Separation of Palladium(II) and Rhodium(III) Using a Polymer Inclusion Membrane Containing a Phosphonium-Based Ionic Liquid Carrier

Effects of membrane content, feed phase, and stripping phase for palladium solution extraction by using a polymer inclusion membrane

Palladium is now frequently utilized in fuel cells, electroplating, electronics, and catalysis. Due to their rarity and high cost, precious metal recovery has taken on a significant role. The extraction method frequently utilized in polymer inclusion membranes (PIMs) is both efficient and simple since it has been demonstrated that precious metal adsorption on the membrane significantly controls the mechanism of chemical adsorption. In this study, polyvinyl chloride (PVC) as a polymer, A336 as a plasticizer, and trioctylamine (TOA) as a carrier were used to produce a PIM by evaporation. After the production of PIMs, palladium extract was studied. The stripping phase, palladium concentration in the feed phase, and components of the membrane were changed to determine the optimum condition with better extraction ability. When 0.5 M of HCl was used, higher kinetic parameter results and higher than 85% extraction efficiency were achieved compared to other concen- trations. When the EDX results were examined, 3.3% palladium was retained on the membrane surface. When the palladium concentration was selected at 2.5 ppm, higher kinetic parameters were observed, and the extraction efficiency was over 90%. The best membrane was the PIM containing 40% PVC-40% A336-20% TOA.

On the Use of Polymer Inclusion Membranes for the Selective Separation of Pb(II), Cd(II), and Zn(II) from Seawater

The synthesis and optimization of polymeric inclusion membranes (PIMs) for the transport of Cd(II) and Pb(II) and their separation from Zn(II) in aqueous saline media are presented. The effects of NaCl concentrations, pH, matrix nature, and metal ion concentrations in the feed phase are additionally analyzed. Experimental design strategies were used for the optimization of PIM composition and evaluating competitive transport. Synthetic seawater with 35% salinity, commercial seawater collected from the Gulf of California (Panakos^®), and seawater collected from the beach of Tecolutla, Veracruz, Mexico, were employed. The results show an excellent separation behavior in a three-compartment setup using two different PIMs (Aliquat 336 and D2EHPA as carriers, respectively), with the feed phase placed in the central compartment and two different stripping phases placed on both sides: one solution with 0.1 mol/dm³ HCl + 0.1 mol/dm³ NaCl and the other with 0.1 mol/dm³ HNO₃. The selective separation of Pb(II), Cd(II), and Zn(II) from seawater shows separation factors whose values depend on the composition of the seawater media (metal ion concentrations and matrix composition). The PIM system allows S(Cd) and S(Pb)~1000 and 10 < S(Zn) < 1000, depending on the nature of the sample. However, values as high as 10,000 were observed in some experiments, allowing an adequate separation of the metal ions. Analyses of the separation factors in the different compartments in terms of the pertraction mechanism of the metal ions, PIMs stabilities, and preconcentration characteristics of the system are performed as well. A satisfactory preconcentration of the metal ions was observed after each recycling cycle.

Sustainable and Selective Modern Methods of Noble Metal Recycling

Noble metals exhibit broad arrange of applications in industry and several aspects of human life which are becoming more and more prevalent in modern times. Due to their limited sources and constantly and consistently expanding demand, recycling of secondary and waste materials must accompany the traditional mineral extractions. This Minireview covers the most recent solvometallurgical developments in regeneration of Pd, Pt, Rh, Ru, Ir, Os, Ag and Au with emphasis on sustainability and selectivity. Processing-by selective oxidative dissolution, reductive precipitation, solvent extraction, co-precipitation, membrane transfer and trapping to solid media-of eligible multi-metal substrates for recycling from waste printed circuit boards to end-of-life automotive catalysts are discussed. Outlook for possible future direction for noble metal recycling is proposed with emphasis on sustainable approaches.

Efficient Recovery of Noble Metal Ions (Pd2+, Ag+, Pt2+, and Au3+) from Aqueous Solutions Using N,N'-Bis(salicylidene)ethylenediamine (Salen) as an Extractant (Classic Solvent Extraction) and Carrier (Polymer Membranes)

This paper presents the results of the first application of N,N'-bis(salicylidene)ethylenediamine (salen) as an extractant in classical liquid-liquid extraction and as a carrier in membrane processes designed for the recovery of noble metal ions (Pd2+, Ag+, Pt2+, and Au3+) from aqueous solutions. In the case of the utilization of membranes, both sorption and desorption were investigated. Salen has not been used so far in the sorption processes of precious metal ions. Recovery experiments were performed on single-component solutions (containing only one type of metal ions) and polymetallic solutions (containing ions of all four metals). The stability constants of the obtained complexes were determined spectrophotometrically. In contrast, electrospray ionization high-resolution mass spectrometry (ESI-HRMS) was applied to examine the elemental composition and charge of the generated complexes of chosen noble metal ions and salen molecules. The results show the great potential of N,N'-bis(salicylidene)ethylenediamine as both an extractant and a carrier. In the case of single-component solutions, the extraction percentage was over 99% for all noble metal ions (molar ratio M:L of 1:1), and in the case of a polymetallic solution, it was the lowest, but over 94% for platinum ions and the highest value (over 99%) for gold ions. The percentages of sorption (%Rs) of metal ions from single-component solutions using polymer membranes containing N,N'-bis(salicylidene)ethylenediamine as a carrier were highest after 24 h of the process (93.23% for silver(I) ions, 74.99% for gold(III) ions, 69.11% and 66.13% for palladium(II) and platinum(II) ions, respectively), similar to the values obtained for the membrane process conducted in multi-metal solutions (92.96%, 84.26%, 80.94%, and 48.36% for Pd(II), Au(III), Ag(I), and Pt(II) ions, respectively). The percentage of desorption (%Rdes) was very high for single-component solutions (the highest, i.e., 99%, for palladium solution and the lowest, i.e., 88%, for silver solution), while for polymetallic solutions, these values were slightly lower (for Pt(II), it was the lowest at 63.25%).

Selective recovery of platinum from spent autocatalyst solution by thiourea modified magnetic biocarbons

The precious platinum group metals distributed in urban industrial products should be recycled because of their rapid decline in the contents through excessive mining. In this work, thiourea modified magnetic biocarbons are prepared via an energy-efficient microwave-assisted activation and assessed as potential adsorbents to recover platinum ions (i.e., Pt(IV)) from dilute waste solution. The physicochemical properties of prepared biocarbons are characterized by a series of spectroscopic and analytic instruments. The adsorption performance of biocarbons is carried out by using batch tests. Consequently, the maximum adsorption capacity of Pt(IV) observed for adsorbents is ca. 42.8 mg g^-1 at pH = 2 and 328 K. Both adsorption kinetics and isotherm data of Pt(IV) on the adsorbents are fitted better with non-linear pseudo second-order model and Freundlich isotherm, respectively. Moreover, the thermodynamic parameters suggest that the Pt(IV) adsorption is endothermic and spontaneous. Most importantly, the adsorbents exhibit high selectivity toward Pt(IV) adsorption and preserve ca. 96.9% of adsorption capacity after six cyclic runs. After adsorption, the regeneration of the prepared adsorbents can be effectively attained by using 1 M thiourea/2% HCl mixed solution as an eluent. Combined the data from Fourier transform infrared and X-ray photoelectron spectroscopies, the mechanisms for Pt(IV) adsorption are governed by Pt-S bond between Pt(IV) and thiourea as well as the electrostatic attraction between anionic PtCl₆^2- and cationic functional groups of adsorbents. The superior Pt(IV) recovery and sustainable features allow the thiourea modified magnetic biocarbon as a potential adsorbent to recycle noble metals from spent autocatalyst solution.

The Application of 2,6-Bis(4-Methoxybenzoyl)-Diaminopyridine in Solvent Extraction and Polymer Membrane Separation for the Recovery of Au(III), Ag(I), Pd(II) and Pt(II) Ions from Aqueous Solutions

The work describes the results of the first application of 2,6-bis(4-methoxybenzoyl)-diaminopyridine (L) for the recovery of noble metal ions (Au(III), Ag(I), Pd(II), Pt(II)) from aqueous solutions using two different separation processes: dynamic (classic solvent extraction) and static (polymer membranes). The stability constants of the complexes formed by the L with noble metal ions were determined using the spectrophotometry method. The results of the performed experiments clearly show that 2,6-bis(4-methoxybenzoyl)-diaminopyridine is an excellent extractant, as the recovery was over 99% for all studied noble metal ions. The efficiency of 2,6-bis(4-methoxybenzoyl)-diaminopyridine as a carrier in polymer membranes after 24 h of sorption was lower; the percentage of metal ions removal from the solutions (%Rs) decreased in following order: Ag(I) (94.89%) > Au(III) (63.46%) > Pt(II) (38.99%) > Pd(II) (23.82%). The results of the desorption processes carried out showed that the highest percentage of recovery was observed for gold and silver ions (over 96%) after 48 h. The results presented in this study indicate the potential practical applicability of 2,6-bis(4-methoxybenzoyl)-diaminopyridine in the solvent extraction and polymer membrane separation of noble metal ions from aqueous solutions (e.g., obtained as a result of WEEE leaching or industrial wastewater).

Environmentally friendly Pd(II) recovery from spent automotive catalysts using resins impregnated with a pincer-type extractant

Extractant-impregnated resins have potential for recovering platinum group metals selectively and efficiently. Herein, 1,3-bis(2-(octylthio)propan-2-yl)benzene (1), a pincer-type extractant, was impregnated in Amberlite XAD-7 resin (1-EIR), and the batch Pd(II) sorption conditions, including impregnated amount, shaking time, Pd(II) concentration, HCl concentration, and Pd(II) desorption reagents, were optimized. The maximum Pd(II) sorption capacity of 1-EIR was 49 mg g⁻¹ after 24 h in a 700 ppm Pd(II) solution. Over 20 adsorption–desorption cycles, 1-EIR showed good reusability, with a sorption percentage (S%) of > 92%. However, not all Pd(II) was desorbed from 1-EIR. Complete Pd(II) collection was achieved by combining desorption with flaking of the Pd–extractant complex from Pd(II)-loaded 1-EIR by Soxhlet extraction, as ~ 13 mg g⁻¹ remained after the 20th adsorption–desorption cycle by absorptiometric method. The sorption mechanism was elucidated based on the Langmuir isotherm model, thermodynamic parameters, and sorption kinetics. Pd(II) sorption by 1-EIR was spontaneous and endothermic, and the sorption kinetics followed a pseudo-second-order model. Notably, 1-EIR also exhibited high selectivity for Pd(II) from a simulated mixed metal solution and a spent automotive catalyst leachate (S% = 98% and > 99%, respectively). Thus, this extractant-impregnated system is promising for selective Pd(II) recovery from spent automotive catalysts and other secondary resources.

A review on the recycling processes of spent auto-catalysts: Towards the development of sustainable metallurgy

Spent auto-catalysts are considered as promising platinum group metals (PGMs) resources based on their rapidly increasing demand along with the underlying uncertainty of the sustainability and long-term availability of PGMs. Recycling spent auto-catalysts presents attractive advantages, particularly for the conservation of primary resources reserves, and for the reduction of negative environmental impact due to exploitation. PGM reclamation is the major aim of recycling operations despite their minor concentration in spent auto-catalysts, which implies that the remaining materials are disposed of as unwanted solid waste after the extraction process. This poses a genuine challenge, as well as a motivation to develop recycling processes for spent auto-catalysts capable of recovering all components/valuable metals, while moderating environmental pollution and global warming. The focus herein involves the description of the available technologies, including pyro- and hydro-metallurgical processes, to recover PGMs from spent auto-catalysts, and specifically an analysis of the developmental trends in recycling methods to ensure "sustainable metallurgy".

Transport of Rhodium(III) from Chloride Media across a Polymer Inclusion Membrane Containing an Ionic Liquid Metal Ion Carrier

Efficient and selective transport of rhodium(III) across a polymer inclusion membrane (PIM) from a 0.1 mol dm^-3 HCl feed solution, also containing iron(III), to a receiving solution containing 0.1 mol dm^-3 HCl and 4.9 mol dm^-3 NH₄Cl was achieved using a phosphonium-type ionic liquid, trioctyl(dodecyl)phosphonium chloride (P₈₈₈₁₂Cl), as the metal ion carrier. The optimum PIM composition for the Rh(III) transport was 50 wt % poly(vinylidene-co-hexafluoropropylene) (PVDF-HFP), 30 wt % P₈₈₈₁₂Cl, and 20 wt % plasticizer 2-nitrophenyl octyl ether (2NPOE). The driving force for the Rh(III) transport was suggested to be the concentration difference of the chloride ion between the feed and the receiving solutions. More than 70% rhodium(III) could be recovered from the receiving solution, and no transport of iron(III) was observed; however, the two metal ions cannot be separated by liquid-liquid extraction. This is the first report of selective transport of rhodium(III) across a polymer inclusion membrane.