Aqueous Nitrate Media Research Articles

Effects of nitrate concentrations on As(III) immobilization via new ferric arsenite hydroxynitrate precipitates

The Fe(III)-As(III)-anion precipitation as layered double hydroxide-like compounds such as tooeleite and ferric arsenite hydroxychloride (FC) has been found in As(III)-contaminated acidic mine soils. However, the question of whether As(III) is immobilized by Fe(III) in aqueous nitrate media, a common constituent in soils and metallurgical wastewater, remains unclear. Herein, we investigated the effects and mechanism of nitrate on As(III) immobilization via Fe(III)-As(III)-nitrate precipitation. Our results indicated that new ferric arsenite hydroxynitrate (FN) with variable Fe(III)/As(III)/nitrate molar ratios crystallized in an initial nitrate content range of 11,160–74,400 mg·L−1 at pH 2.3. This FN precipitation resulted in 60.3–87.9% of As(III) removal and a fall-rise immobilization trend as a function of the initial nitrate concentration. The optimal initial nitrate concentration for As(III) fixation was 44,640 mg·L−1. Although FN shared similar morphology and crystal structure with tooeleite and FC, the substitution of NO3− for SO42− and Cl− in the FeO6-AsO3 interlayers caused a significant local structural distortion due to different ionic radii. The characteristic infrared and Raman bands of the nitrate group in FN occurred at 1,363 cm−1, 1,384 cm−1 and 152 cm−1, 722 cm−1, 1,055 cm−1, respectively. The FN induced significantly enhanced As(III) immobilization relative to its tooeleite and FC counterparts at equimolar concentrations of NO3−, SO42−, and Cl− as the media.

Study of ceria thin films prepared via electrochemical deposition : Role of selected electrochemical parameters on growth kinetics

A three-electrode electrochemical cell was used for the synthesis of ceria thin films in an aqueous nitrate media, using the electrogenerated base method. The choice of the precursor of hydroxide is important regarding the mechanisms involved and the morphology of the deposits. The current-time curves were analyzed for the estimation of the growth kinetics. The scanning electronic microscopy analyses showed that a needle-like shape is characteristic of the CeO2 thin films. For the thin films deposited within 20 and 60 min, the thickness was 336 nm and 1 µm, respectively, confirming the linearity of the thickness with the deposition duration.

Adsorption and separation of terbium(III) and gadolinium(III) from aqueous nitrate medium using solid extractant

ABSTRACT A macroporous copolymer of styrene and divinylbenzene resin (TVEX-PHOR) was examined for adsorption of terbium(III) and gadolinium(III) from nitrate medium. Characterization of TVEX-PHOR before and after adsorption was investigated. Different factors affecting the sorption equilibrium were studied and a maximum separation value of 2.31 was reached at V/m = 0.3 L/g. Adsorption kinetics data indicated that the pseudo-second-order model is more applicable, while the isothermal data were found to be correlated with Freundlich model. The resin uptake capacity towards Tb(III) (24.93 mg/g) was more than that of Gd(III) (15.49 mg/g). Thermodynamic parameters of sorption indicated that the process was spontaneous and exothermic.

Stability of europium(ii) in aqueous nitrate solutions.

In the lanthanide series, Eu3+ is most easily reduced to its divalent state. Reduction of Eu3+ has been studied extensively in aqueous media that are insensitive to reducing conditions. Recently, it has been reported that reduction of Eu3+ is also feasible in aqueous nitrate solutions and that Eu2+ remained sufficiently stable in these media to conduct separation experiments. However, additional fundamental research on the reduction efficiency of Eu3+ and stability of Eu2+ in these media has not been reported yet. In this paper, cyclic voltammetry, magnetic susceptibility measurements, UV-vis absorption spectroscopy and X-ray absorption near edge structure (XANES) spectroscopy were used to gain more insights into the reduction of Eu3+ in aqueous nitrate media. Within the parameters used in this work, near-quantitative reduction of Eu3+ could be achieved within 120 min in highly concentrated nitrate salt solutions, using both chemical and electrochemical reduction techniques. Moreover, Eu2+ was remarkably stable in these solutions, showing just a small percentage of back-oxidation after 5 h in a sealed measurement cell.

Extraction and pre-concentration of lead from copper by emulsion liquid membrane technique using an ionic liquid

The study of the recovery process of lead from aqueous nitrate medium using emulsion liquid membrane technique was achieved by the optimization of the extraction and pre-concentration of Pb(II) ions. This has been conducted by the method of optimizing one experimental parameter at a time. The chemical process of recovery consists of a quaternary amine salt (Aliquat 336) as ionic liquid extractant and a non-ionic surfactant (Tween20) as reagent for dispersion and emulsion formation. Thus, several experimental parameters such as carrier concentration, surfactant concentration, time and stirring speed of feed phase, initial concentration and pH of feed concentration phase were studied. Pb(II) ions extraction was optimized using tri-n-octylphosphine oxide (TOPO) as the solvating organophosphorus compound in the emulsion phase. From the results, the lead ions were extracted at 92 ± 0.04% by Aliquat 336 in the presence of TOPO. For the stage of Pb(II) pre-concentration, the nature and concentration effects of the stripping solution were studied. So, the loss of the Pb(II) ions in the membrane phase was minimal when using the nitric acid solution as a stripping solution. It was preconcentrated at 83.55%. The separation experiments of Pb(II) from Cu(II) were given on the basis of the optimal conditions of lead(II) recovery. Thus, the separation factor of lead over copper was equal to 1.47.

Low-temperature phase formation in the BаF2-CeF3 system

Abstract Phase formation in the BaF 2 -CeF 3 system has been studied in the aqueous nitrate media by co-precipitation technique with the use of HF and NH 4 F as fluorinating agents. Formation and properties of fluorite-type Ba 1-x Ce x F 2+x (х = 0.32–0.58) and tysonite-type Ce 1-y Ba y F 3-y (y = 0–0.20) solid solutions are described in the present paper.

Simultaneous Extraction of Neodymium and Uranium using Hollow Fiber Supported Liquid Membrane

Simultaneous extraction of neodymium and uranium ions from aqueous nitrate media was investigated using hollow fiber supported liquid membrane (HFSLM). The organic phase supported in the membrane pores consisted of extractant N,N,N’,N’-tetraoctyl diglycolamide (TODGA), phase modifier isodecanol, and diluent n-dodecane. Experimental results suggest that there is competition between neodymium and uranium ions for complexation with TODGA. The initial rate of extraction of Nd3+ ions was found to be approximately six times to that of UO22+ ions. Experimental data was explained by a mathematical model for simultaneous transport of two metal ions. The model results were found to be in good agreement with the experimental data when the diffusivities of neodymium-TODGA complex (Dnm) and uranium-TODGA complex (Dum) in the membrane pore are 1.1 x 10−11 and 4 x 10−12 m2/s, respectively.

UV light-induced self-assembly of gold nanocrystals into chains and networks in a solution of silver nitrate

Controllable assemblies of nanocrystals have attracted considerable interest because they often exhibit unique collective properties that differ from those displayed by individual nanocrystals and bulk samples. Reported approaches to prepare nanocrystal assemblies based on the molecular recognitions of small molecules or biomacromolecules are effective, but often require complicated and time-consuming modification processes of nanocrystals. In this paper, we demonstrate a simple and universal approach to assemble gold nanocrystals (AuNCs) into linear chains and complex networks in aqueous silver nitrate medium under irradiation with UV light without the involvement of any modification step. Due to the strong plasmon resonance coupling verified by finite difference time domain calculation, the assembled structures of AuNCs can be used as excellent surface-enhanced Raman scattering substrates and dark-field light-scattering bioimaging probes.

Separation of zinc from lean sphalerite leached liquor in nitrate medium with D2EHPA using supported liquid membrane

Separation of zinc and lead from an aqueous nitrate medium using supported liquid membrane with di(2-ethylhexyl)phosphoric acid (D2EHPA) as mobile carrier was studied. Celgard-2500, a microporous polypropylene film, was used as the solid support for the liquid membrane with a plate and frame type of cell used for the experiments. The effects of different parameters such as pH of feed solution (1–3·5), D2EHPA concentration in the membrane phase (10–100 mol m−3), acid concentration in strip solution and flowrate of the aqueous solution on separation of lead and zinc were studied. It was observed that zinc flux across the membrane increased with pH of the feed solution up to 3·0 and thereafter decreased while zinc flux increased with the D2EHPA concentration in the membrane phase up to 75 mol m−3 and thereafter decreased. The flowrate of 100 mL min−1 was sufficient to reduce the resistances due to the aqueous boundary layer while 950 mol m−3 H2SO4 was found sufficient to strip the metals from the membrane phase in the strip phase. Under the study conditions, the copermeation of lead with zinc was observed to be negligible.

A Simple Two-Phase System Involving the Commercial Organophosphorous Extractant Cyanex<sup>®</sup> 471x for the Preparation of Silver Sulphide Nanoparticles

The facile chemical synthesis of silver sulphide nanocrystals from metal-loaded organic media, containing a silver-selective organophosphorous ligand as extractant, is reported. The method involves the phase-transfer of silver species from aqueous nitrate media to organic solution using the commercial extractant Cyanex? 471x (tri-isobutylphosphine sulphide, Cytec Co.) as extractant, followed by precipitation stripping using ammonium sulphide as strip reagent. The nanoparticles were structurally characterized, and some aspects of the synthetical process, are briefly discussed. Under the conditions studied, the extractant Cyanex? 471x was able to act as stabilizer adsorbing on the particles surface, maintaining the size of the particles nanometrical.

Synergistic effects of organophosphorus compounds on the extraction of copper from aqueous nitrate medium with N-(thioacetyl)benzamide into toluene

Synergistic effects of organophosphorus compounds on the extraction of copper from aqueous nitrate medium with N-(thioacetyl)benzamide into toluene

Synergistic Extraction of Copper from Nitrate Solutions Using β-Hydroxy-Naphthaldoxime and Organophosphorus Compounds into Carbon-Tetrachloride

The extraction behavior of Cu(II) from an aqueous nitrate medium employing β-hydroxy-naphthaldoxime in carbon tetrachloride has been investigated in the presence of several organophosphorus donors like tri-octyl phosphine oxide, tri-butyl phosphine oxide, and tri-butyl phosphate at pH 1.5. The concentration of the metal was measured by atomic absorption spectrophotometry. Synergism was observed when neutral donor was added because of the formation of the adduct [Cu(L)2.(S)] in CCl4 (S denotes neutral donor). The equilibrium constants of the binary system using β-hydroxy-naphthaldoxime and the ternary system involving another addition of an organophosphorus compound were calculated from the extraction date obtained. Furthermore, the temperature dependence of the equilibrium constants was also investigated to evaluate standard enthalpy (ΔH°), entropy (ΔS°), and free energy (ΔG°) of the reactions proposed.

Hollow-Fiber Membrane Extraction of Copper from Aqueous Nitrate Media by LIX® Reagents: Comparison of Extraction Efficiency and Fractional Resistances

Extraction of copper from nitrate/nitric acid aqueous solutions was studied using a HF Membrane Module and four LIX reagents (LIX® 860N-I, LIX® 984N, LIX® 84-I, and LIX® 65N) containing different active compounds (ketoximes and/or salicylaldoximes). Kinetic experiments varying the flow rates of both phases, aqueous and organic, and the extractant concentration were carried out to compare the extraction rate and efficiency from nitrate-aqueous media. A mathematical model based on the “aqueous extraction mechanism” in which the chemical reaction takes place in an aqueous-reaction zone was applied to determine the individual resistances of the copper mass-transfer process. It was found that the fractional resistance due to chemical reaction in the aqueous reaction zone, which varied from 92.5% to 95.8% in the order LIX® 860N-I < LIX® 984N < LIX® 84-I < LIX® 65N, controlled the total rate of the hollow-fiber copper extraction from nitrate aqueous media.

Radiotracer Study of Synergistic Effects of Organophosphorus Compounds on the Extraction of Silver by N-(thio acetyl) benzamide into n-butanol

In the present investigation, systematic study of synergistic effects of phosphine oxides and tributyl phosphate on the extraction of Ag (I) from aqueous nitrate medium with N-(thioacetyl) bezamide into n-butanol is being reported. The ligand was synthesized and cha racter ized in our laborator y. Temperature dependence of extraction equilibrium have been studied in order to evaluate the thermodynamic parameters responsible for the extraction. Finally, IR data were used to support the extraction mechanism. 2. Experimental 2.1. Reagents and instrument. The chelating ligand (Nthio acetyl) benzamide was synthesised by the reaction of thioacetamide and benzoylchloride, derived form benzoic acid, which were obtained from Aldrich, USA. The donor reagents used in this work e.g tri-butyl phosphine oxide (TBPO), triphenyl phosphine oxide (TPPO), tri-butyl phosphate (TBP), were also collected from Aldrich; USA. The solvents were purified by standard procedures. All other reagents used were of A.R. grade. A stock solution of silver was prepared by dissolving A.R. AgNO3 in deionized water and a working stock was prepared by appropriate dilution. In order to spike the solution, an appropriate volume of stock solution of Ag(I) was mixed, with few drops of tracer solution containing, 110m Ag as

Transport of americium(III) across SLM containing CMPO as the carrier extractant

The transport behaviour of Am3+ was investigated from nitric acid as well as from aqueous nitrate media under neutral pH conditions across PTFE flatsheet supports (0.45 micron) containing octyl,phenyl-N,N-di-iso-butyl carbamoylmethyl phosphine oxide (CMPO) as the carrier extractant. The effect of CMPO concentration and presence of tri-n-butyl phosphate (TBP) as phase modifier was studied. The results showed strong influence of hydrogen ion on Am(III) transport which was more pronounced in the presence of TBP. Acid transport data along with permeability coefficients for Am(III) transport are also presented.

Modeling of gadolinium recovery from nitrate medium with 8-hydroxyquinoline by emulsion liquid membrane

The extraction equilibrium of Gd(III) from nitrate medium by 8-hydroxyquinoline (HOX) in toluene was studied. Liquid–liquid investigations were first carried out. Based on the equilibrium results, the extraction of Gd(III) from aqueous nitrate medium into an emulsion liquid membrane system (ELM) containing 8-hydroxyquinoline in toluene as extractant, HNO 3 as stripping solution, Span-80 as surfactant was studied. The stability of the prepared ELM was studied in terms of the degree of membrane breakage. The different parameters affecting the permeation of gadolinium (III) were also studied. A general permeation model for the recovery of Gd(III) by the selected membrane is presented. The internal mass transfer in the water in oil (W/O) emulsion drop, the external mass transfer around the drop, the rates of formation and decomposition of the complex at the external aqueous–organic interface were considered.

Extraction Behavior of Nickel(II) using some of the BTBP‐Class Ligands

Recently the BTBP‐family of solvating ligands have been studied for their ability to separate trivalent actinides from lanthanides. Five of the BTBPs were evaluated for their ability to extract nickel(II) from aqueous nitrate media into cyclohexanone. It was shown by both solvent extraction and X‐ray diffraction experiments that the BTBPs are capable of forming both 1:1 and 1:2 complexes with nickel(II). When the BTBP concentration is low the nickel distribution ratio is governed by the formation of the nickel/BTBP complex while at higher BTBP concentrations the partitioning of the nickel complex between the two phases dictates the nickel distribution ratio.

Solvent Extraction and Extraction Chromatographic Separation of Am3+ and Eu3+ from Nitrate Medium using Cyanex® 301

The separation behavior of trivalent actinides and lanthanides from aqueous nitrate medium has been investigated using purified commercial Cyanex® 301 [bis(2,4,4‐trimethylpentyl)dithiophosphinic acid] in toluene by solvent extraction as well as by extraction chromatography. The separation studies were carried out using Am3+ and Eu3+ as the representative actinide and lanthanide ion, respectively. The stoichiometry of the extracted species as determined by the slope‐analysis method was Am(A)3 and Eu(A)2(NO3), when HA (Cyanex 301) concentration was <0.3 M. At a higher extractant concentration, the stoichiometry of the extracted Eu complex was Eu(A)3. Extraction chromatographic studies were carried out in the presence of several complexing agents that tend to influence the separation factor (D Am/D Eu) values. The solvent extraction and extraction chromatographic studies have yielded separation‐factor values of 4900 and 526, respectively.

Diluent effect on Sr(II) extraction using di- tert-butyl cyclohexano 18 crown 6 as the extractant and its correlation with transport data obtained from supported liquid membrane studies

The effect of organic diluents on the extraction of Sr(II) from an aqueous nitrate medium (containing a mixture of 2.0 M Al(NO 3) 3 + 0.5 M HNO 3) using di- tert-butylcyclohexano 18 crown 6 (DTBCH18C6) as the extractant was investigated. The diluent effect on the Sr(II) transport rates across supported liquid membranes (SLM) containing DTBCH18C6/diluent as the carrier was also investigated. Though diluents containing DTBCH18C6 alone have shown moderate transport rates, their 1:1 mixture with 1-octanol has shown significant enhancement in transport rates: a 1:1 chloroform–octanol mixture resulted in the highest distribution ratio values though the transport rates were at maximum with a tert-butyl benzene–octanol mixture. The extractability of the metal ion was correlated with Schmidt’s diluent parameter.

Effect of Diluents on the Extraction of Zirconium from Nitrate Medium by Thenoyltrifluoroacetone

Solvent extraction of Zr(IV) from aqueous nitrate medium has been studied using thenoyltrifluoroacetone (HTTA) as extractant in six different diluents (kerosene, chloroform (CHCl3), carbon tetrachloride (CCl4), benzene, toluene, and nitrobenzene). The effects of concentration of HNO3, H+, NO3 − and HTTA as well as temperature on the extraction process has been investigated. The species extracted into the organic phase appears to be zirconium with three or four molecules of HTTA. The equilibrium constants (Kex) of the extracted complexes have been evaluated and correlated with the dielectric constants and dipole moments of the investigated diluents.