Extraction And Separation Of Gold(Ⅲ),Palladium(Ⅱ) And Platinum(Ⅳ) By Novel System Constructed With Nitrogen-Contained Ionic Liquids

Environmental pollution and resource scarcity are two major challenges facing the world today.In this context,the concept of green chemistry has received increasing attention from people,prompting researchers to actively seek environmentally friendly and sustainable methods to achieve sustainable development in various industries.In the pursuit of sustainable development,some important precious metal resources such as gold,palladium,and platinum are entering the chemical application arena,which are crucial for green and sustainable applications.Strengthening the recovery and reuse of precious metals in secondary resources is of great significance for sustainable development and the realization of a circular economy.However,the current extraction technology has drawbacks such as complex processes,high energy consumption,long cycles,low recyclability,strong environmental pollution,and poor separation efficiency.Therefore,it is urgent to develop green and environmentally friendly extraction technologies to achieve efficient and highly selective separation and recovery of precious metals from secondary resources.Ionic liquids(ILs),due to their excellent properties such as strong stability,functional design,biodegradability,and recyclability,have received widespread attention in the field of precious metal separation and recovery.In this paper,various functionalized nitrogen-containing ILs were designed and synthesized,and a novel extraction system involving only ILs and water was constructed for the separation and recovery of gold(Ⅲ),palladium(Ⅱ),and platinum(Ⅳ)from HCl media.The specific research contents are described below:(1)Extraction and separation of gold(Ⅲ)and platinum(Ⅳ)from HCl solution with gemini pyridinium-based ILs:An organic-solvent-free IL-water biphasic extraction system was constructed,and the extraction performance of gemini pyridinium-based ILs were investigated in a binary metal solution containing gold(Ⅲ)and platinum(Ⅳ).HPLC and FT-IR confirmed that ILs had low hydrophobicity and strong acid resistance.Experimental parameters such as the amount of extractant,HCl concentration,and temperature were optimized,and the differential extraction behavior of[C6-EtTMEDA-PIP][Tf2N]2 on gold(Ⅲ)and platinum(Ⅳ)under different experimental conditions was studied.In addition,a response surface analysis experiment was designed to further consider the combined effects of the amount of IL and HCl concentration on the extraction of gold(Ⅲ)and platinum(Ⅳ).Furthermore,the thermodynamic and kinetic processes of[C6-Et-TMEDA-PIP][Tf2N]2 extraction of gold(Ⅲ)and platinum(Ⅳ)were investigated.Importantly,[C6-Et-TMEDAPIP][Tf2N]2 successfully selectively separated gold(Ⅲ)and platinum(Ⅳ)from a multimetal solution,with extraction efficiencies of 98.41%and 97.25%,respectively,and the metals were successfully stripped using oxalic acid and thiourea/hydrochloric acid.After five cycles,the extraction efficiencies of gold(Ⅲ)and platinum(Ⅳ)remained above 90.00%.(2)Homogeneous extraction and separation of gold(Ⅲ)in HCl medium by temperature-responsive gemini quaternary ammonium-based ILs:Two gemini quaternary ammonium-based ILs,[EA-TMEDA][Tf2N]2 and[EA-TMHDA][Tf2N]2,were synthesized based on the temperature-responsive phase transition behavior exhibited by the ILs upon mixing with water.Two homogeneous liquid-liquid extraction systems involving the ILs were constructed to overcome the viscosity barrier and phase separation difficulties encountered in traditional two-phase extraction,and were used to recover gold(Ⅲ)from HCl medium.The corresponding UCST phase diagrams were plotted by adjusting the ratio of IL to water.The anion exchange mechanism of the system was verified by maximum metal loading experiments,as well as UV-vis,FT-IR,and NMR spectroscopy.Under optimal conditions,the effect of homogeneous formation on metal ion extraction behavior was investigated,and the formation of a homogeneous phase was shown to accelerate the mass transfer process and improve extraction efficiency by measuring extraction efficiency at different temperatures.The optimal model for extraction was established by RSM,laying a solid theoretical foundation for future practical application of the system in production.(3)Homogeneous extraction and separation of gold(Ⅲ)and platinum(Ⅳ)in HCl medium by temperature-responsive gemini pyridinium-based ILs:By utilizing temperature-dependent UV-Vis spectroscopy and DLS in conjunction with theoretical calculations,the ability of the ILs to form solvation hydrogen bonds and the close relationship between the phase transition temperature and the cation’s electrostatic potential energy value were confirmed.Furthermore,the addition of inorganic salts to the system resulted in an increase in the phase transition temperature.Various pyrazinebased ILs with different side-chain functional groups were screened,and the best extractant for gold(Ⅲ)and platinum(Ⅳ)was determined to be an ester-functionalized pyridinium-based IL[EA-Et-TMEDA-PIP][Tf2N],with extraction efficiencies of 99.12%and 98.75%,respectively.Through a combination of multiple testing methods,it was found that the extraction of gold(Ⅲ)and platinum(Ⅳ)by[EA-Et-TMEDAPIP][Tf2N]2 was mediated by an ion exchange mechanism.The extraction parameters,such as the amount of IL,operating temperature,and aqueous solution acidity,were optimized,and a separation process was designed and integrated.In addition,[EA-EtTMEDA-PIP][Tf2N]2 exhibited high selectivity and extraction efficiency for gold(Ⅲ)and platinum(Ⅳ)in water solutions containing other metal ions.Therefore,this homogeneous system has important reference value for predicting and guiding the recovery of precious metals in secondary resources.(4)Recovery of gold(Ⅲ),palladium(Ⅱ)and platinum(Ⅳ)from waste printed circuit boards by a temperature-responsive triazolium-based ILs:A homogeneous extraction system composed of a temperature-responsive IL[1,4,7-TMTA][Tf2N]and water was investigated for the one-step separation and recovery of gold(Ⅲ),palladium(Ⅱ)and platinum(Ⅳ)from secondary resources.By comparing the electrostatic potential energies of all the ILs in four systems,their ability to form hydrogen bonds with water was found to be:[1,4,7-TMTA]+>[EO-Et-TMEDAPIP]2+>[EA-TMEDA]2+>[EA-Et-TMEDA-PIP]2+.Theoretical calculations demonstrated that the temperature-responsive phase transition system constructed by the IL[1,4,7-TMTA][Tf2N]had the advantage of lower energy consumption during the extraction process,and could achieve efficient extraction of metal ions at lower phase transition temperatures.Compared with other metal ions,[1,4,7-TMTA][Tf2N]exhibited higher selectivity for gold(Ⅲ),palladium(Ⅱ)and platinum(Ⅳ),and the extraction equilibrium could be rapidly achieved within 10 minutes.Moreover,efficient back-extraction of gold(Ⅲ),palladium(II)and platinum(Ⅳ)from the loaded IL phase could be achieved by gradient elution with K2C2O4,NH3.H2O and CS(NH2)2/HCl aqueous solutions,with back-extraction rates of 99.21%,98.54%and 98.67%,respectively.Importantly,a complete process flow diagram for the separation and recovery of gold(Ⅲ),palladium(Ⅱ)and platinum(Ⅳ)from waste PCBs using[1,4,7TMTA][Tf2N]was provided.The extraction study of the practical system confirmed the huge potential of[1,4,7-TMTA][Tf2N]for the one-step separation and recovery of precious metals from electronic waste.