Exploration of As(III)/As(V) Uptake from Aqueous Solution by Synthesized Calcium Sulfate Whisker☆

Although common calcium-containing minerals such as calcite and gypsum may fix arsenic, the interaction be-tween modified calcic minerals and arsenic has seldom been reported. The uptake behavior of As...     

Removal of As(V) and Cr(VI) Ions from Aqueous Solution using a Continuous,Hybrid Field‐Gradient Magnetic Separation Device

Abstract

A continuous flow colloidal affinity magnetic separation device is used for the removal of As(V) and Cr(VI) from aqueous solutions. Langmuir isotherms fit the adsorption behavior of the individual ions on Orica MIEX^® ion exchange particles. In a mixture of equal weight percent As(V) and Cr(VI), the adsorption of As(V) begins only above a critical cut‐off concentration, implying preferential adsorption of the higher valence ion at the available sites. Cr(VI) is removed selectively from the mixture in the continuous flow device, consistent with the presence of a higher concentration of the higher valence ion in the proximity of a charged (anion‐exchange) surface.     

Mutual Separation of (W,As, Mo,V, Ge,B) Oxoanions from Bi‐metallic Solution by Resin having Methyl‐Amino‐Glucitol Moiety

Abstract

The mutual separation of (W, As, Mo, V, Ge, B)‐oxoanions using resin having methyl‐amino‐glucitol polymeric moiety from bimetallic solution was investigated by means of dynamic column experiments. The effect of solution pH on the separation efficiency and on the co‐removal level of metallic impurities was followed in this study. The conditions for efficient desorption of metals were determined in order to get the highly concentrated, impurities free solution suitable for recovery and reuse of separated metal. Effective separation of molybdenum and vanadium from boron or germanium and tungsten from arsenic was achieved.     

Removal of Cr(VI) Oxy‐anions from Aqueous Solution by Sorption into Poly(Acrylamide‐Co‐Maleic Acid) Hydrogels

Abstract

The dynamic removal of hexavalent chromiuim by poly(acrylamide‐co‐maleic acid) hydrogels was studied by a batch equilibrium technique at 35°C. Various kinetic and adsorption parameters such as rate constant for sorption, intraparticle diffusion rate constant, Langmuir constant, and adsorption capacity have been evaluated. The sorption process follows the Langmuir‐type behavior and extent of sorption of Cr(VI) ions depends upon the composition of co‐polymeric gels, presence of other ions in the solution, and temperature of the system. Relatively higher temperature favors the sorption process. The activation energy was found to be ?20.369 kJ mol^?1. Finally, various thermodynamic parameters have also been calculated to elucidate the mechanism involved in the sorption process. The positive enthalpy change indicates the endothermic nature of the process. The presence of fluoride ions causes a decrease in the degree of sorption of Cr(VI). Finally, the sorption of Cr(VI) into the copolymeric sorbent has been explained on the basis of coordination between electron rich O and N atoms of sorbent molecules and the Cr(III) molecules. Moreover, H‐bonding interactions also seem to contribute to the sorption process.     

Separation of the System NaCl-NaBr-Nal by “Solventing Out” from Aqueous Solution

Abstract

The precipitation of NaX (X = Cl, Br, I) from their saturated aqueous solution by three miscible organic solvents (MOS)-acetone, acetonitrile and isopropylamine-was studied for various MOS-aqueous solution volumes ratios. It was found that the fraction precipitated f is given by f = K log V/V_c where V is the volume ratio and K and V _c are constants. For the case of NaCl this plot was found to be a broken line composed of two straight lines intersecting at the point of “salting out.” A scheme is suggested to separate the three electrolytes using isopropylamine to precipitate NaCl and acetone to precipitate NaBr.     

Efficient Separation of Cytosine‐Substituted Mildiomycin Analogue (MIL‐C) from the Fermentation Broth by Ion Exchange

Abstract

Cytosine‐substituted mildiomycin analogue (MIL‐C) was synthesized by supplementing cytosine into the culture medium of Streptoverticillium rimofaciens (one mildiomycin producer) and had a specific and strong inhibitory activity against powdery mildews. In order to facilitate the separation of MIL‐C from this fermentation broth, the cultivation conditions were optimized to increase MIL‐C productivity, and more than 0.9 g/l cytosine was added to the medium to inhibit the biosynthesis of mildiomycin (MIL). According to the ion‐exchange equilibrium and dynamics characteristic of MIL‐C, one weakly cationic resin (DK110) was screened out to separate MIL‐C from fermentation broth with one effective ion‐exchange method. When 2% ammonia aqueous solution was applied as eluent with 2 BVs/h, high recovery yield (97.6%) and purity (70.0%) of MIL‐C were achieved. This novel strategy of combining up‐stream biosynthetic controls and down‐stream purification is very promising for efficient production of this novel nucleoside antibiotic (MIL‐C).     

Separation and Recovery of Silver(I) Ions from Base Metal Ions by Melamine‐formaldehyde‐thiourea (MFT) Chelating Resin

Abstract

Melamine‐formaldehyde‐thiourea (MFT) chelating resin were prepared using melamine (2,4,6‐triamino‐1,3,5‐triazine), formaldehyde, and thiourea and this resin has been used for separation and recovery of silver(I) ions from copper(II) and zinc(II) base metals and calcium(II) alkaline‐earth metal in aqueous solution. The MFT chelating resin was characterized by elemental analysis and FT‐IR spectra. The effect of pH, adsorption capacity, and equilibrium time by batch method and adsorption, elution, flow rate, column capacity, and recovery by column method were studied. The maximum uptake values of MFT resin were found as 60.05 mg Ag⁺/g by batch method and 11.08 mg Ag⁺/g, 0.052 mg Zn²⁺/g, 0.083 mg Cu²⁺/g and 0.020 mg Ca²⁺/g by column method. It was seen that MFT resin showed higher uptake behavior for silver(I) ions than base and earth metals due to chelation.     

Pseudo‐Hydroxide Extraction in the Separation of Sodium Hydroxide from Aqueous Solutions Using Alkyl Phenols

Abstract

Pseudo‐hydroxide extraction of sodium hydroxide from aqueous solution using four alkyl phenols of nearly identical molecular weight in 1‐octanol at 25°C was examined to understand the effect of alkyl substituents. The order of extraction strength among the four alkyl phenols tested was 4‐tert‐octylphenol>3,5‐di‐tert‐butylphenol>2,4‐di‐tert‐butylphenol>2,6‐di‐tert‐butyl‐4‐methylphenol. A good correlation with phenol pK _a was observed, indicating that extraction strength is determined by phenol acidity, as modified by steric effects in proximity to the phenol –OH group. The effective partition ratios (P _eff) of two phenols from 1 M NaOH solution were determined, showing that the phenols remain predominantly in the 1‐octanol phase even when converted to their sodium salts. However, the hydrophobicity of the tested phenols may not be sufficient for process purposes. The equilibrium constants for the governing extraction equilibria were determined by modeling the data using the program SXLSQI, supporting the cation‐exchange extraction mechanism. The proposed mechanism consists of two simple sets of equilibria for

1. Ion‐pair extraction to give Na⁺OH^? ion pairs and corresponding free ions in 1‐octanol the phase and

2. Cation exchange by monomeric phenol molecules (HAs) to form monomeric organic‐phase Na⁺A^? ion pairs and corresponding free organic‐phase ions.

Zirconium and Hafnium Separation,Part 3. Ligand‐Enhanced Separation of Zirconium and Hafnium from Aqueous Solution using Nanofiltration

Abstract

Membrane filtration equipment was used to evaluate zirconium and hafnium separation efficiency by a membrane separation process. High rejection of Zr and Hf species in aqueous solution were obtained with nanofiltration and ultrafiltration membranes. This high rejection could be explained by the formation of high molecular weight polynuclear species. Enhanced transportation across the nanofiltration and ultrafiltration membranes was observed when aminocarboxylic ligands, like EDTA, were introduced in the solution. This enhancement could be explained by a depolymerization process of the polynuclear complexes induced by the ligands. The rejection of Zr and Hf was markedly influenced by the counter anions and the EDTA/metal ratio. By using Zr and Hf oxynitrates instead of oxychlorides a difference of rejection of up to 20% was observed for Zr and Hf indicating that the membrane separation process could be an alternative process for Zr and Hf separation.     

Extraction of 4‐Hydroxycinnamic Acid from Aqueous Solution by Emulsion Liquid Membranes

Abstract

This work reports a study of 4‐hydroxycinnamic acid extraction by emulsion liquid membranes. The effect of the presence of additives in the membrane phase on solute permeation was tested. The membrane with 2 wt.% of isodecanol, 2 wt.% of ECA4360J, and Shellsol T as diluent was selected to examine the permeation of 4‐hydroxycinnamic acid. The modeling of solute extraction was done by taking into account the mass transfer in the external phase and globule, and the reaction between the diffusing component and the stripping reagent. The agreement between the calculated results and the experimental data was found satisfactory.     

Removal of Copper (II) Ions from Aqueous Solutions using Na‐mordenite

Abstract

The potential to remove copper (II) ions from aqueous solutions using Na‐mordenite, a common zeolite mineral, was thoroughly investigated. The effects of relevant parameters solution pH, adsorbent dose, ionic strength, and temperature on copper (II) adsorption capacity were examined. The sorption data followed the Langmuir, Freundlich, and Dubinin‐Radushkevich (D‐R) isotherms. The maximum sorption capacity was found to be 10.69 mg/g at pH 6, initial concentration of 40 mg/dm³, and temperature of 40°C. Different thermodynamic parameters viz., changes in standard free energy (ΔG⁰), enthalpy (ΔH⁰), and entropy (ΔS⁰) have also been evaluated and the results show that the sorption process was spontaneous and endothermic in nature. The dynamics of the sorption process were studied and the values of rate constant of adsorption, rate constant of intraparticle diffusion were calculated. The activation energy (E_a) was found to be 11.25 kJ/mol in the present study, indicating a chemical sorption process involving weak interactions between sorbent and sorbate. The interaction between copper (II) ions and Na‐mordenite is mainly attributable to ion exchange. The sorption capacity increased with the increase of solution pH and the decrease of ionic strength and adsorbent dose. The Na‐mordenite can be used to separate copper (II) ions from aqueous solutions.     

Centrifugal Contactors: Separation of an Aqueous and an Organic Stream in the Rotor Zone (LA‐UR‐05‐7800)

Abstract

A multi‐phase flow code is used to simulate the separation of an aqueous and an organic stream in the rotor zone of an annular centrifugal contactor. Different values for the mixture viscosity and for the initial volume fractions of the components are considered. A simple model for mass transfer of a species between phases is used. Geometrical effects are found to have significant influence on the separation of the two‐phase mixture.     

Solvent Extraction of Heavy Lanthanides(III) with 5,7‐Dibromo‐8‐hydroxyquinoline from Aqueous Perchlorate Solution

Abstract

The extraction of Tb(III), Dy(III), Ho(III), Er(III), Tm(III), and Yb(III) with 5,7‐dibromo‐8‐hydroxyquinoline (Hdbq or HA) in chloroform from aqueous perchlorate solutions was investigated. The formation of the LnA₃ species (where Ln = Tb, Dy, Ho, Er, Tm, and Yb) in the organic phase was supported by the data. The parameters of the extraction processes were determined, and the separation factors between two adjacent lanthanides(III) were calculated.     

Separation of Arsenic from Aqueous Solutions by Amino-Functionalized γ-Fe2O3-β-Zeolite

In this research, γ-Fe₂O₃-β-zeolite nanocomposite was synthesized and functionalized by 3-amino propyl trimethoxysilane. The magnetic functionalized adsorbent was characterized by FTIR, X-ray diffraction, thermal analysis, vibrating sample magnetometry, scattering electron microscopy, and N₂ adsorption-desorption techniques. The adsorbent was then used for adsorption of arsenic from aqueous solutions. At optimized conditions the adsorption capacity of 30 mg.g^?1 was obtained, which was higher than the previously reported values. The loaded adsorbent was easily separated from the solution by applying an external magnetic field. Regeneration of the adsorbent by NaOH solution indicated that 97% of the initial capacity was remained after four adsorption-regeneration cycles.     

The Partition Behavior of Zn(II) using Halide Ions Extractants in Aqueous Peg‐Based Two‐Phase Systems

Abstract

The partition behavior of Zn(II) has been studied in aqueous polyethylene glycol PEG(1550) – (NH₄)₂SO₄ two‐phase system using halide ions (Cl^?, Br^? and I^?) as extracting agents, at two different values of salt stock solution pH. The efficiency of extractants increase in this order: Cl^?>Br^?>I^?. The extracted species were estimated from the distribution coefficients' values determined as a function of halide ions concentration, and the “conditional extraction constants” were calculated. The experimental results suggest that the Zn(II) partition in presence of halide ions in such systems is the result of two competitive processes. The IR spectra of solidified PEG‐rich phases show that the passing of metal species into PEG‐rich phases bring a supplementary water contribution, which makes the extraction process to occurs until it reaches an “equilibrium state”, dependent on the hydrophobicity of these phases and not on the type of extracted metal species.     

Extraction of Lanthanides(III) from Aqueous Nitrate Media with Tetra‐(p‐tolyl)[(o‐Phenylene)Oxymethylene] Diphosphine Dioxide

A novel tridentate neutral organophosphorus compound, tetra‐(p‐tolyl)[(o‐phenylene)oxymethylene] diphosphine dioxide (I) has been synthesized and its extracting ability for microquantities of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y from HNO₃ and NH₄NO₃ aqueous solutions has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant concentration in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes and conditional extraction constants of Ln(III) have been determined. The extraction behavior of compound I is compared with that of the diglycolamide ligand TODGA. The potentialities of polymeric resin impregnated with compound I for the preconcentration of lanthanides(III) from nitric acid solutions are demonstrated.     

Hybrid Properties of Alginate‐PEI Adsorbent for Chromium (VI) Removal from Aqueous Solutions

Abstract

An adsorbent consisting of polyethyleneimine (PEI) immobilized in calcium alginate gel beads was synthesized and evaluated for Cr⁶⁺ removal. An evaluation of the synthesis process showed the importance of the PEI molecular weight on the immobilization efficiency. Polyethyleneimine of 70,000 Da molecular weight displayed the highest immobilization percentage at 52%. Batch kinetics and equilibrium tests showed that alginate‐PEI (APEI) resin displayed considerable affinity for negatively charged Cr⁶⁺ complexes at low pH conditions ranging from pH 1.5‐pH 3. The results also indicated the reduction of Cr⁶⁺ to less toxic Cr³⁺ species by the APEI adsorbent. The column adsorption experiments showed the ability of APEI resin to treat a 10 mg/L Cr⁶⁺ solution with pH influent adjustment from pH 1.5 to pH 3 to concentrations that satisfy effluent standards for Cr⁶⁺ (<0.1 mg/L) and total Cr (<0.5 mg/L). Finally, comparisons with a highly aminated commercial resin Chitopearl CS‐03 highlighted the unique ability of the hybrid APEI beads with its amine and carboxylic groups for the adsorption of Cr⁶⁺ as well as the retention of generated Cr³⁺ ions.     

Retention,Thermodynamics and Adsorption Profile of Th(IV) Ions onto 1‐(2‐Pyridylazo)‐2‐Naphthol (PAN) Loaded Polyurethane Foam from Acetate Media and its Separation from Rare Earths

Abstract

The sorption behavior of 2.7×10^?5 M solution of Th(IV) ions on 1‐(2‐pyridylazo)‐2‐naphthol (PAN) loaded polyurethane foam (PUF) has been investigated. The quantitative sorption was occurred from pH 6 to 9 from acetate buffer solutions. The sorption conditions were optimized with respect to pH, shaking time, and weight of sorbent. The sorption data followed the Freundlich, Langmuir, and Dubinin‐Radushkevich (D‐R) isotherms very successfully at low metal ions concentration. The Freundlich isotherm constant (1/n) is estimated to be 0.22±0.01, and reflects the surface heterogeneity of the sorbent. The Langmuir isotherm gives the maximum monolayer coverage is to be 8.61×10^?6 mol g^?1. The sorption free energy of the D‐R isotherm was 17.85±0.33 kJ mol^?1, suggesting chemisorption involving chemical bonding was responsible for the adsorption process. The numerical values of thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) indicate that sorption is endothermic, entropy driven, and spontaneous in nature. The adsorption free energy (ΔG_ads) and effective free energy (ΔG_eff) are also evaluated and discussed. The effect of different anions on the sorption of Th(IV) ions onto PAN loaded PUF was studied. The possible sorption mechanism on the basis of experimental finding was discussed. A new separation procedure of Th(IV) from synthetic rare earth mixture using batch, column chromatography, and squeezing techniques were reported.     

Separation of Actinides(III) from Lanthanides(III) in Simulated Nuclear Waste Streams using 6,6′‐Bis‐(5,6‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP) in Cyclohexanone

Abstract

An extraction system comprising 6,6′‐bis‐(5,6‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP) dissolved in cyclohexanone was investigated. The main purpose of this investigation was to extract and separate actinides(III) from lanthanides(III), both of which are present in the waste from the reprocessing of spent nuclear fuel. The system studied showed high distribution ratios for the actinides(III) and a high separation factor between actinides and lanthanides (SF_Am/Eu around 150). The extraction kinetics were fast with equilibrium being reached in 5 minutes. The effects of temperature on the extraction and the stoichiometry of the extracted complex were investigated. The extraction of californium(III) was studied and it was found that the BTBP molecule has a higher affinity for californium than for americium (SF_Cf/Am around 4). This system could be used to separate actinides(III) from lanthanide fission products with high efficiency, if used in conjunction with a pre‐equilibrium step.     

Solvent Extraction Separation of Niobium(V), Tantalutn(V) or Titanium(IV), and Vanadium(V) by 2′-Hydroxy-4-methoxy-5′-methyl Chalkone Oxime (HMMCO) from Their Binary Mixtures

Abstract

2′-Hydroxy-4-methoxy-5′-methyl chalkone oxime (HMMCO) has been used for the solvent extraction separation of Nb(V), Ta(V) or Ti(lV), and V(V) from their binary mixtures. V(V) can be quantitatively extracted with HMMCO from 9 M hydrochloric acid. The green-colored chloroform extractable V(V)-HMMCO complex absorbs at a maximum at 630 nm. Nb(V), Ta(V), and Ti(IV) are not extracted at these conditions. However, these metals can be extracted from strong hydrochloric acid medium in the presence of potassium thiocya-nate. The yellow-colored complexes of Nb(V), Ta(V), and Ti(IV) absorb at a maximum at 380, 390 and 390 nm, respectively. The method is simple, rapid, and selective, and affords a clean-cut separation of vanadium from niobium, tantalum, or titanium which are usually present in alloys and ores.