Sorption of uranium on lead hydroxyapatite

The uranium sorption from diluted aqueous solution onto lead hydroxyapatite was studied by using a batch-mode technique and the fluorimetric determination of uranium mass concentration. Partially crystallised lead hydroxyapatite [Pb₁₀(PO₄)₆(OH)₂] was obtained by direct precipitation and mild heating. This material presents very high specific surface, which is the key factor in the sorption of uranium from diluted solution. This material has a high ability to remove uranium (K _d,max from 5,661 to 18,833 ml/g, at 4 and 60 °C, respectively) in the chosen setup conditions (initial concentration of uranium 5 × 10^?6 M and pH 5.65).     

Sorption of inorganic salts on carbon nanomaterials and magnetite

Magnetic composites based on graphene oxides and functionalized carbon nanotubes containing magnetite nanoparticles are synthesized. The dispersing ability of these composites in water at different pH values is studied. It is shown that the solubility of Fe₃O₄ composites is constant in the рН range of 3.5–10, though these composites are unstable at both lower and higher pH values. Magnetic sorbents for extracting Се(NO₃)₃ and La(NO₃)₃ from solutions are tested. Dependences of the volume on the sorbent’s composition, pH value, and salt concentration in the solution are found. Maximum sorption capacity in relation to Се³⁺ and La³⁺ at рН 7.5 and 8.5 are found to be 1040 and 920 mg/g respectively.     

Growing ZnO crystals on magnetite nanoparticles

We report herein on the oriented growth of ZnO crystals on magnetite nanoparticles. The ZnO crystals were grown by hydrolyzing a supersaturated aqueous solution of zinc nitrate. The seeds for the growth were magnetite nanoparticles with a diameter of 5.7 nm and a narrow size distribution. Hollowed ZnO hexagons of 0.15 microm width and 0.5 microm length filled with Fe(3)O(4) particles were obtained. HR-TEM (high-resolution transmission electron microscopy) and selected-area EDS (energy-dispersive spectroscopy) show that the nanoparticles are homogenously spread in the ZnO tubes. Zeta potential measurements were employed to understand the relationship between the nanoparticles and the oriented growth of the ZnO crystals. The results show that the surfactants induced the directional growth of the ZnO crystals.     

Sorption of uranium onto titanosilicate materials

The sorption properties of three titanosilicate materials, AM-4, ETS-4, and Na2Ti2O3SiO4 . 2H2O of different framework structure and cation exchange capacity were studied towards the uptake of uranium from aqueous systems. Selectivity factors were estimated by determining batch distribution coefficient (Kd) and uranium removal (mg) per gram of the exchanger as a function of contact time, uranium concentration and batch factor (solution volume to exchanger mass ratio). The difference in their ability to take up uranium was discussed by in terms of their framework structure and the determination of their cation exchange capacity. Comparisons to ETS-10 have been made.     

Size-controlled synthesis of magnetite nanoparticles

Monodisperse magnetite nanoparticles have been synthesized by high-temperature solution-phase reaction of Fe(acac)3 in phenyl ether with alcohol, oleic acid, and oleylamine. Seed-mediated growth is used to control Fe3O4 nanoparticle size, and variously sized nanoparticles from 3 to 20 nm have been produced. The as-synthesized Fe3O4 nanoparticles have inverse spinel structure, and their assemblies can be transformed into gamma-Fe2O3 or alpha-Fe nanoparticle assemblies, depending on the annealing conditions. The reported procedure can be used as a general approach to various ferrite nanoparticles and nanoparticle superlattices.     

Sorption of uranium and other heavy metals on hydroxyapatite

The immobilization of U^VI and Pb^II from aqueous solutions in a solid phase by interaction with calcium hydroxyapatite has been studied in batch experiments with increasing contact times. The results were compared with those previously found for Cd^II. All these elements are able to be efficiently immobilized by such a method. The sorbed quantities vary in the order Pb>U>Cd. The sorption mechanisms are element dependent. The dominant mechanisms are: dissolutionprecipitation with formation of an amorphous or microcrystalline phase for U, dissolution-precipitation with the formation of two new crystalline phases and with possible incorporation into the initial apatite for Pb, and intracrystalline diffusion and exchange for Cd.     

Sorption of uranium complexes from aqueous solution

Summary The sorption of uranium-Arsenazo III complex was studied using Dowex-1x8 and carbonized apricot stone. The results show a similarity between the two sorbents since the percentage uptake of a uranium complex in the ratio 1 : 1 reaches 100% and 92% on the Dowex-1x8 and the carbonized apricot stone, respectively. Also the uptake of the complex on either sorbents increases with increasing the hydrogen ion concentration to reach a maximum value at pH 2.5. The two sorbents are used to study the sorption of uranium(VI) from seawater in the presence of 0.002% of Arsenazo III and 10^-3M EDTA, where it is found that uranium is completely sorbed by the two sorbents.     

Thermal transformation of water-dispersible magnetite nanoparticles

This paper presents a study on rapid hardening behaviors of β-C₂S by accelerated carbonation curing. β-C₂S cubes compacted at various molding pressures were subjected to different CO₂ concentration for accelerated carbonation curing. The CO₂ uptake and microstructure changes were analyzed by thermogravimetric analysis (TG), QXRD, FT-IR and MAS-NMR. The results indicated that CO₂ uptake was affected by molding pressure and CO₂ concentration seriously. TG analysis indicated that the carbonation reaction was rapid in the first hour. The carbonation degree reached 21.6% and giving a compressive strength of 85.7 MPa after 6 h carbonation in 99.9% CO₂ concentration. And it showed a much less carbonation degree in 20.0% CO₂. Calcite, vaterite and amorphous silica-rich phase formed in the carbonation progress. The FT-IR and NMR analysis indicated β-C₂S was decalcified to C–S–H gel and further decalcified to formation of an amorphous silica gel composed of Q ³ and Q ⁴ silicate tetrahedral. The chain length of C–S–H gel increased from to 2.67 to 6.36 with prolonged carbonation time, showing a lower C/S ratio and higher polymerization and also resulting in a lower C–S–H content.     

Sorption of uranium compounds by zirconium-silica nanosorbents

Bitemplate (solubilization) synthesis was used to obtain new mesoporous zirconium-silica nanosorbents that can be successfully used to recover uranium compounds from sulfate and carbonate solutions.     

Superparamagnetism of magnetite nanoparticles: dependence on surface modification

Superparamagnetic iron oxide nanoparticles (SPION) with an average particle diameter of 6 nm are prepared by controlled chemical coprecipitations. Colloidal suspensions of noninteracting SPION, where the surface has been modified with three different types of biocompatible substances, namely, starch, gold (Au), and methoxypoly(ethylene glycol) (MPEG) have been fabricated via three different techniques. Starch-coated SPION are prepared by coprecipitation in a polymeric matrix, Au-coated SPION are fabricated by the microemulsion method, and MPEG-coated SPION are prepared using the self-assembly approach. The magnetic nanoparticles form a core-shell structure, and the magnetic dipole-dipole interactions are screened by a layer of coating agents. The amounts of coating agents and SPION are indirectly calculated from the thermogravimetric analysis and superconducting quantum interference device measurements by assuming passive oxidation on the surface of the SPION, and the other conditions do not influence the measurements. The dependency of the spectral characteristics of M?ssbauer spectroscopy as a function of an external magnetic field Hext is measured to investigate the effect of dipole-dipole screening of the different coating layers on the SPION. Uncoated SPION show a stable magnetic moment under Hext, and the superparamagnetic (SPM) fraction transforms to a ferrimagnetic state. Starch and Au-coated SPION retain the SPM fraction according to M?ssbauer spectroscopy and magnetization measurements. MPEG-coated SPION show hyperfine magnetic structure without the quadrupole effect with increasing the value of the blocking temperature.     

Sorption of uranium by non-living water hyacinth roots

Summary Many studies have shown that water hyacinth (Eichhornia crassipes) roots can be used to accumulate high concentrations of organic as well as inorganic pollutants. They are currently used to remediate aquatic environments and aqueous solutions. In the present study, sorption of uranium from aqueous solutions by using dried roots of water hyacinth has been investigated. The sorption of uranium was examined as a function of initial concentration, pH, weight of roots and contact time. Five different concentrations 20, 40, 60, 80, and 100 μg ^. ml^-1 were used. Sorption proves to be very rapid and depend on pH, weight of roots and concentration of uranium. Maximum sorption capacity of water hyacinth roots was 64,000 U⁶⁺ μg/g. The sorption of uranium by water hyacinth roots follows a Langmuir isotherm.     

Sorption characteristics of uranium onto composite ion exchangers

The composite ion exchangers were tested for their ability to remove UO₂ ²⁺ from aqueous solutions. Polyacrylonitrile (PAN) composites having natural zeolite, clinoptilolite, and synthetic zeolite, zeolite X, were used as an adsorbents. The influences of pH, U(VI) concentration, temperature and contact time on the sorption behavior of U(VI) were investigated in order to gain a macroscopic understanding of the sorption mechanism. The optimum adsorption conditions were determined for two composites. The sorption behaviors of uranium on both composites from aqueous systems have been studied by batch technique. Parameters on desorption were also investigated to recover the adsorbed uranium.     

Synthesis and characterization of polystyrene-grafted magnetite nanoparticles

Magnetite (Fe₃O₄) nanoparticles were synthesized by chemical precipitation. To reduce the aggregation of Fe₃O₄ nanoparticles, an effective surface modification method was proposed by grafting polystyrene onto the Fe₃O₄ particles. The results of Fourier transform infrared spectra and elemental analysis showed that the polymer chains have been successfully grafted from the surface of the Fe₃O₄ nanoparticles and that the percentage of grafting can reach 73%. Transmission electron microscope showed that grafted polymer chains on nanoparticles could prevent the aggregation of Fe₃O₄ nanoparticles markedly in toluene and improve their compatibility with organic phase. Another finding was the grafting reaction did not alter the crystalline structure of the Fe₃O₄ nanoparticles according to the X-ray diffraction patterns, and the saturation magnetization of PS-Fe₃O₄ nanoparticles was found to be lower than bulk magnetite.     

Dendrimer modified magnetite nanoparticles for protein immobilization

A cascading polyamidoamine (PAMAM) dendrimer was synthesized on the surface of magnetite nanoparticles to allow enhanced immobilization of bovine serum albumin (BSA). Characterization of the synthesis revealed exponential doubling of the surface amine from generations one through four starting with an amino silane initiator. Furthermore, transmission electron microscopy (TEM) revealed clear dispersion of the dendrimer-modified magnetite nanoparticles in methanol solution. The dendrimer-modified magnetite nanoparticles were used to carry out magnetic immobilization of BSA. BSA immobilizing efficiency increased with increasing generation from one to five and BSA binding amount of magnetite nanoparticles modified with G5 dendrimer was 7.7 times as much as that of magnetite nanoparticles modified with only aminosilane. There are two major factors that improve the BSA binding capacity of dendrimer-modified magnetite nanoparticles: one is that the increased surface amine can be conjugated to BSA by a chemical bond through glutaraldehyde; the other is that the available area has increased due to the repulsion of surface positive charge.     

Sorption of uranium using silica gel with benzoylthiourea derivatives

Benzoylthiourea derivatives (N,N-diphenyl-N′-(3-methylbenzoyl)thiourea and diphenyl-N′-(4-methylbenzoyl)thiourea) were impregnated onto silica gel. The preconcentration of uranium(VI) from aqueous solution was investigated. Extraction conditions were optimized in batch method prior to determination by uv–visible absorption spectrometry using arsenazo(III). The optimum pH for quantitative adsorption was found as 3–7. Quantitative recovery of uranium (VI) was achieved by stripping with 0.1 mol L^?1 HCl. Equilibration time was determined as 30 min for 99% sorption of U(VI). Under optimal conditions, dynamic linear range of for U(VI) was found as 0.25–10 μg mL^?1. The relative standard deviation as percentage and detection limit were 5.0% (n = 10) for 10 μg mL^?1 U(VI) solution and 8.7 ng mL^?1, respectively. The method was employed to the preconcentration of U(VI) ions in soil and tap water samples.     

Thermal degradation of magnetite nanoparticles with hydrophilic shell

The aim of this study was the investigation of thermal degradation process at the interface of a core–shell type structure. Such hybrid compound was comprised of an inorganic core of magnetite nanoparticles and an organic shell consisting of 3-aminopropyltriethoxysilane. The thermal degradation has been studied by thermogravimetry in nitrogen atmosphere, up to 500 °C. The evolved gases analysis was performed using a coupling to a quadrupole mass spectrometer and a Fourier transform infrared spectrophotometer equipped with external modulus for gas analyses. Isoconversional kinetic study was conducted and a three stage thermal degradation mechanism was proposed.     

Sorption of silicates on goethite, hematite, and magnetite: experiments and modelling

Sorption of H(4)SiO(4) (including experiments as a function of time, K(d) measurement with different m/v ratios and sorption edges) onto different iron (hydro)oxides as goethite (alpha-FeOOH), hematite (alpha-Fe(2)O(3)), and magnetite (Fe(3)O(4)) has been studied with concentration of silicates under solubility limit. A surface complexation model has been used to account for sorption edge of silicates onto these iron oxide surfaces. It reveals that two types of surface complex namely FeH(3)SiO(4) and FeH(2)SiO(4)(-), are needed to describe properly the experimental observations.     

Sorption properties of oxides VIII: sorption of uranium on hydrous oxides

Sorption of unranium from nitrate solution on four hydrous oxides, namely, hydrous titanium, zirconium, cerium and thorium oxides (TiO₂, ZrO₂, CeO₂, ThO₂) has been studied at pH 3.5 as a function of uranyl concentration and temperature. The sorbed species was uranyl ion in the case of hydrous TiO₂ and CeO₂, while in the case of hydrous ZrO₂ and ThO₂, electrolyte sorption involving uranyl nitrate predominated. Sorption site densities calculated from saturation capacities, evaluated from Langmuir adsorption isotherm and surface areas, bear a direct relationship with the heat of sorption values. Results indicate that, in terms of sorption site density, hydrous CeO₂ seems to be a better sorbent than hydrous TiO₂ for the sorption of uranium.