Solid phase extractive preconcentration of uranium(VI) onto diarylazobisphenol modified activated carbon

Diarylazobisphenol (DAB) 1 and diarylazobisphenol modified carbon 2 were synthesized and characterised. The latter has been used for solid phase extractive preconcentration and separation of trace amounts of uranium(VI) from other inorganics. In this, a column mode preconcentration of uranium(VI) was carried out in the pH range 4.0-5.0, eluted with 1.0 mol l⁻¹ HCl and determined by an Arsenazo III spectrophotometric procedure. Calibration graphs were rectilinear over the uranium(VI) concentrations in the range 5-200 μg l⁻¹. Five replicate determinations of 25 μg of uranium(VI) present in 1 l solution gave a mean absorbance of 0.032 with a relative standard deviation of 2.52%. The detection limit corresponding to three times the standard deviation of the blank was found to be 5 μg l⁻¹. The accuracy of the developed preconcentration method in conjunction with the Arsenazo III procedure was tested by analysing MESS-3, a marine sediment certified reference material. Further, the above procedure has been successfully employed for analysis of uranium(VI) in soil and sediment samples.     

Amberlite XAD-4 functionalized with succinic acid for the solid phase extractive preconcentration and separation of uranium(VI)

Amberlite XAD-4 resin has been functionalized with succinic acid by coupling it with dibromosuccinic acid after acetylation. The resulting resin has been characterized by FT-IR, elemental analysis and TGA and has been used for preconcentrative separation of uranium(VI) from host of other inorganic species prior to its determination by spectrophotometry. The optimum pH value for quantitative sorption of uranium(VI) in both batch and column modes is 4.5-8.0 and desorption can be achieved by using 5.0 ml of 1.0 mol l⁻¹ HCl. The sorption capacity of functionalized resin is 12.3 mg g⁻¹. Calibration graphs were rectilinear over the uranium(VI) concentrations in the range 5-200 μg l⁻¹. Five replicate determinations of 50 μg of uranium(VI) present in 1000 ml of solution gave a mean absorbance of 0.10 with a relative standard deviation of 2.56%. The detection limit corresponding to three times the standard deviation of the blank was found to be 2 μg l⁻¹. Various cationic and anionic species at 200-fold amounts do not interfere during the preconcentration of 5.0 μg of uranium(VI) present in 1000 ml (batch) or 100 ml (column) of sample solution. Further, adsorption kinetic and isotherm studies were also carried out by a batch method to understand the nature of sorption of uranium(VI) with the succinic acid functionalized resin. The accuracy of the developed solid phase extractive preconcentration method in conjunction with Arsenazo III procedure was tested by analyzing marine sediment (MESS-3) and soil (IAEA soil-7) reference material. Further, the above procedure has been successfully employed for the analysis of soil and sediment samples.     

Solid phase extractive preconcentration of trace metals using p-tert-butylcalix[4]arene-1,2-crown-4-anchored chloromethylated polymeric resin beads

5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,26-dihydroxy-27,28-crown-4-calix[4]arene in the cone conformation was synthesized. This p-tert-butylcalix[4]arene-1,2-crown-4 compound was then anchored with Merrifield chloromethylated resin beads. The modified polymeric resin was characterized by ¹H NMR, FT-IR and elemental analysis and used successfully for the separation and preconcentration of Cu(II), Cd(II), Co(II), Ni(II) and Zn(II) prior to their determination by FAAS. Effective extraction conditions were optimized in both batch and column methods. The resin exhibits good separating ability with maximum between pH 6.0-7.0 for Cu(II), pH 6.0 for Cd(II), pH 5.0 for Co(II), pH 4.0-4.5 for Ni(II), and pH 4.5 for Zn(II). The elution studies were carried out with 0.5 mol L⁻¹ HCl for Cu(II), Co(II) and Co(II), 1.0 mol L⁻¹ HCl for Cd(II) and Zn(II). The sorption capacity, preconcentration factor and distribution coefficient of each metal ion were determined. The detection limits were 1.10, 1.25, 1.83, 1.68 and 2.01 μg L⁻¹ for Cu(II), Cd(II), Co(II), Ni(II) and Zn(II). The influence of several ions on the resin performance was also investigated. The validity of the proposed method was checked for these metal ions in NIST standard reference material 2709 (San Joaquin Soil) and 2711 (Montana Soil).     

Simultaneous preconcentration of uranium(VI) and thorium(IV) from aqueous solutions using a chelating calix[4]arene anchored chloromethylated polystyrene solid phase

A new chelating polymeric sorbent is developed using Merrifield chloromethylated resin anchored with calix[4]arene-o-vanillinsemicarbazone for simultaneous separation and solid phase extractive preconcentration of U(VI) and Th(IV). The “upper-rim” functionalized calix[4]arene-o-vanillinsemicarbazone was covalently linked to Merrifield resin and characterized by FT-IR and elemental analysis. The synthesized chelating polymeric sorbent shows superior binding affinity towards U(VI) and Th(IV) under selective pH conditions. Various physico-chemical parameters that influence the quantitative extraction of metal ions were optimized. The optimum pH range and flow rates for U(VI) and Th(IV) were 6.0-7.0 and 1.0-4.0 ml min⁻¹ and 3.5-4.5 and 1.5-4.0 ml min⁻¹, respectively. The total sorption capacity found for U(VI) and Th(IV) was 48734 and 41175 μg g⁻¹, respectively. Interference studies carried out in the presence of diverse ions and electrolyte species showed quantitative analyte recovery (98-98.5%) with lower limits of detection, 6.14 and 4.29 μg l⁻¹ and high preconcentration factors, 143 and 153 for U(VI) and Th(IV), respectively. The uptake and stripping of these metal ions on the resin were fast, indicating a better accessibility of the metal ions towards the chelating sites. The analytical applicability of the synthesized polymeric sorbent was tested with some synthetic mixtures for the separation of U(VI) and Th(IV) from each other and also from La(III), Cu(II) and Pb(II) by varying the pH and sequential acidic elution. The validity of the proposed method was checked by analyzing these metal ions in natural water samples, monazite sand and standard geological materials.     

Solid phase extraction and preconcentration of uranium(VI) and thorium(IV) on Duolite XAD761 prior to their inductively coupled plasma mass spectrometric determination

A simple and effective method is presented for the separation and preconcentration of thorium(IV) and uranium(VI) by solid phase extraction on Duolite XAD761 adsorption resin. Thorium(IV) and uranium(VI) 9-phenyl-3-fluorone chelates are formed and adsorbed onto the Duolite XAD761. Thorium(IV) and uranium(VI) are quantitatively eluted with 2 mol L⁻¹ HCl and determined by inductively coupled plasma-mass spectrometry (ICP-MS). The influences of analytical parameters including pH, amount of reagents, amount of Duolite XAD761 and sample volume, etc. were investigated on the recovery of analyte ions. The interference of a large number of anions and cations has been studied and the optimized conditions developed have been utilized for the trace determination of uranium and thorium. A preconcentration factor of 30 for uranium and thorium was achieved. The relative standard deviation (N = 10) was 2.3% for uranium and 4.5% for thorium ions for 10 replicate determinations in the solution containing 0.5 μg of uranium and thorium. The three sigma detection limits (N = 15) for thorium(IV) and uranium(VI) ions were found to be 4.5 and 6.3 ng L⁻¹, respectively. The developed solid phase extraction method was successively utilized for the determination of traces thorium(IV) and uranium(VI) in environmental samples by ICP-MS.     

Colorimetric detection of uranium(VI) on building surfaces after enrichment by solid phase extraction

A method for detecting and quantifying uranium(VI) levels on building materials that include concrete, Plexiglas, glass and steel surfaces is presented. Uranium(VI) was extracted from building material surfaces using a pH 2.2 buffer rinse and, subsequently complexed by an organic chelating agent, arsenazo III. The application of a uranium-chelating molecule, arsenazo III, allows for concentration enhancement using C₁₈ solid phase extraction and colorimetric detection of the uranium complex using ultraviolet-visible spectroscopy at 654 nm. The method has a detection limit (based on 3σ) of 40 ng/L (5 ng/cm²) and an overall extraction efficiency greater than 80% for each surface type (concrete, Plexiglas, glass, steel). Methods to prevent interference by metal ions commonly found on building materials are discussed.     

A novel extractant-impregnated resin containing carminic acid for selective separation and pre-concentration of uranium(VI) and thorium(IV)

The present work proposes the use of a novel extractant-impregnated resin (EIR) as an adsorbent in trace separation and pre-concentration of U(VI) and Th(IV) ions. The new EIR was prepared by impregnating carminic acid onto Amberlite XAD-16 resin beads. The morphology of new EIR was studied by BET surface area measurements and SEM micrographs. A column packed with CA/XAD-16 was used for selective separation and pre-concentration of the metal ions. Maximum adsorption of Th(IV) and U(VI) ions occurred at pHs of 3.50–5.75 and 3.75–6.50, respectively. The adsorbed metals could be eluted sequentially using 0.55?mol?L^?1 HCl for U(VI) and 2.25?mol?L^?1 HCl for Th(IV). The dynamic capacity of EIR was found to be 0.832 and 0.814?mmol?g^?1 for Th(IV) and U(VI), respectively. The tolerance limit of some foreign ions was also studied. The proposed method showed a good performance in analyzing geological reference materials and a synthetic seawater sample. Furthermore, the above procedure was successfully employed for the analysis of natural water samples.     

Aminothiozolyl maleamic acid based multi chelating hydrogels for the separation of uranium (VI) ions from aqueous environment

Multi chelating hydrogels (MCHs) were synthesized using a simple radical polymerization method from acrylamide, hydroxyethyl acrylate, and N‐(2‐aminothiozolyl)maleamic acid (AMA) monomers, methylenebisacrylamide (MBA) a cross‐linker, and azobisisobutyronitrile (AIBN) an initiator. The resulting MCHs were characterized with Fourier transform infrared spectroscopy and scanning electron microscopy to confirm the formation and morphological properties. The MCHs were highly swellable in aqueous solutions as well as different pH conditions. MCHs were applied to evaluate uptake behavior of Uranium (VI) ion from aqueous solutions. Batch adsorption studies were performed by varying experimental conditions like contact time, pH, and initial metal ion concentration. The kinetics data was best suited with the second‐order equation model. The equilibrium adsorption data was correlated with Langmuir and Freundlich isotherm models. This study suggests that maximum Uranium (VI) ion uptake has been found to be 288 mg.g^?1 and regenerated for 5 cycles without any significant change. Copyright © 2016 John Wiley & Sons, Ltd.     

Solid phase extraction preconcentration of cobalt and nickel with 5,7-dichloroquinone-8-ol embedded styrene-ethylene glycol dimethacrylate polymer particles and determination by flame atomic absorption spectrometry (FAAS)

This article explores the synthesis of styrene-divinyl benzene (DVB)/ethylene glycol dimethacrylate (EGDMA) polymers embedded with quinoline-8-ol (Q) or its dihalo derivatives by thermal means in the presence and absence of 4-vinyl pyridine (VP). The above-synthesized polymers were found to enrich cobalt and nickel present in admixtures. Of these, 5,7-dichloroquinoline-8-ol (DCQ) embedded styrene-EGDMA polymer particles enrich cobalt and nickel quantitatively from dilute aqueous solutions within 5 min of preconcentration time. Styrene-EGDMA, DCQ embedded styrene-EGDMA particles obtained by bulk polymerization and cobalt/nickel bonded polymers were characterized by FTIR, thermogravimetric analysis (TGA), elemental analysis and surface area studies. The use of these polymer particles obtained by bulk polymerization for the solid phase extractive preconcentration of cobalt and nickel was investigated in detail and explores the possibility of employing this procedure for the analysis of cobalt and nickel in soil and sediment samples using a simple, low cost and readily available flame atomic absorption spectrometric instrument was explored.     

Interaction of uranium(VI) with nitrogen containing model ligands studied by laser-induced fluorescence spectroscopy

The complexation of uranium(VI) with two nitrogen containing organic ligands, representing model substances for humic acid building blocks, has been investigated at pH values between 1.5 and 4.5 and an ionic strength of 0.1 M (NaClO₄). Using two independent fluorescence spectroscopic methods, time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses (fs-TRLFS), the complex formation of uranium(VI) with anthranilic and nicotinic acid in aqueous solution was studied. In both systems a decrease in the luminescence intensity was observed with increasing ligand or metal ion concentration. Uranium(VI) complexes of the type M_xL_yH_z were identified. Anthranilic acid forms a 1:1 complex under the given experimental conditions with a stability constant of log β₁₁₁ = 8.00 ± 0.31. For the uranium(VI) nicotinate system 1:1 and 1:2 complexes could be identified. The corresponding formation constants were calculated to be log β₁₁₁ = 8.59 ± 0.17 and log β₁₂₂ = 17.18 ± 0.35.     

A Study on the extraction of uranium(VI) from sulphate leach liquor using LIX63

The sulphate leach liquor obtained from the sulphuric acid leaching process of Egyptian monazite was treated using solvent extraction to recover U(VI) by LIX63. The influence of various basic variables such as pH, concentration of LIX63, temperature, different stripping agent, phase ratio and diluents was examined. Using 10% LIX63 with the aqueous solution at equilibrium pH 5.5 and a phase ratio A/O?=?1/1, a four-stage McCabe-Thiele plot was constructed, which showed 85.57% of U(VI) extraction. The thermodynamic data showed that the extraction process is exothermic with enthalpy change ΔH?=???43.866?kJ/mol, the stripping of U(VI) was quantitative using 4?M HNO₃. The stable complex UO₂(HSO₄)R_org formed during extraction which supports the cation exchange mechanism was confirmed by FTIR spectral analysis. Uranium cake was finally obtained from the strip solution by the addition of hydrogen peroxide and ammonium hydroxide as precipitating agents, and a workable flowsheet was then formulated.     

Spectrophotometric determination of trace amounts of uranium(VI) in water samples after mixed micelle-mediated extraction

A cloud point extraction process using mixed micelle of the cationic surfactant CTAB and non-ionic surfactant TritonX-114 to extract uranium(VI) from aqueous solutions was investigated. The method is based on the color reaction of uranium with pyrocatechol violet in the presence of potassium iodide in hexamethylenetetramine buffer media and mixed micelle-mediated extraction of complex. The optimal extraction and reaction conditions (e.g. surfactant concentration, reagent concentration, effect of time) were studied and the analytical characteristics of the method (e.g. limit of detection, linear range, preconcentration, and improvement factors) were obtained. Linearity was obeyed in the range of 0.20-10.00 ng mL⁻¹ of uranium(VI) ion and the detection limit of the method is 0.06 ng mL⁻¹. The interference effect of some anions and cations was also tested. The method was applied to the determination of uranium(VI) in tap water, waste-water and well water samples.     

Selective extraction of U(VI) over Th(IV) from acidic streams using di-bis(2-ethylhexyl) malonamide anchored chloromethylated polymeric matrix

A new chelating polymeric sorbent has been developed using Merrifield chloromethylated resin anchored with di-bis (2-ethylhexyl) malonamide (DB2EHM). The modified resin was characterized by CPMAS NMR spectroscopy, FT-NIR-FIR spectroscopy, CHN elemental analysis and also by thermo gravimetric analysis. The fabricated sorbent showed superior binding affinity for U(VI) over Th(IV) and other diverse ions, even under high acidities. Various physio-chemical parameters, like solution acidity, phase exchange kinetics, metal sorption capacity, electrolyte tolerance studies, etc., influencing the resin’s metal extractive behavior were studied by both static and dynamic method. Batch extraction studies performed over a wide range of solution acidity (0.01-10 M) revealed that selective extraction of U(VI) could be achieved even up to 4 M acidity with distribution ratios (D) in the order of ∼10³. The phase exchange kinetics studies performed for U(VI) and Th(IV) revealed that time duration of <15 min was sufficient for >99.5% extraction. But similar studies when preformed for trivalent lanthanides gave very low D values (<50), with the extraction time extending up to 60 min. The metal sorption studies performed for U(VI) and Th(IV) at 5 M HNO₃ was found to be 62.5 and 38.2 mg g⁻¹,respectively. Extraction efficiency in the presence of inferring electrolyte species and inorganic cations were also examined. Metal ion desorption was effective using 10-15 mL of 1 M (NH₄)₂CO₃ or 0.5 M α-hydroxy isobutyric acid (HIBA). Extraction studies performed on a chromatographic column at 5 M acidity were found to give enrichment factor values of 310 and 250 for U(VI) and Th(IV), respectively. The practical utility of the fabricated chelating sorbent and its efficiency to extract actinides from acidic waste streams was tested using a synthetic nuclear spent fuel solution. The R.S.D. values obtained on triplicate measurements (n = 3) were within 5.2%.     

Preconcentration of manganese(II) from natural and sea water on a palmitoyl quinolin-8-ol functionalized XAD copolymer resin and spectrophotometric determination with the formaldoxime reagent

A palmitoyl quinolin-8-ol (P.Ox)-functionalized Amberlite XAD-2 copolymer resin (XAD-P.Ox) was used in the column mode to preconcentrate trace Mn(II) from artificial and real seawater, and Mn in the eluate was determined by the formaldoxime (FAD) spectrophotometric method, the results compared with those of FAAS. The optimal pH interval of Mn uptake by the resin was between pH 7 and 10 (best at 8). Other column operation parameters such as adsorption and elution flow rate, and eluent volume were optimized. Since a preconcentration factor of approximately 60 was achieved with the resin column, the detection limits (LOD) of spectrophotometry and FAAS for Mn (i.e. 17 and 12 μg l⁻¹, respectively) were significantly reduced. The most serious interferent to the FAD procedure, i.e. ferric iron, was eliminated using the resin retention-elution procedure. The proposed method of preconcentration and analysis of Mn(II) was not adversely affected from high ionic strength media, rendering the method suitable for Mn determination in seawater.     

Effects of interaction of folic acid with uranium (VI) and basic triphenylmethane dyes on resonance Rayleigh scattering spectra and their analytical applications

In pH 4.2-4.8 HAc-NaAc buffer solution, folic acid (FA) could react with uranium (VI) to form a 2:1 anionic chelate which further reacted with some basic triphenylmethane dyes (BTPMD) such as Ethyl Violet (EV), Methyl Violet (MV) and Crystal Violet (CV) to form 1:2 ion-association complexes. As a result, not only the absorption spectra were changed, but also the intensities of resonance Rayleigh scattering (RRS) were enhanced greatly and the new RRS spectra were observed. The maximum RRS wavelengths were located at 328 nm for EV system, 325 nm for MV system and 328 nm for CV system. The fading degree (ΔA) and RRS intensities (ΔI) of three systems were different. Under given conditions, the ΔA and ΔI were all directly proportional to the concentration of FA. The linear ranges and the detection limits of RRS methods were 0.0039-5.0 μg mL⁻¹ and 1.2 ng mL⁻¹ for EV system, 0.0073-4.0 μg mL⁻¹ and 2.2 ng mL⁻¹ for MV system, 0.014-3.5 μg mL⁻¹ and 4.7 ng mL⁻¹ for CV system. The RRS methods exhibited higher sensitivity, so they are more suitable for the determination of trace FA. The optimum conditions, the influencing factors and the effects of coexisting substances on the reaction were investigated. The method can be applied to the determination of FA in serum and urine samples with satisfactory results. The structure of the ternary ion-association complex and the reaction mechanism were discussed in this work.     

Coordination and extraction studies of an unexplored bi-functional ligand,carbamoyl methyl pyrazole (CMPz) with uranium(VI), lanthanum(III) and cerium(III) nitrates

The bi-functional carbamoyl methyl pyrazole ligands, C₅H₇N₂CH₂CONBu₂ (L₁), C₅H₇N₂CH₂CONⁱBu₂ (L₂), C₃H₃N₂CH₂CONBu₂ (L₃), C₃H₃N₂CH₂CONⁱBu₂ (L₄) and C₅H₇N₂CH₂CON(C₈H₁₇)₂ (L₅) were synthesized and characterized by spectroscopic and elemental analysis methods. The selected coordination chemistry of L₁ to L₄ with [UO₂(NO₃)₂ · 6H₂O], [La(NO₃)₃ · 6H₂O] and [Ce(NO₃)₃ · 6H₂O] has been evaluated. Structures for the compounds [UO₂(NO₃)₂ C₅H₇N₂CH₂CONBu₂] (6) [UO₂(NO₃)₂ C₅H₇N₂CH₂CONⁱBu₂] (7) and [Ce(NO₃)₃{C₃H₃N₂CH₂CONⁱBu₂}₂] (11) have been determined by single crystal X-ray diffraction methods. Preliminary extraction studies of the ligand L₅ with U(VI) and Pu(IV) in tracer level showed an appreciable extraction for U(VI) and Pu(IV) up to 10 M HNO₃ but not for Am(III). Thermal studies of the compounds 6 and 7 in air revealed that the ligands can be destroyed completely on incineration.     

Selective and solventless oxidation of organic sulfides and alcohols using new supported molybdenum (VI) complex in microwave and conventional methods

A new dioxo-molybdenum (VI) complex supported on functionalized Merrifield resin ( MR-Mo ) has been synthesized and characterized by elemental, scanning electron mcroscopy, energy-dispersive X-ray analysis, TGA, Brunauer–Emmett–Teller method, powder-X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy and DRS–UV–vis analysis. The virgin Merrifield resin ( MR ) was functionalized by carbonylation followed by Schiff base formation with ethanolamine ( MR-SB ). Experimental data showed that the Schiff base coordinated with the MoO₂²⁺ moiety via O- and N-atoms. The catalytic activity of MR-Mo was explored under solventless conditions toward the oxidation of organic sulfides and alcohols using 30% aqueous H₂O₂ as oxidant. The oxidation reactions were conducted under microwave and conventional methods. The microwave-assisted oxidation reactions were found to be many times faster than the conventional methods. The oxidation reactions were selective and formed sulfoxides or aldehydes as the sole product with superior TOF values among the molybdenum (VI)-based complexes. Besides these, the MR-Mo was purely heterogeneous in nature and can be recycled for at least five reaction cycles without the loss of catalytic efficiency and product selectivity.     

Preconcentration and determination of ultra-trace amounts of U(VI) and Th(IV) using titan yellow-impregnated Amberlite XAD-7 resin

A simple and sensitive method for the determination of ultra trace amounts of U(VI) and Th(IV) ions by spectrophotometric method after solid-phase extraction on a new extractant-impregnated resin (EIR) has been reported. The new EIR was synthesised by impregnating a weakly polar polymeric adsorbent, Amberlite XAD-7, with titan yellow (TY) as extractant. The analytical method is based on the simultaneous adsorption of analyte ions in a mini-column packed with TY/XAD-7 and performing sequential elution with 0.5% (w/v) Na₂CO₃ for uranium and 2.0 M HCl for thorium. The influences of the analytical parameters including pH, salting out agent and sample volume were investigated. The interference effects of foreign ions on the retention of the analyte ions were also explored. The limits of detection for U(VI) and Th(IV) were as low as 50 and 25 ng L^?1, respectively. Relative standard deviations (n = 7) for U(VI) and Th(IV) were 3.1% and 2.9%, respectively. The method was successfully applied to the determination of ultra trace amounts of U(VI) and Th(IV) in different real matrices including industrial wastewater samples and environmental waters. The proposed method was validated using three certified reference materials and the results were in good agreement with the certified values.     

High-performance liquid chromatographic determination of uranium using solvent extraction and bis(salicylaldehyde) tetramethylethylenediimine as complexing reagent

The reagent bis(salicylaldehyde)tetramethylethylenediimine has been used for the determination of dioxouranium(VI), based on complexation in aqueous solution at pH 6, followed by extraction in chloroform and HPLC determination on a Hypersil ODS (3 μm) column. The complex was eluted with the ternary mixture methanol-acetonitrile-water (40:30:30, v/v/v), with UV detection at 260 nm. Oxovanadium(IV), iron(III), copper(II), cobalt(II), nickel(II) and palladium(II) were completely separated and did not interfere in the determination of uranium. The linear calibration range and detection limits have been obtained. The method has been applied to the determination of uranium together with copper, iron and nickel in mineral ore samples.