Extraction of triaquatrinitrorhodium form with calix[n]arenethiaethers from nitric acid nitrite–nitrate solutions

Abstract

Comparison of extraction properties of macrocyclic calix[4,6]arenethiaethers (CATE) with their acyclic analogs R₂S (R = C₆H₁₃, C₈H₁₇) for the recovery of [Rh(NO₂)₃(H₂O)₃]⁰ rhodium form from nitric acid solutions was carried out. Rhodium recovery with CATE (0.05 M) in the absence of accelerating additives under optimal conditions exceeds 90% at 5–10-fold preconcentration and is only 1–3% for R₂S (1 M). Extraction kinetics was studied and hypothesis on the mechanism of multiple acceleration of rhodium recovery was proposed for CATE extraction, the mechanism includes the formation of intermediate product of colloidal- chemical nature on account of the surface activity of the macrocycle and its reaction with rhodium accompanied by rhodium chelation to the sulfur atoms of neighboring fragments of the macrocycle. The obtained results are of interest for the development of methods for the isolation of fission rhodium from nitrate–nitrite nitric acid solutions.