Study On Separation Of Pt（Ⅳ） And Pd（Ⅱ） By Ionic Liquid And Deep Eutectic Solvents Based Green Extraction Systems

Ionic liquids（ILs）and deep eutectic solvents（DESs）,as novel green solvents,have the characteristics of environmentally friendly,energy saving,high selectivity and good solubility.Thus,they have received extensive attention in the extraction and separation of rare metals.This work has synthesized successfully a variety of new ILs and DESs,and constructed a series of liquid-liquid extraction systems.The separation performance of each extraction system for Pt（Ⅳ）and Pd（Ⅱ）in acidic media has been explored.The main research contents are as follows:（1）Separation of Pd（Ⅱ）from hydrochloric solution by ionic liquid based aqueous biphasic systemIn this study,an environmentally aqueous biphasic system（ABS）was constructed,which was proposed for extraction from hydrochloric solution,using imidazolium-based IL as an adjuvant in PEG/K₂HPO₄ ABS.The results show that the introduction of IL into PEG/K₂HPO₄ ABS can significantly enhance the extraction efficiency of Pd（Ⅱ）.Among three imidazolium-based IL（[C_nmim]Br,n=4,6,and 8）,when the[C₄mim]Br that had the shortest alkyl chains attached to the imidazole ring was added to the ABS,PEG/K₂HPO₄ ABS has the best extraction performance for Pd（Ⅱ）.Under the optimal extraction conditions,when[C₄mim]Br,[C₆mim]Br and[C₈mim]Br was used as an adjuvant in the PEG/K₂HPO₄ ABS for the extraction of Pd（Ⅱ）,the extraction efficiencies of Pd（Ⅱ）can be increased from 40.3%without additives to 98.2%,97.3%,96.2%,respectively,and the extraction effect is significant.To further explore the distribution mechanism of Pd（Ⅱ）in the ABS,FT-IR and TEM were used to characterize the Pd（Ⅱ）-loaded PEG/[C₄mim]Br-rich phase.The results show that the Pd（Ⅱ）was distributed into the PEG–rich phase containing[C₄mim]Br via an anion exchange reaction,and the electrostatic attractions between the cation C₄mim⁺and anion Pd Cl₄^2-is the main driving force for the migration of Pd（Ⅱ）to the PEG-rich phase.The mechanism was confirmed by the stoichiometry of the extracted species of[2C₄mim⁺·Pd Cl₄^2-].Meanwhile,hydrazine hydrate can completely reduce Pd（Ⅱ）in the PEG-rich phase to metallic palladium.These results established that the PEG/K₂HPO₄ ABS with IL as an adjuvant is a green and efficient extraction system for Pd（Ⅱ）recovery from acidic media.（2）Hydrophobic deep eutectic solvents for extraction of Pt（Ⅳ）and Pd（Ⅱ）from hydrochloric solutionThis study proposes an efficient and environmentally friendly extraction systems for recovering Pt（Ⅳ）and Pd（Ⅱ）,which use hydrophobic deep eutectic solvents（DESs）as green extractant.A series of novel hydrophobic DESs were successively designed and synthesized via the combination of methyltrioctylammonium chloride([N₈₈₈₁]Cl)as HBA and saturated fatty acids or saturated fatty alcohols as HBDs.Then,the DESs were used for extraction and separation of Pt（Ⅳ）and Pd（Ⅱ）from hydrochloric acid solution.In this study,the factors affecting the extraction efficiency of Pt（Ⅳ）and Pd（Ⅱ）were systematically optimized.The results show that the DESs based on alcohol and acid have excellent performance for extracting Pt（Ⅳ）and Pd（Ⅱ）.Under optimal conditions,the extraction efficiency of the five DESs(N₈₈₈₁Cl:ethylene glycol（1:1）,N₈₈₈₁Cl:glycerol（1:1）,N₈₈₈₁Cl:1-hexanol（1:1）,N₈₈₈₁Cl:propionic acid（1:2）,N₈₈₈₁Cl:hexanoic acid（1:2）)for Pt（Ⅳ）and Pd（Ⅱ）all exceeded 99%.FT-IR,UV-vis and ~1H NMR spectral characterizations confirm that the extraction mechanism of Pt（Ⅳ）and Pd（Ⅱ）follows the anion exchange reaction whereby Pt Cl₆^2-,Pd Cl₄^2-anions in the aqueous phase replace Cl^-anions in DES to form ion-pairs with[N⁺₈₈₈₁]via electrostatic interactions.N₈₈₈₁Cl:1-hexanol（1:1）and N₈₈₈₁Cl:hexanoic acid（1:2）exhibit excellent selectivity for Pt（Ⅳ）and Pd（Ⅱ）over other impurity metal ions.Also,Pd（Ⅱ）in the loaded DES phase was efficiently reduced as elemental palladium via the hydrazine hydrate（80 wt%）reduction method;thus,the DES could be reused for at least 5 cycles of extraction/stripping,the N₈₈₈₁Cl:hexanoic acid（1:2）still maintains excellent Pd（Ⅱ）extraction performance（the fifth time E%>96%）.In addition,hydrophobic DES synthesized was used to separate Pt（Ⅳ）and Pd（Ⅱ）in the actual leaching solution of Jinbaoshan concentrate.The results show that the hydrophobic DESs synthesized are environmentally benign extractants which show good prospects for efficient recovery of Pt（Ⅳ）and Pd（Ⅱ）from hydrochloric solution.（3）Separation of Pd（Ⅱ）from hydrochloric solution by aqueous biphasic systems based on hydrophilic deep eutectic solventTwo novel hydrophilic DESs were successively synthesized via the combination of tetrabutylphosphorus chloride([P₄₄₄₄]Cl)as HBA and propionic acid or butanol as HBDs.The DES/K₂HPO₄ ABS was constructed for the separation of Pd（Ⅱ）from hydrochloric solution.The factors that affect Pd（Ⅱ）extraction（including the DES species,contact time,DES dose,solution p H,original Pd（Ⅱ）concentration,temperature and other factors）were investigated.The results show that the DES-based ABS has excellent extraction for Pd（Ⅱ）from hydrochloric solution.More than 99%of Pd（Ⅱ）can be extracted into the DES-rich phase under optimal conditions.FT-IR and ~1H NMR spectral characterizations confirm that the extraction mechanism of Pd（Ⅱ）follows the anion exchange reaction.The Pd Cl₄^2-anions in the aqueous phase replace Cl^-anions in[P₄₄₄₄]Cl and form ion-pairs with[P⁺₄₄₄₄]via electrostatic interactions.DES-based ABSs show excellent selectivity to Pd（Ⅱ）comparing with other metal impurity ions.Also,Pd（Ⅱ）in the loaded DES phase was efficiently recovered via the Na BH₄.