Thermodynamic Modeling of Extraction Equilibria of Platinum and Palladium with Nonylthiourea from Hydrochloric Acid Media

Abstract

Models of extraction equilibria of Pt(IV) and Pd(II) with Nonylthiourea (NTH) from HCl media have been studied. The conditional equilibrium constants and the stoichiometry of the extracted species of Pt(IV) with NTH at different ionic strengths obtained by numerical analysis using the LETAGROP‐DISTR program are reported. The dependence of the extraction constant values on the ionic strength has been analysed using the Specific Interaction Theory (SIT), from which the respective thermodynamic equilibrium constants of the extraction of Pt(IV) and Pd(II) with NTH have been determined. The thermodynamic equilibrium constants determined for Pt(IV) are log K ₁₁ ^o  = 5 ± 1 and log K ₁₄ ^o  = 14.6 ± 0.2, while for Pd(II) log K ₁₁ ^o  = 4.9 ± 0.1 and log K ₁₂ ^o  = 9.17 ± 0.08. The interaction coefficients, ϵ, for the pairs (H ⁺, PtCl ₆ ²⁻) and (H ⁺, PdCl ₄ ²⁻) have also been estimated to be 0.30 ± 0.08 and 0.41 ± 0.02, respectively.

Keywords:

• Platinum
• Palladium
• Thermodynamic modeling