N,N,N′,N′-Tetra(2-Ethylhexyl) Thiodiglycolamide T(2EH)TDGA: A Promising Ligand for Separation and Recovery of Palladium from High Level Liquid Waste (HLLW) Solutions

Abstract

The extraction properties of N,N,N 0 ,N 0 -tetra(2-ethylhexyl)thiodiglycolamide T(2EH)TDGA have been evaluated for the separation and recovery of palladium from simulated high-level liquid waste (SHLW). T(2EH)TDGA has shown very high selectivity for Pd (II) over other metal ions present in SHLW. The separation factor (SF) for Pd (II) over other metal ions was found to be more than 10 5 . Reusability studies of the extractant indicate that D Pd remained almost constant even after five successive cycles of extraction and stripping. Palladium was quantitatively recovered from thiourea strip solution by treating it with ammonia and filtering the precipitate of palladium sulphide. The acid uptake constant (K H ) was found to be 0.62 which could be due to the presence of two carbonyl groups of amidic moiety. To account for very high extractability of palladium with T(2EH)TDGA over other 'S' donor extractants, namely Bis-(2-ethylhexyl)sulphoxide (BESO), FTIR, as well as Raman studies were carried out. FTIR and Raman studies suggested the ligation through carbonyl as well as the thio-ether group. Conditional extraction constants (log K 0 ex ) were determined and the thermodynamic parameters were calculated from the dependence of the conditional extraction constant (log K 0 ex ) on temperature. The calculated values of DG ex , DH ex , and DS ex were À41.78 kJmol À1 , À55.12 kJmol À1 and À44.04 JK À1 mol À1 respectively. The extraction process is indicated to be enthalpy driven with the entropy factor counteracting it.

Facilitated transport of Pd(II) through a supported liquid membrane (SLM) containing N,N,N′,N′-tetra-(2-ethylhexyl) thiodiglycolamide T(2EH)TDGA: A novel carrier

“…Among various extractive ligands used in extraction of palladium from HLW, T(2EH)TDGA was found to be most promising in view of its high extractability and selectivity over other metal ions [14,15]. However, this extractant has not been studied for membrane systems till now.…”

“…Based upon this presumption several extractants, namely, tertiary and quaternary amines [7,8], ␣-benzoin oxime (ABO) [9], dioctyl sulphides [10], trialkylphosphine sulphide (TIPS) [11], bis-(2-ethylhexyl) sulphoxide (BESO) [12] and benzoylmethylene triphenylphosphorane (BMTTP) [13], have been developed at various laboratories. Recently, a novel ligand of the class thiodiglycolamides, namely, N,N,N ,N -tetra(2-ethylhexyl)thiodiglycolamide (T(2EH)TDGA) has been synthesized in our laboratory and studied for extraction behavior of palladium from simulated high level waste (SHLW) solution [14,15]. The extractant has shown very high extractability and selectivity for palladium over other metal ions present in SHLW.…”

Adsorption Behaviors of Platinum Group Metals in Simulated High Level Liquid Waste Using Macroporous (MOTDGA-TOA)/SiO2-P Silica-based Absorbent

“…In recent years, a new type of thiodiglycolamide extractants (e.g., N,N 0 -dimethyl-N,N 0 -di-n-octyl-thiodiglycolamide (MOTDGA) (12), N,N,N 0 ,N 0 -tetra-n-octyl-thiodiglycolamide (TOTDGA) (13) or N,N,N 0 ,N 0 -tetra-(2-ethylhexyl)-thiodiglycolamide (T(2EH)-TDGA) (14,15)) were developed and their high selective ability for Pd(II) were reported. It was shown that use of both a thiodiglycolamide of MOTDGA and amine type extractant could improve the extraction ratio of Ru and Rh, leading to the extraction ratio of a combined extraction system using two extractants larger than summation of each extraction ratio which were obtained independently (16).…”

Studies on the Separation and Recovery of Palladium from Simulated High Level Liquid Waste (SHLW) Solution with Novel ExtractantN,N,N′,N′-tetra (2-ethylhexyl) Dithiodiglycolamide DTDGA

“…However, these extractants suffer from various limitations, such as slow kinetics of extraction, instability in nitric acid medium, poor decontamination factor, and poor solubility in n-paraffinic diluents. Earlier, we have synthesized a novel ligand of the class thiodiglycolamides, namely, N,N,N 0 ,N 0 -tetra(2-ethylhexyl)thiodiglycolamide T(2EH)TDGA and studied its extraction behavior for palladium and some of the fission products in nitric acid medium (15)(16)(17). T(2EH)TDGA was found to be hydrolytically as well as radiolytically stable and therefore, can be used for the separation and recovery of palladium from HLW (18).…”