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Mathematical modeling of cadmium(II) solvent extraction from neutral and acidic chloride media using Cyanex 923 extractant as a metal carrier
Abstract
This paper describes experimental work and the mathematical modeling of solvent extraction of cadmium(II) from neutral and acidic aqueous chloride media with a Cyanex 923 extractant in Exxol D-100. Solvent extraction experiments were carried out to analyze the influence of variations in the composition of the aqueous and organic phases on the efficiency of cadmium(II) extraction. In neutral and acidic chloride conditions, the extraction of cadmium(II) by the organophosphorous extractant Cyanex 923 (L) is based on the solvation mechanism of neutral H(n)CdCl((2+n)) species and the formation of H(n)CdCl((2+n))L(q) complexes in the organic phase, where n=0, 1, 2 and q=1, 2. The mathematical model of cadmium(II) extraction was derived from the mass balances and chemical equilibria involved in the separation system. The model was computed with the Matlab software. The equilibrium parameters for metal extraction, i.e. the stability constants of the aqueous Cd-Cl complexes, the formation constants of the acidic Cd-Cl species and the metal equilibrium extraction constants, were proposed. The optimized constants were appropriate, as there was good agreement when the model was fitted to the experimental data for each of the experiments.
... According to the above, easy and environmentally friendly methods for the recovery of cadmium from the acid leachates of the waste that permit the reduction of contamination are necessary. As a result, in this review, functionalized capsules were developed using cellulose acetate and Cyanex 923 as extractant agents [28,29]. These capsules have served as metal extractants due to their large specific interfacial area, high selectivity, and stability. ...
... Thus, hydrochloric acid was added to cadmium solutions to allow the formation of chlorocomplexes neutralized by the presence of protons. The amount of cadmium extracted in Figure 4 shows the increase in HCl concentration due to the formation of neutral species such as CdCl 2 , HCdCl 3 , and H 2 CdCl 4 [29] extracted by the solvation mechanism. Nevertheless, at higher HCl concentrations, the mineral acid can also be extracted, competing with cadmium and decreasing the percentage of metal adsorbed [39]. 1 Experimental conditions: 10 mg L -1 of Cd(II) in aqueous solution in 2 mol L -1 of HCl; FC prepared with 1.5% of Cyanex 923. ...
... Thus, hydrochloric acid was added to cadmium solutions to allow the formation of chlorocomplexes neutralized by the presence of protons. The amount of cadmium extracted in Figure 4 shows the increase in HCl concentration due to the formation of neutral species such as CdCl2, HCdCl3, and H2CdCl4 [29] extracted by the solvation mechanism. Nevertheless, at higher HCl concentrations, the mineral acid can also be extracted, competing with cadmium and decreasing the percentage of metal adsorbed [39]. ...
Cellulose acetate is derived from cellulose and has the characteristics of biodegradability and reusability. So, it has been used for the elimination of toxic compounds capable of producing different diseases, such as cadmium, that result from human and industrial activity. For this reason, capsules functionalized with Cyanex 923 were prepared and characterized by FTIR spectroscopy, Energy Dispersive X-ray Spectroscopy (EDX), and SEM. The functionalized capsules were used for removing and recovering Cd(II) by modifying variables such as HCl concentration in the extraction medium and carrier content in the capsules, among others. The extraction of cadmium from battery leachates and the three isotherm models, Langmuir, Freundlich, and Dubinin Radushkevich, were also tested to model the cadmium removal process. The results showed a favorable physical sorption with a good capacity for extraction and the possibility of reusing the capsules for up to seven cycles without a decrease in the percentage of cadmium recovery.
... This chemical reaction is a part of larger system of possible equilibria that are simultaneously solved within the minimisation procedure (see Figure 1.3). The closure of the Mass Action Law (MAL) along with the method to minimize it then provides directly the extraction isotherms, as is readily done in chemical engineering [61]. The procedure works and provides a cornerstone for the actual plant process design eFgF implemented PAREX code for PUREX process [62]. ...
... Even though the method works, there are few issues with the approach. The minimization procedure requires large amount of experimental data and yields high number of adjusted constants [9,10,61,66]. From Eq. 1.4 it can be seen that every composition yields additional constant. Sometimes, constants cannot be justied from molecular simulations. ...
The object of this thesis was to create models for two applications which readily appear in separation chemistry, namely the solid-liquid and the liquid-liquid extractions. The benefit of modelling in both cases is twofold. Studying the fundamental properties of ions and their solvation properties in the complex media, and simplifying the expression for important effects, enables us to construct the framework which can be used by both chemists in the laboratory, as well as the chemical engineers in the process design. For two applications we adapted two different systems, both of which can be considered as complex. The model system to study the solid-liquid separation were TiO$_{mathrm{2}}$ nanotubes dispersed in the aqueous solution. This system was studied by the means of Classical Density Functional Theory coupled with the charge regulation method, within the Grand-canonical ensemble. Indeed, the method proved to be successful in establishing the full description of the charge properties of TiO$_{mathrm{2}}$ nanotubes. In this case, we were interested in obtaining the description of ion inside the charged nanotubes under influence by the electric field (exhibited by nanotubes). Calculations predicted effects such as the difference in surface charge between the outer and the inner surface, or the violation of electroneutrality inside the nanotubes. It was demonstrated that the model was in the agreement with the experimental data. Moreover, the method can be directly used to predict titration for various techniques. A simple generalization of the proposed approach can be used to study the actual adsorption efficiency of the solid-liquid separation process. The model system to study the liquid-liquid extraction process included three distinct parts. The three parts were devoted to the cases on non-ionic, acidic ion exchangers, and finally the synergistic mixtures of extractants. Simple bulk statistical thermodynamics model, in which we incorporated some of the well-established concepts in colloidal chemistry provided a soft-matter approach for the calculation of actual engineering-scale processes. Were have expanded a classical simple equilibria approach to broader, more intuitive polydisperse aggregates formation that underlines the liquid-liquid extraction. The key finding can be presented as a current opinion or newly-proposed paradigm: at equilibrium, many aggregates completely different in composition but similar in free energy coexist. With obtained polydispersity, we were equipped with a tool to study a more 'global' behavior of liquid-liquid extraction. This urged us to pass our considerations of historical extraction isotherms to extraction 'maps'. Great care was devoted to the study of synergy since it is a 60-year old ongoing question in the separation industrial and science community. To our best knowledge, the first quantitative rationalization total synergistic extraction was proposed within this thesis. Underlying effects of enthalpy and entropy control on the organic phase structuring were decoupled and studied in detail. Hopefully, this thesis demonstrated the importance of mesoscopic modelling to assist both chemists and chemical engineers in practical examples.
... Exxol D-100 HnCdCl (2+n) Sq where n = 0, 1, 2 and q = 1, 2 [27] precipitation [5], ion exchange [6][7][8], adsorption [9][10][11], supported liquid membrane [12][13][14][15], and liquid-liquid extraction [16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Each method has its own advantages and disadvantages. ...
... The authors reported that the selective transfer of Cd(II) by Cyanex 923 followed a solvation mechanism and the extracted species being CdCl 2 ·2S. Leopold et al. [29] developed the mathematical model for solvent extraction of Cd(II) from neutral and acidic aqueous chloride media with Cyanex 923 in Exxol D-100. The extraction of cadmium(II) by Cyanex 923 was based on the solvation mechanism of neutral H n CdCl (2+n) species and the formation of H n CdCl (2+n) S q complexes in the organic phase, where n = 0, 1, 2 and q = 1, 2. These extractants have some advantages as compared to acidic extractants, like no saponification and/or pH adjustment are required. ...
... Numerous organic solvents have been utilized to remove heavy metals (Leopold et al., 2010;Rafighi et al., 2010;Chang et al., 2011;Fu et al., 2011;Mishra and Devi, 2011). Most of them are, in part, made from petroleum. ...
... Cu(II) extraction from aqueous solutions using different organic solvents have been studied extensively. Combination of extractants and solvents used to extract Cu(II) from an aqueous solution in literature include D2EHPA + soybean oil (Chang et al., 2010;Chang et al., 2011), LIX 84 + kerosene (Agrawal et al., 2008), Cyanex 921 + kerosene (Leopold et al., 2010;Mishra and Devi, 2011), and Cyanex 272 + kerosene (Mohapatra et al., 2007;Agrawal et al., 2008;St John et al., 2010). The solvents employed are mostly non-polar in nature. ...
... Mathematical modeling helps to recognize the application and performance of SLM systems [17]. It can be useful for designing an effective operation and scaling up SLM systems [18]. The modeling of ion transport through a liquid membrane is carried out according to one of the following assumptions: (1) considering diffusion layers existing in the organic− aqueous interface [11], (2) considering that an organic molecule (carrier) leaves the membrane phase and reacts with aqueous species in the aqueous phase [19], and (3) ignoring the presence of static layers formed between the liquid membrane and aqueous phase existing in the feed and strip sides [20]. ...
A mathematical model was developed to monitor the facilitated transport of germanium(IV) from oxalic acid solutions through a flat sheet supported liquid membrane (FSSLM) containing four trialkylphosphine oxides (Cyanex 923). The FSSLM modeling was based on the extraction constant (Kext) calculated from the liquid−liquid extraction (LLX) modeling. The LLX model presented a reliable calculation of the extraction constant (Kex= 2.057×10³ L/mol⁴). The FSSLM model was solved using Matlab® software according to extraction constant, Fick's law, and diffusional principles. The model predicts the overall mass transfer coefficient (Korg) to be 3.84 cm/s. Using this value, diffusion coefficients (Dm) for various Cyanex 923 concentrations of 0.126, 0.252, 0.378, 0.505, 0.631 and 0.757 mol/L are found to be 8.50×10⁻⁴, 4.30×10⁻⁴, 1.87×10⁻⁴, 5.87×10⁻⁵, 2.57×10⁻⁵, 2.09×10⁻⁵ cm²/s, respectively. The results show that the diffusion rate of the current study is approximately more than that of similar FSSLM systems containing Cyanex 923 used to transport various metals. The modeling values are in good agreement with the experimental data, showing the good reliability of the mathematical model.
... Mathematical modeling helps to better recognize the application and performance of SLM systems [21]. It can be useful for designing an effective operation and scaling up SLM systems [15]. The modeling of ion transport through a liquid membrane is carried out according to one of the following assumptions: (a) considering diffusion layers existing in the organic-aqueous interface [14], (b) considering that an organic molecule (carrier) leaves the membrane phase and reacts with aqueous species in the aqueous phase [6], (c) ignoring the presence of static layers formed between the liquid membrane and aqueous phase existing in the feed and strip sides [10]. ...
A mathematical model was developed to monitor the facilitated transport of germanium(IV) from oxalic acid solutions through a flat sheet supported liquid membrane (FSSLM) containing Cyanex 923. This model presented a reliable calculation of the extraction constant (K ex = 2.057 × 10 3 1/mol 4). The FSSLM model was solved according to the extraction reaction, Fick's law, and diffusional transport. Consequently, the overall mass transfer coefficient (K org) was found to be 3.84 cm/s. Using this value, diffusion coefficients for various Cyanex 923 concentrations in the range of 5 to 30 %v/v were calculated. Finally, the accuracy of the models was investigated.
... The water co-extraction and the organic solvent influence, as well as the length and branching of the extractant chains, are neglected. 9,35 Traditionally, the extraction (i.e., the transfer of ions between two phases) was identified as (or attributed to) the energy of a similar complex between a multivalent cation and electron donor atoms representing the extractant head groups. 36,37 Note that such considerations are only able to provide a qualitative description of the extraction trends, but they fail completely in quantitative assessment. ...
We propose the statistical thermodynamic model for the prediction of the liquid-liquid extraction efficiency in the case of rare-earth metal cations using the common bis-(2-ethyl-hexyl) phosphoric acid (HDEHP) extractant. In this soft matter based approach the solutes are modeled as colloids. The leading terms in free energy representation account for: the complexation, the formation of highly curved extractant film, lateral interactions between different extractant head groups in the film, configurational entropy of ions in water molecules, the dimerization, and the acidity of HDEHP extractant. We provided a full framework for the multicomponent study of extraction systems. By taking into account these different contributions, we are able to establish the relation between the extraction and general complexation at any pH in the system. This further allowed us to rationalize the well-defined optimum in the extraction engineering design. Calculations show that there are multiple extraction regimes even in the case of the lanthanide/acid system only. Each of these regimes is controlled by the formation of different species in the solvent phase, ranging from multiple metal cation filled aggregates (at the low acid concentrations in the aqueous phase), to the pure acid filled aggregates (at the high acid concentrations in the aqueous phase). These results are contrary to a long-standing opinion that liquid-liquid extraction can be modeled with only a few species. Therefore, a traditional multiple equilibria approach is abandoned in favor of polydisperse spherical aggregate formations, which are in the dynamic equilibrium.
... A variety of organophosphorus-based extractants, viz. di-2-ethyl hexyl phosphoric acid (D2EHPA) (Fatmehsari et al., 2009;Kumar et al., 2008;Mellah and Benachour, 2006;Takeshita et al., 2003), bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272) (Reddy and Priya, 2006;Reddy et al., 2004), bis(2,4,4-trimethylpentyl)thiophosphinic acid (Cyanex 302) (Almela et al., 1995(Almela et al., , 1998, triisobutyl phosphine sulphide (Cyanex 471X) (Reddy et al., 2008), trioctyl phosphine oxide (Cyanex 921) (Dessouky et al., 2008) and Cyanex 923(a mixture of various trialkyl-phosphine oxides) (Gupta et al., 2001;Leopold et al., 2010) have been employed for the solvent extraction and separation of Cd(II) over other metals. Among these, D2EHPA is by far the most useful and widespread extractant for cadmium extraction from complex solutions (Gupta et al., 2001). ...
In this paper, effect of acetate ions on cadmium solvent extraction with di-2-ethyl hexyl phosphoric acid, D2EHPA, in kerosene as diluent has been investigated. Infrared spectroscopy and slope analysis methods were used to determine metal–organic complex and reaction stoichiometry respectively. Results showed that acetate ions did not participate in the complex formation but acted as a buffering agent. It was found that acetate could greatly improve the extraction yield. Maximum distribution coefficients were observed in the presence of 0.05 to 0.25 M acetate corresponding to the equilibrium pH of 4.14 to 4.70. The mechanism of cadmium extraction from acetate solution can be represented at equilibrium by: Cd2 + + 2(H2A2)org ↔ (CdA2(HA)2 )org + 2H+
... Szereg prac odnosi się natomiast do kwestii unikania tego zjawiska lub wykorzystania go poprawy wydajności procesu ekstrakcji, np. [12]. ...
The first step of multiscale model design is choosing numerical models for all significant phenomena. It this paper, the review of existing numerical models for phenomena present in ion-exchange solvent extraction is done. Modelling of this process is focused mainly on calculating of a composition of phases leaving a reactor. Phenomena influencing on a final result are: a flow of two, immiscible fluids, a dispersion of one of them, a gravitational separation and an ion-exchange on phase’s boundaries itself. Each of them should be described with a suitable numerical model. A macroscopic flow is usually described with Computational Fluid Dynamic (CFD). An addition of microscopic effects, like bubbles topology and surface tensions allows modelling of dispersion and separation, as well as improves a reliability of a fluid flow model. In a spatial scale comparable with a size of dispersed bubbles, diffusion and an ion exchange are present. Some additional models for phenomena like a surface eddy and a polymerization should be also considered. Due to a lack of a comprehensive description of modelling of an ion-exchange solvent extraction in the literature, models for all phenomena were reviewed separately. Modelling of a two-fluid flow could treat both phases separately or as a single phase with an additional description of its phase composition and a relative movement of phases. The eddy over the mixing zone could be computed basing on CFD techniques, but due to instabilities on the free surface, very short time steps are enforced. Empirical models, based on experimental data are less accurate, but much more stable. There are no models of polymerization in the solvent extraction context in the literature. Available models were developed for processes, where a polymerization is awaited and they are not applicable in described case. Modelling of diffusion and an ion exchange in the microscale are believed to be very important, but an exact description of a dispersion topology is a necessary condition. In fact, it is not practically possible to calculate such a topology with a presently available computing power. The review, presented in this paper will be used to develop the multiscale model for an ion-exchange solvent extraction. It will be based on Agile Multiscale Modelling (AM3), developed by Authors.
Microfluidic technology has attracted great interest across industry and academia. Its engineering characteristics, through miniaturization, can enhance mass- and heat transfer rates together with allowing operation at high concentrations. Combining this technology with a green designer solvent is one of the most recent advances in separation processes. Ionic liquids have negligible volatility and flammability and have an exceptionally large chemical diversity space, which these days can be better utilised through solvent modelling. Ionic liquids have been demonstrated to increase the efficiency and selectivity of extraction by orders of magnitude.
Different types of microfluidic devices have been designed until now, and among those, the segmented flow with alternate regular slugs is the most prominent. Helical coiling can further intensify the internal recirculation by convection, which is the motor of the advanced mass transfer. This is done by liberating Dean forces. A device that leverages such mass transfer intensification in the best possible way is the Coiled flow inverter (CFI) [1]. The coil periodicity is just 4 turnings, and then the winding direction is inversed, e.g. changed from clockwise to counter-clockwise, and this is repeated multiple times. The CFI extraction performance is typically much better than for a straight and a non-inverted helical capillary.
Separation of metals using liquid–liquid extraction methodology is an important research subject of large economical relevance. The common types of equipment in metal extraction have some disadvantages such as long mixing time and huge plant footprint for the coalescence of the multi-phase, which might take very long due to emulsion formation. In this regard, microfluidic devices and ionic liquids provide an alternative as more compact, more efficient, and faster technology. This review shall help researchers to understand the recent improvement in metal extraction processes, and what the addition of disruptive technology can add to an industrial transformation.
The present review is mainly focused on the overview of carrier mediated extraction (principles and applications) being reported over the last two decades and discusses the extraction process through carriers in various extraction methods such as Bulk liquid membranes, supported liquid membranes, emulsion liquid membranes and polymer inclusion membranes. Several types of carriers such as neutral, anionic, cationic, macrocyclic and supramulecular carriers are discussed. Also their application for metal, anions, drugs and environmental compounds are investigated. Carriers have been demonstrated to be useful for the selective extraction and recovery of numerous cations and anions enhancing the extraction properties of traditional solvent extraction and ion-exchange processes. Several types of carriers have different transport mechanisms. In these mechanisms, transport configurations are addressed and emphasized and the detailed information on the type of carrier are presented along with their specific separation modes. The performance of different carriers in terms of selectivity as well as efficiency are also discussed. Finally, the application of different carriers for the extraction of various compounds are compared and reviewed. To our best knowledge no reviews have been published on carrier-mediated extraction methods.
The discharge of electroplating waste containing nickel ions has led to environmental issues owing to the toxicity problem mainly to the aquatic organisms and humans. Liquid-liquid extraction offers a great potential treatment for nickel removal with several advantages of simple, high efficiency and high separation factor. In this study, a green synergistic liquid-liquid extraction of nickel ions from electroplating waste solution using chelating oxime (LIX63) and organophosphorus (D2EHPA) carriers individually as well as their synergistic mixture has been studied. The result demonstrated that about 83% of nickel ions have been successfully extracted via the mixture system of 0.08 M LIX63 +0.02 M D2EHPA with the maximum synergistic enhancement factor, Rmax of 29.56. Meanwhile, the back extraction study also revealed that HNO3 was the most suitable stripping agent while the diluent screening also showed that palm oil has high potential to be incorporated as a diluent in the green synergistic liquid-liquid extraction of nickel.
The transfer of cadmium(II) from acidic chloride solutions through a smart liquid membrane technology was investigated in a microporous polypropylene hollow fiber membrane contactor. The organic solution of tri-isooactylammonium chloride (TiOAC) in Exxsol D100 was used as carrier. The acidic chloride feed solution containing the metal was passed through the tube side, and the pseudo-emulsion of the organic solution and NH4OH was passed through the shell side in counter-current mode, using a unique contactor in the process. In the pseudo-emulsion based hollow fiber membrane with strip dispersion (PEHFMSD) technology, the aqueous strip solutions of ammonium hydroxide are dispersed in the organic solutions in a tank with a mixing arrangement to provide a strip dispersion. This strip dispersion circulates from the tank to the membrane module to provide constant supply of the organic solution to the membrane pores. Different hydrodynamic and chemical variables, such as variation in feed acidity, metal concentration in the feed, carrier concentration in the organic phase, variation in feed, strip and organic phase volume ratios and variation in the feed and pseudo-emulsion flows, were investigated. Mass transfer coefficients were calculated from experimental data.
Removal characteristics of Cu(II) ions by solid-phase extractant immobilized D2EHPA and TBP in PVC were investigated. Cu(II) ion concentrations in the solution and removal capacity of Cu(II) ion according to operation time were compared. The lower the initial concentration of Cu(II) ion in aqueous solution was, the removal capacity of Cu(II) ion by solid-phase extractant was increased relatively. The bigger the initial concentration of Cu(II) ion was, the removal capacity of Cu(II) ion was increased relatively. The pseudo-second-order kinetics according to operation time was showed more satisfying results than the pseudo-first-order kinetics for the removal velocity of Cu(II) ion. The removal capacity of Cu(II) ion was 0.025 mg/g in aqueous solution of pH 2, but the removal capacity of Cu(II) ion was increased to 0.33 mg/g mg/g in aqueous solution of pH 4 according to increasing pH.
[HMe2pipdt]I3 (Me2pipdt = N,N′-dimethyl-piperazine-2,3-dithione, 1) is capable to quantitatively dissolve elemental Cd and Hg to produce in a one-step reaction the [CdI(Me2pipdt)2]I3 (2) and [HgI2(Me2pipdt)] (3) complexes. Crystals of 2 and 3 have been structurally characterized and crystallize in the P-1 and C2/c space group respectively. In 2 Cd(II) shows a coordination geometry intermediate between the square pyramidal and the trigonal bipyramidal. In 3 Hg(II) adopts a distorted tetrahedral geometry which involves a S,S chelating ligand and two iodine atoms in the coordination sphere. Vibrational spectroscopy findings are in agreement with structural results showing in the far-infrared region to be a diagnostic probe in recognizing triiodides.
The transport of Cd(II) from hydrochloric acid medium in NDSXSD technology is investigated using the ionic liquid CYPHOS IL101 (tetraalkyl)phosphonium salt) dissolved in cumene as carrier phase. The permeation of the metal is investigated as a function of various experimental variables: hydrodynamic conditions, concentration of cadmium(II) and HCl in the feed phase, carrier concentration, support characteristics, etc. In NDSXSD, a pseudo-emulsion is temporarily formed between the organic and stripping solutions. The overall mass transfer coefficient (K=4.1×10−3cms−1) and the thickness of the aqueous boundary layer (daq=1.8×10−3cm) were calculated from experimental data. Of the different reagents used, 1M ammonium hydroxide served most efficiently as the stripping agent. Furthermore, the selectivity of CYPHOS IL101-based membrane towards different metals is investigated, whereas the system is compared with other carriers in the liquid membrane phase.
This paper presents a brief overview of improved Liquid membrane (LM) separation techniques. including modified bulk, supported and emulsion liquid membranes as well as hollow fibre contained liquid membranes, electrostatic pseudo liquid membranes (ESPLIM) reverse micelle and recently developed hybrid (HLM) and other LM configurations. The discussion also includes design of ion specific carriers, analytical importance, aspects of stability and modelling of LMs and their applications in the separation/removal of metal captions from a range of diverse matrices. In general, an attempt has been made to review the literature published from 1990 to 1997 in order to focus on the present status of different liquid membrane configurations. The LM studies dealing with separation and removal of organic compounds and gases are not included in this article owing to limitations of space.
A process to remove and recover cadmium from wastewater has been developed which includes solvent extraction and supported liquid membrane transport for Cd(II) using Cyanex 923 as an extractant/carrier. The influence of acid and chloride ion concentration on the extraction of Cd(II) was studied. In acidic medium, the appearance of a third phase was observed and the limiting organic concentration for Cd(II) in 5 and 10% Cyanex 923/Exxsol D100 at different concentrations of H+ ions were determined. The effect of aliphatic and
aromatic diluents on the extraction and permeation of Cd(II) in neutral and acidic medium was studied and
permeation coefficients were evaluated, together with the influence of third phase and pore size on transport
of Cd(II) through microporous membrane. It was found that the appearance of a third phase in acidic medium
could be avoided by using an aromatic diluent. In order to improve the stability of supported liquid membrane and to scale up for continuous operation, the performance of hollow fiber strip dispersion (HFSD) technique for the extraction/recovery of Cd(II) from acidic as well as neutral chloride media was examined.
This study emphasizes the potential of a HFSD system to be a part of sustainable wastewater treatment
technologies, enabling the separation/recovery of cadmium.
The extraction of gold(III) from hydrochloric acid solutions by the phosphine oxide Cyanex 923 was studied as a function of several variables, such as: equilibration time, temperature, organic phase diluent, metal and extractant concentrations and the presence of inorganic salts in the aqueous solutions. Gold(III) equilibrium loading and stripping isotherms were also obtained at 20°C and 70°C respectively. Experimental data were analyzed numerically using the computer program Letagrop-distrb). The results showed that the data can be explained assuming the formation of an HAuCl4L2 species in the organic phase, where L represents the organic extractant.
Supported emulsion liquid membranes (SELMs) can be used in a variety of applications ranging from wastewater treatment to recovery of valuable fermentation byproducts. The use of a hollow-fiber contactor avoids the mixing between the feed stream and the extracting phase while providing a large contacting area for extraction. The use of an emulsion liquid membrane eliminates the equilibrium limitation of conventional liquid-liquid extraction and substantially improves the efficiency as well as the capacity of separation. In principle. SELMs do not require the use of a surfactant, greatly simplifying the downstream demulsification and product recovery processes. This provides a substantial reduction in energy and volume requirements for the unit. The presence of the stripping phase will sustain a high driving force for the extraction; thus, reducing or eliminating the need for extractants which are likely to be toxic as well as expensive.
The extraction of zinc, cadmium and mercury from chloride and sulphate media by solvating extractants, liquid anion and liquid cation exchangers has been reviewed both from the literature and by experiment. The results have been discussed in terms of both practical process possibilities and the use of slope analysis to identify the extracted species. These show that slope analysis cannot give positive unambiguous identification of extraction stoichiometry in systems in which the extracted metal species contains coordinating ligands from the aqueous phase. However, in the extraction of Zn and Cd from sulphate media by di(2-ethylhexyl)phosphoric acid (DEHPA) the extracted species is shown to be an MR2(HR)2 monomer by slope analysis demonstrating its use in simple systems. In the case of amines and solvating reagents such as TBPc and TOPO zinc appears to be extracted from Cl– media as either ZnCl2 or sometimes HZnCl3 whereas Cd and Hg(II) appear to be always extracted as HCdCl3 and HHgCl3 species. The use of aqueous phase complexing by Cl– to improve the separation of Zn and Cd by extraction is clear. Some results are presented for the recovery of zinc from sulphate media by oximes and mercury from sulphuric acid media by amines and DEHPA.
The extraction of divalent zinc, cadmium and mercury from aqueous solutions containing lithium chloride using tri-n-octylphosphine oxide (TOPO) in benzene has been investigated. By applying the trial and error method of least-squares analysis to the equilibrium equation, M2+ (aq) + 2Cl− (aq) + 2TOPO (org) ⇆ MCl2 · 2TOPO (org), for these extraction systems, the stability constants of the aqueous chloro complexes of divalent zinc, cadmium and mercury have been determined as follows: for zinc (II) β1 = 5.40, β2 = 0.800, β3 = 0.300 and β4 = 0.102, and K = 3 × 104; for cadmium (II) β1 = 320, β2 = 210, β3 = 200 and β4 = 85.0, and K = 3.5 × 104; for mercury (II) β1/K = 1.60 × 10−8, β2/K = 1.20 × 10−4, β3/K = 1.54 × 10−3 and β4K = 1.53 × 10−3. Furthermore, distribution of the species of these metals which exist in aqueous chloride solutions has been calculated by using the values of the stability constants obtained.
Studies have been carried out in the extraction of Cd(II) along with Al(III), Fe(III), In(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Hg(II) and Pb(II) from hydrochloric acid medium using Cyanex 923. The effect of different variables influencing the extraction of Cd(II) such as the concentration of acid, metal ion and extractant and the nature of the diluent has been investigated. The extracting species of Cd(II) is proposed. Based on the partition data, some binary separations of topical interest from Cd(II) have been achieved. The potential of the extractant for the recovery of pure cadmium from some zinc and copper matrices is assessed.
This study was aimed at examining the use of the organophosphine oxides Cyanex®921 and Cyanex®923 for the extraction of formic, acetic and propionic acids from aqueous solutions. The stripping of monocarboxylic acids with water from the loaded extractants was also examined. The studies were aimed at determining the equilibrium conditions for extraction and stripping. Overall, the effect of the kind of extractant was not significant although Cyanex®921 extracted carboxylic acids slightly better than Cyanex®923 with 1:1 complexes being formed by both extractants with the acids during extraction. The efficiency of extraction depended on temperature, acid concentration and solvent, with toluene a better diluent for the extractants than octane or Exxsol®D 220/230. Extraction efficiency increased as the concentration of acid in the feed decreased and, also, as the temperature increased, the amount of acid extracted decreased. The extraction and stripping isotherms were determined. The apparent enthalpy and entropy of the extraction reaction were determined. Distribution data for the transfer of carboxylic acids from aqueous (NaCl) solutions to organic solvents in the presence of trialkylphosphine oxide were determined at 293 K with the distribution ratios increasing as the concentration of NaCl increased. Copyright © 2005 Society of Chemical Industry
An experimental study of Cd(II) transport through a polymer-immobilised liquid membrane (PILM) using Cyanex 923 as carrier has been performed. Factors affecting cadmium permeability, such as stirring speed of the source phase, extractant concentration in the membrane phase, metal, HCl and H3PO4 concentrations in the source phase, etc., have been analyzed. Optimal experimental conditions for Cd(II) permeation and recovery (PCd=34.3 μm/s and 85.8% recovery) were obtained after 3 h using membranes containing 30% v/v Cyanex 923 dissolved in xylene, using a microporous Durapore GVHP support, with water as stripping agent and initial source phase of 0.89 μM Cd, and 100 g/L each of HCl and H3PO4.
The facilitated transport of cadmium (II) from chloride through a flat-sheet supported liquid membrane is studied, using Cyanex 923 (phosphine oxides mixture) as ionophore, as a function of various experimental variables: hydrodynamic conditions, concentration of cadmium (II) (0.01–0.08 g l−1) and HCl (0.1–5 M) in the feed phase, carrier concentration (2.5–40%, v/v) and diluent in the membrane phase. A model is derived that describes the transport mechanism, consisting of diffusion through a feed aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of carrier and the metal complexes through the organic membrane. The organic membrane diffusional resistance (Δorg) and aqueous diffusional resistance (Δaq) were calculated from the model, and their values were 196145 and 260 s cm−1, respectively, whereas the values of the bulk diffusion coefficient (Dorg,b) and diffusion coefficient (Dorg) also calculated from the model were 2.4 × 10−7 and 6.4 × 10−8 cm2 s−1. The separation of Cd(II) against Zn(II), Fe(III), Co(II) and Cu(II) is evaluated.
The transport of cadmium (II) from a high-salinity chloride medium across a flat-sheet supported liquid membrane containing Cyanex 923 in Solvesso 100 supported on a PVDF membrane into a strip solution with water was investigated. Permeability coefficients of metal increased with decreasing the pH of feed from 2.0 to 0.5. It also increases with increasing carrier concentration in the membrane phase, whereas the permeation is dependent on the organic phase diluent but independent of metal concentration in the feed phase. The performance of the present system against other carriers was also studied.
The distribution equilibria of mineral acids: H2SO4, H3PO4, HCI, HClO4 and HNO3 between aqueous solutions and organic solutions of the phosphine oxide Cyanex 923 in toluene or decane are described. Partition studies have shown that the organic diluent only slightly influences the acid extraction. The extraction mechanism can be related to the solvation of the acid and formation of the L · Hm+Xm−1 (m = 1, 2 or 3) species in the organic phase, where L is the extractant; only in the case of initial high HNO33 concentrations is the formation of the L · (HNO3)2 species apparent in this phase. The effect of temperature on the acid extraction is also evaluated.
Kinetic modeling of the facilitatedtransportofcadmium(II)usingCyanex923asionophore
- M Alonso
- A Lopez
- A M Delgado
- F J Sastre
- Alguacil
M. Alonso, A. Lopez-Delgado, A.M. Sastre, F.J. Alguacil, Kinetic modeling of the facilitatedtransportofcadmium(II)usingCyanex923asionophore,Chem.Eng. J. 118 (2006) 213–219.
- S Martinez
- A Sastre
- N Miralles
- F J Alguacil
- Gold
S. Martinez, A. Sastre, N. Miralles, F.J. Alguacil, Gold(III) extraction equilibrium
in the system Cyanex 923–HCl–Au(III), Hydrometallurgy 40 (1996) 77–88.