Extraction of palladium with thiacalix[4]arenes from nitric acid nitrate-nitrite solutions

Abstract

Calix[4]arene 1, thiacalix[4]arenes 2(LH4), and calix[4]arenethioether 3 were compared in palladium extraction from nitric acid solutions; DPd for 2 was shown to be 2–3 orders of magnitude larger than for 1 at pH > 3 (comparable with 3) because of cation-exchange and coordination extraction of palladium. It was shown by extraction methods and IR spectroscopy that thiacalixarenes 2 extract complex species [PdnLmH4 − 2n] (m = 1, n = 1 and 2) and [(PdA2)nLmH4] (A = m = 1, n = 1–4) from nitric acid solutions at pH 3. Extraction constants for these palladium species that satisfactorily describe experimental data were calculated. As distinct from 3, thiacalixarenes 2 are promising for the combined extraction of palladium and silver from alkaline solutions and the selective extraction of fission palladium from nitric acid solutions. Phosphorylated at the upper rim thiacalixarenes 2 can be considered as bifunctional extractants for the separation of fission radionuclides.