Mechanism of Palladium(II) Adsorption from Nitric Acid Solutions by a Styrene-Divinylbenzene Copolymer Functionalized with N,N,N-Trimethylglycine

The ability of AMP03, a styrene-divinylbenzene copolymer functionalized with N,N,N-trimethylglycine moieties, to adsorb Pd(II) from HNO3 solutions was investigated to elucidate the affinity of N,N,N-trimethylglycine for Pd(II). AMP03 effectively adsorbed Pd(II) from 0.10-0.50 M solutions in HNO3, and the adsorption ability decreased with increasing HNO3 concentration owing to competitive adsorption of the acid. In contrast, the presence of added NO3- increased the Pd(II) adsorption ability of the copolymer. On the basis of slope analysis of data for Pd(II) and HNO3 at adsorption equilibrium, the Pd(II)/NO3-/ligand stoichiometry of the adsorbed Pd(II) species was determined to be 1 : 2 : 1. Structural studies performed by means of Fourier transform infrared spectroscopy and extended X-ray absorption fine structure spectroscopy revealed that the N,N,N-trimethylglycine moieties on AMP03 and NO3- coordinated to Pd(II) via their oxygen atoms. The adsorption selectivity of AMP03 for Pd(II), Ni(II), Cu(II), and Fe(III) was compared with the selectivities of commercially available carboxylic acid and iminodiacetic acid resins. AMP03 selectively adsorbed Pd(II) over Ni(II), Cu(II), and Fe(III) compared with that of the other resins. Our results suggest that AMP03 can be used for selective recovery of Pd(II) from HNO3 solution.