Ionic liquids (ILs) are organic salts with melting points near or below room temperature,which have some unique characteristics,such as high thermal stability,negligible volatility and nonflammability [1].ILs also have been extensively employed as solvent media in the recovery or separation of various metal ions.Moreover,Au is the most important metal element,as well as the non-substitutable and indispensable strategic resource.Recently,the gold(Ⅲ) extractions using ionic liquids as extractants or media have been researched.[2-6] In the present work,ionic liquid,1-hexadecyl-3-methylimidazolium chloride ([C16mim]Cl) is exploited as the extractant of Au(Ⅲ).The amphiphilic structure of [C16mim]Cl can significantly reduce the interfacial tension between the aqueous phase and the organic phase,which may effectively accelerate the extraction.The effects of extraction time and [C16mim]Cl concentration were examined for Au(Ⅲ) extraction.It should be noted that [C16mim]Cl containing a hydrophilic head group and a long-chained hydrophobic tails is a good surfactant to significantly reduce the interfacial tension,which can effectively accelerate the extraction.When the concentration reaches approximately 1.3 g L-1 (the mole ratio of [C16mim]Cl to gold(Ⅲ) is about 1.4:1),the extraction yield remains ~ 99.6%.The anion-exchange mechanism of gold(Ⅲ) extraction by [C16mim]Cl was confirmed by the method of continuous variation.[7] According to Job plot analysis and the spectrum analysis of the IL-Au complex,1:1 associates are formed between Au(Ⅲ) and [C16mim]Cl,meanwhile a stronger interaction exists between AuCl4- and [C16mim]+.Furthermore,[C16mim]Cl is composed of [C16mim]+ cation and Cl- anion,so the anion-exchange mechanism of Au(Ⅲ) extraction was supposed.The Au(Ⅲ) extraction by [C16mim]Cl is deduced as the formation of the neutral complex as [C16mim]+AuCl4-.The extraction reaction of Au(Ⅲ) by the [C16mim]Cl/chloroform system can be given as the following equations: AuCl4-aq+[C16mim]Clor←→[C16mim][AuCl]or+Cl-aq (1) To investigate the selectivity of the [C16mim]Cl/chloroform system to extract Au(III),an aqueous multimetal solution was prepared by adding other chloride metal salts in 0.5 mol L-1 HCl solution.Gold is mainly extracted from the aqueous phase: 98.81% extraction.The [C16mim]Cl/chloroform system has very low distribution coefficients and extraction percentages for the other metal ions: 0.14 and 1.42% for Cu(II),0.23 and 2.27% for Co(II),0.56 and 5.34% for Ni(II),0.50 and 4.79% for Fe(III),0.63 and 5.89% for Al(III),0.44 and 4.19% for Sn(IV).Under the experimental conditions,the [C16mim]Cl/chloroform system shows a high extractability for Au(III),also has high selectivity over some metals (Cu(II),Co(II),Ni(II),Fe(III),Al(III) and Sn(IV)).