[en] Extraction behaviors of Pd(II) in the TRUEX and PUREX solvent extractions were studied by using octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide. The effect of scrubbing in the TRUEX solvent extraction was demonstrated by adding oxalic acid. The distribution ratios of palladium (D_Pd's) in the diluted region of [HNO₃] were found to depend strongly on the fraction of cationic species, Pd(NO₃)⁺, existed in the aqueous phase. The gradual decrease of D_Pd with the increase of acidity beyond [H⁺] ∼ 1 mol x dm^-3 was controlled by the formation of the anionic species Pd(NO₃)₃^-. (author)