Layered metal sulfides with MaSbc- framework (M = Sb, In, Sn) as ion exchangers for the removal of Cs(Ⅰ) and Sr(Ⅱ) from radioactive effluents: a review

Abstract

Nuclear power has emerged as a pivotal contributor to the global electricity supply owing to its high efficiency and low-carbon characteristics. However, the rapid expansion of the nuclear industry has resulted in the production of a significant amount of hazardous effluents that contain various radionuclides, such as ¹³⁷Cs and ⁹⁰Sr. Effectively removing ¹³⁷Cs and ⁹⁰Sr from radioactive effluents prior to discharge is a critical challenge. Layered metal sulfides exhibit significant potential as ion exchangers for the efficient uptake of Cs⁺ and Sr²⁺ from aqueous solutions owing to their open and exchangeable frameworks and the distinctive properties of their soft S^2- ligands. This review provides a detailed account of layered metal sulfides with M_aS_b ^c- frameworks (M = Sb, In, Sn), including their synthesis methods, structural characteristics, and Cs⁺ and Sr²⁺ removal efficiencies. Furthermore, we highlight the advantages of layered metal sulfides, such as their relatively high ion exchange capacities, broad active pH ranges, and structural stability against acid and radiation, through a comparative evaluation with other conventional ion exchangers. Finally, we discuss the challenges regarding the practical application of layered metal sulfides in radionuclide scavenging.

Keywords: cesium; ion exchange; layered metal sulfides; radioactive effluents; strontium.

FIGURE 1

Categories of layered metal sulfides based on the framework composition (M_aS_b ^c−) reviewed in this paper.

FIGURE 2

(A) Appearances, (B) Kubelka–Munk spectra, (C) microscopic morphologies and elemental mapping images, (D) powder XRD patterns, and (E) d(002)-spacing variation of pristine SbS-1, activated SbS-1K, and ion-exchanged products SbS-1Cs and SbS-1Sr. Reprinted with permission from Zhao et al. (2022b). Copyright from John Wiley and Sons (2022).

FIGURE 3

(A) Schematic of the membrane fabrication process and the membrane filtration operation. (B,C) External appearances of the SbS-1K/PTFE membrane in its flat and bent forms. (D,E) SEM image of the amplified surface and cross section of the SbS-1K/PTFE membrane. (F) Variation in Cs⁺ and Sr²⁺ removal efficiencies with effluent volume in the membrane filtration for a Cs⁺–Sr²⁺ mixed solution (C ₀ = 1 ppm for each) at pH 6 and pH 2. Reprinted with permission from Zhao et al. (2022b). Copyright from John Wiley and Sons (2022).

FIGURE 4

(A) 16-membered ring of {In₈S₈} and (C) 24-membered ring of {In₁₂S₁₂}. The template-ring relationship for the formation of (B) InS-1 and (D) InS-2. Adapted with permission from Sun et al. (2020). Copyright from American Chemical Society (2020).

FIGURE 5

(A) Representative appearance of NaTS. Effects of (B) contact time (C _Sr = 5.0 mg/dm³, pH = 5.30, m/V = 0.5 g/dm³, t = 1–360 min), (C) initial Sr²⁺ concentration (pH = 5.5, m/V = 0.5 g/dm³, t = 2 h), (D) initial pH value (C _Sr = 5 mg/dm³, m/V = 0.5 g/dm³, t = 2 h), (E) adsorbent dosage (C _Sr = 5.0 mg/dm³, pH = 5.38, t = 2 h), and (F) the coexistence of Na⁺, K⁺, Ca²⁺, and Mg²⁺ (C _Sr = 5 mg/dm³, m/V = 0.5 g/dm³, t = 2 h) on the removal performance of Sr²⁺ by NaTS. Adapted with permission from Zhang et al. (2019b). Copyright from Elsevier (2019).

FIGURE 6

(A) Photographs showing FJSM-SnS crystals; (B) experimental and simulated powder XRD patterns; (C) a 2D [Sn₃S₇] _n ²ⁿ⁻ anionic layer oriented parallel to the ab plane; (D) packing arrangement of the layers along the b-axis. The H₂O molecules and H atoms of organic amines are omitted for clarity. Reprinted with permission from Qi et al. (2015). Copyright from Royal Society of Chemistry (2015).

FIGURE 7

(A) Photographs of FJSM-SnS-2 and FJSM-SnS-3. (B) Experimental and simulated powder XRD patterns of FJSM-SnS-2 and FJSM-SnS-3. The arrangement of [CH₃NH₃]⁺ and [Bmmim]⁺ at the adjacent interlayer spaces of FJSM-SnS-2 (C) and FJSM-SnS-3 (D). H atoms are omitted for clarity. Reprinted with permission from Li W. et al. (2021). Copyright from American Chemical Society (2021).

FIGURE 8

(A) Stacking of the [Sn₃S₇] _n ²ⁿ⁻ layers in FJSM-SnS-4 viewed along the b-axis. Cs⁺, Sr²⁺, K⁺, Na⁺, Mg²⁺, and Ca²⁺ removal efficiencies of FJSM-SnS-4 under (B) neutral or (C) acidic conditions. Here [Cs, Sr] = 5.72–6.43 mg/dm³ and [Na, K, Mg, Ca] = 44.15–51.71 mg/dm³. Adapted with permission from Li et al. (2021a). Copyright from American Chemical Society (2021).

FIGURE 9

(A) Calculated and experimental powder XRD pattern of KTS-3. (B) [Sn₃S₇]²⁻ layer with ideally ordered Sn and vacancy sites. Refinement suggests the presence of some Sn atoms in the vacancies with a fractional occupancy of 31.1% owing to the diffuse nature of the supercell reflections. (C) Schematic of the layer structure and interlayer K⁺. (D) Variation in the K _d of individual and competitive Cs⁺ and Sr²⁺ exchange with pH. The initial concentrations of Cs⁺ and Sr²⁺ were 7.4 and 6.9 ppm, respectively, and the V/m ratio was 1 dm³/g. Adapted with permission from (Sarma et al., 2016). Copyright from Royal Society of Chemistry (2016).

FIGURE 10

Maximum ion exchange capacities q _m ^Cs and q _m ^Sr achieved using layered metal sulfides and other typical ion exchange materials, and the dependence of K _d values on the pH active windows. The corresponding color-coded labels indicate the types of ion exchangers. The q _m values are estimated through data fitting with the Langmuir model. The data for NaFeTiO₄, [(SnO₂)₃·(H₂SiO₃)·(H₂MoO₄)₃]·6H₂O (SnSiMo), (NH₄)₃[PMo₁₂O₃₆]·polyacrylonitrile (AMP-PAN), magnetic Nb-substituted crystalline silicotitanate (Mag-Nb-CST), K_1.34Ni_0.33[NiFe(CN)₆] (KNiFe), SBA-15 embedded CuFe(CN)₆ (CHCF/SBA-15), clinoptilolite, and [(CH)₃NH₂][ZrCH₂(PO₃)₂F] (SZ-4) are obtained from Smičiklas et al. (2007), Park et al. (2010), Michel et al. (2015), Zhao et al. (2018), Abdel-Galil et al. (2019), Zhang et al. (2019a), Xiang et al. (2019), Amesh et al. (2020), respectively.