Study on extraction of Rh(III) by DABCO-based ionic liquid from hydrochloric acid medium

Abstract

Rhodium, as a rare precious metal, has always been a challenge for the chemical industry to efficiently recover rhodium by extraction due to the complex existing situation in hydrochloric acid medium. Herein, a strongly hydrophobic DABCO-based ionic liquid (IL) [C8DABCO][NTf2] was designed and synthesized to construct a solvent-free extraction system of Rh(III) from high-concentration hydrochloric acid medium. At first, the effects of some important parameters on Rh(III) extraction were studied, such as equilibrium time, IL dosage, hydrochloric acid concentration, and initial Rh(III) concentration, the results showed that 81.54% Rh(III) can be extracted under the optimum extraction conditions. Based on the experimental run results, a quadratic model equation was established by using the response surface method (RSM), which can be used to calculate the amount that [C8DABCO][NTf2] will be offered at various HCl concentrations during the actual extraction of Rh(III). Then, using Job's method, the Ultraviolet visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDS), and Electrostatic potential (ESP) prove that the extraction mechanism is an anion exchange mechanism. Finally, in the mixed solution of multi-metals, the extraction efficiency of [C8DABCO][NTf2] for Rh(III) is not disturbed, and the extraction efficiency for other metals is less than 1%. And the single-stage stripping efficiency of Rh(III) was up to 88% through HCl stripping, which solved the problem of difficult stripping of Rh(III) solution and realized the recycling of IL. The study provides a reliable and efficient way for recovering Rh(III) from high-concentrations HCl solutions.