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In this study, four novel functionalized ionic liquids ([C4mim][DDTC], [C5mim][DDTC], [C6mim][DDTC], and [BMPip][DDTC]) were synthesized and used for the selective extraction of Pd(II) from an HCl medium containing Pt(IV), Pd(II), and Rh(III). The extraction mechanism was investigated using Job’s plots, UV–Vis, SXRD, and MS analysis. A mechanistic investigation revealed the formation of hydrophobic extraction complexes Pd(DDTC)2 and PdClDDTC via coordination between [DDTC]− and Pd(II). In addition, the solubility and polarity of the solutes were investigated using DFT calculations to determine the optimal extractant and diluent. From the results of the theoretical analysis, [C5mim][DDTC]/CHCl3 was selected as the optimum system for the selective extraction of Pd(II). The effects that factors have on Pd(II) extraction, including temperature, [C5mim][DDTC] amount, HCl concentration, and O/A ratio, were investigated and optimized using single-factor and response surface experiments. Under the optimized conditions, Pd(II) extraction efficiencies were higher than 99%, and the separation factors (βPd(II)/Pt(IV) and βPd(II)/Rh(III)) were greater than 104. After extraction, Pd and Rh were directly recovered from the organic and aqueous phases via photocatalytic reduction, respectively. TEM, XPS, and PXRD results revealed that the resulting nanoparticles were Rh(0) or Pd(0). The recovery of Pd and Rh exceeded 95%. Overall, a simple hydrometallurgical process with low reagent consumption was developed to yield nanometer-scale Pd(0) and Rh(0) from simulated secondary resource leaching solutions.

Although phosphonium-based ionic liquids (ILs) have become popular green solvents for the separation of precious metals, these solvents have not been used thus far to recover Pd(II) from alkaline cyanide solutions. In this study, three novel phosphonium-based ILs, viz. tributyl(2-ethylhexyl) phosphonium bromide (TBEHPB), trioctyl (2-ethylhexyl) phosphonium bromide (TOEHPB), and trioctyl undecyl phosphonium bromide (TOUPB), were synthesized, respectively, and these ILs were used for the recovery of Pd(CN)42− for the first time. With the increase in the length of the alkyl chain in the phosphonium cation, the extraction percentage of Pd(II) increased. Under optimum conditions (i.e., contact time of 5 min, pH of 10.5, and temperature of 298 K), the TOUPB system exhibited a Pd(II) extraction percentage of greater than 99.0%. Furthermore, the TOUPB system exhibited excellent selectivity for Pd(II) in a mixed solution (separation factors of βPd/Fe and βPd/Co were greater than 2.0 × 103). The Pd(II) recovery percentage was still greater than 90.0% after five consecutive extraction-stripping cycles. The Job’s method, infrared spectroscopy, mass spectrometry, nuclear magnetic resonance spectroscopy, and UV–vis spectroscopy revealed that the extraction mechanism is ion exchange. The supramolecular structure of the extraction complex was established on the basis of density functional theory (DFT) calculations and Karl Fischer titration, and the extraction mechanism was further described at the molecular structure level. This study provides a new process for recovering Pd(II) from an alkaline cyanide medium.

BACKGROUND Thus far, separation and recovery of Pd(CN)42- and Pt(CN)42- from cyanide liquors have not been reported. In this study, the process of co-extracting and separating Pd(II) and Pt(II) over Fe(III), Cu(I), Co(III), and Ni(I) from alkaline cyanide liquors was investigated. RESULTS The results showed that almost all Pd(II) and Pt(II) (>98.0%) could be simultaneously extracted by phenoxyethyl dimethyl palmitylammonium bromide (PDPB), whereas Fe(III), Cu(I), Co(III), and Ni(I) was below 3.0% under optimum conditions. Furthermore, Pd(CN)42- and Pt(CN)42- were separated and recovered by the two-step stripping process. First, Pd(CN)42- in mixed organic phase was stripped by a 2.0 mol L−1 ammonium thiocyanate solution. The stripping percentage of Pd(CN)42- was >98%, whereas the stripped Pt(CN)42- was below 1%. Second, more than 97.5% Pt(CN)42- in the loaded organic phase could be stripped using 1.0 mol L−1 thiodiglycol solution. Recovery ratios for both Pd(II) and Pt(II) were above 95%. The organic phase could be reused for at least 6 cycles of extraction–stripping processes. The mechanisms of extraction reaction were deduced to be ion-association mechanisms. CONCLUSION The process could be applied for extracting and separating palladium and platinum from the cyanide leaching liquor of the flotation concentrate. © 2016 Society of Chemical Industry

A novel functional ion-exchange/adsorption metal organic resin (MOR), TEBAC-HKUST-1, was prepared and characterized. Ethanedithiol was used as the grafting agent to introduce thiol groups onto HKUST-1, and 4-vinylbenzyl chloride was then grafted onto SH-HKUST-1 using thiol groups. Finally, the quaternary ammonium functional group was immobilized onto the carrier by performing a quaternization reaction. The structure and property of TEBAC-HKUST-1 MOR were characterized by TGA, N2 adsorption&ndash, desorption, FTIR, SEM, and XRD. TEBAC-HKUST-1 MOR was used to remove metal cyanide complexes from wastewater. The adsorption was rapid, and the metal cyanide complexes including Pt(CN)42&minus, Co(CN)63&minus, Cu(CN)32&minus, and Fe(CN)63&minus, were removed in 30 min. TEBAC-HKUST-1 MOR exhibited a high stability in neutral and weak basic aqueous solutions. Furthermore, Pt(II) could be efficiently recovered through two-step elution. The recovery rate of Pt(II) for five cycles were over 92.0% in the mixture solution containing Pt(CN)42&minus, The kinetic data were best fitted with the pseudo second-order model. Moreover, the isothermal data were best fitted with the Langmuir model. The thermodynamic results show that the adsorption is a spontaneous and exothermic process. TEBAC-HKUST-1 MOR not only exhibited excellent ability for the rapid removal of metal cyanide complexes, but also provided a new idea for the extraction of noble metals from cyanide-contaminated water.

In this study, quaternary-ammonium-functionalized metal&ndash, organic frameworks (MOFs) Et-N-Cu(BDC-NH2)(DMF), were prepared, characterized, and applied for the highly effective removal of metal cyanide complexes, including Pd(CN)42&minus, Co(CN)63&minus, and Fe(CN)63&minus, Batch studies were carried out, and the maximum adsorption capacities of Pd(II), Co(III), and Fe(III) reached 172.9, 101.0, and 102.6, respectively. Adsorption was rapid, and equilibrium was established within 30 min. Et-N-Cu(BDC-NH2)(DMF) exhibited high thermal and chemical stability. Furthermore, absorbed Pd(CN)42&minus, was selectively recovered by two-step elution. First, Co(CN)63&minus, were eluted with a 1.5 mol L&minus, 1 KCl solution. Elution rates of Co(CN)63&minus, were greater than 98.0%, whereas the elution percentage of Pd(CN)42&minus, was less than 2.0%. Second, &gt, 97.0% Pd(CN)42&minus, on the loaded MOFs was eluted using a 2.0 mol L&minus, 1 KI solution. The recovery rate of Pd(CN)42&minus, was greater than 91.0% after five testing cycles. Adsorption isotherms, kinetics models, and adsorption thermodynamics of Pd(CN)42&minus, on Et-N-Cu(BDC-NH2) (DMF) were also systematically investigated. The Et-N-Cu(BDC-NH2) (DMF) absorbent exhibited a rapid, excellent ability for the adsorption of metal cyanide complexes.

Conventional separation methods are not suitable for recovering palladium present in low concentrations in ore leaching solutions. In this study, a novel isopentyl sulfide (S201)-impregnated α-MnO2 nanorod adsorbent (BISIN) was prepared, characterized, and applied for the selective adsorption and separation of palladium from the leaching liquor of ores. Batch studies were carried out, and the main adsorption parameters were systematically investigated, in addition to the relevant thermodynamic parameters, isotherms, and kinetic models. The thermodynamic parameters reflected the endothermic and spontaneous nature of the adsorption. Moreover, the experimental results indicated that the Langmuir isotherm model fits the palladium adsorption data well and the adsorption was well described by the pseudo-second-order kinetic model. The main adsorption mechanisms of palladium were elucidated at the molecular level by X-ray crystal structure analysis. Thiourea was found to be an excellent desorption agent, and the palladium-thiourea complex was also confirmed by X-ray crystal structure analysis. The results indicated that almost all of the Pd(II) (>99.0%) is adsorbed on BISIN, whereas less than 2% of the adsorbed Pt(IV), Fe3+, Cu2+, Ni2+, and Co2+ is observed under the optimum conditions. The proposed method can be used for the efficient adsorption and separation of palladium from the leaching liquor of ores.