Interphase distribution of palladium(II) different-charged chloride complexes in extraction systems based on liquid anion exchangers

Abstract

The extraction of palladium(II) different-charged chloride acid complexes was investigated depend- ing on structure of the liquid anion exchanger in chloroform and the concentration of ligand. Extractants 0.1 M solutions of primary alkylamine nitrates were studied (using n-dodecylammonium as an example), extrac- tants tertiary alkylamines were also used (dimethyl-n-dodecylammonium and tri-n-octylammonium (TOA) as an examples). The differentiation of the extraction behavior of liquid anion exchangers of various structures during the extraction of palladium(II) mixed-charge chloride complexes has been established. In concentrated chloride solutions with a ratio of [Pd²⁺] /[Cl^–] = 1:1700, where [PdCl₄]^2– is in equilibrium with high charged acid complexes (HCAC) [PdCl₅]^3–, [PdCl₆]^4–, the behavior of 4-n-dodecylammonium and dimethyl-n- dodecylammonium is approximately equivalent (R = 74 and 68%).

Higher degree of extraction compared with three-n-octylammonium (R = 28%) is observed for these extractants. The reducing of tertiary alkylamine radicals volume by replacing of two alkyl radicals with me- thyl ones makes it possible to reduce steric factors and to use different-radicals tertiary alkylamines to extract HCAC of palladium(II) that was not previously used for these purposes. An increase in the concentration of the extractant dimethyl-n-dodecylammonium to 0.2 mol / dm³ leads to the complete extraction of the analyte. In the system with the ratio [Pd²⁺] / [Cl^–] = 1:4 TOA extracts palladium(II) by 58% from the aqueous phase. The separation of anionic forms of palladium in chloride solutions was established by extraction and molecu- lar absorption spectrophotometry. The absorption maximum of palladium associates with n- dodecylammonium and dimethyl-n-dodecylammonium in the extracts and the aqueous phase is at λ = 470nm. In the absorption spectrum of TOA associate with a maximum is observed at λ = 430 nm, which is a cha- racteristic of low-charged acid complex. The composition [C₁₂H₂₅(CH₃)₂NH]₃PdCl₅ of palladium(II) asso- ciate with dimethyl n-dodecyammonium in the organic phase was established by the methods of equilibrium shift and molecular absorption spectrophotometry.