Retention profile, kinetics and sequential determination of selenium(IV) and (VI) employing 4,4'-dichlorodithizone immobilized-polyurethane foams

Polyurethane foams (PUFs) loaded with the chromogenic reagent 4,4′-dichlorodithizone (Cl₂H₂D_Z) have been investigated for the quantitative retention, chemical speciation and sequential determination of traces of inorganic selenium(IV) and (VI) from aqueous media containing bromide ions. The retention profile of selenium(IV) onto the reagent loaded foam followed a dual-mode sorption mechanism involving both absorption related to “solvent extraction” and an added component for surface adsorption. The kinetics and thermodynamic characteristics of selenium(IV) uptake onto PUFs have been studied. The kinetics of selenium(IV) sorption onto PUFs was found fast, reached equilibrium in few minutes and followed a first-order rate constant in presence of bromide ions in the extraction media. The thermodynamic parameters, ΔH, ΔS and ΔG, indicated the exothermic and spontaneous nature of the sorption process. The sorption and the recovery percentages of inorganic selenium(IV) from fresh water by the proposed loaded foam columns were achieved quantitatively. The height equivalent to theoretical plate (HETP), the number of layers (N), breakthrough capacity and the critical capacity for selenium(IV) uptake onto Cl₂H₂D_Z loaded foams columns were found to be 1.3, 103, 8.6 and 7.2 mg/g, respectively. The method was successfully applied for the chemical speciation and sequential determination of inorganic selenium(IV) and/or (VI) species spiked to fresh and industrial wastewaters.     

Kinetics and retention characteristics of some nitrophenols onto polyurethane foams

The kinetics of sorption of the nitrophenols by the unloaded polyurethane foams (PUFs) were found fast, reached equilibrium in few minutes and followed a first-order rate equation with an overall rate constant k in the range (0.16-0.21)±0.01 min⁻¹. The retention of the tested nitrophenols by the unloaded foams is consistent with the “solvent extraction” mechanism. However, the sorption also followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The mean free sorption energy of the nitrophenols onto the PUF was found equal to 7.5±0.4 kJ/mol, which reflects physical sorption. Thus, a dual-mode involves both absorption related to solvent extraction and an added component for surface adsorption seems a more likely sorption mechanism model. While a dual-mode sorption model explains the observed retention behavior, the data suggest that, solvent extraction plays a much larger role than the added component for surface adsorption. The sorption and recovery percentages of the nitrophenols from fresh, natural and industrial wastewater by the proposed unloaded foam columns were quantitatively achieved. The height equivalent to theoretical plates (HETP), N, the breakthrough capacity and the critical capacity for the unloaded foam columns were found in the range of (0.8-1.1)±0.6 mm, (94-132)±3, 3.2-4.02 and 1.5-2.67 mg/g, respectively. The method was successfully applied for the retention and recovery of the tested nitrophenols spiked to fresh and industrial wastewaters.     

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.     

Sorption characteristics and chromatographic separation of gold (I and III) from silver and base metal ions using polyurethane foams

The influence of different parameters on the sorption profiles of trace and ultra traces of gold (I) species from the aqueous cyanide media onto the solid sorbents ion exchange polyurethane foams (IEPUFs) and commercial unloaded polyurethane foams (PUFs) based polyether type has been investigated. The retention of gold (I) species onto the investigated solid sorbents followed a first-order rate equation with an overall rate constant k in the range 2.2-2.8 ± 0.2 s⁻¹. The sorption data of gold (I) followed Freundlich and Langmuir isotherm models. Thus, the a dual-mode of sorption mechanism involving absorption related to “weak base anion exchanger” and an added component for “surface adsorption” seems the most likely proposed dual mechanism for retention profile of gold (I) by the IEPUFs and PUFs solid sorbents. The capacity of the IEPUFs and PUFs towards gold (I) sorption calculated from the sorption isotherms was found to be 11.21 ± 1.8 and 5.29 ± 0.9 mg g⁻¹, respectively. The chromatographic separation of the spiked inorganic gold (I) from de ionized water at concentrations 5-15 μg mL⁻¹ onto the developed IEPUFs and PUFs packed columns at 10 mL min⁻¹ flow rate was successfully achieved. The retained gold (I) species were then recovered quantitatively from the IEPUFs (98.4 ± 2.4%, n = 5) and PUFs (95.4 ± 3.4%, n = 5) packed columns using perchloric acid (60 mL, 1.0 mol L⁻¹) as a proper eluating agent. Thiourea (1.0 mol L⁻¹)-H₂SO₄ (0.1 mol L⁻¹) system was also used as eluating agent for the recovery of gold (I) from IEPUFS (95.4 ± 5.4%, n = 3) and also PUFs (93.4 ± 4.4%, n = 3) packed columns. The performance of the IEPUFs and PUFs packed columns in terms of the height equivalent to the theoretical plates (HETP), number of plates (N), and critical and breakthrough capacities towards gold (I) species were evaluated. The developed IEPUFs packed column was applied successfully for complete retention and recovery (98.5 ± 2.7) of gold (III) species spiked onto tap- and industrial wastewater samples at <10 μg Au mL⁻¹ after reduction to gold (I). The IEPUFs packed column was applied satisfactorily for complete retention and recovery (98.5 ± 2.7) of total inorganic gold (I) and/or gold (III) species spiked to tap- and industrial wastewater samples at <10 μg mL⁻¹ gold. Chromatographic separation of gold (I) from silver (I) and base metal ions (Fe, Ni, Cu and Zn) using IEPUFS packed columns was satisfactorily achieved. The proposed method was applied successfully for the pre-concentration and separation from anodic slime and subsequent FAAS determination of analyte with satisfactory results (recoveries >95%, relative standard deviations <4.0%).     

Mechanism of extraction of the palladium(ii) thiocyanate complex by polyether foam

The mechanism of sorption of the palladium(II) thiocyanate complex by polyether-type Polyurethane foam has been investigated. At low thiocyanate concentration, palladium is most likely extracted as Pd(SCN)(2). The results obtained in the presence of enough thiocyanate for formation of the Pd(SCN)(4)(2-) complex are in disagreement with several possible mechanisms for sorption of the anionic metal complex by the foam, such as adsorption, solvent extraction, ligand addition or exchange, and weak or strong base anion-exchange. The extraction of Pd(SCN)(4)(2-) at high pH increased in the order Li(+)< Na(+) < Cs(+)< Rb(+) < K(+)< NH(4)(+) which is in good relation with the "cation-chelation" mechanism. This mechanism was also found predominant in the extraction of Pd(SCN)(4)(2-) complex from hydrochloric acid solutions.     

Chromatography of inorganic ions o sulfoethyl cellulose layer in hydrochloric acid and in hydrochloric acid-ammonium thiocyanate media

Summary Chromatographic behavior of 51 inorganic ions has been systematically studied on layers of sulfoethyl (SE) cellulose, a strongly acidic exchanger, in hydrochloric acid and in acid-ammonium thiocyanate media. The sorption of most of the ions on he SE-cellulose decreases with increasing concentration of the acid and the thiocyanate. The characteristic retention of some metal ions of SE-cellulose layer can be recognized over a low concentration of the acid or the salt. Feasibilities for separations of analytical interest are also presented in both systems.     

N,N,N',N'-Tetrabutyladipicamide as a new extractant in toluene of nitric acid and uranium (VI)

N,N,N',N'-Tetrabutyladipicamide (TBAA) was used for the extraction of nitric acid and uranyl(II) ion from nitric acid media into toluene. The effects of nitric acid, uranyl(II) ion, and extractant concentration, temperature and back extraction on the distribution coefficient of uranyl(II) ion have been studied. The main adduct of TBAA and HNO₃ is TBAA·HNO₃ in 1.0 mol/l nitric acid solution. The 1:2:2 complex of uranyl(II) ion, nitrate ion and TBAA as extracted species is further confirmed by IR spectra of the extraction of uranyl(II) ion with TBAA. The values of the thermodynamic parameters have also been calculated.     

Chemical enrichment and separation of uranyl ions in aqueous media using novel polyurethane foam chemically grafted with different basic dyestuff sorbents

The new type of the grafted polyurethane foam sorbents were prepared by coupling polyether polyol, toluene diisocyanate and basic dyestuff (Methylene blue, Rhodamine B and Brilliant green). The Me.B-PUF, Rh.B-PUF and Br.G-PUF were characterized using UV/vis, IR and TGA. The adsorption properties and chromatographic behaviour of these new adsorbents for preconcentration and separation of uranium(VI) ions at low concentrations from aqueous thiocyanate media were investigated by a batch process. The maximum sorption of U(VI) was in the pH ranges 1-4. The kinetics of sorption of the U(VI) by the Grafted-PUF were found to be fast with half life of sorption (t_1/2) in 2.43 min. The average sorption capacity of different sorbents 0.124 meq g⁻¹ for uranyl ions, enrichment factors ≈40 and the recovery 98-100% were achieved (R.S.D. ≈ 0.73%). The basic dyestuff Grafted-PUF could be used many times without decreasing their capacities significantly. The value of the Gibbs free energy (ΔG) for the sorbents is −7.3 kJ mol⁻¹, which reflects the spontaneous nature of sorption process. The sorption mechanism of the metal ion onto Grafted-PUF was also discussed.     

The sorption of thiocyanate ions on complex-forming ionites

The ligand sorption of thiocyanate ions on several complex-forming ionites was studied. The ionites were preliminarily transformed into metal forms by saturation with copper(II) ions. ANKB-2 amphoteric ionite in the Cu form had the strongest affinity for thiocyanate ions. The optimum conditions for their extraction were pH ∼ 2 and solution ionic strength 1. IR spectroscopy was used to study the ligand sorption of SCN⁻ ions by ANKB-2 ionite in the Cu form. The stability constants of thiocyanate ionite copper complexes were calculated from formation function [`(n)] \bar n .     

N,N,N′,N′-tetrabutylmalonamide as a new extractant for extraction of nitric acid and uranium(VI) in toluene

N,N,N,N-tetrabutylmalonamide (TBMA) was synthesized and used for extraction of uranyl(II) ion from nitric acid media in toluene. The effects of nitric acid concentration, extractant concentration, temperature and salting-out agent (LiNO₃) on distribution coefficients of uranyl(II) ion have been studied. The extraction of nitric acid is also studied. The main adduct of TBMA and HNO₃ is HNO₃. TBMA in 1.0 mol/l nitric acid solution. The 1:2:3 complex of uranyl(II) ion, nitrate ion and TBMA as extracted species is further confirmed by IR spectra of the extraction of uranyl(II) ion with TBMA, and found that the NO ₃ ^– in the extraction species UO₂(NO₃)₂·3TBMA did not participate in coordination of uranyl(II) ion. The values of thermodynamic parameters have also been calculated.     

Separation of trace amounts of palladium (II) with crown ether from hydrochloric acid and potassium thiocyanate media

A new method for the separation of trace amounts of palladium from hydrochloric acid and potassium thiocyanate media has been established based on the formation of an ion-pair complex of palladium thiocyanate anion Pd(SCN)₄ ^2– and the cationic potassium complex of dicyclohexyl-18-crown-6 (DC18C6) in chloroform. The effect of various factors (solvent, crown ether, potassium thiocyanate, hydrochloric acid, reagent concentration, shaking time, phase volume ratio, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of palladium has been investigated. The method can be combined with subsequent FAAS determination of palladium. The procedure was applied to determine palladium traces in chloroplatinic acid and rhodium chloride.     

Separation of trace amounts of palladium (II) with crown ether from hydrochloric acid and potassium thiocyanate media

A new method for the separation of trace amounts of palladium from hydrochloric acid and potassium thiocyanate media has been established based on the formation of an ion-pair complex of palladium thiocyanate anion Pd(SCN)4(2-) and the cationic potassium complex of dicyclohexyl- 18-crown-6 (DC18C6) in chloroform. The effect of various factors (solvent, crown ether, potassium thiocyanate, hydrochloric acid, reagent concentration, shaking time, phase volume ratio, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of palladium has been investigated. The method can be combined with subsequent FAAS determination of palladium. The procedure was applied to determine palladium traces in chloroplatinic acid and rhodium chloride.     

N-dodecanoylpyrrolidine as a new extractant for uranyl(II) and nitric acid in toluene

N-dodecanoylpyrrolidine (DOPOD) was synthesized and used for the extraction of nitric acid and uranyl(VI) ions from nitric media in toluene. The effects of nitric acid concentration, extractant concentration, temperature, salting-out agent (LiNO₃) have been studied. The main adduct of DOPOD and HNO₃ is HNO₃·DOPOD. The complex formation of uranyl(VI) ion, nitrate ion and DOPOD (UO₂(NO₃)₂·2DOPOD) as extracted species are further confirmed by IR spectra and the values of thermodynamic parameters have also been calculated.     

Uranyi ion transport through tri-n-octylamine-xylene based supported liquid membranes

Tri-n-octylamine (TOA) dissolved in xylene has been used as carrier, constituting liquid membrane supported in Celgard 2400 polypropylene microporous film for the transport of uranyl ions against their concentration gradient from aqueous acid solutions to an alkaline aqueous phase. Effect of sttrring rate, nitric acid concentration and TOA concentration in the organic membrane phase, on the flux of uranyl ions through the membrane has been studied. Viscosity and density data have been obtained to estimate diffusion coefficients and hence the permeability coefficients to compare the same with experimental values, using distribution coefficient data, measured from solvent extraction experiments and available in the literature. Analysis of the flux data has been performed to study the stoichiometry of the chemical reaction involved in complex formation reaction. The results have been compared with simple liquid-liquid extraction data.     

Influence of binary/ternary complex of imprint ion on the preconcentration of uranium(VI) using ion imprinted polymer materials

Ion imprinted polymer (IIP) materials were prepared for uranyl ion (imprint ion) by forming binary (5,7-dichloroquinoline-8-ol (DCQ) or 4-vinylpyridine (VP)) or ternary (5,7-dichloroquinoline-8-ol and 4-vinylpyridine) complexes in 2-methoxy ethanol (porogen) and copolymerizing in the presence of styrene and divinyl benzene as functional and crosslinking monomers, respectively and 2,2′-azobisisobutyronitrile as initiator. IIP particles were obtained by leaching the imprint ion in these polymer materials with 50% (v/v) hydrochloric acid, filtering, drying in an oven at 50 °C and grinding. Control polymer particles were also prepared under identical conditions. The above synthesized polymer particles were characterized by IR, CHN, X-ray diffraction, and pore size analyses. These leached polymer particles can now pick up uranyl ions from dilute aqueous solutions. The IIP particles obtained with ternary complex of uranyl ion alone gave quantitative enrichment of traces of uranyl ions from dilute aqueous solutions. The optimal pH for quantitative enrichment is 4.5-7.5 and eluted completely with 10 ml of 1.0 M HCl. The retention capacity of uranyl IIP particles was found to be 34.05 mg of uranyl ion per gram of polymer. Further, the percent extraction, distribution ratio, and selectivity coefficients of uranium and other selected inorganic ions were also evaluated. Five replicate determinations of 25 μg of uranium present in 1.0 l of aqueous solution gave a mean absorbance of 0.036 with a relative standard deviation of 2.50%. The detection limit corresponding to three times the standard deviation of the blank was found to be 5 μg l⁻¹.     

Nitrate ion transport across TBP-kerosene oil supported liquid membranes coupled with uranyl ions

The role of nitrate ions in uranyl ions transport across TBP-kerosene oil supported liquid membranes (SLM) at varied concentrations of HNO₃ and NaNO₃ has been studied. It has been found that nitrate ions move faster compared to uranyl ions at the uranium feed solution concentrations studied. The nitrate to uranyl ions flux ratio vary from 355 to 2636 under different chemical conditions. At low uranium concentration the nitrate ions transport as HNO₃ · TBP, in addition to as UO₂(NO₃)₂ · 2TBP type complex species. The flux of nitrate ions is of the order of 12.10 · 10^–3 mol · m^–2 · s^–1 compared to that of uranium ions (4.56 · 10^–6 mol · m^–2 · s^–1). The permeability coefficient of the membrane for nitrate ions varies with chemical composition of the feed solution and is in the order of 2.5 · 10^–10 m^–2 · s^–1. The data is useful to estimate the nitrate ions required to move a given amount of uranyl ions across such an SLM and in simple solvent extraction.     

The sorption behaviour and separation of some metal thiocyanate complexes on polyether-based polyurethane foam

The preliminary screening tests on the preconcentration of lanthanum(III), aluminium(III), molybdenum(VI), gallium(III) and tungsten(VI) thiocyanate complexes in aqueous media by unloaded foam indicated a reasonable percentage of metal ions were retained on the foam. The influence of various parameters affecting the retention of these complex species from the aqueous media by the foam were critically studied and the possible mechanisms of the sorption of the compounds were suggested. However, owing to the complex chemical nature of the polyether-polyurethane foam, several mechanisms may be involved simultaneously. Attempts for the quantitative retention and recovery of the tested complexes by the foam columns were also made and satisfactory results were obtained. The height equivalent to theoretical plates (HETP) of the foam columns were calculated from the chromatograms and break through capacity curve and were found in the range 1.8-2.3 mm at flow rates up to 15 cm(3)/min. The proposed foam column method has been successfully used for the separation of a series of complex mixtures of the tested metal thiocyanate complexes in aqueous media. The membrane properties of the foam sorbents offer unique advantages over conventional bulk type granular sorbents in rapid, versatile effective separations and preconcentrations of different complexes from fluid samples.     

Ion exchange properties of crystalline bismuth molybdenum hydrous oxide and its intercalates: Equilibrium and kinetics of UO 2 2+ ions on the crystals

The sorption of uranyl ions on crystalline bismuth molybdenum hydrous oxide and its intercalates were investigated from point of view of both equilibrium and kinetics. Ion exchange isotherms of uranyl ions on the crystals were obtained, and ionic sieve effect was employed to describe the characteristics of ion exchange isotherms. The best fitting for sorption of uranyl ions on BMHO was achieved by means of the Langmuir isotherm, while the Freundlich isotherm appeared to best fit for its intercalates. The slightly negative free-energy change indicates that, thermodynamically, the crystals behave less favourable for uranyl ions. The equation derived from S_N2 chemical reactions was proved to fit the rate curves, and the rate constants were determined. The comparison between the calculated and observed pH values as a function of time further verified the chemical reaction mechanism.     

FTIR Spectroscopy of Ion Solvation of LiClO4 and LiSCN in Acetonitrile, Benzonitrile, and Propylene Carbonate

FTIR spectra of lithium perchlorate and lithium thiocyanate in acetonitrile,benzonitrile, and propylene carbonate were recorded in the temperature range from 5to 45°C. New bands due to solvent molecules in the primary solvation shell ofthe lithium ions were detected in the region of the CN stretching mode of thenitriles and of the CO stretching mode of propylene carbonate. The band structureswere studied in detail by deconvolution with band-fitting procedures and meancation solvation numbers were deduced from the band area of the bulk solvent.For the systems acetonitrile—lithium perchlorate, benzonitrile—lithiumperchlorate, and benzonitrile—lithium thiocyanate, solvation numbers of free andbound lithium ions were calculated with the help of the degree of associationobtained from suitable anion vibrations.     

Structural environment of uranium (VI) species sorbed onto ZrP2O7: X-ray absorption spectroscopy study

The structure of the surface complex formed during the sorption of UO₂²⁺_aq ion onto the selected phosphate solid has been investigated mainly using X-ray absorption spectroscopy. Samples were prepared by batch experiments. L_III U edge measurements have shown that uranyl ions are sorbed on the phosphate surface as a mononuclear bidentate inner-sphere complex.