Kinetics and mechanism of Sr(II) adsorption by Al-Fe 2 O 3 : Evidence from XPS analysis

pH induced incongruent-dissolution impacts Al-ferrihydrite transformations and As mobilization

This study investigated the role of Al and As fate during the transformation process of ferrihydrite influenced by different pH values under oxic conditions. The results indicate that the Al doping greatly enhanced the transformation of ferrihydrite (Fh) to Al-substituted goethite at all acidic or alkaline pH values under oxic conditions by promoting the incongruent dissolution and reprecipitation reactions of Al-substituted ferrihydrite (AlFh). Under acidic conditions, the preferential dissolution of structural Fe (4.73 mg/L) from AlFh occurs, whereas under alkaline conditions, the preferential dissolution of structural Al (1.25 mg/L) takes place. In contrast, under neutral conditions, the low solubility of Fh and AlFh induces the significant particle assembly, with Fe/Al minerals primarily transforming into goethite through oriented aggregation. As predominantly remains in an adsorbed state at all pH values during the transformation of Fh and AlFh, with the highest proportion of adsorbed As (86.9-96.7%) observed under neutral conditions. During the aging process, the adsorbed As gradually transforms into non-extractable As, and the changes in As speciation within Fe/Al minerals are closely coupled with the transformation of AlFh and Fh. Under alkaline and acidic conditions, the proportion of non-extractable As in the transformation products of Fh and AlFh increases by 14.02-19.72% and 12.27-16.28%, respectively, while under neutral conditions, it increases only by 12-13.02%. Therefore, regulating soil pH can partially modify As speciation and mitigate its environmental impact by altering the mineral transformation process. The results of this study facilitate better understanding of the role of Al substitution in the transformation of Fh and the cycling of As in the environment.

Simultaneous adsorption of ammonia nitrogen and phosphate on electro-assisted magnesium/aluminum-loaded sludge-based biochar and its utilization as a plant fertilizer

Herein, Mg/Al-loaded sludge-based biochar was prepared via electro-assisted impregnation. The structure and chemical analysis of modified sludge-based biochar (MgSBC-0.5(@Al) showed that the material was loaded with MgO and Al2O3. The specific surface area of MgSBC-0.5(@Al) was 11.27 times higher than that of unmodified sludge-based biochar (SBC). The simultaneous adsorption performance of MgSBC-0.5(@Al for ammonia nitrogen (NH4+-N) and phosphate phosphorus (PO43--P) was studied. The maximum adsorption capacities of MgSBC-0.5(@Al for NH4+-N and PO43--P at 298 K were 65.19 and 92.10 mg·g-1, respectively, 4.45 and 6.28 times higher than those of SBC. The external and internal elemental compositions of the modified and unmodified biochar specimens were quantitatively characterized using inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, and X-ray fluorescence spectrometry. The results emphasized the importance of Mg-loading for NH4+-N and PO43--P capture. MgO was mainly loaded on the surface of biochar, enabling adsorption through chemical reactions. Analysis showed that the adsorption of NH4+-N and PO43--P on the modified biochar proceeded simultaneously through multiple mechanisms. Particularly, the adsorption of NH4+-N and PO43--P occurred through the precipitation of struvite and physical adsorption, with PO43--P also adsorbed through the formation of MgHPO4 and CaHPO4. Other data indicated that Al, Ca, and Fe had a trapping effect on the adsorbate. Importantly, the biochar after adsorption could be used as a soil amendment.

Immobilization mechanisms of Sr(II), Ni(II), and Cd(II) on glomalin-related soil protein in mangrove sediments at the microscopic scale

Glomalin-related soil protein (GRSP) is a significant component in the sequestration of heavy metal in soils, but its mechanisms for metal adsorption are poorly known. This study combined spectroscopic data with molecular docking simulations to reveal metal adsorption onto GRSP's surface functional groups at the molecular level. The EXAFS combined with FTIR and XPS analyses indicated that the adsorption of Cd(II), Sr(II), and Ni(II) by GRSP occurred mainly through the coordination of -OH and -COOH groups with the metal. The -COOH and -OH groups bound to the metal as electron donors and the electron density of the oxygen atom decreased, suggesting that electrostatic attraction might be involved in the adsorption process. Two-dimensional correlation spectroscopy revealed that preferential adsorption occurred on GRSP for the metal in sequential order of -COOH groups followed by -OH groups. The presence of the Ni-C shell in the Ni EXAFS spectrum suggested that Ni formed organometallic complexes with the GRSP surface. However, Sr-C and Cd-C were absent in the second shell of the Sr and Cd spectra, which was attributed to the adsorption of Sr and Cd ions with large hydration ion radius by GRSP to form outer-sphere complexes. Through molecular docking simulations, negatively charged residues such as ASP151 and ASP472 in GRSP were found to provide electrostatic attraction and ligand combination for the metal adsorption, which was consistent with the spectroscopic analyses. Overall, these findings provided new insights into the interaction mechanisms between GRSP and metals, which will help deepen our understanding of the ecological functions of GRSP in metal sequestration.

Complexation mechanism of Pb2+ on Al-substituted hematite: A modeling study and theoretical calculation

Hematite nanoparticles commonly undergoes isomorphic substitution of Al3+ in nature, while how the Al-substitution-induced morphological change, defective structure and newly generated Al-OH sites affect the adsorption behavior of hematite for contaminants remains poorly understood. Herein, the interfacial reactions between Al-substituted hematite and Pb2+ was investigated via CD-MUSIC modeling and DFT calculations. As the Al content increased from 0% to 9.4%, Al-substitution promoted the proportion of (001) facets and caused Fe vacancies on hematite, which increased the total active site density of hematite from 5.60 to 17.60 sites/nm2. The surface positive charge of hematite significantly increased from 0.096 to 0.418 C/m2 at pH 5.0 due to the increases in site density and proton affinity (logKH) of hematite under Al-substitution. The adsorption amount of hematite for Pb2+ increased from 3.92 to 9.74 mmol/kg at pH 5.0 and 20 μmol/L initial Pb2+ concentration with increasing Al content. More Fe vacancies may lead to a weaker adsorption energy (Ead) of hematite for Pb2+, while the Ead was enhanced at higher Al content. The adsorption affinity (logKPb) of bidentate Pb complexes slightly increased while that of tridentate Pb complexes decreased with increasing Al content due to the presence of ≡ AlOH-0.5 and ≡ Fe2AlO-0.5 sites. Tridentate Pb complexes were dominant species on the surface of pure hematite, while bidentate ones became more dominant with increasing Al content. The obtained model parameters and molecular scale information are of great importance for better describing and predicting the environmental fate of toxic heavy metals in terrestrial and aquatic environments.

Adsorption of Cd(II) ions on magnetic graphene oxide/cellulose modified with β-cyclodextrin: Analytical interpretation via statistical physics modeling and fractal like kinetic approach

In the present study, β-cyclodextrin modified magnetic graphene oxide/cellulose (CN/IGO/Cel) was fabricated for removal of Cd(II) ions. The material was characterized through various analytical techniques like FTIR, XRD, TGA/DTA, SEM, TEM, and XPS. The point of zero charge of the material was obtained as 5.38. The controllable factors were optimized by Taguchi design and optimum values were: adsorbent dose-16 mg, equilibrium time-40 min, and initial concentration of Cd(II) ions-40 mg/L. The material shows high adsorption capacity (303.98 mg/g). The good fitting of Langmuir model to adsorption data (R2 = 0.9918-0.9936) revealed the monolayer coverage on adsorbent surface. Statistical physics model M 2 showed best fitting to adsorption data (R2 > 0.997), suggesting the binding of Cd(II) ions occurred on two different receptor sites (n). Stereographically n > 1 confirming vertical multi-molecular mechanisms of Cd(II) ions adsorption on CN/IGO/Cel surface. The adsorption energies (E1 = 23.71-28.95 kJ/mol; E2 = 22.69-29.38 kJ/mol) concluded the involvement of physical forces for Cd(II) ions adsorption. Kinetic data fitted well to fractal-like pseudo first-order model (R2 > 0.9952), concluding the adsorption of Cd(II) ions occurred on energetically heterogeneous surface. The kinetic analysis shows that both the film-diffusion and pore-diffusion were responsible for Cd(II) ions uptake. XPS analysis was utilized to explain the adsorption mechanism of Cd(II) ions onto CN/IGO/Cel.

Overlooked role of void-nanoconfined effect in emerging pollutant degradation: Modulating the electronic structure of active sites to accelerate catalytic oxidation

The efficient removal of emerging pollutant from water is the ultimate frontiers of advanced oxidation processes (AOPs), yet it is challenging to obtain higher catalytic activity and oxidation rate. Herein, a sustainable solution was proposed by optimizing the curvature of confined structure to modulate the electronic state of the active sites in nanochannels for improving the catalytic activity. In addition, the confined effect can enhance the oxidation rate by shorting the mass transfer of active species and pollutants. A void-nanoconfined nanoreactor was prepared by loading Fe2O3 into the nanochannels (<5 nm) of the hollow carbon sphere. An enhancement of 3 orders of magnitude was obtained in the degradation rate constant of void-nanoconfined catalytic system toward sulfamethoxazole (SMX) (6.25 min-1) compared with the non-confined system. The kinetics enhancement was attributed to the larger electron potential difference between the outer and inner nanochannel caused by the curvature increase of carbon sphere, accelerating the electron transfer, so that the energy barrier of SMX degradation reaction was reduced by 31 kcal/mol with the assistance of confinement energy. Importantly, the NC-IN/PDS system exhibited outstanding removal efficiency for the actual river water using a continuous flow reactor. This work provides a new insight into designing an efficient and stable catalytic nanoreactor, enriching the domain of advanced wastewater treatment strategies.

Sr2+-Doped CuO Nanoribbons with the Hydrophobic Surface Enabling CO2 Electroreduction to Ethane

Electrochemical reduction of carbon dioxide to value-added multicarbon (C2+) products is a promising way to obtain renewable fuels of high energy densities and chemicals and close the carbon cycle. However, the difficulty of C-C coupling and complexity of the proton-coupled electron transfer process greatly hinder CO2 electroreduction into specific C2+ products with high selectivity. Here, we design an electrocatalyst of Sr-doped CuO nanoribbons with a hydrophobic surface for CO2 electroreduction to ethane with high selectivity. Sr doping enhances the chemical adsorption and activation of CO2 by inducing oxygen vacancies and increasing *CO coverage by stabilizing Cu2+ active sites, thus further boosting subsequent C-C coupling. The hydrophobic surface with dodecyl sulfate anions (DS-) adsorption increases the oxophilicity of the catalyst surface, enhancing the conversion of the *OCH2CH3 intermediate to ethane. As a result, the optimized Sr1.97%-CuO exhibits a Faradaic efficiency of 53.4% and a partial current density of 13.5 mA cm-2 for ethane under a potential of -0.8 V. This study provides a strategy to design a Cu-based catalyst by alkaline earth metal ions doping with the hydrophobic surface to engineer the evolution of the intermediates for a desired product during CO2RR.

The recovery of strontium ions from seawater reverse osmosis brine using novel composite materials of ferrocyanides modified roasted date pits

In this study, three types of adsorbents were used to remove and recover strontium ions (Sr2+) from aqueous and brine solution of seawater reverse osmosis (SWRO), namely roasted date pits (RDP) and RDP modified using copper and nickel salts of potassium hexacyanoferrates to obtain RDP-FC-Cu, and RDP-FC-Ni, respectively. Additionally, the influence of various parameters, including pH, temperature, initial concentration, and co-existing ions was also evaluated. The results revealed that pH 10 was the optimum pH in which the maximum Sr2+ ions were adsorbed. Additionally, all adsorbents had a high adsorption capacity (99.9 mg/g) for removing Sr2+ ions at the highest concentration (100 mg/L) and a temperature of 45 °C was found to be the optimum temperature. A scanning electron microscopy for the adsorbents before and after the adsorption of strontium showed the remarkable pore filling onto the active sites of all adsorbents. The thermodynamics parameter demonstrated that the adsorption occurred in an endothermic environment, and that, the reaction was spontaneous, and favorable at all the temperatures investigated. According to isotherm studies, the Langmuir model was the best-fit isotherm model; indicating that strontium adsorption involved the formation of monolayers and multilayers at higher temperatures (45 °C). Furthermore, high desorption percentages (above 90%) were achieved for all the adsorbents when an HCl concentration of 0.5 M was used. This showed the high reusability of the adsorbents. Lastly, the adsorption of strontium from the SWRO brine containing a number of metal ions was extremely sufficient as all the adsorbents were efficient to adsorb a high amount of Sr2+ despite the presence of other competing ions.

A Study of Sr Sorption Behavior in Claystone from a Candidate High-Level Radioactive Waste Geological Disposal Site under the Action of FeOOH Colloids

Colloids have a significant influence on the migration of nuclides in claystone, which is an important geological barrier. The sorption of strontium on claystone in the presence of FeOOH colloids was investigated in samples from the Suhongtu site, a candidate high-level radioactive waste disposal site in China. The effects of colloid amount, solid content, and pH were investigated by batch tests, and the sorption reaction mechanism was analyzed by kinetic modeling and microscopic characterization techniques. The results indicate that the sorption of Sr by claystone increased with the solids content, and the claystone had a stronger Sr sorption capacity under alkaline conditions. The Sr sorption kinetics were best described by the pseudo-first-order and pseudo-second-order models, which revealed that the progress is affected by physical diffusion and chemical sorption. Furthermore, the microscopic characterization results demonstrate that cation exchange reactions and surface complex reactions are the main sorption mechanisms for Sr sorption on claystone. Ca and Mg plasmas in claystone minerals can have cation replacement reactions with Sr, and functional groups such as -OH and [CO₃]^2- can have complexation reactions with Sr to adsorb Sr on the surface of the claystone. Additionally, the presence of the FeOOH colloid inhibited the sorption effect of claystone slightly. The FeOOH colloid could occupy sorption sites on the claystone surface, which reduces the activity of the functional groups and inhibits the sorption of Sr on claystone.

Microstructure of Al-substituted goethite and its adsorption performance for Pb(II) and As(V)

Naturally occurring goethite commonly undergoes Al-substitution, while how changes in microstructure induced by Al-substitution affect the interactive reaction of Pb(II) or As(V) at the goethite-water interface remains poorly understood. This study reveals the structural properties of Al-substituted goethite and its adsorption behavior for Pb(II) and As(V) by multiple characterization techniques and Charge Distribution-Multisite Surface Complexation (CD-MUSIC) modeling. Al-substitution caused an obvious decrease in the length-to-width ratio in goethite particles and a slight decrease in the proportion of (110) facets. The presence of Al-O sites and higher surface roughness induced by Al-substitution contributed to a higher inner Stern layer capacitance (C₁) and surface charge density of goethite. CD-MUSIC modeling results further revealed that the affinity constant of Pb(II) complex (log K_Pb) at the goethite-water interface and the adsorption capacity of goethite for Pb(II) decreased with increasing amount of Al-substitution, while an opposite tendency was observed for As(V) adsorption. The dominant species of both Pb(II) and As(V) on goethite were bidentate complexes, and Al-substitution had a minor impact on the abundance of Pb(II) and As(V) complexes on the surface of goethite. Overall, these experimental and modeling results provide new and important insights into the interfacial reactivity of Al-substituted goethite and facilitate the prediction of the environmental fate of heavy metals.

Production of magnetic sodium alginate polyelectrolyte nanospheres for lead ions removal from wastewater

Polyelectrolyte composite nanospheres are relatively new adsorbents which have attracted much attention for their efficient pollutant removal and reuse performance. A novel polyelectrolyte nanosphere with magnetic function (SA@AM) was synthesized via the electrostatic reaction between the polyanionic sodium alginate (SA) and the surface of a prepared terminal amino-based magnetic nanoparticles (AMs). SA@AM showed a size of 15-22 nm with 6.85 emu·g^-1 of magnetization value, exhibiting a high adsorption capacity on Pb(II) ions representing a common heavy metal pollutant, with a maximum adsorption capacity of 105.8 mg g^-1. The Langmuir isotherm adsorption fits the adsorption curve, indicating uniform adsorption of Pb(II) on the SA@AM surfaces. Repeated adsorption desorption experiments showed that the removal ratio of Pb(II) by SA@AM was more than 76%, illustrating improved regeneration performance. These results provide useful information for the production of bio-based green magnetic nano scale adsorption materials for environmental remediation applications.

Boosting Electrochemical Performance of Hematite Nanorods via Quenching-Induced Alkaline Earth Metal Ion Doping

Ion doping in transition metal oxides is always considered to be one of the most effective methods to obtain high-performance electrochemical supercapacitors because of the introduction of defective surfaces as well as the enhancement of electrical conductivity. Inspired by the smelting process, an ancient method, quenching is introduced for doping metal ions into transition metal oxides with intriguing physicochemical properties. Herein, as a proof of concept, α-Fe2O3 nanorods grown on carbon cloths (α-Fe2O3@CC) heated at 400 °C are rapidly put into different aqueous solutions of alkaline earth metal salts at 4 °C to obtain electrodes doped with different alkaline earth metal ions (M-Fe2O3@CC). Among them, Sr-Fe2O3@CC shows the best electrochemical capacitance, reaching 77.81 mF cm−2 at the current of 0.5 mA cm−2, which is 2.5 times that of α-Fe2O3@CC. The results demonstrate that quenching is a feasible new idea for improving the electrochemical performances of nanostructured materials.

Hydrothermal transformation of geopolymers to bulk zeolite structures for efficient hazardous elements adsorption

This paper reports a facile route to prepare bulk zeolites with tunable phase compositions and microstructures by combining hydrothermal treatment and geopolymer precursor technique. Amorphous Na-based geopolymer (NaGP) is transformed into crystalline analcime following hydrothermal treatments. By systematically investigating the effects of hydrothermal conditions on the phase compositions and microstructures of the products, the optimal hydrothermal procedure is screened as treating NaGP in 1 M NaOH solution at 160 °C for 6 h. Furthermore, we achieve control over phase compositions of the resulting bulk zeolites by tailoring the initial Na/K ratio of geopolymer precursors. For instance, treating the geopolymer precursor with a Na/K ratio of 9: 1 under the optimal hydrothermal procedure leads to the formation of zeolite consisting of analcime and zeolite-P. The as-prepared adsorbents exhibit outstanding adsorption performance for the hazardous elements, among which analcime-zeolite-P shows an adsorption efficiency of 93.3% for Cs⁺, and NaGP exhibits an adsorption efficiency of 99.6% for Sr²⁺. Moreover, we reveal the mechanisms underlying the adsorption of Cs⁺ and Sr²⁺ in the adsorbents to be chemisorption. Meanwhile, ion exchanges also occur in NaGP and analcime-zeolite-P during Cs⁺ adsorption. These results render geopolymers and their derived bulk zeolites promising for hazardous elements adsorption.

Facile synthesis of nanosheet-assembled γ-Fe2O3 magnetic microspheres and enhanced Sb(III) removal

The development and utilization of magnetic nanoadsorption materials with large adsorption capacity and easy separation are the research hotspot nowadays. In this study, nanosheet-assembled maghemite (γ-Fe₂O₃) magnetic microspheres were successfully synthesized by an environmental friendly, quick, and simple method, for enhanced Sb(III) removal from aqueous solution. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), and Brunauer-Emmett-Teller (BET) were used to characterize the material. The results showed that the product contained flower-like γ-Fe₂O₃ microspheres composed of petal-shaped nanosheets interspersed with each other. The specific surface area and pore volume were 69.23 m²/g and 0.15 cm³/g, respectively. The material has a strong magnetic response, which allows rapid solid-liquid separation under the action of an external magnetic field. The effects of different dosages, solution pH, and contact time on the adsorption effect were studied by batch adsorption experiments, and the reusability of the materials was evaluated. Both Freundlich isothermal adsorption model and pseudo-second-order kinetic model were able to describe the uptake of Sb(III). The maximum adsorption capacity of the material was 47.48 mg/g under optimal conditions. The adsorption mechanism is mainly that Sb and lattice oxygen (O_X^2-) form Fe-O-Sb coordination bonds, which is incorporated into the crystal structure of γ-Fe₂O₃ as inner-sphere surface complexes. The synthetic material has the advantage of simple preparation process, good adsorption capacity, operation over a wide range of pH, and easy physical separation from treatment systems with good potential for future application to treat polluted wastewater.

Removal of Sr(II) from water with highly-elastic carboxymethyl chitosan gel

A carboxymethyl chitosan (O-CMC) gel was prepared by crosslinking and functionalizing with ethylenediaminetetraacetic acid (EDTA) using a one-pot reaction under mild conditions. Structural characterizations have revealed that the prepared O-CMC/EDTA gel has 3D porous structure with abundant carboxyl groups distributed in the pores. The prepared O-CMC/EDTA gel was used to adsorb Sr(II) ions in water while X-ray photoelectron spectroscopy (XPS) was used to explore the adsorption mechanism. In order to analyze the adsorption process, we performed the adsorption kinetics and isotherms. The results show that the maximum adsorption capacity of O-CMC/EDTA for Sr (II) ions is about 105.81 mg/g at pH = 7. Notably, it exhibited fairly high compression elasticity due to multiple hydrogen bonds in the network. The showed no deformation after 30 continuous compression cycles. The ratio of O-CMC:EDTA significantly influences the adsorption property by affecting the crosslinking degree as well as the number of active sites. The high adsorption capacity, elasticity, and reusability have demonstrated that the prepared material is an effective and promising adsorbent for Sr(II) removal.

One-pot synthesis of sodium lauryl sulfate-loaded polyacrylonitrile solid-phase extractor for investigating the adsorption behavior of radioactive strontium(II) from aqueous solutions

Sodium lauryl sulfate-loaded polyacrylonitrile (SLSLPAN) was synthesized in the present investigation using an in-situ one step process through gamma radiation-induced polymerization. The structure, composition, surface area and pore size and volume of the employed adsorbent were investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and nitrogen adsorption-desorption measurements. Adsorption of radioactive strontium(II) onto SLSLPAN was studied in the pH range 3-13. Batch kinetic data showed that the equilibrium was attained at 840 min and the pseudo-first-order was the best kinetic model for describing the kinetic data of the present adsorption process. The diffusion of strontium(II) into SLSLPAN was deeply studied using four diffusion models, namely, Bangham, Boyd, Weber-Morris and Mathewas-Weber models. Two-parameter (Freundlich, Langmuir and Temkin) and three-parameter (Redlich-Peterson, Toth and Generalized) isotherm models were used to analyze the adsorption equilibrium data of strontium(II) onto SLSLPAN. The maximum adsorption capacity calculated by the Generalized isotherm model is found to be 0.391 mmol strontium(II) per gram of SLSLPAN. The estimated mean free energy (E = 2.151 kJ/mol) indicated that strontium(II) radionuclides were physically adsorbed onto SLSLPAN. The value of enthalpy change (ΔH^o = 35.325 kJ/mol) and those of free energy change (ΔG^o = -15.278, -16.948, -18.619 and -20.288 at 303, 313, 323 and 333 K, respectively) confirmed that adsorption of strontium(II) radionuclides on SLSLPAN was endothermic and spontaneous process.

Nanostructured chitosan/molecular sieve-4A an emergent material for the synergistic adsorption of radioactive major pollutants cesium and strontium

A fresh adsorbent nanostructured chitosan/molecular sieve 4A hybrid (NSC@MS-4A) was fabricated for the rapid adsorption of strontium (Sr²⁺) and cesium (Cs⁺) ions from aqueous solutions. The as-obtained NSC@MS-4A were thoroughly characterized by XRD, FE-SEM, EDS, BET, XPS and FT-IR. The physio-chemical properties and structural aspects revealed that NSC@MS-4A acquires fine surface area (72 m²/g), porous structure as well as compatible functional groups (-P-O-P and -C-O-C) for the admission of Cs⁺ and Sr²⁺ ions. The batch adsorption studies concluded that prepared adsorbent displayed a maximum adsorption of 92-94 % within 40 min. Fast adsorption of Cs⁺ and Sr²⁺ was achieved at neutral pH (6-7), ambient temperature (25-30 °C) and slow agitation speed (50-60 rpm) which could propose vast benefits such as little power utilization and uncomplicated operation. Among six types of adsorption isotherms, Freundlich isotherm showed the best fit with R²>0.997. Pseudo-second order made a better agreement as compare to other kinetic models. The thermodynamic coefficients suggested the passage of Cs⁺ and Sr²⁺ ions through the liquid solid boundary is exothermic and spontaneous. The NSC@MS-4A displayed excellent regenerability properties over five repetitive adsorption/desorption cycles, which specified that as-obtained NSC@MS-4A is a sustainable as well as efficient adsorbent for practical decontamination of radioactive liquid waste.

Effect of a humic acid colloid on the sorption behaviour of Sr onto soil in a candidate high-level radioactive waste geological disposal site

We explored the effect of the presence or absence of humic acid (HA) on the sorption behaviour of Sr onto soil. We examined three different experimental cases for Sr sorption: (1) sorption in the presence of only colloidal HA, (2) sorption in the presence of only soil and (3) sorption in the presence of both colloidal HA and soil (HS). A batch technique was used to study the influencing factors, including the amount of colloidal HA, solid content, pH, initial concentration of Sr and contact time. The experiments showed that the influencing factors significantly affected the sorption process. For example, in the case of soil and HS, the sorption percentage increased rapidly with increasing solid content at m/V < 20 g/L, changing from 8.35% and 37.54% to 49.09% and 77.03%, respectively. Moreover, scanning electron microscopy and Fourier transform infrared spectroscopy were used to characterize samples. The kinetics and isotherms of Sr were best described by the pseudo-second-order and Langmuir models, which indicated that the process was controlled by chemisorption and uniform monolayer sorption with constant energy on the outer surface. These findings provide valuable information for predicting strontium migration in radioactive waste disposal sites.

Sorption of U(VI) onto natural soils and different mineral compositions: The batch method and spectroscopy analysis

This research studied the sorption behavior of uranium(VI) onto two different kinds of soils: surface soil and undersurface soil that taken from the depth of 30 m undersurface. The soil samples were collected from a low and medium-level radioactive waste disposal site in the southwest of China. The effects of pH, solid-liquid ratio and contact time on the adsorption behavior were studied by batch adsorption method. The experiment results show that the mineral composition of soil and the speciation of U in natural groundwater are two main influencing factors. Muscovite and clinochlore, two of the main minerals of soil samples, dominate the sorption behavior of uranium onto natural soils at weak acidic and near neutral pH range. Under neutral and weak alkaline conditions, the thermodynamic calculation results show that Ca²⁺ and CO₃^2- have significant influence on the species of uranium in aqueous solution. The U sorption reduced sharply due to the formation of the CaUO₂(CO₃)₃^2- (aq) complex. This work provides a better insight of the sorption behavior of uranium onto natural soils, and gives an in-depth understanding about the influence of aqueous and surface speciation.