Synthesis and phosphate uptake behavior of Zr4+ incorporated MgAl-layered double hydroxides

We synthesized Zr(4+) incorporated MgAl-layered double hydroxides, Mg(AlZr)-LDH(A) (where A denotes a counteranion in the interlayer space and is expressed as CO(3) for carbonate and Cl for chloride ions), with different molar ratios of Mg/(Al+Zr). Then we characterized their uptake behavior toward phosphate ions. CO(3)-type tertiary LDH materials synthesized at room temperature show low crystallinity, whereas the highly crystalline Cl-type tertiary LDH, [Mg(0.68)Al(0.17)Zr(0.14)(OH)(2)][Cl(0.26)(CO(3))(0.04)1.24H(2)O], was synthesized for the first time using a hydrothermal treatment at 120 degrees C. The distribution coefficients (K(d)) of oxo-anions were measured with a mixed solution containing trace amounts of the anions. The selectivity sequences were Cl(-), NO(-)(3)相似文献   

Se(IV)在北山花岗岩上的吸附

采用批式法研究了粉碎的甘肃北山花岗岩样品(BS03, 600 m)对Se(IV)的吸附作用. 实验结果表明: 在pH 3-7范围内, Se(IV)的吸附分配比(Kd)基本不随pH变化; 当pH > 7时, Se(IV)在北山花岗岩上的Kd随pH的增大而减小. Se(IV)在北山花岗岩上的吸附不随离子强度变化. 北山地下水条件下的Ca2+(4.10×10-3 mo·lL-1)和SO42- (3.17×10-3 mo·lL-1)对Se(IV)的吸附没有影响. 此外, Se(IV)/Eu(III)/北山花岗岩三元吸附体系的实验结果表明, Se(IV) (1.46×10-5 mo·lL-1)和Eu(III) (3.33×10-6 mo·lL-1)在北山花岗岩上的吸附作用相互之间没有表观影响. 通过假定HSeO3-在广义的吸附位点≡SOH上发生了生成≡SHSeO3和≡SSeO3-的两个表面配位反应, 定量解释了Se(IV)的吸附实验结果.     

Interaction of uranyl with Se(IV) and Se(VI) in aqueous acid solutions by means of capillary electrophoresis

The uranyl–selenium(IV) and uranyl–selenium(VI) interactions were studied by CE in aqueous acid solutions, containing U(VI) and Se(IV) or Se(VI) at different concentrations, at pH 1.5, 2.0 and 2.5. The method proposed in this paper allows one with the use of CE data on metal ion mobilities at different pHs to establish the ligand species interacting with metal ion and complex species formed. In the case of Se(VI) a selenate, as demonstrated, interacts with uranyl ions, in the case of Se(IV) this is a hydroselenite. It was also shown that the equilibria for the U(VI)–Se(VI) and U(VI)–Se(IV) systems can be established from CE data. The formation of UO₂SeO₄, UO₂(SeO₄), UO₂HSeO and UO₂(HSeO₃)₂ species is demonstrated. The stability constant values were measured at different ionic strengths (from 0.02 to 0.2 mol/L). The logarithms of the stability constant values (β°) extrapolated to ionic strength 0 by the specific ion interaction theory (SIT) are found to be log β°₁=2.93±0.06 for UO₂SeO₄ formation, log β°₂=4.030.18 for UO₂(SeO₄) formation, log β°₁=3.270.15 for UO₂HSeO formation and log β°₂=5.510.11 for UO₂(HSeO₃)₂ at 25°C. The results for the first constant values for each of systems are consistent with the published values. For UO₂(SeO₄) formation, a new constant stability value is given. The existence of UO₂(HSeO₃)₂ complex species is demonstrated and its constant stability value is given for the first time.     

Adsorption of51Cr(VI) on manganese dioxide from aqueous solution

Sorption of⁵¹Cr(VI) by MnO₂ has been studied as a function of pH and ionic concentration in the presence of certain added cations and anions. The findings are explained in the light of deprotonation/hydroxyl ion association reaction on oxide surface and its subsequent interaction with the tracer. Infrared spectroscopy has shown the chemical interaction of Cr(VI) on the surface of MnO₂. The influence of certain interfering ions has been shown on the sorption of⁵¹Cr(VI) on MnO₂ surface. An attempt has been made to concentrate traces of⁵¹Cr under optimum experimental conditions. The experimental observation shows that the activity sorbed under specified conditions can be recovered appreciably by leaching the pre-adsorbed carrier.     

The removal of uranium (VI) from aqueous solutions onto natural sepiolite

The adsorption of uranium (VI) from aqueous solutions onto natural sepiolite has been studied using a batch adsorber. The parameters that affect the uranium (VI) sorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated and optimized conditions determined. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of sepiolite and experimental results showed this to be 34.61 mg · g^?1. The experimental results were correlated reasonably well by the Langmuir adsorption isotherm and the isotherm parameters (Q_o and b) were calculated. Thermodynamic parameters (ΔH° = ?126.64 kJ · mol^?1, ΔS° = ?353.84 J · mol^?1 · K^?1, ΔG° = ?21.14 kJ · mol^?1) showed the exothermic heat of adsorption and the feasibility of the process. The results suggested that sepiolite was suitable as sorbent material for recovery and adsorption of uranium (VI) ions from aqueous solutions.     

Adsorption of Cr(VI) from aqueous solutions by HNO3-purified and chemically activated pyrolytic tire char

Pyrolytic tire char adsorbents either demineralized by nitric acid (purified char, PC) or activated with KOH-calcination (activated char, AC) were used for Cr(VI) removal from aquatic solutions and studied by adsorption kinetics, isotherms, and thermodynamics. Adsorbent’s physicochemical characteristics were studied by several techniques such as X-ray diffraction, porosimetry, scanning electron microscopy, elemental analysis, and Boehm titration. For PC, acid treatment leads partially to a mesoporous structure while for AC, KOH activation creates also a microporosity enhancing the specific surface area at 443 m²g^?1. Cr(VI) adsorption onto both adsorbents followed better second-order kinetics and Langmuir isotherm models and it was exothermic (ΔH < 0) and spontaneous (ΔG < 0). The maximum Cr(VI) adsorption capacity for AC and PC was 114 and 79.47 mg g^?1, respectively, at pH = 4. The present work reveals that AC and PC can be efficient sorbents for the removal of heavy metal ions, contributing both positively to wastewater treatment and waste tire pyrolysis plants.     

Adsorption of Th4+ from aqueous solution onto Poly(N,N-diethylacrylamide-co-acrylic acid) microgels

Preparing glass to be used as a radioactive waste immobilizer from municipal waste is the aim of this paper. Up to 90 wt% of municipal waste was obtained by burning the raw waste at 700 °C for 5 h; this were successfully vitrified into borosilicate and sodium borate glasses at ~1,200 °C. The long term behavior of such glass is one of the most important factors, which is determined by their durability in aqueous solution. Experimental durability data of the prepared glass immersed in ground water together with γ-irradiation was found to be affected according to the different irradiation doses. In addition, thermal analysis and glass surface morphology were investigated. The evolution of the damage on the studied properties was correlated to the changes in the glass network depending on their composition and irradiation dose. The results showed that glass matrix containing higher amount of municipal waste possess high durability and low thermal expansion after being gamma irradiated. The results showed that glass containing higher amount of municipal waste possess high durability and low thermal expansion after irradiation.     

Sequential determination of Se(IV) and Se(VI) by flow injection-hydride generation-atomic absorption spectrometry with HCl/HBr microwave aided pre-reduction of Se(VI) to Se(IV)

In this study a flow injection (FI) system used in conjunction with hydride generation (HG), atomic absorption spectrometry (AAS) and microwave (MW) aided pre-reduction of selenite (Se(IV)) to selenate (Se(IV)) with HCl:HBr has been developed in order to differentiate both inorganic selenium species. As full control of the MW reduction step is possible, the experimental approach allows the use of milder acidic conditions (10% v/v of HCl and HBr) than those conventionally accomplished with hydrochloric acid alone (≥50% v/v). Experimental parameters were optimized by the univariate optimization method. In either case, the linear range was from 1.0 to 30 μg l⁻¹. The detection limits based on 3σ of the blank signal were 0.25 μg l⁻¹ for Se(IV) and 0.30 μg l⁻¹ for Se(VI). The reproducibility, about 3% RSD and recoveries of different amounts of Se(VI) and Se(IV) added to water and orange juice samples (97–103%) were good. The main advantage of the proposed method is that the sequential determination of Se(IV) and Se(VI) is performed at a high sampling frequency (ca. 50 samples per h) in a closed system without Se losses, and with a minimum sample waste, operator attention, and sample manipulation.     

Extraction of Zr(IV) by TBP-DMSO and TBP-Py from aqueous solutions containing monobasic acids

The distribution ratios for the extraction of Zr(IV) by TBP and its binary mixtures with DMSO or Py in n-dodecane in the presence of HNO₃, and HClO₄ have been determined. Based on stoichiometric and slope analysis methods a possible mechanism for the extraction has been proposed.     

Anion-exchange separation of Te(IV) from Te(VI), Se(IV) and Se(VI) on deae-cellulose in mixed hydrochloric-acetic acid media

Te(IV) can be separated from Te(VI), Se(IV) and Se(VI) by adsorption of Te(IV) on a DEAE-cellulose column from a mixed 1M hydrochloric acid-acetic acid solution (1:9, v/v). This allows a selective separation of Te (IV) from the other three species in widely different mole ratios.     

Adsorption of Cu(II), Cd(II), Pb(II), Cr(VI) by double hydroxides on the basis of Al oxide and Zr, Sn, and Ti oxides

It was studied the equilibrium adsorption and adsorption kinetics of Cu(II), Cd(II), Pb(II), and Cr(VI) by composite hydroxides formed by Me _x O _y · nH₂O and Me_0.4–0.7Al_0.6–0.3O _y · nH₂O, where Me = Zr, Sn and Ti. It was estimated the values of the diffusion coefficients of adsorbed ions Cu(II) and Cr(VI) from kinetic values. It was established that the estimated diffusion coefficients of adsorbed ions Cu(II) are in the range 0.4 × 10⁻¹²–2.5 × 10⁻¹² m²/s for individual hydroxides and 1.2 × 10⁻¹²–2.8 × 10⁻¹² m²/s for double hydroxides. The obtained values of diffusion coefficients Cr (VI) for double hydroxides are 0.1 × 10⁻¹⁰–0.4 × 10⁻¹⁰ m²/s.     

Diffusion of Re(VII), Se(IV) and Cr(VI) in compacted GMZ bentonite

Journal of Radioanalytical and Nuclear Chemistry - The diffusion of Re(VII), Se(IV) and Cr(VI) in compacted Gaomiaozi bentonite was conducted by an integrated diffusion setup. The effective...     

Preconcentration of uranium(VI) and thorium(IV) from aqueous solutions using low-cost abundantly available sorbent

Olive cake as low-cost abundantly available sorbent has been characterized by N₂ at 77 K adsorption, porosity analysis, elemental analysis and IR spectra and has been used for preconcentrating of uranium(VI) and thorium(IV) ions prior to their determination spectrophotometrically. The optimum pH values for quantitative sorption of U(VI) and Th(IV) are 4–7 and 3–7, respectively. The enrichment factor for the preconcentration of U(VI) and Th(IV) were found to be 125 and 75 in the given order. The sorption capacity of olive cake is in the range of 2,260–15,000 μg g⁻¹ for Th(IV) and in the range of 1,090–17,000 μg g⁻¹ for U(VI) at pH 3–7. The sorbent exhibits good reusability and the uptake and stripping of the studied ions were fairly rapid. The elution of U(VI) and Th(IV) was performed with 0.3–1 M HCl/1–2 M HNO₃ and 0.3–0.8 M HCl/1 M HNO₃, respectively. The precision of the method was 1.8 RSD% for U(VI) and 2.5 RSD% for Th(IV) in a concentration of 1.00 μg mL⁻¹ for 10 replicate analysis. The influence of some electrolytes and cations as interferents was discussed. Separation of U(VI) and Th(IV) from other metal ions in synthetic solution was achieved.     

Investigation of the Cr(VI) removal from aqueous solutions by stabilized iron-nanoparticles using 51Cr-tracer

Stabilized iron-nanoparticles were used for the Cr(VI)-removal from acidic and neutral aqueous solutions (pH 1, 3, 5 and 7). The chromium interaction with the iron-nanoparticles was studied by a batch technique under different experimental conditions (e.g. pH, temperature, contact time, solid to liquid ratio) using ⁵¹Cr as radiotracer and gamma-ray spectroscopy. The results showed that the Cr-removal was fast and the interaction kinetics could be described by a pseudo-second order rate equation. The maximum Cr-removal was observed from solutions of initial pH 3. The sorption showed a positive temperature and solid to liquid ratio dependence. The experimental results were modeled using the Langmuir, Freundlich and Dubinin–Radushkevich isotherm equations and compared with literature data obtained using other sorbents. X-ray photoelectron spectroscopy (XPS) measurements were performed in order to obtain information about the mechanism of the Cr-removal by the iron-nanoparticles. It was demonstrated that the dominated process based on the Cr(VI) reduction followed by the simultaneous oxidation of iron.     

Adsorption of uranium (VI) from aqueous solution by tetraphenylimidodiphosphinate

The adsorption of uranium (VI) using tetraphenylimidodiphosphinate (Htpip) was studied. Factors of affecting sorption efficiency have been investigated and results showed the adsorption of uranium (VI) was equilibrium at pH 4.5, time 20 min, adsorbent dosage 0.005 g and initial concentration 50 mg L^?1 reaching 99.86 mg g^?1 of adsorption capacity and 99.86% of removal efficiency. Additionally, the interfering ions studies showed that the adsorbent possessed excellent adsorption selectivity of uranium (VI). The surface morphology of Htpip was investigated by SEM. The adsorption process of uranium (VI) onto Htpip fit the pseudo-second-order kinetic model and the Freundlich isotherm model very well.     

Adsorptive removal of U(VI) and Th(IV) from aqueous solutions using polymer-based electrospun PEO/PLLA fibrous membranes

Fibrous membranes based on poly(ethylene oxide) and poly(l-lactide) fabricated by electrospinning were evaluated for the first time as substrates for the adsorption of tetravalent thorium (Th(IV)) and hexavalent uranium (U(VI)) from aqueous media. The membranes consisted of microfibers with diameters of approximately 2 μm as revealed by scanning electron microscopy. The adsorption of Th(IV) and U(VI) on the membrane was investigated as a function of pH, ionic strength and initial metal concentration under normal atmospheric conditions. The experimental data indicated increased affinity of the membrane for Th(IV) and U(VI), which was pH depended and reaches maximum values (>90 %) for Th(IV) and U(VI) at pH 3 and pH 6.5, respectively. The maximum adsorption capacity (q _max) at optimum conditions was evaluated from the Langmuir isotherm and was found to amount 50.08 and 9.3 mmol kg^?1 for Th(IV) and U(VI), respectively. In addition, studies on the effect of ionic strength on the adsorption efficiency did not show any significant effect indicating that the adsorption of Th(IV) and U(VI) on the membrane was most probably based on specific interactions and the formation of inner-sphere surface complexes. The significantly higher adsorption efficiency of the membrane for Th(IV) in acidic media (pH ≤ 3) could be utilized for a pH-triggered, selective separation of Th(IV) from U(VI) from aqueous media.     

The removal of uranium(VI) from aqueous solutions onto activated carbon: kinetic and thermodynamic investigations

The adsorption of uranium(VI) from aqueous solutions onto activated carbon has been studied using a batch adsorber. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated and optimized conditions determined (contact time 240 min; pH 3.0+/-0.1; initial uranium concentration 100 mg/L; temperature 293.15 K). The experimental data were analyzed using sorption kinetic models (pseudo-first- and pseudo-second-order equations) to determine the equation that fits best our experimental results. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of activated carbon and experimental results showed this to be 28.30 mg/g. The Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models have been applied and the data correlate well with Freundlich model and that the sorption is physical in nature (the activation energy Ea=7.91 kJ/mol). Thermodynamic parameters (DeltaHads0=-50.53 kJ/mol, DeltaSads0=-98.76 J/mol K, DeltaGads(293.15 K)0=-21.61 kJ/mol) showed the exothermic heat of adsorption and the feasibility of the process.