Selective extraction of vanadium(V) from sulfate solutions into a polymer inclusion membrane composed of poly(vinylidenefluoride-co-hexafluoropropylene) and Cyphos® IL 101

PVDF-HFP-based polymer inclusion membrane functionalized with D2EHPA for the selective extraction of bismuth(III) from sulfate media

This study is the first application of a PVDF-HFP-based polymer inclusion membrane incorporating the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and di(2-ethylhexyl)phosphoric acid (D2EHPA) as the base polymer and extractant for the extraction of bismuth(III), respectively. It is demonstrated that the PIM comprised of 60 wt% PVDF-HFP and 40 wt% D2EHPA is the most effective in the extraction of bismuth(III) from feed solution containing 20 mg L-1 bismuth(III) and 0.2 mol L-1 sulfate adjusted to pH 1.4. The extracted bismuth(III) ions are back-extracted quantitatively to the receiving solution containing 1 mol L-1 sulfuric acid. The stoichiometry experiments reveal that the Bi: D2EHPA ratio in the bismuth(III) extracted complex is 1:6, and D2EHPA is dimer. Moreover, it is shown that the studied PIM has high selectivity in the extraction of bismuth(III) over other interfering ions such as Mo(VI), Cr(III), Al(III), Fe(III), Ni(II), Zn(II), Cd(II), Co(II), Cu(II), and Mn(II). The interference of Fe(III) is also eliminated by masking with fluoride, leading finally to a nearly pure extraction of bismuth(III).

Mechanistic investigation of intensified separation of molybdenum(VI) and vanadium(V) using polymer inclusion membrane electrodialysis

The main challenge in separating molybdenum(VI) and vanadium(V) which have similar properties results in great difficulties in the green recycling of hazardous spent catalysts. Here, selective facilitating transport and stripping are integrated into the polymer inclusion membrane electrodialysis process (PIMED) to separate Mo(VI) and V(V) to overcome the complicated co-extraction and stepwise-stripping in conventional solvent extraction. The influences of various parameters, the selective transport mechanism, and respective activation parameters were systematically investigated. Results revealed that the affinity of the Aliquat 36 as the carrier and PVDF-HFP as the base polymer of PIM towards Mo(VI) is stronger than that of V(V), while the strong interaction between Mo(VI) and carrier caused low migration through the membrane. By the combination of adjusting and controlling the electric density and strip acidity, the interaction was destroyed and the transport was facilitated. After optimization, stripping efficiencies of Mo(VI) and V (V) increased from 44.4% to 93.1% and reduced from 31.9% to 1.8%, respectively, while their separation coefficient increased 16.3 times to 333.4. The activation energy, enthalpy and entropy for the transport of Mo(VI) were determined to be 4.846 kJ mol^-1, 6.745 kJ mol^-1 and - 310.838 J mol^-1 K^-1, respectively. The present work demonstrates that the separation of similar metal ions could be improved by fine tuning the affinity and interaction between metal ions and the PIM, thus providing new insights into the recycling of similar metal ions from secondary resources.

Vanadium recovery by electrodialysis using polymer inclusion membranes

Industrial applications and environmental awareness recently prompted vanadium recovery spell from secondary resources. In this work, a polymer inclusion membrane containing trioctylmethylammonium chloride as carrier was successfully employed in electrodialysis for vanadium recovery from acidic sulfate solutions. The permeability coefficient of V(V) increased from 0.29 µm·s^-1 (without electric field) to 4.10 µm·s^-1 (with the 20 mA·cm^-2 current density)_. The transport performance of VO₂SO₄^-, which was the predominant species containing V(V) in the acidic region (pH <3), was influenced by the aqueous pH value and sulfate concentration. Under an electric field, a low concentrated H₂SO₄ solution (0.2 M) effectively stripped V(V) from the membranes, avoiding the requirement of a highly concentrated H₂SO₄ without electric field. Under the optimum conditions, the permeability coefficient and flux reached 6.80 µm·s^-1 and 13.34 µmol·m^-2·s^-1, respectively. High selectivity was observed for the separation of V(V) and Mo(VI) from mixed solutions of Co (II), Ni (II), Mn (II), and Al (III). Additionally, the separation between Mo(VI) and V(V) was further improved by adjusting the acidity of the stripping solution. The V(V) selectivity for the resulting membrane was higher than that of commercial anion exchange membranes.

On the Potential of a Poly(vinylidenefluoride-co-hexafluoropropylene) Polymer Inclusion Membrane Containing Aliquat® 336 and Dibutyl Phthalate for V(V) Extraction from Sulfate Solutions

A polymer inclusion membrane (PIM) composed of 50 wt% base polymer poly(vinylidenefluoride-co-hexafluoropropylene), 40 wt% extractant Aliquat^® 336, and 10 wt% dibutyl phthalate as plasticizer/modifier provided the efficient extraction of vanadium(V) (initial concentration 50 mg L⁻¹) from 0.1 M sulfate solutions (pH 2.5). The average mass and thickness of the PIMs (diameter 3.5 cm) were 0.057 g and 46 μm, respectively. It was suggested that V(V) was extracted as VO₂SO₄⁻ via an anion exchange mechanism. The maximum PIM capacity was estimated to be ~56 mg of V(V)/g for the PIM. Quantitative back-extraction was achieved with a 50 mL solution of 6 M H₂SO₄/1 v/v% of H₂O₂. It was assumed that the back-extraction process involved the oxidation of VO₂⁺ to VO(O₂)⁺ by H₂O₂. The newly developed PIM, with the optimized composition mentioned above, exhibited an excellent selectivity for V(V) in the presence of metallic species present in digests of spent alumina hydrodesulfurization catalysts. Co-extraction of Mo(VI) with V(V) was eliminated by its selective extraction at pH 1.1. Characterization of the optimized PIM was performed by contact angle measurements, atomic-force microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis/derivatives thermogravimetric analysis and stress–strain measurements. Replacement of dibutyl phthalate with 2-nitrophenyloctyl ether improved the stability of the studied PIMs.

Polymer inclusion membrane applications for transport of metal ions: A critical review

The co-existence of heavy metals in industrial effluents is a prevalent problem. Heavy metals are not biodegradable and can remain in the environment when left untreated. Therefore, metals must be removed from wastewater to protect people's health and the environment. Also, these pollutants usually have dissimilar compositions and properties. Generally, metal treatment is performed using traditional methods, but new processes have been developed due to the disadvantages of traditional methods. Especially in the last 20 years, studies on polymer inclusion membranes have been carried out and the transport performance of metal ions has been investigated. It is a more convenient process than both ion exchange and liquid-liquid extraction methods due to the potential and performance of polymer inclusion membranes. When the studies in the literature are examined, it is seen that the performance of polymer inclusion membranes is higher than expected and also when the production conditions are examined, polymer inclusion membrane is more advantageous than other processes. This review is a summary of the studies on the removal and transport of metal by using polymer inclusion membranes in the literature over the last 20 years.

Liquid membranes for separation of metal ions from wastewaters

The paper reviews application of various liquid membranes (LM), particularly of emulsion and supported liquid membranes, for metal separation from model and industrial wastewaters. A variety of carriers and separation systems is shown. Not only model solutions on a laboratory scale are presented but also some examples of real wastewater separation with LM are reported.

Simultaneous Recovery of Precious and Heavy Metal Ions from Waste Electrical and Electronic Equipment (WEEE) Using Polymer Films Containing Cyphos IL 101

In this article, the application of a polymer film containing the ionic liquid Cyphos IL 101 for the simultaneous recovery of precious and heavy metal ions ((Ni(II), Zn(II), Co(II), Cu(II), Sn(II), Pb(II), Ag(I), Pd(II), and Au(III)) from waste electrical and electronic equipment (WEEE) is described. The experiments were performed for solutions containing metal ions released from computer e-waste due to leaching carried out with concentrated nitric(V) acid and aqua regia. It was found that the applied polymer film allows for the efficient recovery of precious metals (98.9% of gold, 79.3% of silver, and 63.6% of palladium). The recovery of non-ferrous metals (Co, Ni, Cu, Zn, Sn, and Pb) was less efficient (25-40%). Moreover, the results of the performed sorption/desorption processes show that the polymer film with Cyphos IL 101 can be successfully used after regeneration to recover metals ions several times.

Elaboration and characterization of multilayer polymeric membranes: effect of the chemical nature of polymers

The transport phenomena across polymeric membrane may be enhanced by applying various strengths inside or outside the system. Recently, polymer inclusion membrane (PIM) has been considered one of the most popular methods that acts as a sink for the contaminant and immobilizes it. In the literature, there is no report about how to achieve the synthesis of multi-layer PIMs. In this paper, an improvement of a novel category of membrane without carrier for performing ion separation is reported. Different membranes were elaborated from binary mixtures of polymers, cellulose triacetate (CTA), polymethyl methacrylate (PMMA) and polyvinyl chloride (PVC) using 2-nitrophenyl octyle-ether (NPOE) as plasticizer and carrier in the same time, in order to increase specific interactions between the different polymers. The membranes (Polymer 1– NPOE – Polymer 2) were synthesized by phase inversion method modified by changing the procedure of a plasticizer/carrier addition and characterized by FTIR, TGA, SEM, zeta potential and contact angle. The CTA-based membranes exhibited well-defined pores partially filled with the second polymer and NPOE. Overall, our results showed that the addition of NPOE resulted in homogeneous membranes with modified physical properties, such as thickness, and hydrophobicity. A study of transport of Pb(II) using the synthesized membranes was studied. Dialysis experiments of lead ions across a polymeric membrane have shown that (CTA + NPOE + PMMA) and (PMMA + NPOE + PVC) membranes proved a good performance in one stage by fixing 12.15 and 25.31% of lead, respectively, without any additionally added carrier and acids. These results confirm the affinity between a basic polymer (poly-methyl methacrylate) and the metallic ion (Pb2+).

Environmentally friendly approach to recover vanadium and tungsten from spent SCR catalyst leach liquors using Aliquat 336

This research paper deals with an environmentally friendly approach for the treatment of spent selective catalytic reduction (SCR) catalyst. To recover vanadium (V) and tungsten (W) from spent SCR catalyst, leach liquors from hydrometallurgical processing were utilized to develop a proper methodology for extraction and possible separation of vanadium and tungsten from each other. This study investigated the solvent extraction (also called liquid-liquid extraction) of vanadium and tungsten utilizing the alkaline roasted leached solution containing approximately ∼7 g L-1 of tungsten and ∼0.7 g L-1 of vanadium. The commercial extractant, N-methyl-N,N,N-tri-octyl-ammonium chloride [R3NCH3]+Cl- (commercial name Aliquat 336), was dissolved in Exxsol™ D80 (diluent) system and adopted in this research. Solvent extraction studies were performed to determine the following experimental parameters: equilibrium pH, extractant concentration, diluent influence, chloride ion concentration, temperature, and stripping reagent concentration, which were systematically scanned to ascertain the optimum conditions for quantitative extraction of both title metals. An anion exchange mechanism was proposed using the quaternary ammonium chloride solvent reagent after slope analysis. Excess supplement of chloride proved to have adverse effects, further supporting the extraction mechanism. Thermodynamics results show positive values for enthalpy (ΔH) for vanadium and tungsten, favoring the endothermic nature of the extraction reaction towards the uptake of either metal. McCabe-Thiele plots for extraction were constructed, suggesting 2 and 3 stages for vanadium and tungsten extraction, respectively, at the aqueous (A) to organic (O) phase ratio of 7 : 1, ensuring more than 99.9% and 7-fold enrichment of both title metals. The stripping trend follows the order: (NaOH + NaCl) > (NaOH + NaNO3) > NaOH > NaNO3 > NaCl. Stripping isotherm followed by stripping counter-current (CCS) study was carried out for quantitative stripping of the metals.

Selective Separation of Acetic and Hexanoic Acids across Polymer Inclusion Membrane with Ionic Liquids as Carrier

This paper first reports on the selective separation of volatile fatty acids (VFAs) (acetic and hexanoic acids) using polymer inclusion membranes (PIMs) containing quaternary ammonium and phosphonium ionic liquids (ILs) as the carrier. The affecting parameters such as IL content, VFA concentration, and the initial pH of the feed solution as well as the type and concentration of the stripping solution were investigated. PIMs performed a much higher selective separation performance toward hexanoic acid. The optimal PIM composed of 60 wt% quaternary ammonium IL with the permeability coefficients for acetic and hexanoic acid of 0.72 and 4.38 µm s⁻¹, respectively, was determined. The purity of hexanoic acid obtained in the stripping solution increased with an increase in the VFA concentration of the feed solution and decreasing HCl concentration of the stripping solution. The use of Na₂CO₃ as the stripping solution and the involvement of the electrodialysis process could dramatically enhance the transport efficiency of both VFAs, but the separation efficiency decreased sharply. Furthermore, a coordinating mechanism containing hydrogen bonding and ion exchange for VFA transport was demonstrated. The highest purity of hexanoic acid (89.3%) in the stripping solution demonstrated that this PIM technology has good prospects for the separation and recovery of VFAs from aqueous solutions.

Chromium(VI) Removal by Polyvinyl Chloride (PVC)/Aliquat-336 Polymeric Inclusion Membranes in a Multiframe Flat Sheet Membrane Module

A new multiframe flat sheet membrane contactor module containing several flat membranes was designed and implemented. Each frame contains a chamber (central hole) in which the feed and the receiving phases are put in contact with polyvinyl chloride (PVC)/Aliquat-336 polymeric flat sheet membranes for Cr(VI) removal from aqueous solutions (feed phase). To evaluate the efficiency of the system, the experimental design methodology was used to analyze the effect of temperature (T, °C), PVC/Aliquat-336 ratio, and Cr (VI) concentration in the feed phase and the concentration of sodium chloride (NaOH-NaCl) in the receiving phase. Two representative mathematical models of the two responses (extraction and back-extraction) were respectively obtained. A good correlation between the experimental results and those predicted (RS2 = 97.77 and RR2 = 97.87) was achieved, allowing the optimization of the different factors selected for each response, separately. The proposed system showed a good separation performance, leading to Cr(VI) extractions up to 93% when working at the optimized operating conditions.

Ultrasound-assisted oil removal of γ-Al2O3-based spent hydrodesulfurization catalyst and microwave roasting recovery of metal Mo

Currently, roasting-leaching is the main treatment process of spent hydrodesulfurization (HDS) catalyst, but it will produce impurities, such as nickel molybdate and cobalt molybdate (NiMoO₄ or CoMoO₄), which is adverse to recover valuable metals. In this paper, a combined ultrasonic-microwave method was developed to remove oil and recover molybdenum (Mo) from the spent HDS catalyst. Firstly, ethanol was used to extract the surface oil of the spent MoNiCo/Al₂O₃ catalyst with ultrasonic assistance. Effects of temperature, ultrasonic time, liquid-solid ratio and ultrasonic power on the oil removal rate were investigated systematically and the process conditions were optimized using response surface methodology (RSM). The results showed that the oil removal rate was over 99% under the optimum conditions of temperature 55 °C, ultrasonic time 2 h, liquid to solid ratio 5:1, and ultrasonic power 600 W. After oil removal, the sample was roasted in microwave field at 500 °C for 15 min. The generation of toxic gas could be effectively avoided and no hardest-to-recycle impurity CoMoO₄ was found. At last, the roasted sample was subjected to ultrasonic leaching with sodium carbonate (Na₂CO₃) solution for recovering Mo. Extraction of Mo of the deoiled sample after microwave roasting reached 94.3%, which is about 7% higher than that of oily sample. Moreover, microwave roasting method resulted in a much higher Mo extraction than traditional method for both the oily and deoiled spent catalyst. It was concluded that the ultrasonic-microwave assisted method could remarkably improve the recovery of Mo and greatly shorten the processing time.

The Effect of Surface Confined Gold Nanoparticles in Blocking the Extraction of Nitrate by PVC-Based Polymer Inclusion Membranes Containing Aliquat 336 as the Carrier

Clusters of gold nanoparticles (AuNPs) formed on the surface of PVC-based polymer inclusion membranes (PIMs) with a liquid phase containing Aliquat 336 as the carrier and in some cases 1-dodecanol or 2-nitrophenol octyl ether as plasticizers were found to inhibit the extraction of nitrate by the PIMs. This observation was based on gradually increasing the mass of AuNPs on the membrane surface and testing the ability of the membrane to extract nitrate after each increase. In this way, it was possible to determine the so-called “critical AuNP masses” at which the studied membranes ceased to extract nitrate. On the basis of these results, it can be hypothesized that the surfaces of these PIMs are not homogeneous with respect to the distribution of their membrane liquid phases, which are present only at certain sites. Extraction takes place only at these sites, and at the “critical AuNP mass” of a PIM, all these extraction sites are blocked and the membrane loses its ability to extract.