Next Article in Journal
An Approach for Predicting the Apparent Color of Carpets under Different Illuminants
Previous Article in Journal
Two or Four Weeks Acute: Chronic Workload Ratio Is More Useful to Prevent Injuries in Soccer?
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Applied Sciences
Volume 13
Issue 1
10.3390/app13010497
applsci-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Efficient Capture of Sr2+ Ions by a Layered Potassium Neodymium Phosphate

by
Yuexin Yao
1,2,
Haiyan Sun
2,
Yanling Guo
2,
Cheng Cheng
2,
Tinghui Zhuang
2,
Jiating Liu
1,2,
Meiling Feng
2,* and
Xiaoying Huang
2,*
1
College of Chemistry, Fuzhou University, Fuzhou 350116, China
2
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2023, 13(1), 497; https://doi.org/10.3390/app13010497
Submission received: 1 December 2022 / Revised: 23 December 2022 / Accepted: 27 December 2022 / Published: 30 December 2022
(This article belongs to the Section Materials Science and Engineering)
Browse Figures
Versions Notes

Abstract

:
90Sr has a long half-life, strong radioactivity, and high mobility. The removal of radioactive strontium from the water environment is of great significance to human safety and the sustainable development of nuclear energy. In this study, a two-dimensional rare earth phosphate K3Nd(PO4)2 efficiently captured Sr2+ ions in aqueous solutions. At room temperature, the adsorption isotherm, kinetics, and pH dependence experiments of K3Nd(PO4)2 for Sr2+ ions were examined (V/m = 1000 mL/g, 12 h contact time). The experimental results show that the maximum adsorption capacity of K3Nd(PO4)2 for Sr2+ (qmSr) was 42.35 mg/g. The removal efficiency for Sr2+ (RSr) was 87.47% within 24 h. It had a good affinity with Sr2+ ions in neutral or even high alkaline environments (distribution coefficient KdSr = 1.46 × 106 mL/g, RSr = 99.93%). The adsorption mechanism was attributed to the ion exchange between Sr2+ and K+ ions by batch adsorption experiments combined with multiple characterizations, including XPS, EDS, and PXRD. This is the first report of Sr2+ removal by ion exchange via rare earth phosphate materials with a two-dimensional structure. This work provides insight into the future development of rare earth phosphates as ion exchange materials for radionuclide remediation.

1. Introduction

As a clean energy, nuclear energy has developed rapidly, accompanied by the aggravation of spent fuel containing uranium, plutonium, and fission products [1]. Spent fuel generates highly radioactive waste during reprocessing, of which 90Sr is one of the main components and one of the main radioactive sources [2]. 90Sr, with a long half-life (t1/2 = 29 y), can emit highly energetic β particles (0.546 MeV) [3]. It is often present in ionic form and has high environmental mobility [4,5]. After the leakage accident in the Fukushima Daiichi Nuclear Power Plant (FDNPP) in 2011, it was found that the activity of 90Sr was two orders of magnitude higher than the environmental background level in offshore waters 100–200 km from Fukushima [6]. 90Sr is chemically similar to calcium, and once ingested by the human body through the food chain, it will accumulate in bones and teeth and participate in the metabolism, which will lead to bone cancer or leukemia [2,7,8,9]. Part of the concern about nuclear safety is precisely the fear of the dreaded radioactive disease. The Japanese government’s decision in 2021 to discharge nuclear wastewater from the nuclear accident at FDNPP into the Pacific Ocean has raised global concerns about the safety and environmental consequences of nuclear power [10,11]. Thus, it is of vital significance to study Sr2+ removal from radioactive waste streams for the sake of human safety and the sustainable development of nuclear energy.
To date, methods for the removal of strontium from contaminated aqueous solution mainly include chemical precipitation, reverse osmoses, adsorption, solvent extraction, and ion exchange [12,13]. Among these methods, ion exchange receives much concern due to its advantages of low cost, simple operation, high selectivity, and less secondary pollution [12,14,15]. In this regard, various ion exchange agents have been investigated for the elimination of strontium from aqueous liquid radioactive wastes, such as zeolites [16], clays [17], silicotitanates [18], metal organic frameworks [19], and metal sulfides [20,21]. Among these adsorbents, inorganic ion exchange agents are favored because of their high thermal stability, high radiation resistance, chemical stability, and good selectivity [22].
In recent years, the application of metal phosphates in nonlinear optics, catalysis, proton conduction, and batteries has received extensive attention [23,24,25,26,27,28]. Practically, metal phosphates are also a class of momentous ion exchange materials [29]. Benefitting from the rigid structure of PO4 tetrahedron, metal phosphates have the features of high chemical and thermal stabilities and low radiation damage, which make them have broad prospects in the removal of radionuclides [30,31]. Thus far, numerous studies have proven that alkali metal ions or protons as exchangeable ions in metal phosphates can be exchanged for the effective separation of radioactive ions from aqueous solution environments [31,32,33,34,35,36]. As early as in the last century, classical metal phosphate cation exchange materials with a two-dimensional layered structure were developed, namely M(HPO4)2·H2O (M = Zr, Ti, Hf, Ge, Sn, Pb) [37]. Among them, Zr(HPO4)2·H2O (α-ZrP) has been widely studied as the representative for the efficient removal of metal ions, including Sr2+, Cs+, and rare earth cations, which have high thermal stability [38]. In addition, metal phosphates containing alkali metal ions with a layered or porous three-dimensional structure are also considered to be potential materials for the selective separation of radioactive ions [39]. It is worth noting that rare earth metal phosphates are rarely reported for the removal of Sr2+. A tetravalent cerium phosphate with a three-dimensional structure, namely K2Ce(PO4)2, was studied with the Sr2+ ion exchange capacity of 45.65 mg/g [32,39]. In addition, a cerium hydrogen phosphate Ce(PO4)(HPO4)0.5(H2O)0.5 with a two-dimensional structure can remove Sr2+; however, it was concluded that the Sr2+ ions were only adsorbed on the surface of the material without entering the structure [40].
Our research group has been focusing on the development of new inorganic ion exchangers for the removal of radioactive metal ions and has obtained a variety of anionic framework materials with various counter-cations as exchangeable ions for the removal of Sr2+, Cs+, and UO22+ [3,21,41,42,43]. In this work, we screened an anionic layered neodymium phosphate with K+ as the counter-cation, namely K3Nd(PO4)2 [44,45,46], which can be synthesized in gram-scale. K3Nd(PO4)2 exhibits the ion exchange performance for Sr2+, and it has a wide range of pH applicability (pH = 3.07–12.17). In both the neutral and alkaline environment, the removal efficiency (RSr) was greater than 99.7%. Notably, the distribution coefficient Kd was as high as 1.46 × 106 mL/g at pH = 8.07, indicating a strong affinity for Sr2+. In addition, through batch adsorption experiments and various characterization (XPS, EDS, PXRD) verifications, the Sr2+ adsorption mechanism was identified clearly as the ion exchange between Sr2+ and K+ ions in K3Nd(PO4)2. As far as we know, K3Nd(PO4)2 is the first rare earth phosphate with a two-dimensional structure that exhibits as an ion exchange material for the efficient removal of Sr2+ ions. This work paves the way for the development of layered rare earth metal phosphates as ion exchange materials for radionuclide remediation.

2. Materials and Methods

2.1. Materials

K2C2O4·H2O (Greagent, 99%), Nd2O3 (Tianjin Yingda Rare Chemical Reagent Plant, 99%), NH4H2PO4 (Greagent, 99%), SrCl2·6H2O (Tianjin Guangfu Fine Chemical Industry Research Institute, AR), HNO3 (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China, 65∼68%), NaOH (Tianjin Guangfu Fine Chemical Industry Research Institute, Tianjin, China, AR), and ultrapure water generated by a water purifier in the laboratory (Sichuan Water Treatment Equipment Co., Ltd., Sichuan, China, WP-UP-LH-10) were used. All reagents were utilized without further purification.

2.2. Methods

2.2.1. Preparation of the K3Nd(PO4)2

According to the previously reported method [44], a powder mixture of K2C2O4·H2O (0.8290 g, 4.5 mmol), Nd2O3 (0.5047 g, 1.5 mmol), and NH4H2PO4 (0.6905 g, 6.0 mmol) in the molar ratio of 3:1:4 was carefully ground in an agate mortar and then transferred to a 20 mL alumina crucible, which was then put in a muffle furnace. After preheating at 170 °C for 4 h, the temperature was raised to 900 °C, and the alumina crucible was kept in the furnace at this temperature for 16 h and then cooled down to room temperature for 12 h. The resultant solid products were washed with ultrapure water and dried in the air (yield: 1.281 g, 94.58% based on Nd).

2.2.2. Characterizations

Powder x-ray diffraction (PXRD) patterns of samples were obtained in the 2θ range of 5–65° by Miniflex II diffractometer (Rigaku, Japan) with CuKα radiation (λ = 1.54178 Å). Energy dispersive spectroscopy (EDS), elemental distribution mapping, and scanning electron microscopy (SEM) were studied with a JSM-6700F scanning electron microscope (JEOL, Akishima, Japan). Samples used in SEM were pressed by the tablet press and cut by the blade. X-ray photoelectron spectroscopy (XPS) analyses of the samples before and after the exchange were performed on the ESCALAB 250Xi XPS spectrometer (Thermo Scientific, Waltham, MA, USA). The detection of ion concentration was carried out by using inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP-OES) on an XSeries II and a iCAP 7400 (Thermo Scientific, Waltham, MA, USA), respectively. Ultraviolet-visible (UV/Vis) spectra were performed on the samples by using the UV-2600 spectrophotometer (Shimadzu, Japan) with BaSO4 as the reference. pH values of all solutions were tested by the Shanghai Rex PHS-2F pH meter.

2.2.3. Batch Adsorption Experiments

Adsorption studies were performed using the batch method. Before the adsorption experiments, we prepared the required Sr2+ solution. A certain amount of SrCl2·6H2O was dissolved in ultrapure water and then diluted to different concentrations of Sr2+ solution. Such as in a typical adsorption experiment, a certain amount of K3Nd(PO4)2 powder was weighed in a glass bottle and added with a suitable concentration of Sr2+ solution (V/m = 1000 mL/g, V is the solution volume, m is the mass of K3Nd(PO4)2 powder), and then the mixture was stirred using a magnetic stirrer at 800 r/min for 12 h at room temperature. After stirring, the supernatant was filtered with a polyethersulfone (PES) needle filter with a pore size of 0.22 μm. In order to ensure that the concentration of metal ions in the solution met the testing requirements of the ICP-MS/ICP-OES instrument, the filtered solution was diluted with 2% HNO3. This can avoid problems such as clogging the atomizer.
In the adsorption isotherm study, the aqueous solutions with different initial Sr2+ concentrations (12.565–756 mg/L) were used under neutral conditions. The kinetic experiment was performed in a neutral solution with an initial Sr2+ concentration of 3.650 mg/L. The suspensions were taken at selected reaction times (0, 2, 5, 10, 20, 30, 60, 90, 120, 180, 360, 720, and 1440 min). In pH-dependent experiments, the pH range of Sr2+ solutions were from 3.07 to 12.17. The initial Sr2+ concentrations were from 4.445 to 4.750 mg/L. ICP-OES was used to determine the concentration Sr2+ ions in the solutions before and after Sr2+ adsorption, and ICP-MS was used to determine the leaching concentration of Nd3+ in the solutions in the pH-dependent experiments.

3. Results and Discussion

3.1. Crystal Structures

K3Nd(PO4)2 is structurally similar to arcanite (K2SO4) and it is a monoclinic distortion of the glaserite (K3Na(SO4)2) structure [44,46,47,48]. The Nd3+ ion is bonded to a bidentate phosphate group and five monodentate phosphate groups, which belong to the sevenfold coordination (Figure 1a). Each [NdO7] polyhedron is connected to six [PO4] tetrahedra. Among six [PO4] tetrahedra, one [PO4] tetrahedron shares an edge with [NdO7], and the remaining five [PO4] tetrahedra connect with [NdO7] by corner-sharing. Each phosphate group links three Nd3+ ions. Every two [NdO7] are connected by two [PO4] tetrahedra in this way to eventually form a [Nd(PO4)2]n3n− layer parallel to the bc plane (Figure 1b). K+ ions are located in the interlayer spaces as the charge compensation ions (Figure 1c). Previous studies demonstrated that K+ ions in the interlayer space of some layered structures can often serve as exchangeable ions to exchange Sr2+, Cs+, UO22+, La3+, Eu3+, Pr3+, and 241Am3+ in solutions [49,50,51]. Here, exchangeable K+ ions are contained between the infinite layers of K3Nd(PO4)2 [44,46], which provides favorable conditions for ion exchange. We speculate that K+ ions in layered K3Nd(PO4)2 can also be exchanged with Sr2+, as schematically shown in Figure 1c.

3.2. Removal of Sr2+ from Aqueous Solutions

3.2.1. Adsorption Isotherms

Firstly, we studied the adsorption isotherm to obtain the maximum adsorption capacity of K3Nd(PO4)2 for Sr2+ ions at room temperature. Langmuir (Equation (S1)), Freundlich (Equation (S2)) and Langmuir-Freundlich (Equation (S3)) models [52,53] were used to fit the experimental results of adsorption isotherms (Table S1).
Langmuir and Freundlich adsorption models are two-parameter models commonly used to describe the adsorption equilibrium behavior, while the Langmuir–Freundlich adsorption model is a three-parameter model [54]. The Langmuir model assumes that the surface of the adsorbent is uniform, the energy of each adsorption center is the same, and each site receives at most one molecule or ion adsorption. The maximum adsorption capacity (qm) (Equation (S1)) corresponds to the saturation number of ions adsorbed on the surface of the adsorbent in a single layer. The Freundlich and Langmuir–Freundlich isotherms assume that the adsorbent surface is heterogeneous [55,56].
The fitting curves of all models are shown in Figure 2a, and the correlation coefficients are listed in Table 1. The results show that the Langmuir model had the highest coefficient of determination (R2 = 0.9938) compared to the Langmuir–Freundlich model (R2 = 0.9929) and the Freundlich model (R2 = 0.8912). Thus, the adsorption behavior of K3Nd(PO4)2 for Sr2+ can be better fitted with the Langmuir model. The maximum adsorption capacity (qmSr) (Equation (S1)) fitted by the Langmuir model was 42.60 mg/g, which was much larger than that of the commercial AMP-PAN (15 mg/g) [57] and close to the experimental result (40.7 mg/g, Table S1, calculated by Equation (S4)). However, it was quite different from the theoretical adsorption capacity (240.52 mg/g, calculated by Equation (S5)) (assuming that K+ is completely exchanged by Sr2+). This indicates that the K+ ions between the layers were partially exchanged by Sr2+ ions.

3.2.2. Kinetic Studies of Sr2+ Adsorption

In order to obtain the equilibrium time of K3Nd(PO4)2 for Sr2+ removal, we carried out the kinetic study of Sr2+ adsorption at room temperature. As shown in Figure 2b, the removal efficiency of Sr2+ (RSr) (Equation (S6)) increased with time. It captured 87.47% of Sr2+ ions within 24 hours, and the concentration of Sr2+ ions was greatly reduced from 3.425 mg/L to 0.429 mg/L (Table S2). Two classical kinetic models, the pseudo-first-order kinetic equation (Equation (S7)) and the pseudo-second-order kinetic equation (Equation (S8)) [58], were used to fit the experimental results (Table S3). Compared with the pseudo-first-order kinetics, the kinetic data were better fitted by the pseudo-second-order kinetic model with R2 of 0.96059 (Figure 2c,d). It is worth noting that the pseudo-second-order kinetic model is based on the assumption that the chemical interaction is the limiting step of the reaction. The chemical interaction here included the covalent electron or exchange electron reaction between the adsorbent and the metal ions in the solution at the solid–liquid interface [32]. This indicates that the Sr2+ adsorption of K3Nd(PO4)2 was a prosperous chemical adsorption process rather than a mass transfer in solutions [59].

3.2.3. pH-Dependent Experiments

Taking into account that the radioactive waste liquid is treated at different degrees of acidity and alkalinity [14], and the pH of the solution has a great influence on the adsorption process [60], it is not negligible to study the Sr2+ adsorption of K3Nd(PO4)2 under different pH values. Therefore, we investigated the Sr2+ adsorption of K3Nd(PO4)2 in the pH range 3.07–12.17 (Figure 3a, Table S4).
After strenuous stirring of the Sr2+ solutions (pH = 3.07–12.17) for 12 h, K3Nd(PO4)2 was not dissolved. In the powder x-ray diffraction (PXRD) patterns of the sample after stirring in different pH solutions, the characteristic peaks can well match with those of the pristine K3Nd(PO4)2 (Figure 3b). This confirms that the structure of K3Nd(PO4)2 did not collapse during the experiments. At the pH of 3.07, the leaching percentage of Nd (%) (Equation (S9), Figure S1) was 3.76%. It is worth noting that the leaching percentage of Nd (%) was less than 0.5% in the pH range from 7.00 to 12.17. These results demonstrate that the structure of K3Nd(PO4)2 can maintain good stability during the adsorption process. In neutral to strong alkaline solutions with the initial Sr2+ concentration (C0Sr) of about 4.5 mg/L, the RSr values were greater than 99.7%, and the distribution coefficient values (KdSr, Equation (S10)) were greater than 105. Especially at the pH of 8.07, the RSr reached 99.93% and KdSr was up to 1.46 × 106 mL/g, which was greater than those of many absorbents, such as 3D-K2Ce(PO4)2 (~8.0 × 103 mL/g), 2D-K2Zr(PO4)2 (~3.0 × 104 mL/g) and 2D-HUO2PO4·3H2O (6.90 × 103) (Table 2). It is generally believed that, when Kd reaches 104, the adsorbent has an excellent affinity for the targeted ions. This shows that K3Nd(PO4)2 can not only effectively remove Sr2+ in the pH range from 3.07 to 12.17, but it also has a high affinity for Sr2+ under neutral and alkaline conditions.

3.3. Adsorption Mechanism Study

The powder x-ray diffraction (PXRD) patterns of K3Nd(PO4)2 and its Sr2+ adsorption product (K3Nd(PO4)2-Sr) are shown in Figure 4a. By comparing the simulated pattern from K3Nd(PO4)2 single crystal diffraction data with the measured one of K3Nd(PO4)2 and K3Nd(PO4)2-Sr, it was confirmed that the sample of K3Nd(PO4)2 was pure and K3Nd(PO4)2-Sr maintained the layered structure of the pristine. The color of the pristine K3Nd(PO4)2 powder was light purple (Figure 4b(Ⅰ)), while that of K3Nd(PO4)2-Sr powder was white (Figure 4b(Ⅱ), photos taken under the same light intensity). The UV-Vis spectra of K3Nd(PO4)2 and K3Nd(PO4)2-Sr are shown in Figure S2. The band characteristics of K3Nd(PO4)2 are complex. The absorption peaks of K3Nd(PO4)2 are all specially owned to the f-f transition of 4f electrons of Nd3+ ions from 4I9/2 ground level to excitation level [45,66]. After adsorbing Sr2+, no new absorption band appeared. This shows that Sr2+ did not change the original coordination environment of Nd3+ ions in the anion layer after adsorption. Energy dispersive X-ray spectroscopy (EDS) analysis of the adsorption product K3Nd(PO4)2-Sr showed that Sr2+ ions entered the structure of K3Nd(PO4)2, but there still existed the potassium element (Figure S3). This proves that K3Nd(PO4)2 has the ability to adsorb Sr2+ in the solutions. By comparing the elemental distribution of K3Nd(PO4)2 and K3Nd(PO4)2-Sr (Figure 4c), it was confirmed that the strontium was uniformly distributed on the K3Nd(PO4)2-Sr sample. Scanning electron microscopy (SEM) images showed that the surfaces of the K3Nd(PO4)2-Sr were no longer smooth, but they still retained the grain morphology (Figure S4). These prove that Sr2+ ions are indeed successfully adsorbed by K3Nd(PO4)2.
In order to better clarify the adsorption mechanism, we tested the XPS of K3Nd(PO4)2 and K3Nd(PO4)2-Sr samples. In the XPS survey spectra (Figure 5a), the characteristic peak at ~133 eV in pristine K3Nd(PO4)2 was ascribed to P2p (Figure 5b). The characteristic peaks of Sr3d and Sr3p appeared in the XPS survey spectra of K3Nd(PO4)2-Sr at ~134 eV and ~296.66 eV, respectively (Figure 5a). Two obvious peaks (133.6 eV and 135.5 eV) can be clearly observed in the high-resolution XPS spectra of Sr3d for K3Nd(PO4)2-Sr, corresponding to Sr3d5/2 and Sr3d3/2, respectively (Figure 5c). Meanwhile, the characteristic peaks of K2s and K2p of K3Nd(PO4)2-Sr were lower than the pristine K3Nd(PO4)2 at ~377.7 eV and ~292.4 eV, but they did not disappear completely in the XPS survey spectra of K3Nd(PO4)2-Sr (Figure 5a). This phenomenon can be seen more clearly in the high-resolution XPS spectra of K2p for K3Nd(PO4)2 and K3Nd(PO4)2-Sr (Figure 5d). The above results confirm that the Sr2+ adsorption mechanism of K3Nd(PO4)2 is the ion exchange between Sr2+ and K+ ions in the interlayers of K3Nd(PO4)2.

4. Conclusions

A two-dimensional layered neodymium phosphate K3Nd(PO4)2 presented efficient adsorption for Sr2+ ions. The adsorption properties of K3Nd(PO4)2 for Sr2+ were studied by batch experiments. The adsorption capacity of K3Nd(PO4)2 was 42.35 mg/g. The material had good stability in the range of pH from 3.07 to 12.17, with a low leaching percentage of Nd (<3.76%). At a pH of 8.07, the highest value of KdSr was observed (>106), and the removal efficiency was as high as 99.93%. The mechanism of K3Nd(PO4)2 adsorbing Sr2+ ions was the ion exchange between K+ and Sr2+, which was confirmed by XPS, EDS, PXRD, etc. K3Nd(PO4)2 represents the first two-dimensional rare earth phosphate studied for the removal of Sr2+ ions by ion exchange. This work highlights the subsequent research on the removal of radionuclides by rare earth phosphate ion exchange agents.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/app13010497/s1, Figure S1: Leaching percentages of Nd (%) in Sr2+ solutions with different pH; Figure S2: Solid state UV/Vis absorption spectra for the pristine K3Nd(PO4)2 (black line) and K3Nd(PO4)2-Sr (magenta line) measured at room temperature; Figure S3: Energy dispersive spectroscopy (EDS) analysis of the adsorption product K3Nd(PO4)2-Sr; Figure S4: Scanning electron microscope images for the pristine K3Nd(PO4)2 (a) and the adsorption product K3Nd(PO4)2-Sr (b); Table S1: Adsorption capacities for K3Nd(PO4)2 at different initial Sr2+ concentrations; Table S2: The data for the concentrations of Sr2+ (CtSr) and the relative amounts of Sr2+ removed (RSr) for K3Nd(PO4)2 at different time in kinetics experiments under neutral conditions; Table S3: The fitting data with the pseudo-first-order kinetic model and pseudo-second-order kinetic model for the removal kinetics of Sr2+ ions of K3Nd(PO4)2; Table S4: The adsorption results of K3Nd(PO4)2 for Sr2+ in different pH solutions.

Author Contributions

Conceptualization, Y.Y. and M.F.; formal analysis, Y.Y., H.S., Y.G., C.C. and T.Z.; investigation, Y.Y.; data curation, Y.Y.; writing—original draft preparation, Y.Y.; writing—review and editing, M.F., J.L. and X.H.; visualization, H.S. and X.H.; project administration, M.F.; funding acquisition, M.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (grant numbers U21A20296, 22076185 and 21771183) and the Natural Science Foundation of Fujian Province (grant number 2020J06033).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available in this article or supplementary material.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Veliscek-Carolan, J. Separation of actinides from spent nuclear fuel: A review. J. Hazard. Mater. 2016, 318, 266–281. [Google Scholar] [CrossRef] [PubMed]
  2. Inan, S. Inorganic ion exchangers for strontium removal from radioactive waste: A review. J. Radioanal. Nucl. Chem. 2022, 331, 1137–1154. [Google Scholar] [CrossRef]
  3. Lv, T.T.; Ma, W.; Zhang, D.; Zhang, T.; Tang, J.H.; Zeng, X.; Feng, M.L.; Huang, X.Y. Rapid and highly selective Sr2+ uptake by 3D microporous rare earth oxalates with the facile synthesis, high water stability and radiation resistance. Chem. Eng. J. 2022, 435, 134906. [Google Scholar] [CrossRef]
  4. Zhang, J.R.; Chen, L.H.; Dai, X.; Zhu, L.; Xiao, C.L.; Xu, L.; Zhang, Z.Y.; Alekseev, E.V.; Wang, Y.X.; Zhang, C.; et al. Distinctive two-step intercalation of Sr2+ into a coordination polymer with record high Sr-90 uptake capabilities. Chem 2019, 5, 977–994. [Google Scholar] [CrossRef]
  5. Burger, A.; Lichtscheidl, I. Strontium in the environment: Review about reactions of plants towards stable and radioactive strontium isotopes. Sci. Total Environ. 2019, 653, 1458–1512. [Google Scholar] [CrossRef]
  6. Casacuberta, N.; Masque, P.; Garcia-Orellana, J.; Garcia-Tenorio, R.; Buesseler, K.O. Sr-90 and Sr-89 in seawater off Japan as a consequence of the Fukushima Dai-ichi nuclear accident. Biogeosciences 2013, 10, 3649–3659. [Google Scholar] [CrossRef] [Green Version]
  7. Martell, E.A. Atmospheric aspects of strontium-90 fallout. Science 1959, 129, 1197–1206. [Google Scholar] [CrossRef]
  8. Shao, Y.; Yang, G.S.; Tazoe, H.; Ma, L.L.; Yamada, M.; Xu, D.D. A review of measurement methodologies and their applications to environmental Sr-90. J. Environ. Radioact. 2018, 192, 321–333. [Google Scholar] [CrossRef]
  9. Zhang, X.; Liu, Y. Integrated forward osmosis-adsorption process for strontium-containing water treatment: Pre-concentration and solidification. J. Hazard. Mater. 2021, 414, 125518. [Google Scholar] [CrossRef]
  10. Lu, Y.; Yuan, J.; Du, D.; Sun, B.; Yi, X. Monitoring long-term ecological impacts from release of Fukushima radiation water into ocean. Geogr. Sustain. 2021, 2, 95–98. [Google Scholar] [CrossRef]
  11. Xin, X.; Liu, M.H.; Wang, X.L.; Zhang, T.; Gao, L.Y.; Chen, K. Evolutionary analysis of Japan’s nuclear wastewater discharge events considering the impact of participants’ emotions. Ocean Coast. Manag. 2022, 225, 106231. [Google Scholar] [CrossRef]
  12. Rahman, R.O.A.; Ibrahium, H.A.; Hung, Y.-T. Liquid radioactive wastes treatment: A review. Water 2011, 3, 551–565. [Google Scholar] [CrossRef] [Green Version]
  13. Tochaikul, G.; Phattanasub, A.; Khemkham, P.; Saengthamthawee, K.; Danthanavat, N.; Moonkum, N. Radioactive waste treatment technology: A review. Kerntechnik 2022, 87, 208–225. [Google Scholar] [CrossRef]
  14. Manos, M.J.; Kanatzidis, M.G. Metal sulfide ion exchangers: Superior sorbents for the capture of toxic and nuclear waste-related metal ions. Chem. Sci. 2016, 7, 4804–4824. [Google Scholar] [CrossRef] [Green Version]
  15. Sun, H.Y.; Liu, Y.; Lin, J.; Yue, Z.H.; Li, W.A.; Jin, J.C.; Sun, Q.; Ai, Y.J.; Feng, M.L.; Huang, X.Y. Highly selective recovery of lanthanides by using a layered vanadate with acid and radiation resistance. Angew. Chem. Int. Ed. 2020, 59, 1878–1883. [Google Scholar] [CrossRef] [PubMed]
  16. Smiciklas, I.; Dimovic, S.; Plecas, I. Removal of Cs1+, Sr2+ and Co2+ from aqueous solutions by adsorption on natural clinoptilolite. Appl. Clay Sci. 2007, 35, 139–144. [Google Scholar] [CrossRef]
  17. Seliman, A.F.; Lasheen, Y.F.; Youssief, M.A.E.; Abo-Aly, M.M.; Shehata, F.A. Removal of some radionuclides from contaminated solution using natural clay: Bentonite. J. Radioanal. Nucl. Chem. 2014, 300, 969–979. [Google Scholar] [CrossRef]
  18. Chitra, S.; Shanmugamani, A.G.; Sudha, R.; Kalavathi, S.; Paul, B. Selective removal of cesium and strontium by crystalline silicotitanates. J. Radioanal. Nucl. Chem. 2017, 312, 507–515. [Google Scholar] [CrossRef]
  19. Aguila, B.; Banerjee, D.; Nie, Z.M.; Shin, Y.; Ma, S.Q.; Thallapally, P.K. Selective removal of cesium and strontium using porous frameworks from high level nuclear waste. Chem. Commun. 2016, 52, 5940–5942. [Google Scholar] [CrossRef]
  20. Manos, M.J.; Ding, N.; Kanatzidis, M.G. Layered metal sulfides: Exceptionally selective agents for radioactive strontium removal. Proc. Natl. Acad. Sci. USA 2008, 105, 3696–3699. [Google Scholar] [CrossRef]
  21. Qi, X.H.; Du, K.Z.; Feng, M.L.; Li, J.R.; Du, C.F.; Zhang, B.; Huang, X.Y. A two-dimensionally microporous thiostannate with superior Cs+ and Sr2+ ion-exchange property. J. Mater. Chem. A 2015, 3, 5665–5673. [Google Scholar] [CrossRef]
  22. Alberti, G.; Costantino, U. Recent progress in field of synthetic inorganic exchangers having a layered or fibrous structure. J. Chromatogr. A 1974, 102, 5–29. [Google Scholar] [CrossRef]
  23. Deng, Y.L.; Huang, L.; Dong, X.H.; Wang, L.; Ok, K.M.; Zeng, H.M.; Lin, Z.; Zou, G.H. K2Sb(P2O7)F: Cairo pentagonal layer with bifunctional genes reveal optical performance. Angew. Chem. Int. Ed. 2020, 59, 21151–21156. [Google Scholar] [CrossRef] [PubMed]
  24. Zeng, L.C.; Huang, L.C.; Zhu, J.H.; Li, P.P.; Chu, P.K.; Wang, J.H.; Yu, X.F. Phosphorus-based materials for high-performance alkaline metal ion batteries: Progress and prospect. Small 2022, 18, 2201808. [Google Scholar] [CrossRef] [PubMed]
  25. Zhao, H.; Yuan, Z.Y. Insights into transition metal phosphate materials for efficient electrocatalysis. ChemCatChem 2020, 12, 3797–3810. [Google Scholar] [CrossRef]
  26. Munkaila, S.; Dahal, R.; Kokayi, M.; Jackson, T.; Bastakoti, B.P. Hollow structured transition metal phosphates and their applications. Chem. Rec. 2022, 22, e202200084. [Google Scholar] [CrossRef] [PubMed]
  27. Lee, S.K.; Lee, U.H.; Hwang, Y.K.; Chang, J.S.; Jang, N.H. Catalytic and sorption applications of porous nickel phosphate materials. Catal. Today 2019, 324, 154–166. [Google Scholar] [CrossRef]
  28. Colodrero, R.M.P.; Olivera-Pastor, P.; Cabeza, A.; Bazaga-Garcia, M. Properties and applications of metal phosphates and pyrophosphates as proton conductors. Materials 2022, 15, 1292. [Google Scholar] [CrossRef] [PubMed]
  29. Clearfield, A. Role of ion exchange in solid-state chemistry. Chem. Rev. 1988, 88, 125–148. [Google Scholar] [CrossRef]
  30. Lu, X.F.; Chen, Z.H.; Shi, X.R.; Jing, Q.; Lee, M.H. Two pyrophosphates with large birefringences and second-harmonic responses as ultraviolet nonlinear optical materials. Angew. Chem. Int. Ed. 2020, 59, 17648–17656. [Google Scholar] [CrossRef] [PubMed]
  31. Hirose, N.; Kuwano, J. Ion-exchange properties of nasicon-type phosphates with the frameworks [Ti2(PO4)3] and [Ti1.7Al0.3(PO4)3]. J. Mater. Chem. 1994, 4, 9–12. [Google Scholar] [CrossRef]
  32. Bevara, S.; Giri, P.; Patwe, S.J.; Achary, S.N.; Mishra, R.K.; Kumar, A.; Sinha, A.K.; Kaushik, C.P.; Tyagi, A.K. Separation of 90Sr from nuclear waste by crystalline complex phosphates of Ce(IV) and Zr(IV). J. Environ. Chem. Eng. 2018, 6, 2248–2261. [Google Scholar] [CrossRef]
  33. Roelofs, M.G.; Morris, P.A.; Bierlein, J.D. Ion exchange of Rb, Ba, and Sr in KTiOPO4. J. Appl. Phys. 1991, 70, 720–728. [Google Scholar] [CrossRef]
  34. Daneshvar, K.; Giess, E.A.; Bacon, A.M.; Dawes, D.G.; Gea, L.A.; Boatner, L.A. Ion exchange in potassium titanyl phosphate. Appl. Phys. Lett. 1997, 71, 756–758. [Google Scholar] [CrossRef]
  35. Zouad, S.; Jeanjean, J.; Loosneskovic, C.; Fedoroff, M.; Piffard, Y. Sorption of strontium and lanthanum on polyantimonic acid and two phosphatoantimonic acids. J. Radioanal. Nucl. Chem. Art. 1994, 182, 193–204. [Google Scholar] [CrossRef]
  36. Jeanjean, J.; Fedoroff, M.; Zouad, S.; Loosneskovic, C.; Piffard, Y. A comparative study of the sorption of strontium on polyantimonic acid (H2Sb2O6, x H2O) and phosphatoantimonic acid (H3Sb3O6(PO4)2, x H2O). Eur. J. Solid State Inorg. Chem. 1994, 31, 1037–1048. [Google Scholar]
  37. Clearfield, A. Inorganic ion exchangers with layered structures. Annu. Rev. Mater. Sci. 1984, 14, 205–229. [Google Scholar] [CrossRef]
  38. Bashir, A.; Ahad, S.; Malik, L.A.; Qureashi, A.; Manzoor, T.; Dar, G.N.; Pandith, A.H. Revisiting the old and golden inorganic material, zirconium phosphate: Synthesis, intercalation, surface functionalization, and metal ion uptake. Ind. Eng. Chem. Res. 2020, 59, 22353–22397. [Google Scholar] [CrossRef]
  39. Bevara, S.; Achary, S.N.; Patwe, S.J.; Sinha, A.K.; Mishra, R.K.; Kumar, A.; Kaushik, C.P.; Tyagi, A.K. Crystal structure and cation exchanging properties of a novel open framework phosphate of Ce (IV). In Proceedings of the DAE Solid State Physics Symposium, Noida, India, 21–25 December 2015. [Google Scholar]
  40. Romanchuk, A.Y.; Shekunova, T.O.; Larina, A.I.; Ivanova, O.S.; Baranchikov, A.E.; Ivanov, V.K.; Kalmykov, S.N. Sorption of radionuclides onto cerium(IV) hydrogen phosphate Ce(PO4)(HPO4)0.5 (H2O)0.5. Radiochemistry 2019, 61, 719–723. [Google Scholar] [CrossRef]
  41. Gao, Y.J.; Feng, M.L.; Zhang, B.; Wu, Z.F.; Song, Y.; Huang, X.Y. An easily synthesized microporous framework material for the selective capture of radioactive Cs+ and Sr2+ ions. J. Mater. Chem. A 2018, 6, 3967–3976. [Google Scholar] [CrossRef]
  42. Li, J.L.; Jin, J.C.; Zou, Y.M.; Sun, H.Y.; Zeng, X.; Huang, X.Y.; Feng, M.L.; Kanatzidis, M.G. Efficient removal of Cs+ and Sr2+ ions by granulous (Me2NH2)4/3(Me3NH)2/3Sn3S7·1.25H2O/polyacrylonitrile composite. ACS Appl. Mater. Interfaces 2021, 13, 13434–13442. [Google Scholar] [CrossRef] [PubMed]
  43. Feng, M.L.; Sarma, D.; Gao, Y.J.; Qi, X.H.; Li, W.A.; Huang, X.Y.; Kanatzidis, M.G. Efficient removal of [UO2]2+, Cs+, and Sr2+ ions by radiation-resistant gallium thioantimonates. J. Am. Chem. Soc. 2018, 140, 11133–11140. [Google Scholar] [CrossRef] [PubMed]
  44. Hong, H.Y.P.; Chinn, S.R. Crystal structure and fluorescence lifetime of potassium neodymium orthophosphate, K3Nd(PO4)2, a new laser material. Mater. Res. Bull. 1976, 11, 421–428. [Google Scholar] [CrossRef]
  45. Mizer, D.; Macalik, L.; Tomaszewski, P.E.; Lisiecki, R.; Godlewska, P.; Matraszek, A.; Szczygiel, I.; Zawadzki, M.; Hanuza, J. Structural and optical properties of nano-sized K3Nd(PO4)2:Yb3+ orthophosphate. J. Nanosci. Nanotechnol. 2009, 9, 5164–5169. [Google Scholar] [CrossRef]
  46. Farmer, J.M.; Boatner, L.A.; Chakoumakos, B.C.; Rawn, C.J.; Richardson, J. Structural and crystal chemical properties of alkali rare-earth double phosphates. J. Alloys Compd. 2016, 655, 253–265. [Google Scholar] [CrossRef] [Green Version]
  47. Okada, K.; Ossaka, J. Structures of potassium-sodium sulfate and tripotassium sodium disulfate. Acta Crystallogr. Sect. B Struct. Sci 1980, 36, 919–921. [Google Scholar] [CrossRef]
  48. Zubkova, N.V.; Pekov, I.V.; Ksenofontov, D.A.; Yapaskurt, V.O.; Pushcharovsky, D.Y.; Sidorov, E.G. Arcanite from fumarole exhalations of the Tolbachik Volcano (Kamchatka, Russia) and its crystal structure. Dokl. Earth Sci. 2018, 4791, 339–341. [Google Scholar] [CrossRef]
  49. Sarma, D.; Malliakas, C.D.; Subrahmanyam, K.S.; Islama, S.M.; Kanatzidis, M.G. K2xSn4-xS8-x (x = 0.65-1): A new metal sulfide for rapid and selective removal of Cs+, Sr2+ and UO22+ ions. Chem. Sci. 2016, 7, 1121–1132. [Google Scholar] [CrossRef] [Green Version]
  50. Griffith, C.S.; Luca, V.; Cochrane, J.; Hanna, J.V. Lanthanide/actinide ion-exchange and structural investigations of the layered phosphatoantimonic acid, H3Sb3P2O14·ZH2O. Microporous Mesoporous Mater. 2008, 111, 387–403. [Google Scholar] [CrossRef]
  51. Pekarek, V.; Benesova, M. A study on uranyl phosphates—I: Sorption properties of uranyl hydrogen phosphate. J. Inorg. Nucl. Chem. 1964, 26, 1743–1751. [Google Scholar] [CrossRef]
  52. Duong, D.D. Adsorption Analysis: Equilibria and Kinetics, 3rd ed.; Imperial College Press: London, UK, 1998; pp. 1–892. [Google Scholar]
  53. Dabrowski, A.; Oscik, J.; Rudzinski, W.; Jaroniec, M. Effects of surface heterogeneity in adsorption from binary liquid mixtures: II. Adsorption from nonideal bulk solutions. J. Colloid Interface Sci. 1979, 69, 287–300. [Google Scholar] [CrossRef]
  54. Zeng, L.; Li, X.M.; Liu, J.D. Adsorptive removal of phosphate from aqueous solutions using iron oxide tailings. Water Res. 2004, 38, 1318–1326. [Google Scholar] [CrossRef] [PubMed]
  55. Wang, Y.Q.; Zhang, Z.B.; Liu, Y.H.; Cao, X.H.; Liu, Y.T.; Li, Q. Adsorption of U(VI) from aqueous solution by the carboxyl-mesoporous carbon. Chem. Eng. J. 2012, 198, 246–253. [Google Scholar] [CrossRef]
  56. Lin, M.L.; Zhao, Z.W.; Cui, F.Y.; Xia, S.J. Modeling of equilibrium and kinetics of chlorobenzene (CB) adsorption onto powdered activated carbon (PAC) for drinking water treatment. Desalin. Water Treat. 2012, 44, 245–254. [Google Scholar] [CrossRef]
  57. Park, Y.; Lee, Y.C.; Shin, W.S.; Choi, S.J. Removal of cobalt, strontium and cesium from radioactive laundry wastewater by ammonium molybdophosphate-polyacrylonitrile (AMP-PAN). Chem. Eng. J. 2010, 162, 685–695. [Google Scholar] [CrossRef]
  58. Ho, Y.S.; McKay, G. A comparison of chemisorption kinetic models applied to pollutant removal on various sorbents. Process Saf. Environ. Protect. 1998, 76, 332–340. [Google Scholar] [CrossRef] [Green Version]
  59. Zhang, L.; Liu, Y.H.; Wang, Y.L.; Li, X.H.; Wang, Y.Y. Investigation of phosphate removal mechanisms by a lanthanum hydroxide adsorbent using p-XRD, FTIR and XPS. Appl. Surf. Sci. 2021, 557, 149838. [Google Scholar] [CrossRef]
  60. Liu, X.; Pang, H.; Liu, X.; Li, Q.; Zhang, N.; Mao, L.; Qiu, M.; Hu, B.; Yang, H.; Wang, X. Orderly porous covalent organic frameworks-based materials: Superior adsorbents for pollutants removal from aqueous solutions. Innovation 2021, 2, 100076. [Google Scholar] [CrossRef]
  61. Pekarek, V.; Vesely, V. A study on uranyl phosphates—II sorption properties of some 1- to 4-valent cations on uranyl hydrogen phosphate heated to various temperatures. J. Inorg. Nucl. Chem. 1965, 27, 1151–1158. [Google Scholar] [CrossRef]
  62. Li, Z.Q.; Vivas, E.L.; Yang, C.Y.; Suh, Y.J.; Cho, K.K. Layered potassium calcium phosphate with multiple exchangeable cations for Sr(II) and Co(II) removal from water. Sep. Purif. Technol. 2022, 299, 121789. [Google Scholar] [CrossRef]
  63. Ivanets, A.I.; Shashkova, I.L.; Kitikova, N.V.; Maslova, M.V.; Mudruk, N.V. New heterogeneous synthesis of mixed Ti-Ca-Mg phosphates as efficient sorbents of Cs-137, Sr-90 and Co-60 radionuclides. J. Taiwan Inst. Chem. Eng. 2019, 104, 151–159. [Google Scholar] [CrossRef]
  64. Ma, B.; Oh, S.; Shin, W.S.; Choi, S.J. Removal of Co2+, Sr2+ and Cs+ from aqueous solution by phosphate-modified montmorillonite (PMM). Desalination 2011, 276, 336–346. [Google Scholar] [CrossRef]
  65. Mironyuk, I.; Tatarchuk, T.; Vasylyeva, H.; Naushad, M.; Mykytyn, I. Adsorption of Sr(II) cations onto phosphated mesoporous titanium dioxide: Mechanism, isotherm and kinetics studies. J. Environ. Chem. Eng. 2019, 7, 103430. [Google Scholar] [CrossRef]
  66. Mullica, D.F.; Wilson, G.A.; Sappenfield, E.L. Application of an optical beam condenser for UV-Vis spectral studies on monoclinic LnPO4 single-crystals. Appl. Spectrosc. 1994, 48, 345–349. [Google Scholar] [CrossRef]
Applsci 13 00497 g001 550
Figure 1. (a) Coordination of Nd3+ ion by [PO4] tetrahedra in K3Nd(PO4)2; (b) an anionic layer of [Nd(PO4)2]n3n− in K3Nd(PO4)2; (c) the schematic diagram of ion exchange between Sr2+ and K+ ions in layered K3Nd(PO4)2. (The purple tetrahedra are PO4 and the lavender polyhedra are NdO7).
Figure 1. (a) Coordination of Nd3+ ion by [PO4] tetrahedra in K3Nd(PO4)2; (b) an anionic layer of [Nd(PO4)2]n3n− in K3Nd(PO4)2; (c) the schematic diagram of ion exchange between Sr2+ and K+ ions in layered K3Nd(PO4)2. (The purple tetrahedra are PO4 and the lavender polyhedra are NdO7).
Applsci 13 00497 g001
Applsci 13 00497 g002 550
Figure 2. (a) The equilibrium curves of K3Nd(PO4)2 for Sr2+ adsorption fitted by the Langmuir (blue line), Langmuir–Freundlich (red line), and Freundlich model (black line) isothermal adsorption models (C0Sr = 12.565−756.000 mg/L, pH = 6.03−6.82); (b) kinetics of K3Nd(PO4)2 plotted as Sr2+ concentration (mg/L) (black line) and removal efficiency (%) (blue line) vs. time t (min) under neutral conditions; (c) the pseudo-first-order kinetic model and (d) the pseudo-second-order kinetic model were used to fit the Sr2+ adsorption kinetics of K3Nd(PO4)2.
Figure 2. (a) The equilibrium curves of K3Nd(PO4)2 for Sr2+ adsorption fitted by the Langmuir (blue line), Langmuir–Freundlich (red line), and Freundlich model (black line) isothermal adsorption models (C0Sr = 12.565−756.000 mg/L, pH = 6.03−6.82); (b) kinetics of K3Nd(PO4)2 plotted as Sr2+ concentration (mg/L) (black line) and removal efficiency (%) (blue line) vs. time t (min) under neutral conditions; (c) the pseudo-first-order kinetic model and (d) the pseudo-second-order kinetic model were used to fit the Sr2+ adsorption kinetics of K3Nd(PO4)2.
Applsci 13 00497 g002
Applsci 13 00497 g003 550
Figure 3. (a) The effect of different pH on the Sr2+ adsorption of K3Nd(PO4)2 studied by plotting the relationship of KdSr (mL/g) (column) and RSr (line chart) vs. pH values; (b) PXRD patterns of K3Nd(PO4)2 samples before and after Sr2+ adsorption in the pH range from 3.07 to 12.17.
Figure 3. (a) The effect of different pH on the Sr2+ adsorption of K3Nd(PO4)2 studied by plotting the relationship of KdSr (mL/g) (column) and RSr (line chart) vs. pH values; (b) PXRD patterns of K3Nd(PO4)2 samples before and after Sr2+ adsorption in the pH range from 3.07 to 12.17.
Applsci 13 00497 g003
Applsci 13 00497 g004 550
Figure 4. (a) Simulated and experimental PXRD diagrams of K3Nd(PO4)2; (b) photographs of powder samples for K3Nd(PO4)2 (I) and K3Nd(PO4)2-Sr (II); (c) SEM of K3Nd(PO4)2 and K3Nd(PO4)2-Sr and their elemental distribution maps of K, Nd, P, and Sr elements.
Figure 4. (a) Simulated and experimental PXRD diagrams of K3Nd(PO4)2; (b) photographs of powder samples for K3Nd(PO4)2 (I) and K3Nd(PO4)2-Sr (II); (c) SEM of K3Nd(PO4)2 and K3Nd(PO4)2-Sr and their elemental distribution maps of K, Nd, P, and Sr elements.
Applsci 13 00497 g004
Applsci 13 00497 g005 550
Figure 5. (a) XPS survey spectra of the pristine K3Nd(PO4)2 and the adsorption product K3Nd(PO4)2-Sr; (b) high-resolution XPS spectra of P2p for the pristine K3Nd(PO4)2; (c) high-resolution XPS spectra of Sr3d for the adsorption product K3Nd(PO4)2-Sr; (d) high-resolution XPS spectra of K2p for the pristine K3Nd(PO4)2 and the adsorption product K3Nd(PO4)2-Sr.
Figure 5. (a) XPS survey spectra of the pristine K3Nd(PO4)2 and the adsorption product K3Nd(PO4)2-Sr; (b) high-resolution XPS spectra of P2p for the pristine K3Nd(PO4)2; (c) high-resolution XPS spectra of Sr3d for the adsorption product K3Nd(PO4)2-Sr; (d) high-resolution XPS spectra of K2p for the pristine K3Nd(PO4)2 and the adsorption product K3Nd(PO4)2-Sr.
Applsci 13 00497 g005
Table
Table 1. The isothermal adsorption fitting results of K3Nd(PO4)2 for Sr2+.
Table 1. The isothermal adsorption fitting results of K3Nd(PO4)2 for Sr2+.
ModelR2qm (mg/g)b (L/mg)nk
Langmiur0.993842.60 ± 1.430.02255 ± 0.00--
Freundlich0.8912--4.8673 ± 0.0611.01 ± 0.17
Langmuir–Freundlich0.992940.91 ± 2.620.02845 ± 0.010.8932 ± 0.16-
Table
Table 2. The comparison of the adsorption abilities of K3Nd(PO4)2 and other reported adsorbents for Sr2+.
Table 2. The comparison of the adsorption abilities of K3Nd(PO4)2 and other reported adsorbents for Sr2+.
AdsorbentqmSr
(mg/g)		teSr
(min)		Removal MechanismpH 1Solution
Composition 2		Distribution Coefficient (mL/g)Ref
2D 3-K3Nd(PO4)242.601440IE 48.03Sr1.46 × 106This work
2D-K2Zr(PO4)252.8390IE7.00Sr~30,000[32]
2D-UO2HPO4·4H2O98.57UM 5OTH 62.00Sr6.90 × 103[61]
2D-K3HCa(PO4)2384.00120IE7.00Sr2.30 × 104[62]
2D-H3Sb3P2O14314.73<15IE2.1–2.5Sr>106[36]
2D-Ce(PO4)(HPO4)0.5(H2O)0.5UMUMAD 7>9.00Np, Am, U, Th, SrUM[40]
3D-K2Ce(PO4)245.6560IE14.00Sr~8000[32]
3D-H5Sb5O12(PO4)2·7.3H2O123.19NC 8IE<1.00Sr>105[35]
Ca0.7Mg0.3HPO4·2H2OUMUMNC5.00Cs, Sr, Co0.14 × 103[63]
Ca2.65Mg3(NH4)1.3(PO4)4(CO3)0.3·6H2OUMUMNC5.00Cs, Sr, Co7.91 × 103[63]
phosphated montmorillonite12.5UMIE/SC 95.00Sr, CsUM[64]
2P-TiO294.160AD8.00SrUM[65]
8P-TiO2128.960AD9.00SrUM[65]
4P-TiO2172.560AD9.00SrUM[65]
1 The pH of solutions corresponding to the distribution coefficient values; 2 the composition of solutions corresponding to the distribution coefficient values; 3 the dimension is displayed in front of the adsorbent, the mixture is not displayed; 4 IE: ion exchange; 5 UM: not mentioned; 6 OTH(other): the formation of the Sr2+ formation of UO2HPO4·4H2O; 7 AD: adsorbent; 8 NC: not clear; 9 IE/SC: ion-exchange (pH < 8) and surface complexation (pH > 8).
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Yao, Y.; Sun, H.; Guo, Y.; Cheng, C.; Zhuang, T.; Liu, J.; Feng, M.; Huang, X. Efficient Capture of Sr2+ Ions by a Layered Potassium Neodymium Phosphate. Appl. Sci. 2023, 13, 497. https://doi.org/10.3390/app13010497

AMA Style

Yao Y, Sun H, Guo Y, Cheng C, Zhuang T, Liu J, Feng M, Huang X. Efficient Capture of Sr2+ Ions by a Layered Potassium Neodymium Phosphate. Applied Sciences. 2023; 13(1):497. https://doi.org/10.3390/app13010497

Chicago/Turabian Style

Yao, Yuexin, Haiyan Sun, Yanling Guo, Cheng Cheng, Tinghui Zhuang, Jiating Liu, Meiling Feng, and Xiaoying Huang. 2023. "Efficient Capture of Sr2+ Ions by a Layered Potassium Neodymium Phosphate" Applied Sciences 13, no. 1: 497. https://doi.org/10.3390/app13010497

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop