Ultrafast and highly capture of U(VI) by hierarchical mesoporous carbon

In this study, the hierarchical mesoporous carbon (HMC) was synthesized by the hydrothermal method. The batch adsorption experiments showed that HMC exhibited the ultrafast equilibrium fate (80 % U(VI) capture efficiency within 5 min), high UO22+ capture capacity (210 mg/g, pH = 4.5) and well recyclability. The investigations of XPS techniques indicated the oxygen-containing functional groups were responsible for high efficient UO22+ adsorption. The pH-dependent adsorption was simulated by three surface complexation modellings, revealing that UO22+ adsorption on HMC was excellently fitted by triple layer model using two inner-sphere complexes (i. e. SOUO2+ and SOUO2(CO3)35− species) compared to constant capacitance model and diffuse layer model. These findings are crucial for expanding actual applications of HMC towards the removal of radionuclides under environmental cleanup.

Application of fly ash-based geopolymer for removal of cesium, strontium and arsenate from aqueous solutions: kinetic, equilibrium and mechanism analysis

Geopolymerization is a developing reaction process for the utilization of solid wastes. In the present study, fly ash-based geopolymer and its derivative (Fe(II)-modified geopolymer) were synthesized and characterized using XRD, SEM, FTIR, BET, UV-Vis DRS as well as TG-DTA, and adopted as adsorbents for removal of Cs+ and Sr2+, and from solutions. Each sorption kinetic was well fitted to the pseudo-second-order model. The sorption of Cs+ and Sr2+ onto original geopolymer were better fitted to the Langmuir model. However, the Freundlich model is more befitting for sorption of onto Fe(II)-modified geopolymer. The free energies calculated from the D-R isotherm indicated that the sorption for Cs+ and Sr2+ were dominantly ion exchanges. Ring size plays a decisive role in ion exchanges for both Cs+ and Sr2+. Furthermore, the arrangement of SiO4 and AlO4 tetrahedrons has significant impacts on the ion exchange of Sr2+. XPS results indicated that a part of Fe2+ in Fe (II)-modified geopolymer had been oxidized to Fe3+ after sorption. Precipitation of FeAsO4 could partially contribute to the arsenate removal from solution. sorption has also occurred through the formation of inner-sphere complexes via ion exchange reaction, which could be predominantly attached by bidentate linkages.

Removal of tetracycline antibiotics from aqueous solutions using easily regenerable pumice: batch and column study

Mineral pumice as an adsorbent was explored for tetracycline (TC) removal from water. Pumice was characterized by X-ray diffraction, X-ray fluorescence and Fourier transform infrared spectroscopy. Batch and column studies were conducted to investigate the adsorbability of pumice towards TC. Results showed that the TC adsorption amount declined as the pH increased from 3 to 9 and was strongly dependent on ionic strength. Adsorption kinetic data fitted to the pseudo-first-order, pseudo-second-order and Elovich model very well (R2 > 0.9). Intraparticle diffusion was the main rate controlling step during TC adsorption. The Langmuir and Freundlich models were utilized to simulate isotherm data (10–30°C). The obtained Langmuir uptake amount (20°C) was 3.345 mg/g. Thermodynamic analyses showed that the TC uptake amount increased with the temperature rising, suggesting its endothermic nature. At pH 6 and 8, both Pb2+ and Cu2+ significantly promoted the TC removal (>25%) via ion bridging action. Adsorption mechanisms mainly involved physisorption (Van der Waals & electrostatic forces) and chemisorption via the formation of inner-sphere complexes. Column tests showed that the exhausted column could be effectively regenerated using alkaline EDTA solution. Current results suggest that pumice is a promising adsorbent for TC removal from aqueous solutions.

Solubility and spectroscopic study of AnIII/LnIII in dilute to concentrated Na–Mg–Ca–Cl–NO3 solutions

The complexation of AnIII/LnIII with nitrate was investigated in dilute to concentrated Na–Mg–Ca–Cl–NO3 solutions at 2.94 ≤ pHm ≤ 13.2 and T = 22 ± 2 °C. Comprehensive solubility experiments with Nd(OH)3(s) were performed from undersaturation conditions and complemented by extensive spectroscopic studies using Cm(III)–TRLFS (time resolved laser fluorescence spectroscopy) and Nd–LIII EXAFS (extended X-ray absorption fine structure) under analogous pHm, Im and mNO3− conditions. Solid phases recovered from batch solubility experiments were characterized by XRD and SEM-EDS. A significant influence of nitrate on the solubility of Nd(OH)3(s) is observed in concentrated weakly alkaline MgCl2–Mg(NO3)2 solutions with total salt concentration ≥ 2.83 m and mNO3− ≥ 1.13 m. Nitrate has no effect in any of the studied NaCl–NaNO3 and CaCl2–Ca(NO3)2 mixtures, thus highlighting the key role of Mg2+ in the Nd(III)–NO3 interaction. The formation of inner-sphere complexes with the participation of Mg2+ is further confirmed by Cm(III)–TRLFS and Nd–LIII EXAFS. Based on these experimental evidences, the proposed chemical model includes the definition of two new aqueous species Mg[AnIII/LnIIINO3OH]3+ and Mg[AnIII/LnIIINO3(OH)2]2+ in equilibrium with solid Nd(OH)3(s) and allows to derive the thermodynamic and activity models (Pitzer) for the system Nd3+/Cm3+–H+–Mg2+–OH−–Cl−–NO3−–H2O.

Quantum chemical study of inner-sphere complexes of trivalent lanthanide and actinide ions on the corundum (110) surface

Summary Sorption plays a major role in the safety assessment of nuclear waste disposal. In the present theoretical study we focused on understanding the interaction of trivalent lanthanides and actinides (La3+, Eu3+ and Cm3+) with the corundum (110) surface. Optimization of the structures were carried out using density functional theory with different basis sets. Additionally, Møller-Plesset perturbation theory of second order was used for single point energy calculations. We studied the structure of different inner-sphere complexes depending on the surface deprotonation and the number of water molecules in the first coordination shell. The most likely structure of the inner-sphere complex (tri- or tetradentate) was predicted. For the calculations we used a cluster model for the surface. By deprotonating the cluster a chemical environment at elevated pH values was mimicked. Our calculations predict the highest stability for a tetradentate inner-sphere surface complexes with five water molecules remaining in the first coordination sphere of the metal ions. The formation of the inner-sphere complexes is favored when a coordination takes place with at most one deprotonated surface aluminol group located beneath the inner-sphere complex. The mutual interaction between sorbing metal ions at the surface is studied as well. The minimal possible distance between two inner-sphere sorbed metal ions at the surface was determined to be 530 pm.

Adsorption Behaviors of Arsenic(V) onto Fe-Based Backwashing Sludge Produced from Fe(II)-Removal Plants

This study investigates the adsorption characteristics of As(V) onto the Fe-based backwashing sludge (FBBS), which was produced in the Fe(II) removal process. FBBS exhibits rough surfaces and shows high BET surface area of 148.41 m2/g. According to the results of EDS and XRD, the main constituents include sulfate inter-layered Fe hydroxide [Fe(SO4)OH], ferric oxhydroxide (γ-FeOOH), quartz (SiO2), and calcium carbonate (CaCO3). The adsorption kinetics data were well described by the Elovich model (r2 = 0.993), indicating the highly heterogeneous adsorption. The maximum adsorption capacity of As(V) increased from 40.04 to 88.76 mg/g as temperatures increased from 298 to 318 K, suggesting an endothermic process. The removal of As(V) was inhibited with elevated solution pH, especially from pH 7.0 to pH 10.0. Moreover, the removal of As(V) was enhanced with an increase in ion strength (0.01-1 M NaNO3), implying that the adsorption of As(V) was mainly through inner-sphere complexes mechanism.

Effects of common dissolved anions on the reduction of para-chloronitrobenzene by zero-valent iron in groundwater

Batch tests were conducted to evaluate the influences of several common dissolved anions in groundwater on the reduction of para-chloronitrobenzene (p-CNB) by zero-valent iron (ZVI). The results showed that p-CNB reduction was enhanced by both Cl− and SO42−. HCO3− could either improve or inhibit p-CNB reduction, depending on whether the mixing speed was intense enough to rapidly eliminate Fe–carbonate complex deposited on ZVI surface. Above a concentration of 100 mg L−1, NO3− increased the p-CNB reduction rate. The reduction rate by ClO4− decreased because the ClO4− competed with p-CNB for electrons. The p-CNB reduction was inhibited by PO43−, SiO32− and humic acid, in the order humic acid < PO43− < SiO32−, since these ions could form inner-sphere complexes on iron surface. The reaction even ceased when the ion concentrations were greater than 4, 0.5, and 30 mg L−1, respectively. The results indicated that common dissolved anions in groundwater should be taken into account when ZVI is applied for contaminated groundwater remediation.