Adsorption of aqueous neodymium, europium, gadolinium, terbium, and yttrium ions onto nZVI-montmorillonite: kinetics, thermodynamic mechanism, and the influence of coexisting ions

Phyllite/bentonite mixture-an alternative effective buffer material for a geological disposal of radioactive waste

The use of phyllite (Phy) instead of quartz in mixtures with bentonite (B) is recommended as a buffer material for engineering barriers in a geological repository of nuclear waste. The recommendation is based on experimentally determined sorption properties of various Phy/B mixtures. The adsorption capacity of Phy/B mixtures (Phy/B: 75/25, 50/50, and 25/75), the removal efficacy of Eu(III) ions (an analog for fissiongenic lanthanides and actinides), and the rate of their binding reaction were studied using the batch adsorption equilibrium and kinetic experiments at different Eu(III) initial concentrations, solution pH, and solution to adsorbent (L/S) ratio. The adsorption capacity of the Phy/B mixtures increased with the increased bentonite content in the mixture depending on the L/S ratio and solution pH. The highest increase in the adsorption capacity of the Phy/B mixtures compared to phyllite was observed for the Phy/B proportions of 25/75 and 50/50. The rate of the Eu(III) adsorption was the best fitted by the pseudo-second-order kinetic model indicating that the adsorption rate was controlled by chemisorption. The Sips model provided the best correlation of the adsorption experimental data, indicative of more than one adsorption site. The results of this study show the advantage of the Phy/B mixtures in immobilizing Eu and certain fission products by combining adsorption properties of the materials.

Improved recovery selectivity of rare earth elements from mining wastewater utilizing phytosynthesized iron nanoparticles

While rare earth elements (REEs) play key roles in many modern technologies, the selectivity of recovering of REEs from mining wastewater remains a critical problem. In this study, iron nanoparticles (FeNPs) synthesized from euphorbia cochinchinensis extracts were successfully used for selective recovery of REEs from real mining wastewater with removal efficiencies of 89.4% for Y(III), 79.8% for Ce(III) and only 6.15% for Zn(Ⅱ). FTIR and XPS analysis suggested that the high selective removal efficiency of Y(III) and Ce(III) relative to Zn(Ⅱ) on FeNPs was due to a combination of selective REEs adsorption via complexing with O or N, ion exchange with H+ present in functional groups contained within the capping layer and electrostatic interactions. Adsorptions of Y(III) and Ce(III) on FeNPs conformed to pseudo second-order kinetics and the Langmuir isotherm model with maximum adsorption capacities of 5.10 and 0.695 mg∙g-1, respectively. The desorption efficiencies of Y(III) and Ce(III) were, respectively, 95.0 and 97.9% in 0.05 M acetic acid, where desorption involved competitive ion exchange between Y(III), Ce(III) and Zn(Ⅱ) with H+ contained in acetic acid and intraparticle diffusion. After four consecutive adsorption-desorption cycles, adsorption efficiencies for Y(III) and Ce(III) remained relatively high at 52.7% and 50.1%, respectively, while desorption efficiencies of Y(III) and Ce(III) were > 80.0% and 95.0%, respectively. Overall, excellent reusability suggests that FeNPs can practically serve as a potential high-quality selectivity material for recovering REEs from mining wastewaters.

"One-pot" preparation and adsorption performance of chitosan-based La3+/Y3+ dual-ion-imprinted thermosensitive hydrogel

Temperature-sensitive materials are increasingly of deep interest to researchers. Ion imprinting technology is widely used in the field of metal recovery. In order to solve the problem of rare earth metal recovery, we designed a temperature-sensitive dual-imprinted hydrogel adsorption product (CDIH) with chitosan as the matrix, N-isopropylacrylamide as a thermally responsive monomer, and La³⁺ and Y³⁺ as the co-templates. The reversible thermal sensitivity and ion-imprinted structure were determined by differential scanning calorimetry, Fourier transform infrared spectrometer, Raman spectra, Thermogravimetric analysis, X-ray photoelectron spectroscopy, Scanning electron microscopy and X-ray energy spectroscopy various characterizations and analyses. The simultaneous adsorption amount of CDIH for La³⁺ and Y³⁺ was 87.04 mg/g and 90.70 mg/g, respectively. The quasi-secondary kinetic model and Freundlich isotherms model well described the adsorption mechanism of CDIH. It's worthy to mention that CDIH could be well regenerated through washing with deionized water at 20 °C, with a desorption rate of 95.29 % for La³⁺ and 96.03 % for Y³⁺. And after 10 cycles of reuse, 70 % of the adsorption amount could be maintained, revealing excellent reusability. Furthermore, CDIH expressed better adsorption selectivity to La³⁺ and Y³⁺ than its non-imprinted counterparts in a solution containing six metal ions.

Co-transport of biochar nanoparticles (BC NPs) and rare earth elements (REEs) in water-saturated porous media: New insights into REE fractionation

The present study investigated the co-transport behavior of three REEs³⁺ (La³⁺, Gd³⁺, and Yb³⁺) with and without biochar nanoparticles (BC NPs) in water-saturated porous media. The presence of REEs³⁺ enhanced the retention of BC NPs in quartz sand (QS) due to decreased electrostatic repulsion between BC NPs and QS, enhanced aggregation of BC NPs, and the contribution of straining. The distribution coefficients (K_D) in packed columns in the co-transport of BC NPs and three REEs³⁺ were much smaller than in batch experiments due to the different hydrodynamic conditions. In addition, we, for the first time, found that REE fractionation in the solid-liquid phase occurred during the co-transport of REEs³⁺ in the presence and absence of BC NPs. Note that the REE fractionation during the co-transport, which is helpful for the tracing application during earth surface processes, was driven by the interaction of REEs³⁺ with QS and BC NPs. This study elucidates novel insights into the fate of BC NPs and REEs³⁺ in porous media and indicates that (i) mutual effects between BC NPs and REE³⁺ should be considered when BC was applied to REE contaminated aquatic and soil systems; and (ii) REE fractionation provides a useful tool for identifying the sources of coexisting substances.

Photocatalytic Treatment of Methyl Orange Dye Wastewater by Porous Floating Ceramsite Loaded with Cuprous Oxide

It is well known that water treatment of printing and dyeing wastewaters is problematic. In order to decompose dyes from dyestuff wastewater and convert them into almost harmless substances for the natural environment, an easily prepared, efficient, practical, and easy-to-regenerate composite material was produced from porous floating ceramsite loaded with cuprous oxide (PFCC). The PFCC samples were prepared and characterized by X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The material was applied for photocatalytic degradation of methyl orange (MO) in water. The results show that the maximal degradation rate of MO was 92.05% when the experimental conditions were as follows: cuprous oxide loading rate of 8%, PFCC dosage of 20 g/L, the reaction time of 2 h, pH value of 8, and solution initial concentration of 30 mg/L. The degradation processes of MO fits well with the Langmuir–Hinshelwood model in reaction kinetics, and the Freundlich model in reaction thermodynamics, respectively. The degradation mechanism of MO was considered from two perspectives—one was the synergetic effect of adsorption and photocatalytic oxidation, and the other was the strong oxidation of hydroxyl radicals produced by photocatalysts.

A Review on Montmorillonite-Supported Nanoscale Zerovalent Iron for Contaminant Removal from Water and Soil

Nanoscale zerovalent iron (nZVI) has shown great promise for water treatment and soil remediation. However, the rapid aggregation of nZVIs significantly affects their mobility and reactivity, which considerably limits the practical applications. Montmorillonite- (Mt-) supported nZVI (Mt-nZVI) has received increasing attention for the past decade because it can prevent the aggregation of nZVI and incorporate the advantages of both nZVI and Mt in soil and water treatment. This work thus had a comprehensive review on the use of Mt-nZVI for soil and water treatment. We first summarized existing methods used to prepare Mt-nZVI, indicating the advantages of using Mt to support nZVI (e.g., increase of the dispersion and mobility of nZVI, reduction of the size and oxidation tendency of nZVI). We then presented the reaction mechanisms of Mt-nZVI for contaminant removal and evaluated the critical factors that influence the removal (e.g., pH, temperature, and dosage of the adsorbent). We further presented examples of applications of Mt-nZVI for the removal of typical contaminants such as heavy metals and organic compounds in soil and water. We finally discussed the limitations of the use of Mt-nZVI for water treatment and soil remediation and presented future directions for the application of nZVI technology for soil and water treatment.

Removal of chromate ions from leachate-contaminated groundwater samples of Khan Chandpur, India, using chitin modified iron-enriched hydroxyapatite nanocomposite

Chromite ore processing residues (COPR) are real environmental threats, leading to CrO42-, i.e., Cr (VI) leaching into groundwater. It is of serious concern as Cr (VI) is proven to be carcinogenic. Here we emphasize the application of novel and eco-friendly chitin functionalized iron-enriched hydroxyapatite nanocomposite (HAP-Fe0-Ct) in the remediation of Cr (VI)-contaminated groundwater samples collected from Khan Chandpur, India, where the level of Cr (VI) is found to be 11.7 mg/L in a complex aqueous matrix having 793 mg/L of total dissolved solids. Chitin functionality in the composite has resulted in positive zeta potential at circum-neutral pH, favoring electrostatic attraction of chromate ions and resulting in its bulk surface transport. The HAP-Fe0-Ct showed faster kinetics of removal with efficiency (qm = 13.9 ± 0.46 mg/g) for Cr (VI). The composite has shown sorption equilibrium and 100% removal of Cr (VI) within 3 h of interaction time in groundwater samples. No Cr (VI) leaching in the acid wash process at pH 3.5 also suggests chromium's strong chemisorption onto nanocomposite. During the interaction in aqueous solutions, the reduced iron (Fe0) on the nanocomposite becomes oxidized, suggesting the probable simultaneous reduction of Cr (VI) and its co-precipitation. Continuous column extraction of chromate ions was also efficient in both spiked solutions (39.7 ± 0.04 mg/g) and COPR contaminated water (13.2 ± 0.09 mg/g). Reusability up to three cycles with almost complete Cr (VI) removal may be attributed to surface protonation, new binding sites generation, and electron transfer from Fe0 core through defects. The study concludes that HAP-Fe0-Ct could be utilized for continuous Cr (VI) removal from COPR contaminated complex groundwater matrices.

Equilibrium studies of yttrium adsorption from aqueous solutions by titanium dioxide

This research evaluates the adsorption of yttrium from aqueous solutions by titanium dioxide with surface arsenate groups (4As-TiO₂) and titanium dioxide with surface arsenate groups doped by neodymium (Nd/4As-TiO₂). The impacts of various adsorption parameters such as contact time, pH and initial metal concentrations were investigated in batch adsorption experiments. Experimental data for yttrium ions adsorption onto Nd/4As-TiO₂ fits well with the Elovich kinetic model (R² = 0.99) and the Lagergen kinetic model based on pseudo-first order equation (R² = 0.97). Yttrium ions adsorption onto 4As-TiO₂ fits well with the Lagergen kinetic model based on pseudo-second order equation (R² = 0.999). The process of yttrium adsorption in equilibrium conditions was adequately described by Langmuir adsorption theory. The assumption is that possible mechanisms for yttrium adsorption onto investigated adsorbents is surface complexation in the form of Y(OH)²⁺ or Y(OH)₂⁺ in neutral medium and surface precipitation in alkali medium. It was shown that modification of the TiO₂ surface by arsenate groups promotes the adsorption of yttrium ions. The introduction of neodymium into the TiO₂ structure with surface arsenate groups increases the difference in adsorption of yttrium and strontium ions, therefore Nd/4As-TiO₂ can be useful to separate ⁹⁰Sr and ⁹⁰Y in nuclear forensics.

Preparation of an ion imprinted chitosan-based porous film with an interpenetrating network structure for efficient selective adsorption of Gd(iii)

In this work, a new Gd(III) ion imprinted CS-based porous film with interpenetrating network structure was fabricated by a simple polymerization–evaporation approach for the efficient selective adsorption of Gd(III) from aqueous solution.

Application of a Low-Cost Cellulose-Based Bioadsorbent for the Effective Recovery of Terbium Ions from Aqueous Solutions

The preparation of a low-cost cellulose-based bioadsorbent from cellulosic material extracted from rose stems (CRS) was carried out; rose stems are considered agricultural waste. After the required pretreatment of this waste and further treatment with an acidic mixture of acetic and nitric acids, the CRS product was produced. The resulting bioadsorbent was characterized by several techniques, such as X-ray diffraction, which revealed diffraction maxima related to the cellulose structure, whose calculated crystallinity index (CrI) was 75%. In addition, Fourier Transform Infrared spectroscopy (FTIR), 13C Nuclear Magnetic Resonance (NMR), and X-ray Photoelectron Spectroscopy (XPS) showed signs of acetylation of the sample. The thermal properties of the solid were also evaluated through Thermogravimetric Analysis (TGA). Scanning Electron Microscopy (SEM) showed cellulose fibers before and after the adsorption process, and some particles with irregular shapes were also observed. The CRS bioadsorbent was used for the effective adsorption of valuable Tb(III) from an aqueous solution. The adsorption data showed a good fit to the Freundlich isotherm and pseudo-second-order kinetic models; however, chemisorption was not ruled out. Finally, desorption experiments revealed the recovery of terbium ions with an efficiency of 97% from the terbium-loaded bioadsorbent.

Environmental application of emerging zero-valent iron-based materials on removal of radionuclides from the wastewater: A review

Owing to high surface energy, strong chemical reactivity and large surface area, nanoscale zero-valent iron (nZVI) as a novel emerging material has been extensively utilized in environmental cleanup. Although a lot of reviews regarding the removal of organic contaminants and heavy metals on nZVI are summarized in recent years, the advanced progress concerning the removal of radionuclides on nZVI is still scarce. In this review, we summarized the removal of technetium (Tc), uranium (U), selenium (Se) and other radionuclides on nZVI and nZVI-based composites, then their interaction mechanisms were reviewed in details. This review is crucial for the environmental chemist and material engineer to exploit the actual application of nZVI-based composites as the emerging materials of permeable reactive barrier on the removal of radionuclides from aqueous solutions.

Trend of the research on rare earth elements in environmental science

Rare earth elements (REEs) consist of 17 transition metals which are the 15 lanthanides and yttrium and scandium. These elements have great utility in the production of modern technology, especially electronics. However, these materials may pose a serious threat to the environment if handled or disposed of incorrectly; the effects of which are being studied by the field of environmental toxicology. A multitude of studies have indicated that rare earth elements have harmful impacts on biological life, making a reform to the disposal of rare earth elements increasingly pressing. Scientific interest in REEs is constantly rising due to the increased use of REEs due to their utility. In this paper, we display our meta-analysis of a scientific literature database, PubMed, to quantitatively map the temporal flux of research and interest pertaining to REEs, especially in the field of environmental science. Our findings may prove useful for planning research on REEs or predicting the future of REE usage.

Fluorescence Enhancement Method for Enrofloxacin Extraction by Core–Shell Magnetic Microspheres

In this work, we present novel kinds of γ-Fe2O3@SiO2-NH2-CMC/MOF5 and γ-Fe2O3@SiO2-NH2-CMC/IRMOF3 magnetic metal–organic framework (MOF) nanoparticles which possess both magnetic characteristics and fluorescent properties. Here, [Zn4O(bdc)3] (MOF-5, bdc=1,4-benzenedicarboxylate) is a kind of shell. IRMOF3, a known MOF with a cubic topology prepared from Zn(NO3)2⋅4H2O and 2-amino-1,4-benzene dicarboxylic acid, is another kind of shell which is attractive due to its highly porous, crystalline structure and the presence of non-coordinating amino groups on the benzenedicarboxylate (bdc) linker, which are amenable to post-synthetic modification. γ-Fe2O3@SiO2-NH2-CMC magnetic nanoparticles (MNPs) could be prepared by covalent modification of sodium carboxymethyl cellulose (CMC). The structure of γ-Fe2O3 nanoparticles could be determined by X-ray powder diffraction (XRD). X-ray photoelectron spectroscopy (XPS) spectra could be used for the characterisation of γ-Fe2O3@SiO2-NH2, γ-Fe2O3@SiO2-NH2-CMC, γ-Fe2O3@SiO2-NH2-CMC/MOF5, and γ-Fe2O3@SiO2-NH2-CMC/IRMOF3 nanoparticles. Magnetic solid-phase extraction (MSPE) of enrofloxacin (Enr) experiments exhibited that, for γ-Fe2O3@SiO2-NH2-CMC/IRMOF3, the best effects of adsorption could be obtained at pH 4 and 6, while elution conditions of 0.1mol L−1 NaOH and 1% sodium dodecyl sulfate could achieve the best elution effect. The addition of Tb3+ ions could sensitise the fluorescence of Enr. At the same time, via the addition of Tb3+ ions, coordination could occur between nanoparticles and Tb3+ ions, which could be verified by XPS.

Terbium Ion Adsorption from Aqueous Solution by Using Magnetic γFe2O3-NH4OH@SiO2 Nanoparticles Functionalized with Amino Groups

New magnetic stabilized and functionalized core@shell nanoparticles (NPs) were synthesized in a simple way and characterized in order to adsorb Tb³⁺ from aqueous solution with a very low Tb³⁺ concentration. For the fluorescence determination of adsorption efficiency and capacity, tiron monohydrate as a ligand was used. The obtained results confirm the potential of the synthesized magnetic γ-Fe₂O₃-NH₄OH@SiO₂ NPs, functionalized with (3-Aminopropyl) trimethoxysilane (APTMS), to be used for adsorption of Tb³⁺ from aqueous solution, with the possibility of its removal from aqueous solution via an external magnet. The endothermic and spontaneous adsorption follows a pseudo-second-order kinetic model, and the adsorption equilibrium data fit the Temkin isotherm well. The maximum adsorption efficiency from aqueous solution with a 2 × 10^-6 M concentration of Tb³⁺ is over 90% at pH 7.

Preparation of a novel nano-Fe3O4/triethanolamine/GO composites to enhance Pb2+/Cu2+ ions removal

In this paper, a magnetic nano-Fe₃O₄/triethanolamine/GO composite (TEA-GO-FE) was prepared by using graphene oxide (GO), triethanolamine (TEA), and ferric chloride. The result indicates that triethanolamine acted as an important role for the growing of Fe₃O₄ and adsorption ability of composite material. The synthesis mechanism of TEA-GO-FE was investigated through the medium of SEM-EDS, XRD, FT-IR, and TEM. The characterization results indicated Fe₃O₄ nanoparticles have been successfully loaded on the surface of graphene oxide and they were encapsulated by TEA and have excellent stability. According to the results of XRD, the general particle size of Fe₃O₄ on TEA-GO-FE was 27.5 nm. In order to understand the adsorption properties of TEA-GO-FE for Pb²⁺ and Cu²⁺, this article uses a static adsorption study method. The optimized adsorption conditions are as follows: pH = 5.0, temperature is 293.15 K, and the ion concentration is 100 mg/L. Under the optimized prerequisites, the adsorption capacities of Pb²⁺ and Cu²⁺ were 121.5 mg/g and 68.7 mg/g, separately. Through thermodynamic as well as kinetic studies, the adsorption process of Pb²⁺ and Cu²⁺ on TEA-GO-FE is a self-heating process.