Efficient removal of cesium from aqueous solution with vermiculite of enhanced adsorption property through surface modification by ethylamine

Enhanced removal of cesium from hydrobiotite using polyacrylonitrile (PAN)-based nickel ferrocyanide beads

The desorption of cesium (Cs) from contaminated clay minerals remains challenging because of the restricted efficiency of the removal process. Therefore, in the present study, a bead-type adsorbent was added during the conventional acid washing process to improve the removal of Cs⁺ from a clay mineral. As the Cs⁺ adsorbent, polyacrylonitrile-based nickel potassium hexacyanoferrate (NiFC-PAN) was used to selectively adsorb Cs⁺ in a strongly acidic solution containing competing ions. To prevent erosion of the adsorbent under harsh environmental conditions and to facilitate the separation of clay particles, PAN was deliberately constructed as large beads. The synthesized adsorbent (NiFC/PAN in a 2:1 ratio) showed high selectivity for Cs⁺, with a maximum capacity for Cs⁺ adsorption of 162.78 mg/g in 0.5 M HNO₃ solution. Because the NiFC-PAN demonstrated greater Cs⁺ selectivity than the clay mineral (hydrobiotite, HBT), the addition of NiFC-PAN during the acid washing significantly increased Cs⁺ desorption (73.3%) by inhibiting the re-adsorption of Cs⁺ on the HBT. The radioactivity of ¹³⁷Cs-HBT was substantially decreased from 209 to 27 Bq/g by the acid treatment in the presence of NiFC-PAN, corresponding to a desorption efficiency of 87.1%. Therefore, these results suggest that the proposed technique is a potentially useful and effective method for decontamination of radioactive clay.

Organo-Montmorillonite Modified by Gemini Quaternary Ammonium Surfactants with Different Counterions for Adsorption toward Phenol

The discharge of industrial phenol pollutants causes great harm to the natural environment and human health. In this study, phenol removal from water was studied via the adsorption of Na-montmorillonite (Na-Mt) modified by a series of Gemini quaternary ammonium surfactants with different counterions [(C₁₁H₂₃CONH(CH₂)₂N⁺ (CH₃)₂(CH₂)₂ N⁺(CH₃)₂ (CH₂)₂NHCOC₁₁H₂₃·2Y^-, Y = CH₃CO₃^-, C₆H₅COO^- and Br^-, 12-2-12·2Y^-]. The results of the phenol adsorption indicated that MMt-12-2-12·2Br^-, MMt-12-2-12·2CH₃CO₃^- and MMt-12-2-12·2C₆H₅COO^- reached the optimum adsorption capacity, which was 115.110 mg/g, 100.834 mg/g and 99.985 mg/g, respectively, under the conditions of the saturated intercalation concentration at 2.0 times that of the cation exchange capacity (CEC) of the original Na-Mt, 0.04 g of adsorbent and a pH = 10. The adsorption kinetics of all adsorption processes were in good agreement with the pseudo-second-order kinetics model, and the adsorption isotherm was better modeled by Freundlich isotherm. Thermodynamic parameters revealed that the adsorption of phenol was a physical, spontaneous and exothermic process. The results also showed that the counterions of the surfactant had a certain influence on the adsorption performance of MMt for phenol, especially the rigid structure, hydrophobicity, and hydration of the counterions.

Synthesis of heated aluminum oxide particles impregnated with Prussian blue for cesium and natural organic matter adsorption: Experimental and machine learning modeling

Heated aluminum oxide particles impregnated with Prussian blue (HAOPs-PB) are synthesized for the first time using different molar ratios of aluminum sulfate and PB to improve the adsorption of cesium (¹³³Cs⁺) and natural organic matter (NOM) from an aqueous solution. The Cs⁺ adsorption from various aqueous solutions, including surface, tap and deionized water by synthesized HAOPs-PB, is investigated. The influencing factors such as HAOPs-PB mixing ratio, pH and dosage are studied. In addition, pseudo 1st and 2nd order is tested for adsorption kinetics study. A machine learning model is developed using gene expression programming (GEP) to evaluate and optimize the adsorption process for Cs⁺ and NOM removal. Synthesized adsorbent showed maximum adsorption at a 1:1 M ratio of aluminum sulfate and PB in DI, tap, and surface water. The pseudo 2nd order kinetics model described the Cs ⁺ adsorption by HAOPs-PB more accurately that indicating physiochemical adsorption. Adsorption of Cs⁺ showed an increasing trend with higher HAOPs-PB concentration, while high pH also favored the adsorption. Maximum NOM adsorption is found at a higher HAOPs-PB dosage and a neutral pH value. Furthermore, the proposed GEP model shows outstanding performance for Cs⁺ adsorption modeling, whereas a modified-GEP model presents promising results for NOM adsorption prediction for testing dataset by learning the relationship between inputs and output with R² values of 0.9348 and 0.889, respectively.

Efficient removal of heavy metal ions by diethylenetriaminepenta (methylene phosphonic) acid-doped hydroxyapatite

Diethylenetriaminepenta (methylene phosphonic) acid (DTPMP) was first used as a dopant to modify hydroxyapatite and applied to remove Pb²⁺. The adsorption capacity of modified hydroxyapatite for Pb²⁺ can reach 2185.92 mg/g, which was 10.4 times that of commercial nanohydroxyapatite. The characterizations after adsorption of Pb²⁺ indicated the existence of chelation and the formation of the low bioavailability Pb₁₀(PO₄)₆(OH)₂. Moreover, the interaction of different components containing DTPMP, HAP, and pollutant Pb²⁺ was investigated by molecular dynamics (MD) simulation, which indicated that the organic-phosphonic group of DTPMP (PO₃H^-) had a stronger complex effect with calcium ions or lead ions than that of the inorganic-phosphate group of HAP (PO₄^3-) with the two metal ions, which affected the crystallinity of HAP, and greatly improved the removal effect of DTPMP doped HAP composites for Pb²⁺ contaminants, the existence of amino groups can further enhance the affinity between DTPMP and HAP or lead ions. The chelation mechanism of DTPMP and Pb²⁺ was probed in depth by combining basin analysis, topology analysis of atoms in molecules (AIM), electron localization function (ELF) analysis, bond order density (BOD) & natural adaptive orbital (NAdO)analysis and orbital component analysis.

Single and binary adsorption of lead and cadmium ions in aqueous solutions and river water by butylamine functionalized vermiculite: performance and mechanism

Lead and cadmium are toxic to human, animal, and plant health; they enhance oxidative stress indirectly while simultaneously acting through other toxicodynamic mechanisms. In this study, pristine vermiculite (VER) was functionalized with butylamine (BUT) and a novel organoclay (BUT-VER) adsorbent material was produced for simultaneous removal of Pb(II) and Cd(II) in aquatic medium. The adsorbents were characterized by spectroscopic, microscopic, spectrometric, and potentiometric techniques. The adsorption affecting parameters, including pH, time, initial concentration, temperature, and co-existing cations were investigated and optimized. The kinetic data results were in better agreement with pseudo-second-order (PSO) model (R² > 0.992). Multiple isotherm models were used to study the adsorption system and results showed that adsorption was monolayer. The BUT-VER showed an improvement in adsorption capacity in a single system (Pb(II): from 134.2 to 160.6 mg g^-1) and (Cd(II): from 51.1 to 58.9 mg g^-1) while in binary system (Pb(II): from 107.3 to 114.5 mg g^-1) and (Cd(II): from 33.7 to 39.7 mg g^-1), respectively. Furthermore, BUT-VER was tested in real river water and removed efficiency of >99% was achieved in just 1 h. The dominant mechanisms were electrostatic attraction and complexation. BUT-VER was regenerated for five consecutive cycles and showed >90% removal efficiency. These findings suggest that the proposed inexpensive adsorbent has the potential for practical applications of toxic metals removal from water.

Adsorption of lead and antimony in the presence and absence of EDTA by a new vermiculite product with potential recyclability

A new two-step modification method has been proposed where 1.8% HCl and 3.1% HNO₃ were applied to modify the interlayer of vermiculite (VMT). This product was given 90 °C of heat in 30% H₂SO₄ solution that was used for Pb (II) and Sb (III) adsorption. The EDTA presence on the individual adsorption was assessed. X-ray diffraction revealed that the VMT inter-stratified reflection through acid intercalation within the interlayer decreased the parallel gaps between the atoms, witnessing on the outer-sphere adsorption. The driving force was found electrostatic, which fits well with pseudo-second-order kinetics and Langmuir isotherm. The Pb (II) and Sb (III) uptake followed descending order adsorption with increasing concentration of chelating EDTA. Three consecutive desorption cycles revealed that the prepared adsorbent was suitable that may be regarded as a good candidate for complex wastewaters.

Effective cesium removal from Cs-containing water using chemically activated opaline mudstone mainly composed of opal-cristobalite/tridymite (opal-CT)

Opaline mudstone (OM) composed of opal-CT (SiO2·nH2O) has high potential use as a cesium (Cs) adsorbent, due to its high specific surface area (SSA). The objective of this study was to investigate the Cs adsorption capacity of chemically activated OM and the adsorption mechanism based on its physico-chemical properties. We used acid- and base-activation methods for the surface modification of OM. Both acid- and base- activations highly increased the specific surface area (SSA) of OM, however, the base-activation decreased the zeta potential value more (- 16.67 mV), compared to the effects of acid-activation (- 6.60 mV) or non-activation method (- 6.66 mV). Base-activated OM showed higher Cs adsorption capacity (32.14 mg/g) than the others (acid: 12.22 mg/g, non: 15.47 mg/g). These results indicate that base-activation generates pH-dependent negative charge, which facilitates Cs adsorption via electrostatic attraction. In terms of the dynamic atomic behavior, Cs cation adsorbed on the OM mainly exist in the form of inner-sphere complexes (IS) containing minor amounts of water molecules. Consequently, the OM can be used as an effective Cs adsorbent via base-activation as an economical and simple modification method.

Interpretation of the interaction between cesium ion and some clay minerals based on their structural features

Cesium (Cs⁺) is known to have a strong interaction with various clay minerals; however, it is not interpreted from the structure of clay minerals and the adsorption isotherm. The adsorption interactions between Cs⁺ and hydrobiotite (H-Bio), biotite (Bio), vermiculite (Verm), and exfoliated vermiculite (E-Verm) were evaluated by analyzing adsorption isotherm, basal spacing, and adsorption/desorption experiments. The Cs⁺ adsorption of H-Bio and Verm fitted well to the Langmuir adsorption isotherm, while the Cs⁺ adsorption of Bio and E-Verm fitted well to the Freundlich adsorption isotherm. The basal spacing of H-Bio and Verm was approximately 1.4 nm, while Bio and E-Verm basal spacing was 1.0 nm. The adsorption experiment results for Cs⁺ under the coexistence of Ca²⁺ and K⁺ indicated that the contribution of the interlayer sites to Cs⁺ adsorption on H-Bio and Verm was 25-40%, while the contribution of the interlayer sites to that on Bio and E-Verm was almost 0%. The adsorption isotherms reflected this interlayer contribution to Cs⁺ adsorption, which was dependent on the basal spacing. Therefore, the basal spacing of clay minerals is one of the key structural properties controlling both the adsorption capacity and the adsorption mechanism of Cs⁺ in clay minerals.

Cesium removal using acid- and base-activated biotite and illite

Biotite and illite have excellent cesium (Cs) adsorption capacity due to their negative charges in addition to adsorption sites of the planar, interlayer, and frayed edge sites (FES). The aim of this study is to investigate the Cs adsorption capacity using acid- and base-activated biotite and illite based on their mineralogical characteristics. The acid-activated biotite and base-activated illite exhibited high Cs removal efficiency from the low-level Cs-containing DI water (97.5 % and 97.3 %, respectively). The acid-activation of biotite increased the specific surface area (SSA, 12.08 → 43.04 m²/g), Fe(III)/Fe(II) ratio (0.56 → 0.76), and wedge zone d-spacing (1.017 → 1.065 nm), while the zeta potential (-4.06 → -4.82 mV) decreased. The base-activation of illite resulted to a decrease in the SSA (22.14 → 18.49 m²/g), zeta potential (-7.68 → -31.64 mV), and Fe(III)/Fe(II) ratio (0.92 → 0.79). However, only acid-activated biotite appeared to have a high capacity of Cs removal from Cs-containing seawater (73.9 %; base-activated illite: 26.1 %). These results indicate that the FES of biotite owing to acid-activation showed better results in regards to Cs adsorption as compared to the pH-dependent negative charges of the base-activated illite.

The advantages of clay mineral modification methods for enhancing adsorption efficiency in wastewater treatment: a review

This review discusses the recent trends in the research over the last 30 years to use clay minerals in natural and modified forms for removing different toxic organic/inorganic pollutants. The natural and modified forms of clay minerals have an exceptional ability to remove different contaminants. However, the modification methods can improve the clay mineral adsorption properties that consequently increase more adsorption sites and functional groups to adsorb different environmental pollutants. This review shows the importance of modification methods and more extension of novel clay preparation based on nanotechnology which could raise the control of pollution. The syntheses of functionalized clays such as pillared clays and porous clay heterostructures introduce the new class of heterostructure materials with high adsorption capacity, capability, and selectivity. Due to the acceptable properties of heterostructure materials including high specific surface area, thermal and mechanical stability, and the existence of multifunctional groups to selective adsorption, this review collects more literature of research related to environmental protection issues. However, it is expected much attention to get a better understanding of the adsorption mechanism, regeneration, and recovery process of these materials.

Cesium ion-exchange resin using sodium dodecylbenzenesulfonate for binding to Prussian blue

Radioactive Cs ions are extremely harmful to the human body, causing cancers and other diseases. Treatments were performed on radioactive Cs present in wastewater after use in industrial or medical fields. Prussian blue (PB) has been widely used for the removal of Cs ions from water but its colloidal structure hinders reuse, making it problematic for practical use. To solve this problem, we used a commercial macroporous polymer resin as a PB matrix. To provide an efficient anchor for PB, the surface of the polymer resin was decorated with sodium dodecylbenzenesulfonate to produce a negatively charged surface. The successful chemical binding between the polymer resin and PB prevented leakage of the latter during adsorption and crosslinked structure of the matrix provided regeneration of the adsorbent. The adsorbent maintained its removal efficiency after five repeats of the regeneration process. The PB-based, Cs ion-exchange resin showed excellent selectivity toward Cs ions and good reusability, maintaining its high adsorption capacity.

A novel composite of layered double hydroxide/geopolymer for co-immobilization of Cs+ and SeO42- from aqueous solution

Geopolymers are always considered as promising materials for the treatment of radioactive wastes. In order to extend the application of geopolymer to the immobilization of anionic species, a novel composite of layered double hydroxide/geopolymer (LDH/GEO) was synthesized and applied for cosorption of Cs⁺ and SeO₄^2-. The ability of LDH/GEO to sorb Cs⁺ was maintained as that of pure GEO, even though the surface of geopolymer was homogeneously covered by the LDH platelets. The sorption of Cs⁺ onto LDH/GEO composite occurred via ion exchange, which was controlled by particle diffusion. It is different with Cs⁺ sorption onto pure GEO governed by film diffusion. Therefore, "Pocket diffusion" was proposed for the particle diffusion as the case of LDH/GEO because this kind of diffusion would be restricted in a certain distance around the ring entrance gate due to the amorphous essence of GEO. For SeO₄^2- sorption by LDH/GEO, ion-exchange with the interlayer NO₃^- and surface sorption could be the main mechanisms. Importantly, the sorption speed of SeO₄^2- achieved by LDH/GEO composite was much faster than that by pure LDH. In the binary system (Cs⁺+ SeO₄^2-), the sorption of Cs⁺ was slightly suppressed compared to the single system, which might be due to the formation of ion-pair complex of [CsSeO₄]^-. However, it did not have negative effect on the SeO₄^2- sorption. In the presence of other cations or anions, the cosorption performances of Cs⁺ and SeO₄^2- were satisfactorily obtained. Furthermore, the Cs⁺ and SeO₄^2- sorption densities were superior to the previously reported values. The combined MgAl-LDH/geopolymer composite could be a promising material for the immobilization of Cs⁺ and SeO₄^2-, and this work would provide guidance for the development of geopolymer-based materials for environmental applications.

Nano-sized Prussian blue immobilized costless agro-industrial waste for the removal of cesium-137 ions

For human health and safety, it is of great importance to develop innovative materials with a vast capacity for powerful removal of radioactive ions from aqueous solutions. Prussian blue functionalized sugarcane bagasse (PB-SCB) was successfully prepared for the efficient elimination of radioactive cesium (¹³⁷Cs) using a nontoxic, environmentally friendly, and costless method. The prepared renewable material was characterized using different techniques to emphasize morphology, functional groups, crystal structure, and the adsorption process. The adsorption of Cs(I) was better fitted to the pseudo-second-order model than pseudo-first-order model which revealed a chemical adsorption mechanism. The experimental isotherm results were best illustrated by the Freundlich model (R² = 0.98). Besides, the obtained values for the thermodynamic parameters indicating that the adsorption process was endothermic and spontaneous in nature. In addition to demonstrating high adsorption capacity for Cs ion removal (56.7 mg/g at 30 °C), PB-SCB might consider being an efficient and cost-effective adsorbent for the decontamination of cesium, where an estimated cost analysis revealed that the expenditure for the removal of 1000 mg/L cesium from alkaline radioactive wastewater is likely to be US$0.12. Graphical abstract.

Two-dimensional transition metal carbide (Ti3C2Tx) as an efficient adsorbent to remove cesium (Cs+)

Industrial utilization of nuclear resources greatly depends on the effective treatment of nuclear waste.

Sorption of Ag+ and Cu2+ by Vermiculite in a Fixed-Bed Column: Design, Process Optimization and Dynamics Investigations

Vermiculite has been used for the removal of Cu 2 + and Ag + from aqueous solutions in a fixed-bed column system. The effects of initial silver and copper ion concentrations, flow rate, and bed height of the adsorbent in a fixed-bed column system were investigated. Statistical analysis confirmed that breakthrough curves depended on all three factors. The highest inlet metal cation concentration (5000 mg/dm3), the lowest bed height (3 cm) and the lowest flow rate (2 and 3 cm3/min for Ag + and Cu 2 + , respectively) were optimal for the adsorption process. The maximum total percentage of metal ions removed was 60.4% and 68.7% for Ag+ and Cu2+, respectively. Adsorption data were fitted with four fixed-bed adsorption models, namely Clark, Bohart–Adams, Yoon–Nelson and Thomas models, to predict breakthrough curves and to determine the characteristic column parameters. The adsorbent was characterized by SEM, FTIR, EDS and BET techniques. The results showed that vermiculite could be applied as a cost-effective sorbent for the removal of Cu 2 + and Ag + from wastewater in a continuous process.

Decontamination of radioactive cesium ions using ordered mesoporous monetite

We report herein the fabrication of an environmentally friendly, low-cost and efficient nanostructured mesoporous monetite plate-like mineral (CaHPO₄) as an adsorbent for removal of radioactive cesium ions from aqueous solutions. The phase and textural features of the synthesized mesoporous monetite were well characterized by XRD, FTIR, SEM, HRTEM, DLS, TGA/TDA, and N₂ adsorption/desorption techniques. The results indicate that the cesium ions were effectively adsorbed by the mesoporous monetite ion-exchanger (MMT-IEX) above pH 9.0. Different kinetic and isotherm models were applied to characterize the cesium adsorption process. The fabricated monetite exhibited a monolayer adsorption capacity up to 60.33 mg g⁻¹ at pH of 9.5. The collected data revealed the higher ability of CaHPO₄ for the removal of Cs(i) from aqueous media in an efficient way.

This study involves the identification of environmentally friendly, low-cost and efficient nanostructured mesoporous monetite plate like mineral as an adsorbent for removal of cesium from aqueous solutions.

Ion-recognizable hydrogels for efficient removal of cesium ions from aqueous environment

At present, selective and efficient removal of cesium ions (Cs⁺) from nuclear waste is of significant importance but still challenging. In this study, an easy-to-get and low-cost hydrogel adsorbent has been developed for effective adsorption and removal of Cs⁺ from aqueous environment. The novel Cs⁺-recognizable poly(acrylic acid-co-benzo-18-crown-6-acrylamide) (poly(AAc-co-B18C6Am)) hydrogel is specifically designed with a synergistic effect, in which the AAc units are designed to attract Cs⁺ via electrostatic attraction and the B18C6Am units are designed to capture the attracted Cs⁺ by forming stable 2:1 "sandwich" complexes. The poly(AAc-co-B18C6Am) hydrogels are simply synthesized by thermally initiated free-radical copolymerization and display excellent Cs⁺ adsorption from commonly coexisting metal ions. Important parameters affecting the adsorption are investigated comprehensively, and the adsorption kinetics and adsorption isotherms are also discussed systematically. The poly(AAc-co-B18C6Am) hydrogels exhibit rapid Cs⁺ adsorption within 30min and the adsorption process is governed by the pseudo-second order model. Adsorption isotherm results demonstrate that the equilibrium data are well fitted by the Langmuir isotherm model, indicating that the Cs⁺ adsorption is probably a monolayer adsorption process. Such Cs⁺-recognizable hydrogel materials based on the host-guest complexation are promising as efficient and feasible candidates for adsorption and removal of radioactive Cs⁺ from nuclear contaminants.

Efficient and fast removal of Pb(ii) by facile prepared magnetic vermiculite from aqueous solution

Magnetic modified vermiculite was prepared by a simple one-pot solvothermal method to remove lead from aqueous solution.