Upper-rim modified thioether thiacalix[4]arene used for liquid–liquid extraction of Au(Ⅲ) and Pd(Ⅱ) in hydrochloric acid medium

Gold (Au) and palladium (Pd) play an increasing role in the production and human life, therefore, it is of great significance to study their recovery. A 5,11,17,23-tetra-ethylthio-25,26,27,28-tetra-hydroxyl thiacalix[4]arene (TCAET) was synthesized specifically for the capture of Au(Ⅲ) and Pd(Ⅱ) from HCl medium by liquid–liquid extraction. In a 0.1 mol·L –1 HCl medium, the transfer of Au(Ⅲ) and Pd(Ⅱ) from the aqueous phase to the organic phase was highly efficient, with a transfer ratio of 100% for Au(Ⅲ) and 98% for Pd(Ⅱ). Furthermore, the extraction equilibrium time for Au(Ⅲ) was just 5 min. Job's method data demonstrated that TCAET formed complexes with Au(III) and Pd(II) in a ratio of 2:3 and 1:1, respectively, during the extraction process. TCAET showed high selectivity toward Pd(II) and Au(III) over other competing metal ions. Moreover, both Au(Ⅲ) and Pd(II) could be successfully stripped from the loaded organic phases with a 1.0 mol·L –1 thiourea in 0.5 mol·L –1 HCl and 0.5 mol·L –1 thiourea in 0.5 mol·L –1 HCl, respectively. Results obtained from five consecutive extraction-stripping cycles showed good reusability of TCAET toward Au(Ⅲ) and Pd(Ⅱ) recovery. The conclusion can provide a certain reference for thiacalixarene in the recovery of precious metal species.