Study On Recovery Of Palladium By Aqueous Biphasic Extraction And Electrodeposition Based On Ionic Liquid

Palladium is of high value and widely used.Because the resource of palladium in China is extremely scarce,it is important to recover palladium from secondary resources.The recovery process generally involves two steps:enrichment and reduction.The most common enrichment method is extraction,using normally the volatile organic solvents,which are one of the most emphasized problems of air pollution in China.Ionic liquids,which are known as"green solvents"due to their extremely low volatility,can form aqueous biphasic systems with inorganic salts.The ionic liquid-base aqueous biphasic systems?IL-ABSs?have the advantages of environmentally friendly,efficient,and easy to separate for extraction.However,there are not reports on extraction of Pd?II?by IL-ABS yet.In addition,due to the excellent conductivity of the ionic liquid,the palladium-rich phase obtained after the extraction can be directly subjected to electrodeposition to obtain palladium substance.In this paper,we studied the effect of ionic liquid structure on the ability to form IL-ABS and extract Pd?II?.The mechanism of palladium extraction by different IL-ABSs was discussed.The Pd?II?solutions containing multiple metal ions were extracted by IL-ABS,studying the selectivity of IL-ABS and the feasibility of the recovery process.Finally,the palladium riched phase was electrodeposited to obtain elemental palladium,which formed a complete palladium recovery process.The main results are as follows:?1?There was no statistical difference in the phase-forming ability of the ionic liquid based on Cl^-and Br^-.The longer the cation alkyl chain is,the stronger the phase-forming ability of the ionic liquid is.The introduction of hydrophilic functional groups reduces the phase-forming ability.The order of phase forming ability of the 8 ionic liquids is:[C₃SO₃mim][Cl]<[C₃CNmim][Cl]<[C₃NH₂mim][Br]<[C₂OC₁mim][Br]<[C₃mim][Br]?[C₃mim][Cl]<[C₄mim][Cl]<[C₆mim][Cl].The extraction percentage of Pd?II?by the IL-ABSs ranged from 50.13%to 100%.The extraction percentage by functional IL-ABSs is generally higher than that of the conventional ionic liquids.The extraction percentages of Pd?II?by IL-ABS containing sulfonate and nitrile groups were the highest?96.32%and 100%,respectively?.The extraction percentages of Pd?II?by conventional IL-ABSs decreased with the growth of alkyl chains prolonging,and[C₃mim][Cl]had the highest?65.74%?When the concentration of ionic liquid concentration and the potassium phosphate increased within a certain range,the extraction percentages d also increased.?2?In the extraction by conventional IL-ABS,the main mechanism is the coordination substitution mechanism and anion exchange mechanism.when the Pd?II?is extracted,the hydrogen atom on the C?2?atom on the cationic imidazole ring loses,and then the electrons interact with the Pd?II?forming a complex to enter the ionic liquid-rich phase.In the process of extracting Pd?II?by functionalized IL-ABS,the imidazole ring in the cation loses the hydrogen atom on C?2?and coordinates with Pd?II?,the same as the conventional ionic liquid.In addition,functional groups such as nitrile groups and sulfonic acid groups can also coordinate with Pd?II?,which enhances the coordination capacity and increases the coordination capacity of the ionic liquid.?3?In the extraction of Pd?II?solutions containing multiple metal ions,different metal ions have different effects on palladium ion extraction percentages.The presence of zinc ions and iron ions at 30 mg/L¹50 mg/L has no effect on the extraction percentage of Pd?II?,which maintained at 100%.When the copper ion concentration exceeds 90 mg/L and the nickel ion exceeds 120 mg/L,the selectivity to palladium is generally poor.The selectivity to Pd?II?by different functionalized IL-ABS varied greatly.[C₃CNmim][Cl]has the best selectivity.?4?The electrochemical window of[C₃CNmim][Cl]is 2 V,and the reduction potential of the Pd?II?in the ionic liquid-rich phase is-0.53 V.During the constant voltage electrodeposition process,the deposition rate and deposition current of palladium gradually decreased with time,and the final deposition efficiency reached 67.72%.The characterization results show that the electrodeposited material is nano-sized particles,and the main component is palladium oxide.After calcination,elemental palladium can be obtained,and a protocol of palladium recovering from solution is completed.In this study,the"green solvent"-ionic liquid was used to realize the efficient enrichment of metal palladium in the solution,and its excellent conductivity was used to electrodeposit palladium ions from the ionic liquid phase.Finally,a complete process for recovering metallic palladium from solution was formed.This provides basic data and more research ideas for the clean and efficient recovery of platinum group metals in secondary resources,the promotion of resource recycling and the realization of green chemistry.