Selective Exchange Research Articles

Assessment of salt-free electrodialysis metathesis: A novel process for brine management in brackish water desalination using monovalent selective ion exchange membranes

Since reverse osmosis (RO) is often limited to a water recovery of 70–85 %, implementing a secondary process like electrodialysis metathesis (EDM) to treat concentrate can increase system water recovery. This study explores salt-free electrodialysis metathesis (SF-EDM) as an alternative to conventional EDM to investigate its performance in the zero discharge desalination (ZDD) process. SF-EDM utilizes monovalent-selective ion exchange membranes, eliminating the need for sodium chloride (NaCl) as a substitution solution. This approach generates one diluate stream and two highly soluble concentrate streams enriched in calcium and sulfate, respectively. In this article, a series of lab-scale tests based on synthetic and real RO concentrate were performed to investigate how SF-EDM performs operating at high water recovery with a feedwater with high scaling potential. We critically analyze the performance in terms of salinity reduction, selectivity, and energy consumption. Results of the study show that without the addition of NaCl, the process was able to selectively separate sulfate and calcium into two concentrate streams achieve a salinity reduction of 93 % and a total system water recovery (RO and SF-EDM) of 90 %. A technoeconomic analysis found SF-EDM to be 80 % of the cost of conventional EDM making it a competitive technology for brackish water RO concentrate management.

Ecofriendly synthesized Zeolite 4A for the treatment of a multi-cationic contaminant-based effluent: Central composite design (CCD) statistical approach

One of the key aspects of futureproofing the sustainability of life on earth lies in the protection of the hydrosphere, particularly from soluble heavy metal ion pollutants. In the current study, the central composite design and optimization of the ion-exchange process have been carried out for the simultaneous removal of selected cations; Cd2+, Cu2+, and Zn2+ cations using synthesized zeolite 4A. X-ray diffraction analysis confirmed the formation of zeolite 4A. The Brunauer-Emmett-Teller (BET) surface area of the synthesized zeolite was 32 m2/g. Results mainly indicate that there is a strong relationship between the experimental data and central composite design-based models of ion removal efficiency with R2 > 0.9 and the lack of fit less than 0.1 %. All the selected ion exchange parameters (time, dosage, pH, and temperature) were found to be statistically significant, with a p-value less than 0.05.For the complete simultaneous removal of selected cations, the optimal zeolite dosage, pH, and contact time are 1.2 g/100 cm3, 6, and 3 h. The optimal temperature ranges from 25 to 27 °C. The initial concentration of each selected cation is 450 mg/L. The ion exchange is in good agreement with the Freundlich and Langmuir isotherm models. Based on the Langmuir isotherm model, the maximum Cd2+, Cu2+, and Zn2+ uptake capacity values of zeolite are 103, 99.89, and 82.08 mg/g, respectively. In this study, it has been mainly inferred that CCD can be considered a useful tool for the modeling and optimization of zeolite ion exchange applications.

Hf-Doped CoP Hollow Nanocubes as High-Performance Electrocatalyst for Oxygen Evolution Reaction.

Designing and synthesizing hollow frame structures with unique three-dimensional open structures in electrocatalysis remain a challenge. Etching is an effective method to synthesize metal-organic frameworks (MOFs) with a hollow structure and rich function. Herein, we report the design and synthesis of Hf-doped CoP hollow nanocubes by selective etching and ion exchange. Different from the traditional etching method, we used acid xylenol orange solution to etch typically the (211) crystal face of ZIF-67, obtaining the unique bell-like structure, named XO-ZIF-67. Subsequently, Hf-doped CoP hollow nanocubes were formed by Hf4+ doping and simple phosphating treatment. Electrochemical tests showed that the overpotential of the obtained catalyst is only 291 mV at the current density of 10 mA cm-2 when applied in catalyzing the oxygen evolution reaction (OER). Furthermore, the catalyst shows excellent stability when running in 1 M KOH solution for 25 h.

A chromium-incorporated all-inorganic polyoxoniobate framework material: Good chemical stability and selective ion exchange capability

An all-inorganic three-dimensional (3D) polyoxoniobate (PONb) framework, Na6K4[(Nb6O19)CrIII(H2O)2]2·38H2O (1) has been synthesized via the hydrothermal method. The fundamental building unit of [(Nb6O19)CrIII(H2O)2]210− is connected by K+ ions, forming a 3D framework structure with channels along the b-axis. Compound 1 exhibits good thermal stability, and selectively absorbs Co2+ ions while excluding Ni2+ ions from acetonitrile solutions, PXRD analysis confirms that its framework remains intact after adsorption, indicating its potential as an effective ion-exchange material.

Removal of heavy metal ions from wastewater using ion exchange resin in a batch process with kinetic isotherm

Techniques such as selective ion exchange can be used to remove traces of heavy metals. The recently created resins provided quicker sorption kinetics and a high resin capacity for metal ions such as Lead (Pb²⁺), Copper (Cu²⁺), Zinc (Zn²⁺), Cadmium (Cd²⁺), and Nickel (Ni²⁺) ions. The elimination of Pb²⁺ and Cu²⁺ ions from aqueous solutions was examined in the current work. Purolite® C100, a strong acid cation-exchange resin, was used in experimental studies. Using packed-column chromatography, the impacts of operating factors on metal ion exchange were examined. These parameters included resin dose, initial pH, residence time, and metal ion concentration with ranges of 40 - 80 gs, 3 - 12, 30 - 90 min, and 50 -150 parts per million respectively. As part of exchange research, different doses of resin are brought into contact with a fixed volume of solution containing different concentrations and pHs of Pb²⁺ and Cu²⁺ ions for different periods. An Atomic Absorption Spectrophotometer (AAS) approach was used to measure the concentrations of metal ions. Experimental data on ion exchange were evaluated using Langmuir, Freundlich, and Temkin models.The results showed that there is a clear competition between lead and copper, as it was found that there is a convergence between the removal rates for both metals under the same conditions. The ion-exchange recovery of Cu approached 94.37 %, but Pb recovery was 92.9 % with Purolite® C100 resin dose range of 40 g to 80 g in the pH range of 3 to 12.

Single crystal polarization-orientation Raman spectroscopy of zeolite LTA with confined S3− anions - High dielectric constant nanoporous material

We apply polarization-orientation Raman spectroscopy, as an alternative to X-ray diffraction, to LTA single crystals containing S3− in sodalite cages additionally to S8 rings in large cavities. The sample was obtained via sulfur vapor adsorption at ∼550 °C (LTA-S-550). We show that S3− is located in the (110) plane with its 2-fold axis along the LTA 4-fold axis. The anion position suggests strong interaction of its terminal atoms with Na+ localized in LTA 6-membered rings. The anions display optical absorption band at ∼590 nm (2.1 eV) and resonant Raman enhancement. We observe a record-high S3− bond-bending mode frequency ∼274 cm−1 due to a strong bond-angle contraction. This leads to the Fermi resonance of its overtone with the symmetric bond-stretching mode in the frequency range of 544–552 cm−1. An anomalous Raman downshift of the S3− bond-stretching modes with a decrease of temperature is observed and attributed to partial compressive stress relaxation. Luminescence band at ∼845 nm is observed suggesting considering LTA-S-550 as an interesting light-emitting material. We discuss a role of S3− in the high dielectric constant up to ∼160 and a possible contribution of the anion to the ion-exchange selectivity to Sr2+/Cs+ enhancements of LTA with sulfur.

Recovery of Rare Earth Elements from Acidic Mine Waters: A circular treatment scheme utilizing selective precipitation and ion exchange

Acidic Mine Waters (AMW) pose significant environmental hazards due to their high acidity and metal content. Traditional treatment methods involve neutralizing the acidity and removing metals as hydroxides, but they generate hazardous sludge. However, a more sustainable approach has emerged, considering AMW as a secondary source for Critical Raw Materials (CRMs), such as Rare Earth Elements (REEs), through a circular treatment scheme integrating selective precipitation and ion exchange. This study focused on recovering REEs, with a total content of 18.6 mg/L, from AMW obtained from the Aznalcóllar open-pit in Sevilla, Spain, which also contained significant amounts of Al (216 mg/L), Fe (47 mg/L), and Zn (548 mg/L). The AMW was initially pre-treated to precipitate Fe and Al with high removal efficiencies (>99.9% and >90%, respectively). Furthermore, optimization studies were conducted to remove Zn as sulphide, achieving removals of Zn, Cd, and Cu >99% under the optimum conditions of NaHS dose and pH. The selective recovery of REEs was carried out using the commercial ion exchange resin impregnated resin containing an organophosphinic functional group (Lewatit TP272) in column mode, with a special focus on understanding the effect of Zn presence. It was observed that the presence of Zn influenced the concentration factor achieved during elution, resulting in at least two times greater concentration when Zn was removed from the solution, impacting the content and purity of the REEs oxalates obtained. This research demonstrates a promising approach for sustainable and efficient recovery of valuable REEs from AMW while mitigating environmental hazards associated with hazardous sludge generation.

Functionalized graphite carbon nitride nanofluid membranes for enhanced osmotic energy harvesting

Reverse electrodialysis is a promising technology that using ion exchange membrane to obtain electrical energy directly between seawater and river water. Current attempts that based on the ion exchange membrane are limited due to the channel size and low charge density. Graphitic carbon nitride (g-C3N4, GCN) is a type of graphite-layered polymer that combined with inherent nanopore structure and adjustable surface charge, which provides a shortcut for the preparation of highly selective ion exchange membrane. However, carbon nitride membranes still exhibit low power density. Herein, g-C3N4 was successfully functionalized with three different negatively charged molecules (carboxylation, polyacrylic acid (PAA) and poly (sodium 4-styrenesulfonare) (PSS)), which benefited from its rich nitrogen-containing groups. These functionalized g-C3N4 were combined with anodized aluminum oxide (AAO) membrane to form heterochannel membranes, which can transport counter-ions and harvest osmotic energy. The results showed that the surface charge density of functionalized g-C3N4 was obviously improved, which enhanced the output power density. Among them, the heterochannel membrane functionalized with PSS (PSS-CN/AAO) had the highest output power density of 31 mW/m2 (effective area 4.9 mm2), which was 3.1 times higher than that of the unfunctionalized heterochannel membrane (GCN/AAO, 9 mW/m2). In this base, two-dimensional PSS-CN/ANF membranes were designed by compositing PSS-functionalized g-C3N4 (PSS-CN) nanosheets with aramid nanofiber (ANF), which can maintain high output power density (50 mW/m2) and further improve the mechanical property of membrane, providing a guarantee for the long-term stable use of nanofluid membrane.

Separation of Boron and Arsenic from Geothermal Water with Novel Gel-Type Chelating Ion Exchange Resins: Batch and Column Sorption-Elution Studies

In this research, the removal of boron and arsenic from geothermal water was examined by using novel N-methyl-d-glucamine functionalized gel-like resins (abbreviated as 1JW and 2JW) synthesized by the membrane emulsification method. The outcomes were compared with those of commercially available boron selective chelating ion exchange resin (Diaion CRB 05). According to the results obtained with the novel resins, it was possible to reduce both boron and arsenic concentrations in geothermal water by using these novel gel-like chelating resins below their permissible levels for agricultural irrigation (<1 mg B/L) and drinking water (<0.01 mg As/L) by using the batch method. The optimum resin concentration required for almost complete boron removal (more than 95%) with the two chelating resins was determined to be 2 g/L. The novel gel-like chelating resins 1JW and 2JW achieved 94% of arsenic removal by using the resin concentration of 8 g/L, while the required resin concentration was 32 g/L for 94% of arsenic removal using commercially available Diaion CRB05 resin. In addition, the column performance characteristics of the novel chelating resins for the separation of boron were studied, and the results were compared to those obtained with Diaion CRB05. According to the column data obtained, the total resin capacities of the Diaion CRB05, 1JW, and 2JW resins were calculated as 6.29, 5.08, and 4.64 mg B/mL-resin, respectively.

Development of medium-scale filtration device for supplying drinking water during flood situations

A scaled-up device for rapid water treatment is presented based on technologies described in earlier effort (“Point of use drinking water filtration: A microfluidic solution providing safe drinking water during flood situation,” J. Water Process Eng. 52 (2023) 103545). It comprises inertia-based microfluidic filtration, selective ion-exchange, antimicrobial activated carbon, and ultraviolet disinfection stages. The overall performance of the device is tested using synthetic, field, and flood water samples. The size of the bypass port is optimized to achieve ∼99 % filtration efficacy. The length of IX media encapsulated in mini channels is adjusted by studying its effect in limiting the dissolved solids and the hydraulic resistance. The adsorption performance and capacity of the AC at equilibrium conditions is evaluated by tests using methylene blue. To augment the filtrate throughput, both unit and module level parallelization scheme is developed. Unit filters are arranged both in planar and vertical levels to form a parallelized module (PM). Subsequently, PMs are multiplexed with a carefully designed inlet distributary, outlet, and bypass collection network. The prototype device can treat nearly 400 L of raw water in six days of continuous operation. Integrated UV reactors in the full-scale device, show complete sterilization of the influent water.

Thermal Behaviour and Sorption Studies of Ion-Exchange Resin

Copolymer resin 2,4-DAPOF-II has been synthesized by condensation polymerization and its composition was determined on the basis of elemental analysis. Non-aqueous conductometric titration was used to determine the average molecular weight and the intrinsic viscosity was also determined. The formation of copolymer resin was confirmed by FT-IR, 1H-NMR and 13C-NMR spectroscopy. The semi-crystalline nature of synthesized copolymer was established by Scanning electron microscopy (SEM). Thermal degradation curve has been discussed with minute details by applying Freeman-Carroll8, Sharp-Wentworth47, Friedman and Chang equations9 to evaluate the kinetic parameters i.e. activation energy (Ea), order of reaction (n) and frequency factor (z). This copolymer is proved to be selective chelating ion exchanger for certain metal ions such as Fe3+, Co2+, Cd2+ and Pb2+. A batch equilibrium method was employed to study the selectivity of metal ion uptake involving the measurements and distribution of a given metal ion between the copolymer sample and a solution containing the metal ion. The study was carried out over a wide pH range, shaking time and in media of various ionic strengths.

Some molecular-sieve peculiarities of natural zeolite of Georgia

Ion exchange property of fibrous zeolite scolecite of Georgian origin has been studied against mono (Li, Na, NH4, K Cs and Rb), divalent (Sr, Ba Ca, Mg) and transition (Cd, Cu, Mn, Zn, Co and Ni) metal cations. Selectivity series of the above cations for scolecite have been compiled. The structure of scolecite, charge and sizeof the cations (both in hydrated and dehydrated state) and cation concentration in the solution (0.1N, 0.3N, 0.5N 1.0N and 1.5N) greatly influence on the ion-exchange property and selectivity order of scolecite. Dynamic Exchange Capacity (DEC) values for the studied cations on scolecite have been calculated. Kinetics of ion exchange in dynamic conditions for the above cations has been studied. Analysis of the obtained data shows that the external diffusion processes have influence on the establishment of equilibrium between the ions on the surface and in the micro porous structure of scolesite. The time of dynamic exchange equilibrium is directly proportional to the cation radios.

Ca–La layered double hydroxide (LDH) for selective and efficient removal of phosphate from wastewater

Adsorption showed advantages in removing phosphorus (P) at low concentrations. Desirable adsorbents should have sufficiently high adsorption capacity and selectivity. In this study, a Ca–La layered double hydroxide (LDH) was synthesized for the first time by using a simple hydrothermal coprecipitation method for phosphate removal from wastewater. A maximum adsorption capacity of 194.04 mgP/g was achieved, ranking on the top of known LDHs. Adsorption kinetic experiments showed that 0.02 g/L Ca–La LDH could effectively reduce PO43–P from 1.0 to <0.02 mg/L within 30 min. With the copresence of bicarbonate and sulfate at concentrations 17.1 and 35.7 times of that of PO43–P, the Ca–La LDH showed promising selectivity towards phosphate (with a reduction in the adsorption capacity of <13.6%). In addition, four other (Mg–La, Co–La, Ni–La, and Cu–La) LDHs containing different divalent metal ions were synthesized by using the same coprecipitation method. Results showed much higher P adsorption performance of the Ca–La LDH than those LDHs. Field Emission Electron Microscopy (FE-SEM)-Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), and mesoporous analysis were performed to characterize and compare the adsorption mechanisms of different LDHs. The high adsorption capacity and selectivity of the Ca–La LDH were mainly explained by selective chemical adsorption, ion exchange, and inner sphere complexation.

Part II: Predicting performance of DOWEX 21K resin for remediation of comingled contaminants in groundwater

The selectivity of ion exchange (IX) resins for aqueous contaminant removal can be impacted by changing concentrations of competing natural groundwater ions. In a two-part investigation, the Hanford Site 200 West Area pump-and-treat (P&T) facility in Washington State, USA is used as a case study to evaluate the performance of two IX resins for groundwater treatment: Purolite® A532E for pertechnetate (TcO4-) removal, explored in Part I, and DOWEX 21K (DOWEX) for uranium (U) removal. In Part II, DOWEX selectivity for U, as uranyl carbonate species, and uptake kinetics is quantified in a series of laboratory-scale aqueous batch experiments containing Hanford-relevant concentrations of competing anions nitrate (NO3-), sulfate (SO42-), chloride (Cl-), and carbonate (CO32-), as well as co-mingled contaminant TcO4-. The results demonstrate that DOWEX trimethylammonium functional groups are highly selective for U carbonate species (85–100 % uptake) under all conditions investigated. Only NO3- concentrations of 100 mM were shown to decrease U removal, with the extent (85–99 %) depending on competing anion concentrations present in solution. However, at the highest NO3- concentrations reported for groundwaters treated at the P&T facility (25 mM), the effect on U uptake is minimal. The batch sorption results are modeled to obtain chloride normalized equilibrium exchange coefficients (K) for predicting DOWEX performance: KSO4--/Cl- = 2.0, KNO3-/Cl- = 5.0, KHCO3-/Cl- = 1.5, KTcO4-/Cl- = 2,000, and KU/Cl- = 50,000. These K values predict little effect of current and future influent chemistries on U removal by DOWEX, where both uranyl carbonate species and TcO4- are removed such that effluent concentrations meet groundwater treatment requirements.

Ion exchange selectivity (Mg2+, Ca2+ and K+) in hydrated Na-montmorillonite: insights from molecular dynamic simulations

ABSTRACT The cation exchange selectivity in the Na-montmorillonite interlayer has been extensively studied as a part of the mechanism of the cation exchange reaction, which also provides an important insight into the inhibition of montmorillonite expansion by inorganic salts. While the variation of interlayer structure associated with interlayer Na+ and water molecules during the ion exchange process has less been explored, to determine the possibility of replacing interlayer Na+ ions by the ion exchange reaction, the present study focuses on the effects of the added electrolyte cation (Mg2+, Ca2+ and K+) on the structure properties, diffusion features and the number of surface hydrogen bonds in hydrated Na-montmorillonite at different hydration stages by using molecular dynamic (MD) simulations. The simulation results showed that Ca2+ has a better tendency to exchange Na+ ions at a high hydration degree, and K+ is easier to exchange Na+ at a low hydration degree. The lower mobility of interlayer species and the relativity large change in the number of hydrogen bonds with the addition of Mg2+ reflected its weak possibility of exchanging Na+ .

Stepwise conversion of methane to methanol over Cu-mordenite prepared by supercritical and aqueous ion exchange routes and quantification of active Cu species by H2-TPR

Copper-exchanged mordenite prepared by supercritical ion exchange (SCIE) and aqueous ion exchange (AIE) were investigated in stepwise conversion of methane to methanol. Increasing the oxygen activation temperature and methane reaction time enhances the methanol yield of copper-exchanged mordenite prepared by SCIE (Cu-MORS). The reducibility of Cu-MORS was compared with those of Cu-MORA prepared by aqueous ion exchange (AIE) using H2-TPR. It was demonstrated for the first time that deconvoluted H2-TPR profile coupled with effects of Cu loading and oxygen activation temperature on methanol yield data can be used to distinguish the active Cu sites from inactive ones based on their reduction temperature. The copper species responsible for methane activation were found to be reduced below 150 °C by H2 in both Cu-MORS and Cu-MORA. From the stoichiometry of the reaction of H2 with Cu2+ species, the average number of copper atoms of active sites were calculated as 2.07 and 2.80 for Cu-MORS and Cu-MORA, respectively. Differences in structure of copper species caused by the synthesis routes were also detected by in-situ FTIR upon NO adsorption indicating a higher susceptibility of Cu-MORS towards autoreduction. The results demonstrated the potential of TPR based methods to identify copper active sites and suggested the importance of site selective ion exchange in order to controllably synthesize active Cu species in zeolites.

Functionalized carbon nanotube and carbon nanodot modified multiblock poly(arylene ether ketone sulfone) copolymer as proton exchange composite membranes for fuel cell applications

AbstractThe present study describes the successful synthesis of –COOH functionalized carbon nanodots (f‐CNDs) via pyrolysis of citric acid and 4,4′‐bis(4‐hydroxyphenyl)valeric acid (DPA‐OH, Sigma Aldrich, St. Louis, Missouri, United States) based hydrophilic oligomer at 250 °C. The multiblock copolymers were prepared by a coupling reaction between phenoxide terminated valeric acid based poly(arylene ether ketone) (DPA‐OH) hydrophilic oligomer and decafluorobiphenyl (DFBP, Alfa Aesar, Haverhill, Massachusetts, United States) end‐capped poly(arylene ether sulfone) (BP‐X‐F) hydrophobic oligomers (where X is 6, 9 and 12). Multiblock poly(arylene ether ketone sulfone) copolymer crosslinked membranes were prepared using 6F‐bisphenol‐A based novolac epoxy resin (EFN) and –COOH functionalized multiwalled carbon nanotubes/functionalized carbon nanodots (f‐MWCNTs/f‐CNDs, Nanoshell company, Utah, U. S) were used for the preparation of acid doped composite membranes for fuel cell applications. From high resolution TEM images, the average size of the prepared f‐CNDs found to be ca 10–12 nm. The N1 multiblock copolymer membrane with loading of 0.9 wt% ratio of CNTs showed better proton exchange membrane related properties such as proton conductivity (0.136 S cm−1), ion exchange capacity (1.18 meq g−1) and selectivity ratio (0.17) compared to the prepared pristine, crosslinked and CND based composite membranes. The overall results revealed that the composite membranes with loading of 0.9 wt% of CNTs and CNDs exhibited a superior combination of fuel cell related properties such as higher proton conductivity, high dimensional and oxidative stability and low methanol permeability and also showed better fuel cell performance compared to the respective pristine and EFN crosslinked membranes. © 2022 Society of Industrial Chemistry.

Influence of Components Deposition Order on Silver Species Formation in Bimetallic Ag-Fe System Supported on Mordenite

In the present work, various experimental and theoretical methods were combined to study in detail the modifying effect of differences in the order of deposition of components on the state of silver in bimetallic iron–silver samples based on mordenite. In each of the silver-containing samples, the formation of large (≥2 nm in diameter) varieties of silver was observed, which differed from the varieties in the other samples, and in varying degrees. The formation of large Ag NPs on the outer surface of mordenite is explained by the redox interaction of Ag+-Fe2+ and the selectivity of ion exchange. The local surrounding of Ag in the studied samples is different: for AgMOR—monatomic species dominate, FeAgMOR—silver dimers and AgFeMOR—metal particles. In all investigated samples, the partially charged intra-channel Agnδ+ clusters (~0.7 nm in size) were formed due to partial Ag+ reduction and subsequent Ag0 agglomeration into the mordenite channel. Most of the silver in the bulk of the zeolite is represented in the cationic state attached to the mordenite framework by differently coordinated electrostatic forces, which can be Ag-O, Ag-Si or Ag-Al, with variations in interatomic distances and do not depend on the order of metal deposition. In addition, the arrangement of the cations in the side pockets means that the transport channels of mordenite are free, which is favorable for the application of the materials under study in catalysis and adsorption.

Problems of the Theory of Ion Exchange II: Selectivity of Ion Exchangers

Problems of the Theory of Ion Exchange II: Selectivity of Ion Exchangers

High Li-Ion Selectivity of Five-Coordinate Layered Titanate K2Ti2O5.

Selectivity of ion exchangers is an important topic in adsorption science owing to its specific application in resource recovery and environmental remediation. In this study, the cation exchange property of the submillimeter-sized five-coordinate K2Ti2O5 (KTO) crystals is demonstrated. Adsorption isotherm measurements were performed on KTO crystals ion-exchanged with alkali metal cations including Li+, Na+, Rb+, and Cs+. The maximum adsorption amounts of Li+, Na+, Rb+, and Cs+ on KTO were 2.70, 1.15, 0.59, and 0.42 mmol g-1, respectively, which is contradictory to the "normal" selectivity sequence (Cs+ > Rb+ > K+ > Na+ > Li+) of conventional ion exchangers, including clays and organic resins. The Kielland plots for the Li+ and Cs+ exchange experiments showed preferential Li+ adsorption on KTO, which supports the high Li+ selectivity. The interlayer distance for M+-exchanged KTO (M = Li, Na, Rb, and Cs) was dependent on cation type. Raman and X-ray absorption near-edge structure spectroscopic analyses of the KTO samples indicated that certain Ti species in KTO underwent hydrolysis, and thereby formed hydroxyl groups on the KTO surface during ion exchange. The origin of the high Li+ selectivity of KTO is discussed herein based on experimental characterization results.