Easily prepared and stable functionalized magnetic ordered mesoporous silica for efficient uranium extraction

Functionalized magnetic Fe_3O_4@SiO_2 composite nanoparticles were prepared by simply embedding iron oxide nanoparticles into MCM-41 through one-step synthesis process, followed by aminopropyls grafting on the mesopore channels, aiming to efficiently and conveniently uptake U(VI) from aqueous solution. The resultant material possesses highly ordered mesoporous structure with large surface area, uniform pore size, excellent thermal stability, quick magnetic response, and desirable acids resistance, confirmed by Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM), N_2 adsorption/desorption experiments, powder X-ray diffraction(PXRD), and thermogravimetric analysis(TGA). Detailed U(VI) sorption test indicated that this material is indeed an effective U(VI) sorbent with fast sorption kinetics of less than 2 h, large sorption capacity of 160 mg/g at p H 5.0±0.1, and desirable selectivity towards U(VI) ions over a range of competing metal ions. The absorbed U(VI) can be easily desorbed by 0.01 mol/L or more concentrated HNO_3 solution, and the reclaimed sorbent can be reused with no obvious decrease of sorption capacity even after 4 sorption-desorption cycles. The present results suggest the vast opportunities of this kind of magnetic composite on the solid-phase extraction of U(VI).     

Removal of U(VI) from aqueous solutions by using attapulgite/iron oxide magnetic nanocomposites

The attapulgite/iron oxide magnetic nanocomposites were prepared by coprecipitation method and characterized by scanning electron microscopy, X-ray diffraction, vibrating sample magnetometer and Fourier transform infrared sorption spectroscopy. The results of characterization showed that iron oxides were successfully deposited on the surfaces of attapulgite. The prepared magnetic nanocomposites were applied to remove radionuclide U(VI) ions from aqueous solutions by using batch technique and magnetic separation method. The results showed that the sorption of U(VI) on attapulgite/iron oxide magnetic composites was strongly dependent on ionic strength and pH at low pH values, and was independent of ionic strength at high pH values. The interaction of U(VI) with the magnetic nanocomposites was mainly dominated by outer-sphere surface complexation or ion exchange at low pH values, and was controlled by inner-sphere surface complexation or multinuclear surface complexation at high pH values. With increasing temperature, the sorption of U(VI) on attapulgite/iron oxide magnetic composites increased and the thermodynamic parameters calculated from the temperature dependent sorption isotherms suggested that the sorption of U(VI) on the magnetic nanocomposites was a spontaneous and endothermic process. The high sorption capacity and easy magnetic separation of the attapulgite/iron oxide magnetic composites make the material as suitable sorbent in nuclear waste management.     

Mesoporous silica SBA-15 functionalized with phosphonate and amino groups for uranium uptake

Mesoporous silicas have a very attractive ability of sorption and enrichment of metal ions due to their huge surface area and facile functionalization by organic ligands.In this work,phosphonate-amino bifunctionalized mesoporous silica SBA-15(PA-SBA-15) as U(VI) sorbent was fabricated through post-grafting method.The obtained mesoporous silica was characterized by SEM,XRD,NMR and nitrogen sorption/desorption experiments,which revealed the existence of ordered mesoporous structure with uniform pore diameter and large surface area.The adsorptivity of PA-SBA-15 for U(VI) from aqueous solution was investigated using batch sorption technique under different experimental conditions.The preliminary results show that the U(VI) sorption by PA-SBA-15 is very quick with equilibrium time of less than 1 h,and the U(VI) uptake is as large as 373 mg/g at pH 5.5 under 95 ℃.The sorption isotherm has been successfully modeled by the Langmuir isotherm,suggesting a monolayer homogeneous sorption of U(VI) in PA-SBA-15.The sorption is pH-dependent due to the pH-dependent charge of sorbent in the aqueous solution.The thermodynamics research shows that the sorption is a feasible and endothermic process.Based on these results,PA-SBA-15 could be a promising solid phase sorbent for highly-efficient removal of U(VI) ions from waste water and enrichment of U(VI) from a solution at a very low level.     

Sorption profile and chromatographic separation of uranium (VI) ions from aqueous solutions onto date pits solid sorbent

The retention profile of uranium (VI) as uranyl ions (UO(2)(2+)) from the aqueous media onto the solid sorbent date pits has been investigated. The sorption of UO(2)(2+) ions onto the date pits was achieved quantitatively (98+/-3.4%, n=5) after 15 min of shaking at pH 6-7. The sorption of UO(2)(2+) onto the used sorbent was found fast, followed by a first order rate equation with an overall rate constant, k of 4.8+/-0.05 s(-1). The sorption data were explained in a manner consistent with a "solvent extraction" mechanism. The sorption data were also subjected to Freundlich isotherm model over a wide range of equilibrium concentration (1-20 microgmL(-1)) of UO(2)(2+). The results revealed that, a "dual-mode" of sorption mechanism involving absorption related to "solvent extraction" and an added component for "surface adsorption" is most likely operated simultaneously for uranyl ions uptaking the solid sorbent. The thermodynamic parameters (-DeltaH, DeltaS and DeltaG) of the uranyl ions uptake onto the date pits indicated that, the process is endothermic and proceeds spontaneously. The interference of some diverse ions on the sorption UO(2)(2+) from the aqueous media onto the date pits packed column was critically investigated and the data revealed quantitative collection of UO(2)(2+) at 5 mLmin(-1) flow rate. The retained UO(2)(2+) was recovered quantitatively with HCl (3.0 molL(-1)) from the column at 5 mLmin(-1) flow rate. The mode of binding of the date pits with UO(2)(2+) was determined from the IR spectral date bits before and after extraction of uranium (VI). The height equivalent (HETP) and the number (N) of theoretical plates of the date pits packed column were determined from the chromatograms. Complete retention and recovery of UO(2)(2+) spiked to wastewater samples by the date pits packed column was successfully achieved. The capacity of the used sorbent towards retention of uranium (VI) from aqueous solutions was much better than the most common sorbents.     

Surface modification to improve the sorption property of U(VI) on mesoporous silica

Polyoxometalates K₇[α-PW₁₁O₃₉]·14H₂O (PW11) modified mesoporous silica (MCM-48) with cubic structure, was prepared by impregnation and calcination methods. The modified mesoporous silica sorbent (PW11/MCM-48) was studied as a potential adsorbent for U(VI) from aqueous solutions. MCM-48 and PW11/MCM-48 were confirmed by X-ray diffraction and nitrogen physisorption techniques. The results indicate the original keggin structure of PW11 and mesoporous structure of MCM-48 are maintained after supporting PW11 on mesoporous silica MCM-48. The effects of contact time, solid-to-liquid ratio (m/V), solution pH and ionic strength on U(VI) sorption behaviors of the pure and modified mesoporous silicas were also studied. Typical sorption isotherms such as Langmuir and Freundlich isotherms were determined for sorption process. The results suggest that the sorption of U(VI) on MCM-48 or PW11/MCM-48 are strongly dependent on pH values but independent of ionic strength. The sorption capacity of PW11/MCM-48 for U(VI) is about ten times more than that of MCM-48.     

Immobilization of uranium(VI) onto Mg2Al layered double hydroxide: role of key geochemical parameters

In this study, the sorption of U(VI) from aqueous solution on Mg₂Al layered double hydroxide (Mg₂Al LDH) was studied as a function of various water quality parameters such as contact time, pH, ionic strength, soil fulvic acid (FA), solid content and temperature by using a batch technique. The sorption of U(VI) on Mg₂Al LDH was dependent on pH. The presence of FA increased U(VI) sorption at low pH, whereas decreased U(VI) sorption at high pH. Both kinetics and thermodynamic parameters of the sorption process were evaluated. It was found that the pseudo-second-order model was more suitable for our experiment. The Langmuir model fitted the sorption isotherms of U(VI) better than the Freundlich and D-R model at three different temperatures of 298, 303 and 313 K. The thermodynamic parameters (ΔH°, ΔS°, and ΔG°) were calculated from the temperature dependent sorption isotherms, and the results suggested that U(VI) sorption was a spontaneous and endothermic process. The results demonstrate that Mg₂Al LDH is a promising sorbent material for the preconcentration and separation of uranium pollution from large volumes of aqueous solutions.     

A high efficient sorption of U(VI) from aqueous solution using amino-functionalized SBA-15

Uranium is one of the most hazardous heavy metal due to its long half-life radioactivity, high toxicity and mobility as aqueous uranyl ion (UO₂ ²⁺) under ordinary environmental conditions. Herein, amino functionalized SBA-15 (APSS) was developed as a rapid and efficient sorbent for removal of U(VI) from the environment. The APSS sample was synthesized by grafting method and was characterized by SEM, NMR, SAXS, and N₂ sorption/desorption isothermal experiments. The sorption of U(VI) by APSS was investigated under different conditions of pH, contact time, initial U(VI) concentration, ionic strength and solid–liquid ratio. The results show that the sorption of U(VI) by APSS is strongly dependent on pH but independent of ionic strength and solid–liquid ratios (m/V). The sorption is ultrafast with an equilibrium time of less than 30 min, and the sorption capacity is as large as 409 mg/g at pH 5.3 ± 0.1. Besides, the U(VI) sorption by APSS from extremely diluted solution and the desorption of U(VI) from APSS were also studied. It is found that 100 mg of APSS can almost completely remove the U(VI) ions from 4 L aqueous solution with the U(VI) concentration as low as 4.2 ppb and the sorbed U(VI) can be completely desorbed by 0.1 mol/L nitric acid. The results strongly reveal the high performance of the APSS material in the removal and preconcentration of U(VI) from the aqueous solution.     

Solid phase extraction method for the separation and determination of chromium(III) in the presence of chromium(VI) using silica gel modified by N,N'-bis-(α-methylsalicylidene)-2,2-dimethyl-1,3-propanediimine

N,N'-bis-(α-methylsalicylidene)-2,2-dimethyl-1,3-propanediimine (SBTD) modified silica gel was prepared and used as sorbent for solid phase extraction of Cr(III) ions from aqueous solution. This sorbent showed a high sorption affinity for Cr(III) while recovery of Cr(VI) was very low. The analyte ion retained on the column was eluted with 1 mol L(-1) HNO(3). The chromium ion in the eluent was determined by graphite furnace atomic absorption spectrometry. The effects of different parameters such as pH, eluent type and volume, Schiff's base concentration, sample and eluent flow rate, interfering ions and adsorbent amount were investigated.     

Solid phase extraction using silica gel functionalized with Sulfasalazine for preconcentration of uranium(VI) ions from water samples

Silica gel surface was chemically functionalized by reaction the silanol from the silica surface with 3-chloropropyltrimethoxysilane followed by reaction with Sulfasalazine. This new sorbent has been used for the preconcentration of low levels of U(VI) ions from an aqueous phase. Parameters involved in extraction efficiency such as pH, weight of the sorbent, volume of sample and eluent were optimized in batch and column methods prior to determination by spectrophotometry using arsenazo(III) reagent. The results showed that U(VI) ions can be sorbed at pH range of 5.0–6.0 in a minicolumn and quantitative recovery of U(VI) (>98.0?±?1.6%) was achieved by stripping with 2.5 mL of 0.1 mol L^?1 HCl. The sorption capacity of the functionalized silica gel was 1.15 mmol g^?1 of U(VI). A linear calibration graph was obtained over the concentration range of 0.02–27.0 μg mL^?1 with a limit of detection of 1 μg L^?1 in treatment with 1000 mL of the U(VI) solution in which the preconcentration factor was as high as 400. The method was employed to the preconcentration of U(VI) ions from spiked ground water and synthetic sea water samples.     

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.     

Characterization of Co(II) removal from aqueous solution using bentonite/iron oxide magnetic composites

The bentonite/iron oxide magnetic composites were prepared by co-precipitation method, and characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction and scanning electron microscope. The prepared bentonite/iron oxide magnetic composites were used as a sorbent for the removal of Co(II) ions from radioactive wastewater. The results demonstrated that the sorption of Co(II) was strongly dependent on pH and ionic strength at low pH values. The sorption of Co(II) was dominated by outer-sphere surface complexation or ion exchange at low pH whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of iron oxide in the composites also contributes to the sorption of Co(II) ions on the magnetic composites. The experimental data were well described by Langmuir model. The thermodynamic parameters (∆G ^°, ∆S ^°, ∆H ^°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Co(II) on bentonite/iron oxide magnetic composites was an endothermic and spontaneous processes.     

Removal of U(VI) from aqueous solutions by using MWCNTs and chitosan modified MWCNTs

In this paper, the multiwalled carbon nanotubes (MWCNTs) were modified with chitosan (CS) by using low temperature plasma grafting technique (denoted as MWCNT-CS). The prepared MWCNTs and MWCNT-CS were characterized by SEM, TEM, FTIR and Raman spectroscopy in detail and the results suggested that CS molecules were successfully grafted on the surfaces of MWCNTs. The materials were applied as adsorbents in the removal of U(VI) ions from large volumes of aqueous solutions as a function of environmental conditions. The removal of U(VI) from aqueous solution to MWCNTs and MWCNT-CS increased with increasing pH values at pH < 7, and then decreased with increasing pH values at pH > 7. The sorption of U(VI) on MWCNTs and MWCNT-CS was strongly dependent on pH and independent of ionic strength. The sorption of U(VI) on MWCNTs and MWCNT-CS was dominated by inner-sphere surface complexation rather than by ion exchange or outer-sphere surface complexation. The surface grafted chitosan molecules can enhances U(VI) sorption on MWCNTs obviously, which was also evidenced from the XPS spectroscopy analysis. The results of high sorption capacity of U(VI) on MWCNT-CS suggest that the MWCNT-CS nanomaterial is a suitable candidate in the preconcentration of U(VI) ions from large volumes of aqueous solutions.     

Sorption of U(VI) onto a decarbonated calcareous soil

Sorption of U(VI) from aqueous solution to decarbonated calcareous soil (DCS) was studied under ambient conditions using batch technique. Soil samples were characterized by XRD, FT-IR and SEM in detail and the effects of pH, solid-to-liquid ratio (m/V), temperature, contact time, fulvic acid (FA), CO₂ and carbonates on U(VI) sorption to calcareous soil were also studied in detail using batch technique. The results from experimental techniques showed that sorption of U(VI) on DCS was significantly influenced by pH values of the aqueous phase, indicating a formation of inner-sphere complexes at solid–liquid interface, and increased with increasing temperature, suggesting the sorption process was endothermic and spontaneous. Compared to Freundlich model, sorption of U(VI) to DCS was simulated better with Langmuir model. The sorption equilibrium could be quickly achieved within 5 h, and sorption results fitted pseudo-second-order model well. The presence of FA in sorption system enhanced U(VI) sorption at low pH and reduced U(VI) sorption at high pH values. In absence of FA, the sorption of U(VI) onto DCS was an irreversible process, while the presence of FA reinforced the U(VI) desorption process reversible. The presence of CO₂ decreased U(VI) sorption largely at pH >8, which might due to a weakly adsorbable formation of Ca₂UO₂(CO₃)₃ complex in aqueous phase.     

Study of the effect of oxidative-bisulfite modification of the cotton cellulose on its ion exchange properties

The effect of chemical modification on the sorption properties of cotton cellulose toward Cu(II) and Ni(II) ions was studied. The modification was carried out in two stages: oxidation of cellulose with the formation of dialdehydocellulose, followed by its sulfonation. The optimal conditions for modifying the cellulose to produce a sorbent capable to remove effectively the heavy metal ions from aqueous solutions of corresponding salts were elucidated. The modified sorbent exceeds the native cellulose in the sorption capacity (in terms of sorption maximum) about 3 times, therewith the time of extraction of heavy metal ions is reduced from 45 to 8 min. The high sorption properties are defined by the formation of new sorption sites -SO₃Na along with initially formed -COOH groups on the sorbent surface.     

Sorption of iron(III) in ionic and colloidal states on iron(III) oxide deposited on a silica gel sufrace

The sorption of iron(III) in ionic and colloidal states on iron(III) oxide deposited on a silica gel surface has been studied as a function of pH of aqueous solution by batch equilibrations. The behaviour of Fe³⁺ and colloidal Fe(III) on the sorbent column has also been investigated. Conditions for sorption of iron from aqueous solutions are given. The colloidal iron(III) can be quantitatively separated from Fe³⁺ on the sorbent column under given experimental conditions.     

Preparation and sorption performance of magnetic 18-crown-6/Fe3O4 nanocomposite for uranium(VI) in solution

A new magnetic nanocomposite material, magnetic 18-crown-6/Fe₃O₄ nanocomposite (MCFN), was prepared for the removal of U(VI) from aqueous solution. The MCFN was composed of Fe₃O₄ nanoparticales modified by covalent attachment of 18-crown-6, which can help the material to be removed easily from solution by magnetic force. As a new adsorbent for U(VI) removal, MCFN was characterized by infrared radiation, scanning electron microscopy with energy dispersive X-ray spectroscopy, vibrating sample magnetometer and thermal gravimetric analysis. Those factors affecting the sorption behavior of U(VI), such as acidity, temperature, initial concentration of U(VI) and the amount of crown ethers were studied by orthogonal experiments. A maximum U(VI) sorption capacity of 91.12 mg g^?1 was achieved at 45 °C, pH 5.5 for 30 min. The experimental results showed that MCFN had great sorption capacity, high selectivity and strong potentiality of enrichment and recovery for U(VI). In summary, MCFN is a promising candidate for U(VI) separation in future practical applications.     

Synthesis,characterization, and analytical applications of 1,3-dimethyl-4-acetyl-2-pyrazolin-5-one

The synthesis of a new chelating reagent, 1,3-dimethyl-4-acetyl-2-pyrazolin-5-one (DMAP), is described. The reagent is characterized by physical, spectral and thermal methods. The reagent is soluble in water and forms neutral, water-soluble complexes with a number of metal ions, including Zr(IV), Th(IV), and U(VI). The complexed metal ions can be concentrated from dilute aqueous solution by adsorption onto a small column of Amberlite XAD-4 resin. The synthesis and characterization of the uranium (VI) complex of DMAP are described. The complex has the formula UO₂ (DMAP)₂, with a logarithmic formation constant of 8.64. A procedure is given for concentrating trace levels of U(VI) from solution by complexation with DMAP and sorption on XAD-4 resin. The method shows good recovery and precision for the concentration of trace U(VI) from artificial seawater.     

Efficiency of Cd(II) removal from aqueous media using chemically modified polystyrene foam

The removal of Cd(II) using polystyrene foam chemically modified with 2,2′-bipyridine has been investigated. The modified polystyrene foam has been characterized by FT-IR spectroscopy, thermogravimetry, elemental analysis and scanning electron microscopy. The solid was employed as a Cd(II) adsorption from aqueous solutions at room temperature. The effects of several variables (pH, shaking speed, agitation time, metal concentration and presence of other ions in the medium) have been studied using batch technique. Flame atomic absorption spectrometry was used to determine the Cd(II) ion concentration in the filtrate after the adsorption process. Maximum sorption 90% was achieved at pH 7 after 30 min of shaking time. Sorbed metal ions have been desorbed with 5 ml of 2 M HNO₃ with the detection limit of 16.7 ng ml⁻¹. The Langmuir, Freundlich and D–R isotherm equation were used to describe partitioning behavior of the system at room temperature. Kinetic and thermodynamic behavior of modified polystyrene foam for Cd(II) ion removal was also studied. Br⁻, PO₄³⁻, Pb²⁺, Ni²⁺ and Cr(VI) suppress the sorption to some extent. The possible sorption mechanism of Cd(II) ions onto modified sorbent is also discussed. Method was utilized to remove Cd(II) ions from aqueous media.     

Development of Thiol-Functionalized Mesoporous Silicate MCM-41 as a Modified Sorbent and Its Use in Chromatographic Separation of Metal Ions from Aqueous Nuclear Waste

Surface modified adsorbent mesoporous silicate MCM-41 has been prepared by grafting thiol containing functional group onto mesoporous silicate MCM-41. XRD, N₂ adsorption/desorption measurements, SEM, FT-IR, thermogravimetry and elemental analysis have been made to confirm the ordered mesoporous framework and the functionalization of the thiol groups. Sorption of 18 metal ions on this sorbent have been studied and discussed. Chromatographic separation of Rb(I)–U(VI)–Sr(II)–Zr(IV), has been achieved on column of this sorbent.     

A chelating resin containing 1-(2-thiazolylazo)-2-naphthol as the functional group; synthesis and sorption behavior for trace metal ions

A new polystyrene-divinylbenzene resin containing 1-(2-thiazolylazo)-2-naphthol (TAN) functional group was synthesized and its sorption behavior for 19 metal ions including Zr(IV), Hf(IV) and U(VI) was investigated by batch and column experiments. The chelating resin showed a high sorption affinity for Zr(IV) and Hf(IV) at pH 2. Some parameters affecting the sorption of the metal ions are detailed. The breakthrough and overall capacities were measured under optimized conditions. The overall capacities of Zr(IV) and Hf(IV) that were higher than those of the other metal ions were 0.92 and 0.87 mmol/g, respectively. The elution order of metal ions at pH 4 was evaluated as: Zr(IV)>Hf(IV)>Th(IV)>V(V)>Nb(V)>Cu(II)>U(VI)>Ta(V)>Mo(VI)>Cr(III)>Sn(IV)>W(VI). Quantitative recovery of most metal ions except Zr(IV) was achieved using 2 M HNO₃. Desorption and recovery of Zr(IV) was successfully performed with 2 M HClO₄ and 2 M HCl.