Extraction Equilibrium of Palladium in Aqueous Acid Solution with Di(2-Ethylhexyl) Amine in Toluene

Extraction equilibria of hydrochloric acid by toluene solution of a long-chain secondary alkyl amine, di(2-ethylhexyl) amine, and of palladium from aqueous hydrochloric acid by the toluene solution of the amine were studied under various experimental conditions. The results were analyzed by the following reaction model: (BHCl)2 + PdCl42– = (BH)2PdCI4 + 2Cl– (1) 2(BHCl))2 + PdCl)42– = (BH)2PdCl4(BHCl)4 + 2Cl– (2) Water content and IR spectra for alkyl ammonium chloride salt solution equilibrated with aqueous palladium chloride solution were also measured to estimate the complexes formed by the reactions. The amine reacts with hydrochloric acid to form dimer of ion-paired ammonium chloride salt together with water as (BHCl)2(2/3)H2O. The results for the extraction equilibrium of palladium by the amine were interpreted by a reaction model in which two kinds of ion-paired species (BH)2PdCl4 and (BH)2PdCl4(BHCl)2 are formed. Water dissolved in the organic solution was confirmed not to take part in the formation of the complexes. The equilibrium constants for reactions (1) and (2) were determined as 1.0 × 102 and 2.6 × 104 m3/kmol respectively.