium dioxide, that is able to recover high amounts of lithium from the lithium bearing water and has the option to be recyclable.

BACKGROUND

The lithium (Li) demand has been growing over the past decade and it is anticipated to continue to increase¹. Li is one of the fundamental elements used to manufacture batteries and other high voltage energy storage devices like auxiliary power backup systems. The high voltage, energy density, and light weight of Li batteries over the conventional alkaline battery has helped Li to dominate the battery industry for the past couple of decades². The strain in the Li supply chain since 2016 has been because of the increase in the demand for electric vehicles (EV's)¹. The strain is also caused by policies made to replace internal combustion engines within the next 20 years³. Li sourced from the conventional Li deposits are not enough to meet the increasing demand. The increase in exploration efforts in USA, Canada, and China has led to finding alternate sources of Li. According to the US geological survey, the Li bearing water (LBW) are a good resource, especially the resources available in arid regions like Clayton Valley, Andes mountains of south America, and Tibetan plateau^4-7. Among the brines, the oilfield brines are an untapped Li resource. The US geological survey and the Alberta geological survey results show that the Li concentrations range from sub 100 to 700 ppm^7,8. These deposits occur at greater than one kilometer in depth. The oil and gas production in such areas produce large amounts of wastewater known as “Flowback and produced water” (FPW) which gets filled back into the reservoir. Once the reservoir is depleted of oil this type of “oil wells” are left with high concentrations of Li with some dissolved organics.

The conventional lithium extraction technology uses solar evaporation technique to concentrate lithium in a multiple pond setup⁹. The evaporation process is slow and time consuming. The conventional technology cannot be used for oilfield LBW because of the low Li concentration and high Mg/Li ratio⁹. The newer ion-exchange type adsorption technology has shown promising results in the past few years¹⁰. The ion-exchange technology popularly known as “direct lithium extraction” (DLE) uses an adsorbent to extract the monovalent Li from the brine with less impurities thus reducing the time required for lithium recovery. These adsorption technologies are mostly based on three types of adsorbents; 1) Titanium based; 2) Manganese based; and 3) Aluminum based. Among these sorbents manganese (Mn)-based sorbents have the highest Li extraction capacity and have been extensively studied for the past few decades^10-12. The theoretical uptake capacity of Li_1.6Mn_1.6O₄ (LMO) is 72.9 mg/g. The experimental results show that the adsorbent reaches saturation at 40 mg/g at room temperature after 3 days in low concentration of Li in seawater¹³, whereas in flowback and produced water, the adsorbent extracted 80% of Li with a capacity of 18 mg/g within 30 mins at well head water temperature of 70° C.¹¹ Such high Li uptakes are very promising for lithium extraction at a commercial scale.

To extract Li from the LBW, first the pristine (Pr) LMO adsorbent is protonated (P) to remove Li by topotactic exchange of Li to proton using an acid solution (equation 1). Then the delithiated LMO is introduced into LBW for selective extraction (E) at optimal condition for relithiation by ion-exchange mechanism (equation 3). This extraction (E) and the protonation (P) steps are repeated to recover Li from LBW. One of the factors affecting the scale up of Mn-based LMO adsorbent is the adsorbent loss because of the dissolution of Mn in acid during the protonation cycle (equation 2). The adsorbent loss is majorly because of the Mn dissolution thus called Mn-loss (%). In a simulated LiCl solution this loss is 0.5%¹⁴. This is because of the formation of Mn³⁺ ions as a result of the Jahn-Teller effect¹⁵. This is at least 10 times higher than that of a battery of similar spinel chemistry¹⁶. Such dissolution is accelerated by the presence of reducing agents in the LBW like dissolved organics and H₂S (equation 4). This type of Mn loss is called reductive dissolution and is usually 5 to 10 times higher the Mn-loss of simulated LiCl solution^11,17.

( Li 1.6 ) [ Mn x III ⁢ Mn 1.6 - x IV ] ⁢ O 4 + n ⁢ H + → ( H ) [ Mn 1.6 IV ] ⁢ O 4 + 1.6 Li + + x ⁢ Mn II + H 2 ⁢ O equation ⁢ 1 2 ⁢ Mn III → Mn II + Mn IV equation ⁢ 2 ( H ) [ Mn 1.6 IV ] ⁢ O 4 + n ⁢ Li + → ( Li n ⁢ H 1.6 - n ) [ Mn x III ⁢ Mn 1.6 - x IV ] ⁢ O 4 equation ⁢ 3 ( H ) [ Mn 1.6 IV ] ⁢ O 4 + n ⁢ Li + + organics → ( Li n ⁢ H 1.6 - n ) [ Mn x III ⁢ Mn y III ⁢ Mn 1.6 - x - y IV ] ⁢ O 4 equation ⁢ 4

Thus, there exists a need for a coating on the LMO surface to reduce manganese loss and increase sorbent recyclability.

SUMMARY OF THE INVENTION

The present invention provides a method for extracting lithium from a lithium bearing water. The method includes preparing a lithium manganese oxide (LMO) adsorbent having a ceramic coating on a surface thereof; protonating the LMO adsorbent to remove lithium therefrom by topotactic exchange of Li to proton using an acid solution to form a delithiated LMO adsorbent; introducing the delithiated LMO adsorbent into the lithium bearing water for selective extraction of lithium from the lithium bearing water; and recovering lithium from the lithium bearing water. According to embodiments the LMO adsorbent is Li_1.6Mn_1.6O₄. According to embodiments, the ceramic coating is zirconium dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further detailed with respect to the following drawings that are intended to show certain aspects of the present of invention, but should not be construed as limit on the practice of the invention, wherein:

FIG. 1 shows a representation of the hypothesis behind the zirconium coating on LMO adsorbent;

FIGS. 2A-2D show SEM images of bare LMO (a) and 7.5 nm LMO (b) with inset images indicating the particle size distribution. HR-TEM images of bare LMO (c) and 7.5 nm LMO (d) with inset images indicating the lattice spacing;

FIG. 3 shows XANES spectra of pristine (Pr) bare LMO and 7.5 nm LMO with other spinel and Mn model compounds;

FIG. 4 shows a correlation between coating thickness to Li uptake and Mn-loss of E1 in field-collected LBW;

FIGS. 5A-5C show the relationship between particle size on Li uptake and Mn-loss for bare LMO (a), 1.5 nm LMO (b), and 7.5 nm LMO (c) with their respective linear fits indicating linear correlation;

FIGS. 6A-6D show the selectivity of bare LMO (a), 1.5 nm LMO (b), and 7.5 nm LMO after cycles 1, 2, 3, and 4. Li uptake and Mn-loss of the LMO at different coating thickness (d);

FIG. 7 shows the LBW TDS and Li concentration dependency of Li uptake capacity and selectivity;

FIG. 8 shows O, Mn(III), Mn(IV) TEM-EELS mapping of individual nanoparticles at different stages of DLE for bare LMO and 7.5 nm coated LMO with their respective line spectra;

FIG. 9 shows Li and Mn adsorption/dissolution kinetics of the bare LMO and 7.5 nm coated LMO at different stages P1, E1, and P2 of Li extraction and recovery in the DLE process. All the models are fitted to >0.99 accuracy on the R2-error;

FIGS. 10A and 10B show XANES comparison of the Mn K-edge data for bare LMO, 1.5 nm LMO, and 7.5 nm LMO during extraction cycles (a) and protonation cycles (b);

FIG. 11 shows oxidation state of bare LMO, 1.5 nm LMO, and 7.5 nm LMO at different stages of DLE. Inset image is the Mn calibration curve;

FIGS. 12A-12D show EXAFS plot of bare LMO comparing Pr and E3 Li loaded samples (a), 7.5 nm LMO comparing Pr and E3 Li loaded samples (b), bare LMO comparing P1 and P5 Li recovered samples (c), and 7.5 nm LMO comparing P1 and P5 Li recovered samples (d). The dotted lines are their respective EXAFS model fits;

FIG. 13 shows change in the average Mn—Mn distances during different DLE cycles for bare LMO, 1.5 nm LMO and 7.5 nm LMO;

FIG. 14 shows HR-TEM image showing the ZrO2 coating layer on LMO with an average coating thickness of 7.5 nm;

FIG. 15 shows pH controlled direct lithium extraction (DLE) from LBW using LMO powders;

FIG. 16 shows effect of coating thickness on Li uptake and Mn-loss for DLE in simulated LBW;

FIG. 17 shows the increasing trend of amount of Mg adsorbed by LMO with increase in the Mg concentration in the LBW;

FIG. 18 shows HR-TEM, EELS mapping, surface and line plots of Bare LMO at E1, 7.5 nm LMO at E1, and 7.5 nm LMO at E5;

FIG. 19 shows the first protonation Zr loss kinetics;

FIG. 20 shows the comparison of average oxidation state of all the processes of DLE for the bare LMO, 1.5 nm LMO, and 7.5 nm LMO; and

FIG. 21 shows EXAFS spectra and model fits of Pr, P1, E1, P2, E2, P3, E3, P4, and P5 for bare LMO, 1.5 nm LMO, and 7.5 nm LMO.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has utility as a ceramic zirconia ZrO₂ coating for a LMO, such as Li_1.6Mn_1.6O₄, surface to reduce manganese loss and increase sorbent recyclability. By coating ZrO₂ on the LMO surface using solvent evaporation-crystallization method to get a uniform coating layer, the coated sorbent improves manganese loss with no reduction in Li uptake. Furthermore, the recyclability of LMO is doubled in field-collected LBW with high redox conditions. The coating layer also improves the structural stability of the spinel thus doubling the recyclability.

According to some inventive embodiments, to reduce reductive dissolution (Mn-loss), the sorbent is coated with ceramic materials like Zirconium dioxide (zirconia). The coating layer acts as a barrier, the sorbent is protected from the effects of organics in the brine as shown in FIG. 1. The smaller Li ions can diffuse through the ZrO₂ layer whereas the larger organics cannot come in direct contact with the sorbent^18-20. The acid and temperature resistant zirconia layer also provides structural stability to the adsorbent and thus improving recyclability. Zhang et al., showed surface fluorination can improve the Li uptake by 6% and reduce the Mn-loss by 5-15% 17. Wang et al., showed that coating with ZrO₂ can reduce the Li uptake and reduce the Mn-loss in Salt Lake brine by 60%^19,20.

Certain embodiments of the present invention use a unique method for applying a coating layer of Zirconia (or other ceramic material) onto LMO as electrode or adsorbents for battery applications and Li extraction applications. This application method uniquely controls the coating thickness, which provides significant results, not previously possible.

Atomic layer deposition (like Zhao et al., 2013) by nature, can only be deposited to the surface of LMO which is exposed to the inert gas environment (very similar to Scanning Electron Microscopy sample preparation using gold/carbon/platinum coating). But it is hard to control which plane of LMO has been coated and which plane needs to be coated as these are nanoparticles. This approach is suitable for electrode applications where the LMO remains stationary. In such cases, the coating layer serves two primary purposes: it acts as a barrier between the solid electrode and the liquid electrolyte (such as LiPF6), and it enhances the rate of electron transfer. However, when the LMO is mobile, and it gets into contact with the water at all times, this application method is difficult. Such application needs uniform coating of all planes of LMO. Using higher coating thickness can affect the efficiency of the process so precise control of coating layer has higher significance (see the attached manuscript).

Solvent evaporation method (like Luo et al., 2022) is similar to the present method. The inventive method uses zirconium butoxide, the other method uses AlZr coupling agent (a resin). The method of application appears to be similar which is using a beaker to mix LMO and the coating solution together and evaporating the solvent. The difference is that our method is using the amount of zirconium butoxide to precisely control the coating thickness by adding the coating solution stepwise. Adding the coating solution together with the LMO particles did not give a uniform coating, and zirconium precipitated separately after evaporation of the solvent.

Solid state combustion (like Wang et al., 2022) does not produce a uniform coating layer (from their EDS map). Their study is to reduce the Mn-loss, which is similar to our study, but the difference in our study is to reduce the Mn-loss caused by organics in formation water. Formation water has more dissolved organics than Salt Lake brine. These dissolved organics are the primary reason for the failure of LMO adsorbents. Our study shows that if this method is applicable for formation water (which has low economic value than Salt Lake brine and high amount of pollutants like dissolved organics) then it can be applied to any brine.

The present invention will now be described with reference to the following specific inventive embodiments. As is apparent by these descriptions, this invention is embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. For example, features illustrated with respect to one embodiment can be incorporated into other embodiments, and features illustrated with respect to a particular embodiment may be deleted from the embodiment. In addition, numerous variations and additions to the embodiments suggested herein will be apparent to those skilled in the art in light of the instant disclosure, which do not depart from the instant invention. Hence, the following specification is intended to illustrate some particular embodiments of the invention, and not to exhaustively specify all permutations, combinations, and variations thereof.

It is to be understood that in instances where a range of values are provided that the range is intended to encompass not only the end point values of the range but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range of from 1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Unless indicated otherwise, explicitly or by context, the following terms are used herein as set forth below.

As used in the description of the invention and the appended claims, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Also as used herein, “and/or” refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative (“or”).

EXPERIMENTAL SECTION

Reagents

Lithium hydroxide (98%), manganese chloride tetrahydrate (MnCl2·4 H2O, >99%), manganese (II) oxide (MnO, >99%), manganese (II,III) oxide (Mn₃O₄, >99%), Lithium manganese oxide (LiMnO₂, >99%), Lithium manganese oxide (LiMn₂O₄, >99%), hydrogen peroxide (H2O2, 30% in water), sulfuric acid (H2SO4, 98%), sodium hydroxide (NaOH, >99%), lithium chloride (LiCl, >99%) and Zirconium butoxide solution (C16H36O4Zr, 80% in 1-Butanol) were purchased from Fischer Scientific, Canada. All the solutions are prepared using deionized water with a resistivity of 18.2 M (2 cm at 25° C.

Adsorbent Preparation

The lithium manganese oxide (LMO) precursor is prepared using a co-precipitation method described by Seip et al.¹¹ inspired by the method proposed by Tien et al.²¹. The co-precipitation method is improved in this study by making the synthesis of the nanoparticles more consistent by controlling the droplet size using a peristaltic pump. 3 M LiOH is added in dropwise at 10 mL/min to 0.375 M MnCl₂ solution at room temperature to produce a brown slurry. The LiOH and MnCl₂ is mixed in a Li:Mn ratio of 3:1 as optimized by Seip et al.¹¹. Hydrogen peroxide is added to the brown slurry at a rate of 5 mL/min to reduce the (MnO₂)⁻ to from the LMO precursor. The final mixture is stirred for 30 mins, dried in a convection oven at 90° C. for 16 h in a polypropylene dish. The dried sorbent precursor is ground using a mortar and pestle to a fine powder. 2 g of the sorbent is calcinated in a tube furnace at 450° C. for 4 h under atmospheric air. The calcinated sorbent is washed twice with 50 mL of deionized water. The sorbent is later sifted into five different size fractions from <75 to 1000 microns.

Zirconium Dioxide Coating

Zirconium dioxide is coated on the sorbent using solvent evaporation-crystallization method. 500 mg of the adsorbent is added to 5 mL of hexane at room temperature. Hexane is chosen as the coating medium as it readily dissolves zirconium butoxide without precipitation of Zirconia. The sorbent-hexane mixture is stirred at 400 RPM to suspend the sorbent in hexane to get a uniform coating. The suspension is heated to 60° C. in a water bath for uniform heating. Zirconium butoxide solution is added dropwise at the rate of 25 μL every 15 mins using a syringe. After complete addition of zirconium butoxide the mixture is heated until the hexane evaporates, and a dry coated sorbent is obtained. The coated sorbent is then calcinated in a tube furnace at 400° C. for 4 h under atmospheric air. The calcinated coated sorbent is washed twice in 50 mL DI water and dried in a convection oven at 90° C. for 16 h in a polypropylene dish.

Lithium Adsorption

Protonation (P): The dry resulting sorbent is protonated with 0.5 M H₂SO₄ at a sorbent concentration of 10 g L⁻¹ at room temperature for 12 h. An aliquot of the supernatant is collected to measure the first protonation Mn-loss. The sorbent is then washed twice using DI water. The sorbent is then air dried.

Extraction (E): The formation water is collected form Clearwater area, Alberta, Canada. The brine is treated to remove heavy hydrocarbons, H₂S, and other heavy materials. Table 1 shows the composition of the formation water. To study the Lithium adsorption in a controlled environment, a simulated LBW of comparable ionic concentration is used. The TDS is matched with that of the field brine and the composition is reported in table 1. The field-collected LBW is adjusted to pH 8 using 0.1 M NaOH solution. The simulated LBW is adjusted to pH 8 using 150 ppm NaHCO₃ (acts as a buffer). The protonated sorbent is added to the brine at a solid concentration of 2 g L⁻¹. The mixture is constantly mixed for 1 h at room temperature. The pH is adjusted to 8 with 0.01 M NaOH and 0.01 M HCl solution during reaction as shown in FIG. 15. All the parameters used during extraction are shown in Table 2. After sorption, the mixture is centrifuged at 4000 g for 4 min. The lithiated sorbent is washed twice with DI water.

TABLE 1
Major ion compositions of field-
collected LBW and simulated LBW.

	Major ions	LBW (ppm)	Simulated LBW (ppm)

	Li	65	100
	Na	54679	55000
	K	5498	1600
	Mg	2400	820
	Ca	18298	10000
	Sr	719	—
	Fe	0.5	—
	B	280	—
	pH	7	8.1
	TN	767	—
	TIC	52.18	500
	TOC	70	—
	TDS	221938	167000

TABLE 2
Li adsorption and protonation parameters; where RT: reaction temperature,
Rt: reaction time, s: speed of agitation, S: reactor size, I: propeller size,
Rs: extraction solid loading, Rl: volume of brine, Ri-pH: initial brine pH,
RpH: reaction pH, Rf-pH: final brine pH, B[Li+]: brine Li+
concentration, BTDS: brine TDS, BpH: brine pH, Ps: adsorbent particle size,
Pa: adsorbent age, T: adsorption temperature, Li/Mn: Lithium-Manganese
ratio of the adsorbent, Ct: calcination time, CT: calcination temperature,
ZMn: average Mn oxidation state, Ac: acid concentration, Pt: Protonation
time, Ps: protonation solid loading.

	Reaction vessel
	Extraction (E)
	Process parameters
	RT = 20° C.
	Rt = 1 h
	s = 300 rpm
	S = 5 cm × 7.2 cm
	I = 1.5 in. (low shear - high flow)
	bore size = 5/16 in.
	Rs = 2 g L−1
	Rl = 50 mL
	Ri-pH = 8
	RpH = 8(±0.05) (control)
	Rf-pH = 8(±0.05)
	Adsorption parameters
	B[Li+] = 65/100
	BTDS = 221938/167000
	BpH = 8
	Ps = <75 μm-1000 μm (control)
	Pa = 1st cycle
	T = 20° C.
	Chemical parameters
	Li/Mn = 1
	Ct = 4 h
	CT = 450° C.
	ZMn = 3.7-4
	Protonation (P)
	Ac = 0.5M
	Pt = 30 min
	Ps = 10 g L−1

Protonation (P): The adsorbent is dilithiated using 0.5 M H₂SO₄ at a solid concentration of 6 g L⁻¹ for 30 mins at room temperature. After desorption, the delithiated sorbent is washed twice with DI water. The protonation and extraction cycles are repeated to test the recyclability of the adsorbent.

The aliquots of the supernatant are collected after each process and analyzed using Agilent 8000 ICP-MS/MS to find the concentrations of major ions including Li, Na, K, Ca, Mg, Mn, Zr, Fe, and Sr.

X-Ray Absorption Spectroscopy

X-ray absorption spectroscopy (XAS) experiments are performed at the HXMA beam line at the Canadian Light source using synchrotron radiation with Si(111) crystal monochromator. The energy is calibrated using a standard Mn foil by assigning E0 to the first derivate of the absorption edge. The XANES spectra is collected from 200 eV before and 100 eV after the edge with a step size of 0.5 eV. The EXAFS spectra are collected up to 14 Å-1 in the k-space. The data is collected in both transmission and fluorescence modes (using Cr filter). Mn foil is placed in the third ionization chamber in order to correct for the instrumental drift. Each sample scans are triplicated. The samples are diluted in boron nitride, pelletized, and placed in a plastic sample holder with Kapton tape.

The data analysis of the XANES and EXAFS spectra of the Mn K-edge is performed using the Demeter software package and FEFF8. The XANES spectra is analysed using Linear combination fitting (LCF) of the experimental standards chosen based on the chemical speciation of Mn in the spinel. The LCF is fit by using the protonated version of Li_1.33Mn_1.67O₄ (H_1.33Mn_1.67O₄) and Mn₃O₄. The protonated species fit the H_1.33Mn_1.67O₄ model and the extracted species fit the H_1.33Mn_1.67O₄ and Mn₃O₄ model with a reduced chi squared error of 0.002%^22,23.

The EXAFS modelling of the species is fit using the FEFF8 calculation of the single and multiple scattering paths of the structure model compound Li_1.33Mn_1.67O₄²⁴. The paths are fit for the R-space range of 1.15 to 6 Å. The Fourier transformed K-space range of 2.8 to 10.2 Å⁻¹. The fit results are fit whilst monitoring the values of the ΔE, Debye-Waller factor σ² along with statistical fit results like R² and red χ² errors. The model is fit for the range of 1.15 to 6 Å in the R-space to account for the good fit of the first two shells of the LMO.

TEM-EELS

The transmission electron microscope energy loss spectroscopy (TEM-EELS) data is acquired using Thermo scientific talos 200× microscope equipped with an extreme field emission gun (X-FEG) source. The microscope is operated at 200 kV in STEM mode. The resolution is <0.16 nm. EELS data are acquired using a Gatan continuum S system equipped with a complementary metal oxide semiconductor (CMOS) detector. Data are acquired using a dispersion of 0.15 eV channel and a constant drift tube voltage is used for standards and test samples. Spectra processing and generation of maps are performed using GMS 3.4 software with plural scattering removed by deconvolution.

Brine Properties

Brine samples are diluted 50:1 (v/v) in DI water prior to both non-purgeable organic carbon (NPOC) and total inorganic carbon (TIC) analysis. A shimadzu TOC-L CPH model total organic carbon analyzer with an ASI-L Toc autosampler is used for both analyses. For NPOC measurement, samples are acidified using 1 M HCl before being sparged in order to strip the sample of purgeable organic and inorganic carbon.

Results and Discussion

Surface Morphology

The bulk Pr bare LMO contains aggregates of different sizes ranging from 75 μm to 2 mm. The scanning electron microscopy (SEM) image of LMO shows heterogeneous cubic nanoparticles ranging from 40 nm to 90 nm. The surface area of the protonated LMO is 144 m²·g⁻¹. The varying size of the dry LMO aggregates affects the quality of the coating layer and the Li uptake kinetics of the LMO. Hence particles of known sizes are coated using ZrO₂ using solvent evaporation-crystallization technique. The comparison of the 75 μm LMO particles shows that the surface of the bare LMO and the 7.5 nm coated LMO have very similar surface characteristics. The retention of the cubic form of the LMO is seen in FIGS. a-2d. The ZrO₂ acted as a binder during coating process reducing the gas adsorption surface area to 40 m²·g⁻¹, although no apparent morphological or phase change is noticed in the XANES spectra²⁵. The HR-TEM image shown in FIG. 14 shows that the coating layer has formed on top the LMO crystal with thickness ranging from 6 nm to 10 nm averaging at 7.5 nm. The coating thickness is thus 7.5 nm±33%. Henceforth, all the different coating amounts of Zirconium butoxide will be represented in nanometers. The d-spacing of the lattice fringes of the bare LMO is 0.47 nm which do not change after coating. The ZrO₂ region having a distinctive d-spacing of 0.28 nm shows a coating layer on top of the cubic LMO²⁰. Particle size analysis on the FE-SEM images in FIG. 2a&b shows that the average particle size has increased slightly from 73 nm to 78 nm. This is because of the presence of ZrO₂ coating layer on the surface of the coated LMO. FIG. 3 shows the XANES Mn K-edge spectra of Bare LMO and 7.5 nm coated LMO with spinel standards Li_1.33Mn_1.67O₄, LiMn₂O₄, and LiMnO₂ and other Mn standards like Mn₂O₃, MnO, and MnO₂. The bare and the coated LMO show similar structural characteristics and align perfectly with the spinel standards. XANES spectra for spinel type materials has five import features as indicated. Pre-edge peaks A caused by the 3d orbital transitions. B and C are on the rising edge associated with different Mn components in the spinel. The white line features D and E can vary based on the size of the unit cell²⁶. Thus, confirming that all the samples are of cubic spinel type of the Fd-3m spinel group with Li mostly in the 8a tetrahedral sites (some Li also occupy the octahedral 16d sites, forming structural Li which are not involved in the ion-exchange mechanism), Mn³⁺/Mn⁴⁺ in the 16d octahedral sites, and O in the 32e framework²⁷. The structural 16d Li prevents from complete protonation of the LMO in bare, coated, and spinel standards. The standards contain varying amounts of Li stoichiometry, but this doesn't affect the Mn K-edge spectra of the samples as the Mn—Li distances are greater than 6 Å, greater than the scope and the accuracy of the XANES analysis. Thus, confirming that the presence of ZrO₂ (1.5 nm to 30 nm coating) on the surface do not affect the spinel nature of the LMO and shows no signs of surface doping. The ZrO₂ coating layer do not affect the mean oxidation state of LMO indicting passive presence of the coating layer to the binding nature of the LMO, this is because of the low calcination temperature after the solvent evaporation-crystallization process as compared to the calcination temperature of bare LMO.

Bare LMO has excellent dispersibility in solution which makes the recoverability of the adsorbent after DLE difficult. The dispersibility of the aggregates in solution as separate nanoparticles is dependent on the shear force (rate of agitation) applied during the DLE process. Dispersing bare LMO in acetone and agitation at 1000 rpm do not disperse the particles, as 90% of the particles do not pass though 5 μm PTFE membrane. The coated LMO prevents the adsorbent from dispersing in solution, making the recoverability of the adsorbent easier. This also keeps a separation between the adsorbent and the solution, thus reducing the environmental pollution that is caused by using this type of adsorbent.

Effect of Coating Thickness on Li Adsorption

The lithium adsorption experiments in this study are studied under optimized conditions shown in FIG. 15 to reduce the variability caused by the reduction in pH during Li⁺ adsorption in both LBW and simulated LBW. The variability could also be caused by the mixture of particle sizes in a particular batch of LMO. The <75 μm LMO particles are used to study the effect of the coating amount on Li uptake. In 1 hr extraction (E) reactions in field-collected LBW, increasing the coating thickness decreased the Li uptake showing correlation between the coating thickness and reaction rate. The slow reaction rate is responsible for lower Li uptake of LMO with coating thickness greater than 15 nm. The 1.5 nm and 7.5 nm coating do not show any change in the Li uptake. The Mn-loss caused by reductive dissolution is reduced by 25% with 1.5 nm coating and 50% with 7.5 nm coating. The Mn-loss do not improve further by increasing the coating thickness. This shows that the coating range between 1.5 nm and 7.5 nm works with minimal reduction in Li uptake and significant decrease in Mn-loss. FIG. 16 shows the effect of coating thickness on simulated LBW. In the coating thickness range between 1.5 nm and 7.5 nm, there is minimal change in the Li uptake. The Mn-loss for the bare LMO and all the coated LMO are 0.5-0.8%. The difference in the Mn-loss in the field-collected LBW and simulated LBW represents the reductive dissolution of Mn caused by the organics in the field-collected LBW. The minimal change in the Mn-loss in simulated brine indicates that reduction in Mn-loss in field-collected LBW is attributed to the ZrO₂ barrier to the organics.

Effect of Particle Size on Li Adsorption

Lithium extraction studies on bare LMO in field collected LBW showed that the Li uptake capacity had a positive correlation with the particle size of the LMO. Thus, the particles are separated by size before coating them with ZrO₂. Based on the relationship between coating thickness and Li uptake/Mn-loss from FIG. 4, two different coatings are studied to find the best particle size with highest Li uptake capacity and lowest Mn-loss. FIGS. 5A-5C show the relationship between particle size on Li uptake and Mn-loss for bare LMO (a), 1.5 nm LMO (b), and 7.5 nm LMO (c) with their respective linear fits indicating linear correlation FIGS. 5a-5c shows the effect of particle size on the Li uptake and Mn-loss before and after coating and the linear line fit results are shown in Table 3. The linear line fits of the Li uptake and Mn-loss to LMO particle size, shows a strong correlation between Li uptake capacity and particle size. The slope of the Li uptake correlation is a constant 0.02 mg·g⁻¹ μm⁻¹ for all cases. This also means that the statistical change in the Li uptake is very minimal after coating. As for the <75 μm particles coated with 7.5 nm ZrO₂ the lithium uptake capacity only reduced by 4% whereas there is 70% reduction in capacity for the 1000 μm particles coated with 7.5 nm ZrO₂. This shows that the binding effect of ZrO₂ negatively affects the larger particles than it does for the smaller particles.

TABLE 3
Fit results for FIGS. 5a-5c, effect of particle size on Li adsorption
and Mn-loss before and after ZrO2 coating. The Li uptake capacity
is fit using exponential polynomial fit using the following equation
y = y0 + A * exp(R * x). The Mn-loss is fit using
linear fit using the following equation y = a + b * x.

Li uptake

Mn-loss

Sample	y0	A	R	R-square	a	b	R-square

Bare	7.50	19.04	−0.002	0.99	4.18	−2.84	0.17
LMO
1.5 nm	2.51	21.99	−0.003	0.99	2.82	−3.45	0.26
LMO
7.5 nm	2.76	21.56	−0.003	0.99	1.94	−8.43	0.84
LMO

The Mn-loss linear line fits also indicate a positive correlation to the particle size. This is because of the ZrO₂ acting as a physical barrier to the reducing agents in the field-collected LBW. Smaller LMO particles have higher Mn-loss because of the larger surface area as reductive dissolution is a surface phenomenon¹¹. In bare LMO a constant 4% Mn-loss is noticed as the Mn-loss is directly correlated to the amount of LMO exposed to the LBW surface and not dependent on the Li uptake capacity. Coating with 1.5 nm ZrO₂ improved the Mn-loss by 30% indicating a positive correlation with the particle size where larger particles tend to have lower Mn-loss. This is further improved by using 7.5 nm ZrO₂ coating where the Mn-loss is reduced by 53% on average.

Form this analysis we can see that the <75 μm particle size LMO coated with 7.5 nm ZrO₂ had the highest lithium uptake to Mn-loss ratio. Further, coating with higher amounts of ZrO₂ on the <75 μm particle only reduced the Li uptake capacity as the binding effect of the ZrO₂ likely made the Li diffusion thorough the coating layer slower. Coating LMO with higher amounts of ZrO₂ don't have a significant effect on Mn-loss, showing that the 7.5 nm coating has the best Li adsorption capacity to Mn-loss ratio. This is likely caused by the coating layer acting as a barrier for the organics and other reducing agents in the field collected LBW but permeable to monovalent and multivalent ions in solution. The coating layer does not reduce the Mn-loss in simulated LBW as shown in FIG. 16 because the ZrO₂ coating layer doesn't correct for the Jahn-Teller effect of the Mn-type adsorbents. This type of Jahn-Teller effect is seen during every topotactic transition of LMO from protonation to extraction cycles because of the formation of the Mn³⁺ degenerate ions. Thus, there will always be ˜0.5% Mn-loss per cycle unless such structural distortion is corrected for using doping methods.

Adsorbent Recyclability and Selectivity in Field Collected LBW

Cycle testing the adsorbents in field-collected LBW is shown in FIGS. 6a-6d where bare LMO, 1.5 nm coated LMO, and 7.5 nm coated LMO are compared. The cycle testing includes repeated use of the LMO in protonation and extraction cycles for Li extraction and recovery. Cycling testing bare LMO in FPW showed 4-5% Mn-loss per-cycle²⁸. After 4 cycles the bare LMO lost 16% of total Mn, this is significantly lower in 1.5 nm and 7.5 nm coated LMO. For 1.5 nm LMO the loss is 30% lower and for 7.5 nm LMO the loss is 50% lower than that of the bare adsorbent. This shows that the 7.5 nm coated LMO is cycled at least 4 times more than the bare LMO¹⁹. 7.5 nm LMO showed a maximum lithium extraction capacity of 24 mg·g⁻¹ in 1 hr extraction under room temperature. There is slight drop in the Li uptake capacity per-cycle; after 4 cycles 97% of the capacity is retained. On average the Mn-loss are less than 2% during cycling of the 7.5 nm LMO. The Mn-loss for the 1.5 nm LMO is lower than that of the bare LMO but during cycling the adsorbent showed higher Mn-loss after the 4th cycle indicating that the adsorbent is losing its coating layer because of mechanical wear as this type of Zr-loss cannot be observed during acid desorption. The 7.5 nm LMO do not show such mechanical degradation. The Zr-loss per cycle is less than 0.1% for the 7.5 nm LMO. This makes the 7.5 nm LMO more durable to mechanical wear and chemical wear than the bare LMO as shown in FIG. 19.

The first protonation Zr loss was 0.5%. During cycling the adsorbent, the Zr loss was less than 0.1%. Such change in Zr loss could be because of the formation of polymorphs of ZrO₂. This was verified by digesting the adsorbent in two ways; HCl digestion and HF digestion. For HCl digestion, 100 mg of the 7.5 nm LMO was added to a mixture of 20 mL of 6 M HCl and 1 mL of 30% H₂O₂ at 80° C. for 1 h. This did not dissolve the 7.5 nm LMO. For HF digestion, 100 mg of the 7.5 nm LMO was digested using 10 mL of 6 M HCl and 2 mL of H₂O₂ at 80° C. for 1 h. To this solution 5 mL of HF was added at room temperature and the solution was heated to 120° C. for 12 h. The final solution was pale yellow in color with visible LMO particles. Aliquots of the supernatant was analyzed using ICP-MS/MS. The results showed some dissolution of Mn, Li, Zr but the total amount of coated LMO digested was less than 20% by mass. This shows that the ZrO₂ coating is durable to harsh chemical conditions because of its innate ceramic nature. Table 4 shows fit results of the bare LMO and 7.5 nm LMO adsorption kinetics.

TABLE 4
Fit results of the bare LMO and 7.5 nm LMO adsorption kinetics

	Bare LMO	7.5 nm LMO

P1 Li kinetics	Equation	y = a +	Equation	y = a +
		b*x		b*x
	Plot	t Q\+(−1)	Plot	t Q\+(−1)
	Weight	No	Weight	No
		Weighting		Weighting
	Intercept	−0.00322 ±	Intercept	0.02802 ±
		0.00508		0.01458
	Slope	0.35584 ±	Slope	0.36839 ±
		0.00107		0.00307
	Residual	0.00397	Residual	0.03269
	Sum of		Sum of
	Squares		Squares
	Pearson's	0.99993	Pearson's	0.99944
	r		r
	R-Square	0.99986	R-Square	0.99889
	(COD)		(COD)
	Adj. R-	0.99985	Adj. R-	0.99882
	Square		Square
P1 Mn-loss kinetics	Equation	y = a +	Equation	y = a +
		b*x		b*x
	Plot	t Q\+(−1)	Plot	t Q\+(−1)
	Weight	No	Weight	No
		Weighting		Weighting
	Intercept	5.94766E−7 ±	Intercept	0.00138 ±
		7.55376E−4		0.00122
	Slope	0.03454 ±	Slope	0.03567 ±
		1.59105E−4		2.57958E−4
	Residual	8.77E−05	Residual	2.31E−04
	Sum of		Sum of
	Squares		Squares
	Pearson's	0.99983	Pearson's	0.99958
	r		r
	R-Square	0.99966	R-Square	0.99916
	(COD)		(COD)
	Adj. R-	0.99964	Adj. R-	0.99911
	Square		Square
E1 Li kinetics	Equation	y = a +	Equation	y = a +
		b*x		b*x
	Plot	t Q\+(−1)	Plot	t Q\+(−1)
	Weight	No	Weight	No
		Weighting		Weighting
	Intercept	0.01029 ±	Intercept	0.01671 ±
		0.00207		0.00447
	Slope	0.03066 ±	Slope	0.03038 ±
		2.76264E−4		6.07076E−4
	Residual	0.00109	Residual	0.00575
	Sum of		Sum of
	Squares		Squares
	Pearson's	0.99919	Pearson's	0.99583
	r		r
	R-Square	0.99838	R-Square	0.99168
	(COD)		(COD)
	Adj. R-	0.9983	Adj. R-	0.99129
	Square		Square
P2 Li kinetics	Equation	y = a +	Equation	y = a +
		b*x		b*x
	Plot	t Q\+(−1)	Plot	t Q\+(−1)
	Weight	No	Weight	No
		Weighting		Weighting
	Intercept	0.00487 ±	Intercept	0.00443 ±
		9.63885E−4		0.00156
	Slope	0.03547 ±	Slope	0.03485 ±
		1.11326E−4		1.80574E−4
	Residual	5.49E−05	Residual	1.44E−04
	Sum of		Sum of
	Squares		Squares
	Pearson's	0.99996	Pearson's	0.99989
	r		r
	R-Square	0.99992	R-Square	0.99979
	(COD)		(COD)
	Adj. R-	0.99991	Adj. R-	0.99976
	Square		Square
P2 Mn-loss kinetics	Equation	y = a +	Equation	y = a +
		b*x		b*x
	Plot	t Q\+(−1)	Plot	t Q\+(−1)
	Weight	No	Weight	No
		Weighting		Weighting
	Intercept	0.07186 ±	Intercept	0.08546 ±
		0.03441		0.06862
	Slope	0.316 ±	Slope	0.39082 ±
		0.00397		0.00793
	Residual	0.06995	Residual	0.27816
	Sum of		Sum of
	Squares		Squares
	Pearson's	0.99937	Pearson's	0.99836
	r		r
	R-Square	0.99874	R-Square	0.99672
	(COD)		(COD)
	Adj. R-	0.99858	Adj. R-	0.99631
	Square		Square

The selectivity of all the LMOs are shown in FIGS. 6(a-c). The selectivity of bare LMO has a trend of Li>>Na>Ca>Mg>K. The Li gets adsorbed to the interstitial sties in the MnO₆ octahedron. The other cations occupy the surface deformations on the surface of LMO²⁹. This trend is because of the speciation of LBW at pH 8 where the sodium and calcium forming hydroxide species have higher activity. The dissolution of Mn should be mostly from the surface of LMO as the reductive dissolution responsible for 90% of the Mn-loss is because of the reducing agents coating the adsorbent surface. The 4% Mn-loss per cycle is mostly from the surface of the LMO deforming the surface making more unconformities. Thus, after each cycle more undesired ions are adsorbed to the surface reducing the Li selectivity. Reducing the surface deformations can help in improving the selectivity of LMO during cycling. This is noticed in 1.5 nm LMO where the Li selectivity does not change after 4 cycles. This same is true for the 7.5 nm LMO. The coated LMO (1.5 nm LMO and 7.5 nm LMO) showed higher selectivity towards Li with lower Mg and K ions in protonation acid than that of the bare LMO. This is beneficial in the downstream processing after the DLE step. The changing nature of the LMO's selectivity could mean that the final acid could carry varying amounts of ions depending on the amount of degradation of the LMO. The high stability of the 7.5 nm LMO is because of the low Mn-loss. The Li uptake capacity for all LMO adsorbents is only 24 mg·g⁻¹ which is only 33% of the theoretical uptake (72 mg·g⁻¹) of LMO. Counting all the adsorption sites on bare LMO the total uptake of the LMO is 38 mg·g⁻¹ (Li, Na, K, Mg, and Ca) or 61% of theoretical uptake. The amount of impurities in the LMO is a factor of total dissolved solids in the LBW. Table 5 shows the selectivity data complied from various published work. Comparing the data from this table shows that the ratio of Li uptake to the total uptake of the LMO is only 60-80% of the total uptake by mass.

TABLE 5
Selectivity data collected from various peer-reviewed work.

								Li
	TDS of	Li	Na	K	Mg	Ca	Total	uptake/
	the LBW	uptake	uptake	uptake	uptake	uptake	uptake	Total
Author	(ppm)	(mg · g−1)	(mg · g−1)	(mg · g−1)	(mg · g−1)	(mg · g−1)	(mg · g−1)	uptake

30	108716.7*	16.44	0.8	2.21	2.11	0.91	22.47	0.712061
17	104239.5*	15.36	0	1.89	0.08	0	17.33	0.886324
31	113893*	433	24.1	23.6	69.8		550.5	0.786558
32	859.902	18.55	47.38	4.68	0.192	0.04	70.842	0.26185
33	—	29.68	10.58	3.51			43.77	0.67809
33	20239.22*	31.08	27.6	2.73	0.72	0	62.13	0.500241
34	41779*	35	3.42	1.07	0.44	0.09	40.02	0.874563
28	1716ζ	23.1	5.06	2.73			30.89	0.747815
35	19599.78*	18.97	5.06	9.36	0.384	0.08	33.854	0.560347
36	2860	34.61	4.4	3.1	1.1	0.4	43.61	0.793625
37	20320.1*	29.26	0.46	1.17	0.48	0.04	31.41	0.93155
38	146091*	26.16	0.69	1.57	1.31	1.07	30.8	0.849351
39	122349.2*	6.26	1.07	0.647	1.93	0.32	10.227	0.612105
*TDS values collected from the selectivity tables;
ζequimolar solution.
The theoretical uptake of L1.6Mn1.6O4 is 85 mg · g−1.

FIG. 7 shows the relationship between Li uptake, TDS, Li concentration in LBW, and ratio of Li/TDS in the LBW. The cluster analysis shows 4 different clusters forming. Cluster C1 is formed from LBW with low TDS, low Li concentration and medium Li uptake. C2 has higher Li uptake because of the high Li conc in the brine. The high Li concentration makes the Li adsorption kinetics faster. C3 shows high TDS LBW with low Li concertation where the Li uptake is very low. Cluster C4 represents high TDS LBW with high concentration Li, as a reason has high Li uptake. This analysis shows that the high TDS (>50,000 ppm) is not favourable for Li extraction if the Li concentration is between 3-160 ppm. Although such apparent trend exists by comparing selectivity data from published works, it is to be noted from this study that by just adjusting the process variables like (constant pH during the reaction, particles of known particle size) it is possible to retain the high Li uptake even in a LBW with high TDS (highest among other published work compared in this study), low Li concentration with high selectivity towards Li. It should also be noted that the Mg concentration in the LBW could significantly affect the selectivity as shown in FIG. 17. Despite the presence of hydroxide forming Ca ion at pH 12, in some of the examples it is noticed that Mg ions have an increasing trend in uptake when the TDS of the LBW increase. This could affect Li purity in the acid (protonation acid) as this could affect the downstream processing to produce Li salts.

Electron Energy Loss Mapping of LMO During DLE

Field collected LBW has a complex speciation of organic and inorganic compounds. Formation waters contain dissolved organics because of the interaction with the organics containing sedimentary rocks⁴⁰. The complete organic profile of the field collected LBW is complex and include compounds like polycyclic aromatic hydrocarbons (PAH), polyethylene glycols (PEG), octylphenol ethoxylates (OPE), and H₂S^41-43. These compounds coat LMO during extraction process and reduce the Mn on the surface of LMO. Although some of these organic acids are Mn reductants, dissolution of Mn cannot be measured during extraction process. Seip et al., predicts that the reduced Mn stays in the LMO spinel changing the adsorbents average Mn—Mn distance¹¹. This reduced Mn later dissolves in acid. TEM-EELS visualization of spatial distribution of Mn on LMO in Li extractions from field-collected LBW shows a layer of Mn³⁺ on the surface of the samples as shown in FIG. 8. The surface dissolution indicates that during Li adsorption, Mn⁴⁺ on the surface of LMO gets reduced to Mn³⁺ as a direct result of contact with the organics in the LBW. It is noticed that in Bare LMO the reduction of Mn is mostly on the surface but also present throughout the sample. Based on the amount of dissolution on the surface of the sample, we can conclude that most of the dissolution is on the surface of Bare LMO. In the coated LMO such dissolution is minimal. Mn³⁺ EELS data shows significant decrease in reduction of Mn on the surface as well as the bulk phase. This is because of the barrier provided by the ZrO₂ coating layer which prevents direct contact of larger Mn reducing organics to the surface Mn⁴⁺. This is the reason for 50% less Mn-loss observed in the 7.5 nm LMO samples during DLE. FIG. 18 shows the presence of ZrO₂ coating layer in on top of the LMO in 7.5 nm LMO during first extraction and fifth extraction cycles. The surface plots of the Zr EELS spectra also shows the presence of a uniform coating of 7.5 nm ZrO₂. After 5 cycles of 7.5 nm LMO the Mn³⁺ distribution resembles that of the bare LMO. This is because of significant damage of the LMO in 5 cycles. The E1 bare LMO had 4% Mn-loss and the cumulated Mn-loss of 7.5 nm LMO after E5 is 10% (which is 50% lower than the cumulate loss of bare LMO after 5 cycles). Such cumulative loss can also be noticed in the O EELS map as in 7.5 nm LMO at E5 shows significant loss of oxygen as 0244. This is a result of the Mn reduction. Ooi et al., predicted that during Li insertion an equivalent of 90% oxygen is lost, as well as reduction of Mn⁴⁺ to Mn^{3+ 45}. This can also be interpreted as that the Mn-loss is directly responsible for such oxygen loss in the cubic framework. Such irreversible change in oxygen framework is detrimental to the recyclability of the bare LMO and TEM-EELS or EDX mapping is a useful technique to monitor the quality of LMO at any point in the DLE process²⁰. Comparing the line spectra of O, Mn⁴⁺, Mn³⁺, the degradation of the LMO has slowed down by the coating layer. Shi et al., shows that the LMO can withstand 55% degradation without loosing Li uptake capacity³¹. The coating layer is helpful in at least doubling the recyclability of LMO for Li extraction from LBW containing dissolved organics in the DLE process.

Adsorption Kinetics

The Li and Mn kinetics of LMO during protonation and extraction is fitted using a pseudo-second order model³². This shows that the ion-exchange of Li to H is governed by chemisorption⁴⁶. The protonation kinetics of Li and dissolution kinetics of Mn during the first protonation (P1) show that the coating layer does not affect the Li adsorption kinetics and allows free exchange of ions though the ZrO₂ framework. The Li adsorption kinetics during E1 are identical for both versions of the adsorbent with an equilibrium Li uptake of 33 mg·g⁻¹. For a brine containing 65 ppm of Li, with an adsorbent to brine ratio of 2 g·L⁻¹ shows 100% lithium recovery. The low brine concentration is the reason for the low Li uptake of bare LMO and 7.5 nm LMO. The ratio of adsorbent mass to LBW volume and Li extraction time changes with the amount of Li in the brine^11,47. LMO has two adsorption rate constants. The first rate constant for both versions of LMO is 0.4 mg·min⁻¹ responsible for 75% of the Li uptake and the second rate constant is 0.004 mg·min⁻¹ responsible for rest of the Li uptake. The first rate constant is attributed to the surface adsorption of Li to LMO and the second rate constant is attributed to the bulk intercalation of Li into LMO. From the rate models it is observed that the rate limiting step is the intercalation of Li. During the second protonation (P2), the Li desorption from both versions of the LMO are identical as before but the Mn dissolution kinetics are different. The Mn-loss kinetics for 7.5 nm LMO still had a pseudo-second order behaviour but the amount of Mn dissolution is ˜50% lower. By comparing Mn dissolution in P1 and P2, it is apparent that the coating layer allows free exchange of Mn ions. Thus, the reduction in Mn-loss should be because of the barrier provided by the coating layer to the larger organic molecules in LBW.

Evolution of Local Structure with Li Extraction and Protonation

The XANES line comparison of the extracted samples and protonated samples provide some clues on the degradation of the spinel at different points during the DLE process. Three types of features is noticed in the XANES spectra. Pre-edge peaks A1 and A2 responsible for 3d transitions, peaks B1 and B2 are responsible for the rising edge of the spinel, and peaks C1 and C2 indicating expansion and contraction of the unit cell. Comparing the spectra to that of the standards it can seen that during the extraction cycle the rising edge moves to the left and during protonated cycle the rising edge moves to the right. From the XANES of the bare LMO at extracted state shows change in position of the C1 and C2 features to higher energy in extracted samples and lower energy in protonated sample. This shows the resonating expansion and contraction of the unit cell⁴⁸. But as the bare LMO ages, a shift to the higher energy in the extracted samples can also be noticed. This change is not reversible unlike the resonating unit cell at extracted and protonated states. This type of shift shows structural damage in the spinel after 4 cycles. The expansion of the unit cell with increase in DLE cycles does not affect the protonated states. This is one of the reasons for the retention of Li uptake of bare LMO. Such change is not noticed in both the coated versions of the LMO.

Linear combination fitting (LCF) of the standards to the bare LMO, 1.5 nm LMO, and 7.5 nm LMO shows that the samples are closer to the XANES spectra of the spinel standards (LiMn₂O₄ and Li_1.33Mn_1.67O₄). From TEM-EELS Mn mapping inference, it is clear that most of the spinel is Mn⁴⁺. Thus, using protonated version of the of the spinel standards and a Mn³⁺ standard (Mn₃O₄) the state of the LMO samples is monitored at different DLE cycles. Table 6 shows the results form the LCF fit. The bare LMO showed at least 10% transformation of spinel Mn⁴⁺ to Mn³⁺ every cycle. Although this change in the Mn state is completely recoverable as the bare LMO returns to the Mn⁴⁺ state during protonation. With increase in the coating thickness a reduction in the formation of Mn³⁺ is noticed. Phase transition of the octahedral cubic spinel to the tetragonal LiMnO₂ is not noticed in any samples with LCF even after 4 cycles.

TABLE 6
Linear combination fitting results. The samples
are modeled as protonated version of a spinel standard
(H1.33Mn1.67O4) and Mn3+ impurity (Mn3O4).

Sample	XANES model	Bare LMO	1.5 nm LMO	7.5 nm LMO

Pr	H1.33Mn1.67O4	0.9	0.914	0.95
	Mn3O4	0.1	0.086	0.05
P1	H1.33Mn1.67O4	1	1	1
E1	H1.33Mn1.67O4	0.899	0.9	0.957
	Mn3O4	0.101	0.1	0.043
P2	H1.33Mn1.67O4	1	1	1
E2	H1.33Mn1.67O4	0.906	0.886	0.971
	Mn3O4	0.094	0.114	0.029
P3	H1.33Mn1.67O4	1	1	1
E3	H1.33Mn1.67O4	0.908	0.891	0.936
	Mn3O4	0.092	0.109	0.064
P4	H1.33Mn1.67O4	1	1	1
P5	H1.33Mn1.67O4	1	1	1
Energy range: −20 eV to 100 eV
R2 = <0.006
Red χ2 = <0.002

The edge energy has a linear relationship with the oxidation state of the Mn standards. The oxidation states of the unknown compounds are determined using linear regression model formed by the oxidation state of the standards and the arctangent function fit to the first infliction point of the rising edge of the respective standards^22,23. The oxidation state of the Pr bare LMO is determined as +3.87 and 7.5 nm LMO is +3.949. This slight improvement in oxidation state is caused by the second calcination step where more oxygen is available for oxidation of Mn³⁺ present in the LMO as impurity. Oxidation state of all the protonated samples are +4 indicating complete dissolution of Mn³⁺ in acid^48-50. The resonating protonation and extraction oxidation states indicates dissolution and production of Mn³⁺ during DLE processing, which forms the basis of Mn-loss. After coating with 7.5 nm ZrO₂, the oxidation states of the extracted samples increased indicating decreased Mn³⁺ formation. This can also be seen in the mean oxidation state analysis of all the samples during 4 cycles of the DLE process shown in FIG. 20.

The complete compilation of all the EXAFS spectra of bare LMO, 1.5 nm LMO, and 7.5 nm LMO during different cycles of DLE and their respective model fits are shown in FIG. 21. Comparing the EXAFS spectra of bare LMO and 7.5 nm LMO in Pr state and cycled state are shown in FIGS. 12a-12d. In FIG. 12a, cycling the adsorbent three times in field collected LBW shows slight change in the second maxima in the R-space. The absence of the shoulder peak and the subsequent change in position and shape of the following peaks show structural change in the spinel caused by the reductive dissolution of Mn³⁺. This change in the spinel structure can also be noticed in FIG. 12c. The change in the spectra after 3 Å in the cycled protonated sample also show structural change in the MnO₆ octahedron. This change in the structure is not noticed in the coated 7.5 nm LMO samples. Both extracted and protonated versions of the 7.5 nm LMO shown in FIGS. 12c&d do not show any change in the R-space peaks.

The structural parameters of the first two shells are fit using Li_1.33Mn_1.67O₄ model compound^11,48. The first shell (Mn—O) and the second shell (Mn—Mn) fits along with the fit results are shown in Table 7. The Mn—O distance stayed constant for all the samples as 1.90 Å. The average Mn—Mn distances change during Li insertion and extraction as shown in FIG. 13. The reversible change in Mn—Mn distances is because of the formation and dissolution of Mn³⁺ ions (Mn⁴⁺—Mn³⁺ bond is larger than the Mn⁴⁺—Mn⁴⁺ bond)⁴⁸. This is not the case for the bare LMO beyond E3. The bare LMO spinel is starting to deteriorate with a cumulative Mn dissolution of 16%. A slight change in the Mn—O distance can also be noticed after 16% cumulative loss of Mn.

Longer Mn—O and Mn—Mn distances may result in phase change from cubic spinel to tetragonal spinel⁵¹. In coated LMO, the Mn—Mn distance is partially recovered beyond E2 in 1.5 nm LMO and fully recovered in 7.5 nm LMO. Although this reversible change should be understood concurrently with Mn dissolution. It is understood that LMO at 16% Mn dissolution can show some structural damage. The coating layer only managed to lose only <8% Mn. Yet, such improvements in the dissolution is crucial in the recyclability of the adsorbent. This gives 7.5 nm LMO at least twice as much cycles as bare LMO before showing any structural damage.

TABLE 7
EXAFS fit results for the first shell (Mn—O)
and the second shell (Mn—Mn).

Mn—O

Mn—Mn

LMO species	R (Å)	σ (Å)	R (Å)	σ (Å)

Bare LMO

Pr	1.895	0.003	2.89	0.004
	(±0.01)	(±0.004)	(±0.02)	(±0.003)
P1	1.895	0.004	2.87	0.007
	(±0.01)	(±0.002)	(±0.01)	(±0.001)
E1	1.90	0.003	2.886	0.005
	(±0.009)	(±0.001)	(±0.009)	(±0.001)
P2	1.90	0.004	2.868	0.006
	(±0.008)	(±0.001)	(±0.01)	(±0.001)
E2	1.891	0.001	2.873	0.003
	(±0.01)	(±0.002)	(±0.01)	(±0.002)
P3	1.889	0.005	2.865	0.007
	(±0.01)	(±0.01)	(±0.02)	(±0.01)
E3	1.90	0.002	2.874	0.006
	(±0.01)	(±0.002)	(±0.02)	(±0.002)
P4	1.895	0.002	2.866	0.005
	(±0.01)	(±0.002)	(±0.01)	(±0.001)
P5	1.895	0.003	2.861	0.005
	(±0.01)	(±0.001)	(±0.01)	(±0.001)

1.5 nm LMO

Pr	1.899	0.003	2.889	0.006
	(±0.05)	(±0.009)	(±0.02)	(±0.006)
P1	1.899	0.003	2.87	0.006
	(±0.04)	(±0.01)	(±0.05)	(±0.008)
E1	1.902	0.003	2.897	0.006
	(±0.02)	(±0.004)	(±0.02)	(±0.003)
P2	1.908	0.003	2.869	0.007
	(±0.04)	(±0.006)	(±0.04)	(±0.005)
E2	1.897	0.006	2.881	0.006
	(±0.06)	(±0.009)	(±0.05)	(±0.007)
P3	1.899	0.008	2.870	0.007
	(±0.01)	(±0.02)	(±0.09)	(±0.01)
E3	1.90	0.003	2.884	0.008
	(±0.02)	(±0.005)	(±0.03)	(±0.005)
P4	1.90	0.002	2.867	0.006
	(±0.04)	(±0.006)	(±0.04)	(±0.006)
P5	1.90	0.002	2.872	0.005
	(±0.05)	(±0.01)	(±0.08)	(±0.01)

7.5 nm LMO

Pr	1.90	0.002	2.892	0.005
	(±0.007)	(±0.001)	(±0.008)	(±0.001)
P1	1.90	0.002	2.875	0.005
	(±0.01)	(±0.001)	(±0.03)	(±0.002)
E1	1.90	0.003	2.889	0.005
	(±0.01)	(±0.001)	(±0.01)	(±0.001)
P2	1.896	0.002	2.870	0.005
	(±0.01)	(±0.002)	(±0.01)	(±0.002)
E2	1.91	0.004	2.885	0.008
	(±0.01)	(±0.005)	(±0.01)	(±0.006)
P3	1.90	0.007	2.868	0.01
	(±0.02)	(±0.004)	(±0.03)	(±0.002)
E3	1.90	0.002	2.885	0.007
	(±0.01)	(±0.003)	(±0.02)	(±0.004)
P4	1.90	0.010	2.87	0.01
	(±0.03)	(±0.01)	(±0.01)	(±0.007)
P5	1.899	0.002	2.869	0.005
	(±0.009)	(±0.001)	(±0.01)	(±0.001)

CONCLUSION

The LMO is coated with 7.5 nm ZrO₂ using evaporative crystallization method combined with calcination at 400° C. The coating layer does not affect the Li adsorption kinetics and showed significant reduction in Mn-loss. Cycle testing showed improved reversibility, recyclability, and Li selectivity of 7.5 nm LMO which is 4 times better than bare LMO. The selectivity order in a field-collected LBW is Li>>Na>Ca>Mg>K. The reductive dissolution is identified to be reducing the Mn⁴⁺ on the surface of the LMO and the coating layer reduced 50% of such material loss by creating a barrier of ZrO₂. Mn—Mn distances form the EXAFS modeling of the bare LMO and coated LMO showed reversible change in Mn—Mn distances after coating. This is directly responsible for the improved recyclability performance of LMO in a LBW with high amounts of dissolved organics. This shows that coated adsorbents can make LBW with high amounts of dissolved organics useful for Li extraction using the emerging DLE technology.

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While at least one exemplary embodiment has been presented in the foregoing description and attached appendix, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the described embodiments in any way. Rather, the foregoing description and incorporated references will provide those skilled in the art with a convenient roadmap for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes may be made in the function and arrangement of elements without departing from the scope as set forth in the appended claims and the legal equivalents thereof.