Extraction behavior of gold(III) from hydrochloric acid solutions by protic ionic liquids

Abstract

Ionic liquids (ILs) with protonated cations were investigated as extraction solvents for gold(III) (5 × 10 -7 to 6 × 10 -4 mol dm -3) in hydrochloric acid (0.1 to 4 mol dm -3) at 25°C. The protic ILs used were salts of bis(trifluoromethanesulfonyl)amide ([NTf 2 ] -) with 1-butylimidazolium ([BImH] +), 1-butylpyrrolidinium ([BPyrH] +), and trioctylammonium ([TOAH] +). The extractability of gold(III) increases with decreasing hydrochloric acid concentration and with increasing gold(III) concentration. The gold(III) extracting ability of the ILs follows the sequence [TOAH][NTf 2 ] > [BImH][NTf 2 ] > [BPyrH][NTf 2 ]. Almost quantitative extraction is possible from a 0.10 mol dm -3 hydrochloric acid solution with a 1/10 volume of [TOAH][NTf 2 ]. From equilibrium analysis, it is suggested that gold(III) is extracted as electrically neutral species, [AuCl 3 ] and [Au 2 Cl 6 ]. The equilibrium constants for the reactions [AuCl 4 ] - (W) ⇆ [AuCl 3 ] (IL) + Cl - (W) and 2[AuCl 3 ] (IL) ⇆ [Au 2 Cl 6 ] (IL) (W: aqueous phase, IL: IL phase) are determined. The dimerization constant of [AuCl 3 ] is largest in [TOAH][NTf 2 ], which is a main cause for the highest extracting ability of the IL. © 2014 The Japan Society for Analytical Chemistry.