Transport of carbonate ions through supported liquid membrane by using Alamine 336 and trioctylphosphine oxide as carriers

Abstract

Transport studies were carried out for carbonate ions through supported liquid membrane (SLMs) by using Alamine 336 and trioctylphosphine oxide (TOPO) as carriers. Experimental variables were investigated, such as concentration of carbonate ion (10^?5 to 4×10^?2 M), carriers (10^?5 to 10^?1 M), and alkali (0.01–0.5); and stirring speed (50–150 rpm) of bulk solutions. The use of combined carriers Alamine 336 and TOPO shows a synergic transport of carbonate ions. The stability of the SLM system in relation to the transport of carbonate ions has been studied. The enrichment of carbonate ions (10^?6 to 4×10^?2 M) from the dilute solution was explored. The different combinations of amines with TOPO show synergic permeability of the carbonate ions through SLM system.     

Emulsion liquid membrane extraction of Ni(II) and Co(II) from acidic chloride solutions using bis-(2-ethylhexyl) phosphoric acid as extractant

An emulsion liquid membrane process using bis-(2-ethylhexyl) phosphoric acid (D2EHPA) to extract and separate Ni(II) and Co(II) from acidic chloride solutions is described. Liquid membrane consists of a diluent, a surfactant (Span 80), and an extractant (D2EHPA). Hydrochloric acid was used as the stripping solution. The important parameters governing the permeation of nickel and their effect on the separation process have been studied. These parameters are stirring speed, feed phase pH, surfactant concentration, extractant concentration, stripping phase concentration, phase ratio, initial concentration of metal, and treatment ratio. The optimum conditions have been determined. The separation factors of Ni(II) with respect to Co(II), based on initial feed concentration, have been experimentally determined. Furthermore, the extraction selectivity for Co(II) over Ni(II) has been improved by using D2EHPA during the initial minutes.     

Modelling and simulation of integrated membrane processes for recovery of Cr(VI) with Aliquat 336

Extraction processes which employ porous membranes as a barrier between aqueous and organic phases provide a versatile means for selective removal and enrichment of solutes from aqueous streams. They require relatively little maintenance, their energy consumption is very low and the organic liquid losses are negligible if the pressure is controlled properly. The modelling and simulation of a complete plant for the removal and recovery of Cr(VI) with Aliquat 336 using hollow fibre modules have been studied. Both single and dual function membrane modules have been analyzed. Simulated concentration profiles through the module were obtained by solving mass transfer balances corresponding to all the species involved in the process.     

Facilitated Cd(II) transport across CTA polymer inclusion membrane using anion (Aliquat 336) and cation (D2EHPA) metal carriers

PIMs have been involved as affinity membranes for recovery of metals (Cd, Pb, Zn) by facilitated transport from aqueous solutions under different speciation forms, either anionic or cationic. The motivation of this work is to compare the efficiency of the recovery process in the case of Cd(II) using extractants such as D2EHPA and Aliquat 336 that can form complexes with the cation Cd²⁺ or the anions CdCl₃⁻ and CdCl₄²⁻, respectively. The maximal Cd(II) recovery factors obtained in 8 h are 97.5% and 91.8% with D2EHPA and Aliquat 336, respectively. Although the transport fluxes with both carriers are not strongly different (ca. 2 μmol m⁻² s⁻¹), the recovery process in case of mixture of metals is better achieved with Aliquat 336. PIMs have shown a very good stability and a constancy of the transmembrane transport flux over 12 replicate measurements, each one lasting for 8 h repeated every 24 h.     

Preparation of NOx modified PMMA-EGDM composite membrane for the recovery of chromium (VI)

A non-interpenetrating cross-linked poly (methyl methacrylate-ethylene glycol dimethacrylate) copolymer ultrafiltration membrane on a microporous ceramic support has been prepared from the monomers in two stages. The polymer membranes thus obtained have been nitrated using NO_x (a mixture of NO and NO₂) by the gas phase reaction at 80 °C. Separation experiments on the chromium (VI) salt solution have been carried out using unmodified (giving 68% rejection per pass) and nitrated membranes (giving as much as 67% rejection per pass). For nitrated membranes, the water flux and the solute flux increased with time of nitration about hundred folds because of the increase in the hydrophilicity as well as the pore size.     

Separation and concentration of cobalt from ammoniacal solutions containing cobalt and nickel by emulsion liquid membranes using 5,7-dibromo-8-hydroxyquinoline (DBHQ)

The separation and concentration of cobalt from ammoniacal solutions containing nickel and cobalt by an emulsion liquid membranes (ELMs) using 5,7-dibromo-8-hydroxyquinoline as extractant has been presented. Membrane solution consists of a diluent (kerosene), a surfactant (Span 80), a modifier (tributylphosphate), and an extractant (DBHQ). Very dilute sulphuric solution containing EDTA as complexing agent, buffered at pH 5.0, has been used as a stripping solution. pH of ammoniacal feed solution containing cobalt and nickel was adjusted to 9.0 with hydrochloric acid. The important variables governing the permeation of cobalt have been studied. These variables are membrane composition, pH of the feed solution, cobalt and nickel concentrations of the feed solution, mixing speed, surfactant concentration, extractant concentration, EDTA concentration and pH of the stripping solution, and phase ratio. After the optimum conditions had been determined, it was possible to selectively extract 99.0% of cobalt from ammoniacal feed solution containing Co²⁺ and Ni²⁺ ions. The separation factors of cobalt with respect to nickel, based on initial feed concentration, have experimentally found to be of as high as 247.5 for about equimolar Co–Ni feed solutions.     

Potentiality of methyltrioctylammonium chloride ligand for selective extraction of the Uranium(VI) metal ions from selective carbonate leach liquor

In the present study, the use of 5% Aliquat-336/kerosene was evaluated in the liquid–liquid extraction of Uranium(VI) and some impurities of Thorium(IV) and rare earth elements (REEs(III)). Experiments were carried out to determine the factors affecting U(VI) and some impurities of Th(IV) and REEs(III) extraction. McCabe–Thiele diagram was constructed to define the theoretical stages for extraction mixer settler process. The effect of stripping factors from the loaded extractant was also tested. Uranium cake was finally obtained from the strip solution and a workable flow sheet was then formulated.     

Spectrophotometric determination of Chromium(VI) using cyclam as a reagent

A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5?×?10⁴?L?mol^?1?cm^?1 at 379?nm. Under optimum experimental conditions, a pH of 4.5 and 1.960?×?10³?mg?L^?1 cyclam were selected, and all measurements were performed 10?min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20?mg?L^?1 with a detection limit of 0.001?mg?L^?1. The standard deviation in the determination is ±0.5?mg?L^?1 for a 15.0?mg?L^?1 solution (n?=?7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.     

Synchronized extraction and purification of L-lactic acid from fermentation broth by emulsion liquid membrane technique

This study aims to investigate the recovery of L-lactic acid from fermentation broth by an emulsion liquid membrane (ELM), made up of sunflower oil as the diluent, Sorbitan monooleate (Span 80) as the surfactant, Aliquat 336 as the carrier, and sodium hydroxide (NaOH) solution as the internal aqueous phase. Particularly, the ELM process was properly set up, through the identification of the optimal ELM operating parameters on the final extraction efficiency of L-lactic acid, including Span 80 concentration, NaOH concentration, Aliquat 336 concentration, stirring speed, phase ratio, and treatment ratio. The obtained results showed that the extraction efficiency of L-lactic acid reached up to 99% under the following optimal conditions: 10 minutes after contact time, 4% w/w Span 80, 3% w/w Aliquat 336, 0.1?N solution of NaOH, stirring speed of 300?rpm, phase ratio 1, and treatment ratio 0.25. A stable system without considerable emulsion swelling and breakage was monitored using a dynamic light scattering (DLS) apparatus for the selected optimal ELM operating parameters.     

Separation of cobalt(II) from nickel(II) by solid-phase extraction into Aliquat 336 chloride immobilized in poly(vinyl chloride)

A solid-phase absorbent obtained by the immobilization of Aliquat 336 chloride in poly(vinyl chloride) is reported to extract preferentially Co(II) from its 7 M hydrochloric acid solutions containing Ni(II). Under the experimental conditions there was no extraction of Ni(II) which allowed the complete separation of these two ions. Co(II) was rapidly and quantitatively back-extracted with deionised water. A mechanism for the extraction of Co(II) is proposed based on the formation of the ion-pair A⁺[HCoCl₄]⁻ where A⁺ is the Aliquat 336 cation. Fe(III) and Cd(II), usually present in Co(II) and Ni(II) samples, were also extracted into the solid-phase absorbent though at a slower rate than Co(II) and they did not interfere with the separation of Co(II) from Ni(II). It was also demonstrated that this approach allowed the complete separation of Ni(II) from the other metal ions mentioned above.     

Kinetics and mechanism of oxidation of N-substituted phenothiazines by chromium(VI)

The kinetics of oxidation of N-acetylphenothiazine (NAPT) by Cr(VI) in 80% acetic acid-20% water (v/v) mixture is first-order each in [NAPT] and [Cr(VI)]. The reaction is catalysed by added acid with a third-order dependence in [HCIO₄], Increase in polarity of the solvent medium decreases the rate. The oxidation is insensitive to variations in ionic strength as well as added acrylamide. Oxidations of phenothiazine (PT) and N-methylphenothiazine (NMPT) under similar conditions are found to be very fast. However kinetic investigations with NMPT in an acetic acid-sodium acetate buffer show first-order dependence each in [NMPT] and [Cr(VI)] and a fractional-order dependence in [H⁺] in the pH range 1.80-3.09. Increase in polarity of the medium increases the rate. In both the cases, the corresponding sulphoxides are identified as oxidation products. Based on the kinetic results, mechanisms for oxidations are proposed.     

Studies on the applicability of artificial neural network (ANN) in emulsion liquid membranes

An artificial neural network (ANN) model of emulsion liquid membrane (ELM) process is proposed in the present study which is able to predict solute concentration in feed during extraction operation and ultimate % extraction at different initial solute concentration in feed phase, internal reagent concentration, treat ratio, volume fraction of internal aqueous phase in emulsion and time. Because of the complexity in generalization of the phenomenon of ELM process by any mathematical model, the neural network proves to be a very promising method for the purpose of process simulation. The network uses the back-propagation algorithm (BPA) for evaluating the connection strengths representing the correlations between inputs (initial solute concentration in feed phase, internal reagent concentration, treat ratio, volume fraction of internal aqueous phase in emulsion and time) and outputs (solute concentration in feed during extraction operation and % extraction). The network employed in the present study uses five input nodes corresponding to the operating variables and two output nodes corresponding to the measurement of the performance of the network (solute concentration in feed during extraction and % extraction). Batch experiments are performed for separation of nickel(II) from aqueous sulphate solution of initial concentration in the 200–100 mg/l ranges. The network employed in the present study uses two hidden layers of optimum number of nodes being thirty and twenty. A leaning rate of 0.3 and momentum factor of 0.4 is used. The model predicted results in good agreement with the experimental data and the average deviations for all the cases are found to be well within ±10%.     

Ionic liquid as a complexation and extraction medium combined with high-performance liquid chromatography in the evaluation of chromium(VI) and chromium(III) speciation in wastewater samples

A simple method has been proposed for the determination of chromium species by high-performance liquid chromatography (HPLC) after preconcentration by the ionic liquid, 1-butyl-3-methyimidazolium hexafluorophosphate ([C₄MIM][PF₆]). The simultaneous preconcentration of Cr(VI) and Cr(III) in wastewater was achieved with ammonium pyrrolidinedithiocarbamate (APDC) as the chelating agent and the ionic liquid [C₄MIM][PF₆] as the extractant. Baseline separation of the APDC chelates of Cr(III) and Cr(VI) was realised on a RP-C18 column using a mixture of methanol–acetonitrile–water (53:14:33, v/v) as the mobile phase at a flow rate of 1.0 mL min^{− 1}. The influences of several variables on the complexation and extraction were evaluated: pH, reaction time, APDC concentration and metal ion interference. Our results showed that when the linear concentration of Cr(VI) and Cr(III) ranged from 25 to 200 μg L^{− 1}, their linear correlation coefficients were between 0.9977 and 0.9978, their recoveries ranged from 91.8% to 95.8% and their relative standard deviations (n = 3) were between 0.31% and 1.8%. Common metal ions in water did not interfere with the determination. This method is a simple, fast, accurate, highly stable and selective method and has successfully been applied to the speciation of chromium in wastewater.     

Evaluation of ammonia buffer containing EDTA as an extractant for Cr(VI) from solid samples

A novel procedure for the extraction of soluble, sparingly soluble and insoluble Cr(VI) from solid samples was presented. EDTA was added to an ammonia buffer commonly used only for the extraction of soluble and sparingly soluble Cr(VI). In the course of extraction in an ultrasonic bath cations which form insoluble chromates are complexed with EDTA while Cr(VI) is transferred to the solution. A concentration of EDTA equal to 0.01 mol L⁻¹ was chosen. The presence of EDTA in the extraction solution enables not only dissolution of insoluble Cr(VI) but also, as reported previously in literature, minimises oxidation of Cr(III) to Cr(VI). The extraction procedure was optimised and applied to Cr(VI) determination in the paint chips real sample. The results obtained were compared with the results obtained using two other extraction procedures. The results show that the novel extraction procedure can be used for the extraction of soluble, sparingly soluble and insoluble Cr(VI) from real solid samples.     

Determination of trace chromium(VI) by an inhibition-based enzyme biosensor incorporating an electropolymerized aniline membrane and ferrocene as electron transfer mediator

A novel inhibition-based glucose oxidase (GOx) biosensor for environmental chromium(VI) detection is described. An electropolymerized aniline membrane has been prepared on a platinum electrode containing ferrocene as electron transfer mediator, on which GOx is cross-linked by glutaraldehyde. The mechanism of the redox reaction on the electrode and the performance of the sensor are studied. The sensor's response to glucose decreases when it is inhibited by chromium(VI), with a lower detection limit of 0.49?µg?L^?1, and the linear response range is divided into two parts, one of which is 0.49–95.73?µg?L^?1 and the other is 95.73?µg^?1 to8.05?mg?L^?1. The enzyme membrane is shown to be completely reactivated after inhibition, retaining 90% activity over more than forty days. Interference to chromium(VI) determination from lead(II), copper(II), cadmium(II), chromium(III), cobalt(II), tin(II) and nickel(II) is found to be minimal, while high concentrations of mercury(II) and silver(I) may interfere with the determination of trace chromium(VI). The sensor has been used for chromium(VI) determination in soil samples with good results.     

Adsorption of metal anions of vanadium(V) and chromium(VI) on Zr(IV)-impregnated collagen fiber

The metal anions of vanadium (V) and chromium (VI) in aqueous solution can be effectively adsorbed by Zr(IV)-impregnated collagen fiber (ZrICF). The maximum adsorption capacity of V(V) takes place within the pH range of 5.0 to 8.0, while that of Cr(VI) is within the pH range of 6.0 to 9.0. When the initial concentration of metal ions was 2.00 mmol L⁻¹ and the temperature was 303 K, the adsorption capacity of V(V) on Zr-ICF was 1.92 mmol g⁻¹ at pH 5.0, and the adsorption capacity of Cr(VI) was 0.53 mmol g⁻¹ at pH 7.0. As temperature increased, the adsorption capacity of V(V) increased, while that of Cr(VI) was almost unchanged. The adsorption isotherms of the anionic species of V(V) and Cr(VI) can be fit by the Langmuir equation. The adsorption rate of V(V) follows the pseudo-first-order rate model, while the adsorption rate of Cr(VI) follows the pseudo-second-order rate model. Furthermore, ZrICF shows high adsorption selectivity to V(V) in the mixture solution of V(V) and Cr(VI). Practical applications of ZrICF could be expected in consideration of its performance in adsorption of V(V) and Cr(VI).     

以TTA—TBPO为协同流动载体的液膜法富集钪(Ⅲ)

提出用TTA-TBPO为协同流动载体的乳状液膜分离它集抗（Ⅲ）的方法。其最佳液膜体系的组成为4％Span80.5％TTA、3％TBPO、4％液体石蜡、84％煤油和内相水溶液（4mol/L），最优实验条件，提取钪（Ⅲ）的外相试液为pH=1．3～2．3，Roi（油内比）为1：1，Rew（乳水比）为20：100。本法用于分离富集稀土元素中的微量钪（Ⅲ），其回收率可达99．1％以上，相对标准偏差为3．5％以下，结果十分满意。     

Solvent extraction of chromium(VI) from base metal ions with diphenyl-2-pyridylmethane as a liquid anion exchanger

The extraction of chromium(VI) from aqueous hydrochloric, nitric and sulfuric acid solutions by diphenyl-2-pyridylmethane(DPPM) dissolved in chloroform has been studied. Chromium(VI) is quantitatively extracted from hydrochloric acid solutions in the range 0.1–1M. With increasing acid concentration, the extraction of chromium diminishes and in concentrated acid solutions practically all the chromium remains in the aqueous phase. The quantitative back-extraction of chromium from the organic phase is possible with HCl or HNO₃ at concentrations higher than 5M through the use of reducing agents. The composition of the extracted chromium(VI) species was studied in solution. The complexes (DPPMH)⁺HCrO ₄ ⁻ and (DPPMH)₂Cr₂O ₇ ⁻ are extracted for tracer and macro amounts of chromium(VI) respectively. The data have been utilized for the separation of chromium(VI) from base metal ions.     

Nucleophilic attack by bromide ions as a first step of conversion of Se(VI) to Se(IV)

Numerous commonly used analytical methods allow only determination of a total amount of selenium in a given sample. Electroanalytical methods as well as those based on hydride generation or on formation of piazselenol allow only determination of Se(IV). To determine Se(VI) by these procedures, present alone or in mixtures with Se(IV), it is first necessary to convert Se(VI) to Se(IV). Such conversion is effective in the presence of excess of halides in acidic media or by photoreduction. In the often used conversion of Se(VI) in the presence of chlorides or less frequently of that of bromides, it has been assumed that the halide ion acts as a reducing agent. Kinetic studies of conversion of Se(VI) in acidic solutions containing an excess of bromide ions indicated that the rate determining first step of the reaction with Se(VI) is a nucleophilic substitution of the OH₂⁺ group in the protonated form of H₂SeO₄ by bromide ions. For the overall reaction with rate −d[Se(VI)]/dt = k₁[H⁺][Br⁻]^1.15[Se(IV)] the rate constant 1 × 10⁻³ L² mol⁻² s⁻¹ was found. The following formation of Se(IV) from the bromo derivative is a fast reaction probably resulting in elimination of HBrO.     

Chemical speciation of chromium(III,VI) employing extractive spectrophotometry and tetraphenylarsonium chloride or tetraphenylphosphonium bromide as ion-pair reagent

A simple and accurate extractive spectrophotometric procedure for the chemical speciation of chromium(III,VI) species in aqueous media has been developed. The method is based upon the extraction of the complex ion-associate formed between the chloro chromate (CrO₃Cl⁻) anion and the ion-pair reagent tetraphenylarsonium chloride (TPAs⁺Cl⁻) or tetraphenylphosphonium bromide (TPP⁺Br⁻) at pH ≤ 0 in chloroform followed by direct spectrophotometric measurement at 355 nm. The optimum concentration range evaluated by Beer-Lambert's law, Ringbom's plot, the molar absorptivity, the Sandell's sensitivity, the extraction and stability constants (K_D, K_ex and β), the stoichiometry and the extraction equilibria of the produced complex ion-associates have been determined and gave a convenient applications of the investigated system for analytical purposes. Chromium(III) was also determined by the proposed procedure after prior oxidation to chromate with H₂O₂ in alkaline solution. The method has been applied successfully for the analysis of chromium(VI) and total chromium(III,VI) in industrial wastewater of electroplating plant.