Extraction and Complexation Investigation of Palladium(II) by a Nitrilotriacetate-Derived Triamide Ligand

Abstract

Effective and selective separation and recovery of the fission product palladium from high-level liquid waste are conducive not only to reducing its hazards to the public health and environment but also to alleviate the pressure on the increasing demand for natural palladium. Herein, the Pd 2+ extraction in an HNO 3 solution with a nitrilotriacetate-derived triamide ligand NTAamide(n-Oct) and the complexation between them were investigated. Using n-octanol as a diluent, NTAamide(n-Oct) demonstrated an excellent selectivity, strong extractability, and high loading capacity for Pd 2+ extraction. Combined with the results of single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, electrospray ionization-mass spectroscopy, microcalorimetric titration, and slope analysis, the extracted complexes were determined as [PdL 2 ](NO 3 ) 2 and [PdL 2 ][Pd(NO 3 ) 4 ] (where L denotes the NTAamide ligand) in 0.10 and 3.0 mol/L HNO 3 solutions, respectively. The extraction model closely depended on the solvation state of Pd 2+ in the HNO 3 solution. An ion-pair extraction model was proposed and discussed.

Efficient and Selective Removal of Palladium from Simulated High-Level Liquid Waste Using a Silica-Based Adsorbent NTAamide(C8)/SiO2-P

“…However, due to the stronger characteristic peak of Si-O-Si at 1108 cm −1 , the double peaks become a wider peak. After adsorption, the characteristic peaks are slenderer, indicating that the tertiary amine structure may coordinate with Pd(II), which is consistent with the composition of NTAamide(C8)/SiO 2 -P. According to the relative literature [ 22 , 42 ], the 2:1 ligand/Pd 2+ complexes were formed in a low concentration of HNO 3 solution. Two NTAamide(C8) ligand molecules coordinated with one four-coordinated Pd 2+ via one of the three carbonyl groups and the central N atom, forming a complex cation.…”

“…Two NTAamide(C8) ligand molecules coordinated with one four-coordinated Pd 2+ via one of the three carbonyl groups and the central N atom, forming a complex cation. There are two NO 3 − ions anion as the counterpart ions for charge balance, and the NO 3− ions only have a salting-out effect on the ligands under this condition [ 22 ]. The single peak originally located at 1650 cm −1 was split into two peaks at 1650 and 1595 cm −1 , which is also consistent with the adsorption mechanism.…”

“…Sasaki et al [ 21 ] used NTAamide(C8) to recover Pd(II) through extraction electrodeposition, and the extraction rate could reach above 91% in all cycles. Wang et al [ 22 ] studied the extraction ability of NTAamide(n-Oct) for Pd(II) and confirmed its good selectivity, extraction efficiency, and loading capacity. Sasaki et al [ 23 ] studied the extraction behavior of NTAamide(C8) for 70 metals and found that the extraction rate for Pd(II) was the highest, indicating that NTAamide(C8) had good selectivity for Pd(II) and could be used to separate Pd(II) from multi-element mixed solutions, such as HLLW.…”

Efficient Extraction in High-Acidity HNO3 Solution for Selective Separation of Am3+ Over Eu3+ by Amine-Diamide Ligands

“…In the spectrum of pure L III ligand, the absorption band at 1650 cm –1 can be attributed to the stretching vibration of amide-carbonyl (CO) . After the formation of the L III -Eu extracted complex, this characteristic absorption band is split into two peaks at 1662 and 1633 cm –1 , suggesting that the CO group participates in the coordination with Eu 3+ . Besides the DAMIA ligand during the extraction process, the NO 3 – ion can also interact with Eu 3+ by means of playing as either a ligand to coordinate with Eu 3+ or a counterion to balance the charge of the coordinated Eu 3+ .…”

“…38 After the formation of the L III -Eu extracted complex, this characteristic absorption band is split into two peaks at 1662 and 1633 cm −1 , suggesting that the C�O group participates in the coordination with Eu 3+ . 39 Besides the DAMIA ligand during the extraction process, the NO 3 − ion can also interact with Eu 3+ by means of playing as either a ligand to coordinate with Eu 3+ or a counterion to balance the charge of the coordinated Eu 3+ . In the spectrum of the L III -Eu complex, there are two characteristic absorption bands at 1297 and 1482 cm −1 , which can be assigned to the symmetric and asymmetric stretching vibration of the coordinated NO 3 − , respectively.…”