Equilibria and Kinetics of Extraction of Citric Acid from Aqueous Solutions in Alamine 336–Cyclohexanone System

Abstract

Equilibria and kinetics for the extraction of citric acid by Alamine 336 in cyclohexanone as diluent are reported. The theory of extraction accompanied by a chemical reaction has been used to obtain the intrinsic kinetics of extraction of citric acid by Alamine 336 in cyclohexanone. The reaction has been found to be first order in both Alamine 336 and citric acid with a rate constant of 8.8×10^?3 m³ kmol^?1 s^?1.     

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.

Kinetic Aspects of Copper‐LIX ® Extraction from Nitrate/Nitric Acid Aqueous Solutions

Abstract

A comparative kinetic study of the extraction of copper from nitrate/nitric acid aqueous solutions by different classes of LIX ^® reagents (LIX 984N, LIX 860N‐I, LIX 84‐I, LIX 65N) was performed. Using a Rotating Diffusion Cell, the rate constants of the chemical reactions (forward and reverse) were estimated and compared. In the case of the mixed extractant LIX 984N, a synergistic effect was observed. The values of the forward reaction constants of all the extractants were found to be an order of magnitude higher than those of the reverse reaction. The relatively low E _a ‐values prove the substantial influence of the diffusion on the extraction kinetics under the experimental conditions studied.     

Effect of the Alkyl Chain Length in N,N‐Dialkylpyridine‐3‐carboxamides upon their Extraction of Copper(II) from Aqueous Chloride Solutions

Abstract

Three nicotinamide derivatives with two butyl, hexyl, or octyl alkyl chains at amide nitrogen were synthesized. These model individual compounds were used for copper(II) extraction from acidic chloride solutions at constant ionic strength I = 1.0. It was found that during the extraction N,N‐dialkylpyridine‐3‐carboxamides form two complexes with copper(II) and chloride ions; these can transfer into the organic phase. In these complexes the molar ratio of copper:chlorine:extractant = 1:2:2 or 1:2:3. The obtained stability constants of N,N‐dihexyl‐ and N,N‐dioctylpyridine‐3‐carboxamides complexes with copper(II) chloride in water are comparable, but N,N‐dibutylpyridine‐3‐carboxamide complexes stability constants are significantly lower. The partition constants of these complexes in toluene–water system depend on amide hydrophobicity, increasing with increasing carbon chain length in N,N‐dialkylpyridine‐3‐carboxamides.     

Liquid—Liquid Extraction of Mercury with High-Molecular-Weight Amines from Iodide and Bromide Solutions

Abstract

New systems are described for the highly efficient solvent extraction of mercury with high-molecular-weight amines from aqueous iodide or bromide solutions. Mercury extracts essentially quantitatively at both the sub-nanogram and macro levels. The quaternary amines are especially attractive because of their ability to extract mercury from alkaline as well as acidic solutions. Regeneration of the amine solvent is readily achieved by stripping the mercury with alkaline solutions of cysteine.     

Synergistic Enhancement of the Extraction of Trivalent Lanthanides and Actinides by Tetra‐(n‐Octyl)Diglycolamide from Chloride Media

Abstract

This work describes a unique synergistic enhancement of the extraction of trivalent actinides and lanthanides by extraction chromatographic resins containing tetra‐n‐octyldiglycolamide (TODGA) from hydrochloric acid containing anionic metal chlorides. The presence of mg/L quantities of trivalent Fe, Ga, In, Tl, or Bi in HCl leads to several orders of magnitude enhancement of the extraction of trivalent actinides and lanthanides. The synergistic effect persists, even when the amount of metal chloride exceeds the capacity of the resin. The application of this synergistic enhancement for the separation of actinium from stainless steel and the preconcentration of americium and plutonium from large soil samples will be described.     

The Influence of Alkyl Chain Length and Steric Effect on Extraction of Zinc(II) Complexes with 1‐Alkyl‐2‐Methylimidazoles

Abstract

The extraction of Zn(II) complexes with six 1‐alkyl‐2‐methylimidazoles (alkyl is from C₅H₁₁ up to C₁₂H₂₅) from nitric solution was studied as a function of pH of the aqueous phase. As the organic solvents toluene, p‐xylene and 1,2,3,4‐tetrahydronaphthalene were used. The stability constants of the complexes in the aqueous phase as well as partition constants of the extractable species were determined. It was demonstrated that both the stability constants (β_c) and the partition constants (P_c) of the complexes increased with increasing alkyl chain length. Pseudo‐tetrahedral complexes were found to dominate at the second and third complexation steps, thus increasing the stability constants and facilitating extraction of the Zn(II) complexes with 1‐alkyl‐2‐methylimidazoles.     

Fixed‐Bed Removal of Free and Complexed Ni from Synthetic and Industrial Aqueous Solutions

Abstract

This paper evaluates the application of several biosorbents for Ni removal from aqueous solutions in the absence and in the presence of EDTA. Fixed bed experiments were performed (Ni influent concentration, 2 mg dm^?3; EDTA doses, 0, 5, and 10 mg dm^?3; pH=7) to study the process feasibility as refining after conventional physicochemical treatment. In absence of EDTA, uptake capacity followed the order peat > Posidonia oceanica > chitosan > chitin ? Scharlau AC. Maximum uptakes of 8.95 mg g^?1 and 5.10 mg g^?1 were found for peat and Posidonia oceanica, respectively. In the presence of EDTA, removal capacity decreased for all biosorbents; Ni was detected in the effluent from the beginning of the operation, indicating low ability to retain Ni EDTA‐complexes. Activated carbon presented the ability to remove complexed Ni. Peat exhibited the best performance for the treatment of an industrial spill from a metal‐finishing facility, with effluent Ni concentration lower than 0.2 mg dm^?3 for more than two weeks of treatment (3500 pore volumes of treated wastewater).     

Solid‐Liquid Extraction of Taxane Compounds from Yew Needle

Abstract

Solid‐liquid extraction of the taxane compounds in yew needles is carried out with methanol. The concentration of each component in the raffinate is estimated from the observed concentration in the extract and material balance equations with a solvent‐permeation model that solvent permeates the solid. The obtained distribution coefficient is found to be independent of the particle size. It suggests a possibility that the extract is in equilibrium with the liquid solution in the raffinate. Based on the experimental results, the effect of operating conditions on separation performance of countercurrent‐multistage extraction is studied by using the ideal stage calculation.     

Study on Reactive Extraction Kinetics of 1,3‐Propanediol in Dilute Aqueous Solutions

Abstract

In this work, the separation of 1,3‐propanediol (1,3‐PD) from dilute fermentation broth coupling the reversible reaction 1,3‐PD with acetaldehyde to form 2‐methyl‐1,3‐dioxane (2MD) and a synchronous extraction of 2MD by o‐xylene was studied experimentally. The equilibrium and reaction kinetics of the reactive extraction were established catalyzed by cation exchange resin HD‐8. After eliminating the influence of internal and external diffusion, the rate constants of positive and reverse reaction were obtained by fitting the experimental data to a pseudo‐homogeneous model. The results indicated that the reaction was a weakly exothermal reaction. The kinetics was found to be first‐order in the concentrations of the reactants and the products. The results can help to design the reactor of reactive extraction of 13,‐PD.     

Extraction of Palladium(II) from Nitric Acid Solutions with 1‐Benzoyl‐3‐[6‐(3‐benzoyl‐thioureido)‐hexyl]‐thiourea

The extraction of palladium (II) from HNO₃ solutions with 1‐Benzoyl‐3‐[6‐(3‐benzoyl‐thioureido)‐hexyl]‐thiourea (Ia) and several monodentate thiourea derivatives in 1,2‐dichloroethane has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant in the organic phase on the Pd(II) extraction is considered. The stoichiometry of the extracted complexes has been determined. The increasing number of thioamide groups in the molecule of Ia increases its extraction efficiency towards Pd(II). The potentialities of a polymeric resin impregnated with compound Ia for selective extraction of Pd(II) from nitric acid solutions are demonstrated.     

Flowsheet Modeling and Testing of Pseudohydroxide Extraction from Aqueous Sodium Hydroxide Solutions with 3,5‐di‐tert‐Butylphenol in Isopar® L Modified with Exxal® 8

Abstract

A conceptual counter‐current process flowsheet was developed for sodium hydroxide recovery from alkaline solutions via pseudohydroxide extraction (PHE). PHE relies on a simple sodium ion/proton exchange mechanism at elevated pH using a weak organic acid extractant. The contact of the sodium‐loaded organic phase with water results in the reconstitution of the extractant in the organic phase and sodium hydroxide in the aqueous phase. In this work, the 3,5‐di‐tert‐butylphenol (35‐DTBP) cation exchanger was used in the Isopar^® L diluent modified with isooctyl alcohol Exxal^® 8. Equilibrium isotherms determined for PHE from pure sodium hydroxide solutions and simulated radioactive waste leachate were used to develop a semi‐empirical model that could be used for designing PHE process flowsheets. Using this model, a conceptual PHE flowsheet was developed for recovering NaOH from solutions generated by caustic leaching of radioactive tank sludges. The flowsheet consists of the extraction, scrub, and strip processes, each employing four equilibrium stages. The modeling of this flowsheet indicates 97% recovery of the sodium hydroxide from the waste leachate feed solution. An experimental demonstration, performed with a simulated radioactive waste leachate using batch contacts in a co‐current analog of the counter‐current flowsheet, confirmed the potential for practical application of PHE technology.     

Recovery of 1,4‐Dimethyl Piperazine from Aqueous Solutions Using Polymeric Adsorbent and Ion‐Exchange Resins

Abstract

Strong and weakly acidic ion exchange resins and polymeric adsorbents are used for recovery of 1,4‐dimethyl piperazine (DMP) from aqueous solutions. Sorption of the amine in undissociated form is the primary mechanism of uptake of DMP on the ion‐exchange resins. Equilibrium adsorption data for DMP on the resins, at various temperatures, are fitted in Langmuir adsorption isotherm. Kinetic studies show that intraparticle diffusional resistance controls the sorption of DMP into the resin matrix. A mathematical model based on intraparticle diffusion and external mass transfer is used for simulating breakthrough profiles and compared with the experimental results for a fixed bed of weakly acidic Indion‐652 resin. The DMP loaded bed of the resin was effectively regenerated with methanol.     

Extraction of Zinc with Long-Chain β-Diketones and 4-Acyl-5-pyrazolones

Abstract

The extraction of zinc with long-chain 4-acyl-5-pyrazolones and β-diketones was studied. For comparison with the commercial extractant LIX 54, the extraction parameters were studied for their dependence on pH and on the influence of ammonia and tartrate. Among the examined compounds, 1-phenyl-3-methyl-4-(2-ethylhexanoyl)-5-pyrazolone shows the best extraction results. Zinc as well as nickel and cadmium can be extracted from tartrate solution. The separation of zinc and cadmium is possible. The extraction is disturbed by the presence of complexing agents such as ammonia or cyanide.     

Pseudohydroxide Extraction from Aqueous Sodium Hydroxide Solutions with 3,5‐di‐tert‐Butylphenol in Isopar® L Modified with 1‐Octanol

Abstract

Pseudohydroxide extraction (PHE) was investigated for recovering sodium hydroxide (NaOH) from alkaline process solutions. PHE relies on the deprotonation of a lipophilic weak acid by hydroxide ion with concomitant transfer of sodium ion into an organic phase. Contact of the sodium‐loaded organic phase with water results in the reconstitution of the extractant in the organic phase and NaOH in the aqueous phase, thus leading to a process in which NaOH equivalents are transferred from an alkaline feed solution to an aqueous stripping solution. In this work, we investigated PHE using a process‐friendly diluent—Isopar^® L. The lipophilic cation exchanger 3,5‐di‐tert‐butylphenol (35‐DTBP) was used as the extractant. The Isopar^® L diluent was modified with 1‐octanol to improve its solvation properties and the solubility of 35‐DTBP so that practical Na⁺ concentrations could be achieved in the process solvent. The PHE mechanism at process‐relevant conditions was explored by Raman and Fourier transform infrared spectroscopic measurements. Complementary electrospray ionization mass spectrometry studies were also performed. Equilibrium computer modeling suggested that the Na⁺ extraction behavior can be largely explained by the formation of 1∶1 and 1∶2 Na/35‐DTBP species in the organic phase. Extraction isotherms obtained using simulated caustic leaching solutions indicate the potential utility of this approach for recycling NaOH from complex alkaline mixtures.     

Liquid–Liquid Extraction of Butanol from Dilute Aqueous Solutions Using Soybean-Derived Biodiesel

Liquid–liquid extraction (LLE) of mixtures of butanol, 1,3-propanediol (PDO), and ethanol was performed using soybean-derived biodiesel as the extractant. The composition of the mixtures simulated the product of the anaerobic fermentation of biodiesel-derived crude glycerol, which has recently been reported for the first time by the authors. Using a biodiesel: with an aqueous phase volume ratio of 1:1, butanol recovery ranged from 45 to 51% at initial butanol concentrations of 150 and 225 mM, respectively. Less than 10% of the ethanol was extracted, and essentially no PDO was extracted. The partition coefficient for butanol in biodiesel was determined to be 0.91 ± 0.097. This partition coefficient is less than that of oleyl alcohol, which is considered the standard for LLE. However, butanol is suitable for blending with biodiesel, which would eliminate the need for separating the butanol after extraction. Additionally, biodiesel is much less costly than oleyl alcohol. If biodiesel-derived glycerol is used as the feedstock for butanol production, and biodiesel is used as the extractant to recover butanol from the fermentation broth, production of a biodiesel/butanol fuel blend could be a fully integrated process within a biodiesel facility. This process could ultimately help reduce the cost of butanol separation and ultimately help improve the overall economics of butanol fermentation using renewable feedstocks.     

Modification and Evaluation of Non‐Polar Sorbents for Solid‐Phase Extraction

Abstract

Modification of packings for solid‐phase extraction through high‐frequency low‐temperature plasma treatment is a new method to obtain a wide variety of sorbents. This method is still in the process of investigation and application. In this study, several commercial sorbents have been modified in high‐frequency low‐temperature plasma with the mixed hydrogen/benzene system. The solvation parameter model is used to characterize the sorption properties of commercially available and plasma treated sorbents for solid‐phase extraction. Chromatographic test mixtures from the literature were used to probe hydrophobicity, free silanol interactions and shape selectivity of the sorbents. The physical and retention properties of the plasma treated sorbents indicate their suitability to be used in solid‐phase extraction. Some suggestions concerning the possible practical application of the newly obtained sorbents have been made.     

The Solvent Extraction of Boron with Synthesized Aliphatic 1,3‐Diols: Stripping and Extraction Behavior of Boron by 2,2,5‐Trimethyl‐1,3‐hexanediol

Abstract

A variety of aliphatic 1,3‐diols (4a–c, 5a–c, 6a–c) was synthesized from β‐hydroxy carbonyl compounds (1–3) for potential use in the solvent extraction of boron. Primary‐secondary and primary‐tertiary alcohol structures of 1,3‐diols substituted with isopropyl, isobutyl, and isopentyl groups have been demonstrated to be very efficient for the solvent extraction of boric acid from aqueous solutions. The extraction ability of 2,2,5‐trimethyl‐1,3‐hexanediol (5b) was investigated as a function of 5b concentration, solution pH, solvent properties, and stripping conditions. Extraction efficiency increased with increasing concentration of 5b, and the best extraction of boron (96.8%) was found to be at an equilibrium pH of 2 with 0.5 M of 5b. Chloroform, toluene, chlorobenzene, 2‐octanol, and n‐amyl alcohol were found to be suitable solvents for the solvent extraction of boron. The boron complex can be recovered from the organic phase by treatment with an aqueous solution of sodium hydroxide. The highest ratio (96.7%) of boron was recovered by 0.1 M of sodium hydroxide solution.     

Development of Effective Solvent Modifiers for the Solvent Extraction of Cesium from Alkaline High‐Level Tank Waste

Abstract

A series of novel alkylphenoxy fluorinated alcohols were prepared and investigated for their effectiveness as modifiers in solvents containing calix[4]arene‐bis‐(tert‐octylbenzo)‐crown‐6 for the extraction of cesium from alkaline nitrate media. The structure of the fluorinated portion of the modifier influences the chemical stability, and a modifier that contained a terminal 1,1,2,2‐tetrafluoroethoxy group was found to decompose following long‐term exposure to warm alkaline solutions. However, replacement of the tetrafluoroethoxy group with a 2,2,3,3‐tetrafluoropropoxy group led to a series of modifiers that possessed the alkaline stability required for a solvent extraction process. Within this series of modifiers, the structure of the alkyl substituent (tert‐octyl, tert‐butyl, tert‐amyl, and sec‐butyl) of the alkylphenoxy moiety was found to have a profound impact on the phase behavior of the solvent in liquid–liquid contacting experiments, and hence on the overall suitability of the modifier for a solvent extraction process. The sec‐butyl derivative [1‐(2,2,3,3‐tetrafluoropropoxy)‐3‐(4‐sec‐butylphenoxy)‐2‐propanol] (Cs‐7SB) was found to possess the best overall balance of properties with respect to third phase and coalescence behavior, cleanup following degradation, resistance to solids formation, and cesium distribution behavior. Accordingly, this modifier was selected for use as a component of the solvent employed in the Caustic‐Side Solvent Extraction (CSSX) process designed for the removal of cesium from high‐level nuclear waste (HLW) at the U.S. Department of Energy's (DOE) Savannah River Site. In batch equilibrium experiments, this solvent has also been successfully shown to extract cesium from both simulated and actual solutions generated from caustic leaching of HLW tank sludge stored in tank B‐110 at the DOE's Hanford Site.     

Affinity of Clinoptilolite‐based Zeolites towards Removal of Cd from Aqueous Solutions

Abstract

Cd removal from aqueous solutions using as‐received and pretreated forms of two different clinoptilolite samples (denoted GC and BC) was investigated and dissimilar sorption affinities were revealed. Equilibrium behavior of systems were modeled using six different adsorption isotherms. The maximum sorption capacities, as obtained from the solubility‐normalized Dubinin‐Astakhov model for as‐received samples, were determined as 0.18 meq/g and 0.12 meq/g for GC and BC, whereas 0.72 meq/g and 0.41 meq Cd/g was determined for their pretreated forms, respectively. Examination of the release of exchangeable cations into the solution at equilibrium and the change of pH were discussed in terms of varying prevalence of ion exchange, dissolution of the sorbent and adsorption.