Synthesis And Study On Gold Extraction Of Gemini-benzimidazolium Ionic Liquids

Based on the current situation of resource shortage and increasingly serious environmental pollution,low-carbon environmental protection and efficient recycling of limited resources have become the focus of attention.In view of its wide application and limited reserves,the recovery and recycling of gold become more important.Liquid-liquid extraction is widely used in gold recovery due to its advantages of simple operation,automation,and continuity.However,use of traditional organic solvents is limited by their high toxicity and low selectivity for gold.Therefore,use of ionic liquids as a green and stable organic salt to replace traditional extractants is one of the current research hotspots.Imidazole ionic liquids have higher ionic conductivity and lower viscosity than pyridine,quaternary phosphines and quaternary ammonium ionic liquids due to high charge delocalization.However,there are few studies on benzimidazolium ionic liquids similar to imidazole ionic liquids,and there are fewer studies on the synthesis and extraction of gemini-benzimidazolium ionic liquids.In view of this,we explored the synthesis of gemini-type benzimidazolium ionic liquids and applied them to gold extraction,providing a theoretical basis for developing more efficient functionalized ionic liquids.First,we systematically studied the synthesis of gemini-benzimidazolium ionic liquids.nine ionic liquids were synthesized:N,N’-dialkyl gemini-benzimidazolium ionic liquid:[C4-6-C4BIm]Br2,[C8-6-C8BIm]Br2,[C4-4-C4BIm]Br2;protic gemini-benzimidazolium ionic liquid:[H-4-HBIm]Br2,[H-6-HBIm]Br2;Tf2N gemini-benzimidazolium ionic liquid:[C4-4-C4BIm](Tf2N)2,[C4-6-C4BIm](Tf2N)2,[H-4-HBIm](Tf2N2),[H-6-HBIm](Tf2N)2.The synthetic ionic liquids were characterized by nuclear magnetic resonance spectroscopy and mass spectrometry.Then,for the gemini-type benzimidazolium ionic liquids,in order to study its application potential in the field of extraction,we used gold as the target metal and the ionic liquid[C4-6-C4BIm]Br2 to extract gold(Ⅲ)from hydrochloric acid medium.The effects of extractant concentration,sodium chloride concentration,sodium bromide concentration and initial metal ion concentration on the extraction efficiency were investigated in detail.The mechanism between[C4-6-C4BIm]Br2 and Au(Ⅲ)was proven by 1H NMR spectra FT-IR spectra and Job’s method.At the same time,quantum chemical calculations were carried out to evidence the mechanism theoretically.The equilibrium,thermodynamic and kinetic models of Au(Ⅲ)extraction were also studied,which has a high reference value for predicting and guiding the extraction behavior of Au(Ⅲ)in industrial applications.Finally,we also explored the selectivity of this extractant for gold extraction.The results show that[C4-6-C4BIm]Br2 is an efficient extractant,and a small amount of[C4-6-C4BIm]Br2 can obtain excellent extraction efficiency.In addition,in view of the better hydrophobic properties of Tf2N gemini-benzimidazole ionic liquids,we selected the ionic liquid[C4-4-C4BIm](Tf2N)2 to study its performance in extracting gold from hydrochloric acid medium.The effects of extractant concentration,sodium chloride concentration,hydrochloric acid concentration and initial metal ion concentration on extraction efficiency were investigated in detail.The mechanism of gold(Ⅲ)extraction was studied according to FT-IR and Job’s method.Furthermore,the mechanism is verified from the perspective of theoretical calculation.It was found that this type of ionic liquid also has excellent extraction performance,and due to its good stability and hydrophobicity,it will have broad application prospects in the extraction field.