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  • Author: R.C. Hubli, x
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Abstract

A novel neutral multidentate ligand NNN′, N′-tetra(2-ethylhexyl) thiodiglycolamide T(2EH)TDGA was synthesized and examined for the extraction of palladium from nitric acid medium. Extraction equilibrium studies showed that almost complete extraction of palladium was obtained within 5 min. The influence of nitric acid, nitrate ion and T(2EH)TDGA concentration on the distribution of palladium has been investigated. With the increase in nitric acid/nitrate ion concentration, increase in extraction of palladium was observed. Stoichiometry of the extracted species was found to be Pd(NO3)2·2T(2EH)TDGA by slope analysis method. Loading studies with 10−3 M T(2EH)TDGA/n-dodecane show maximum uptake of 5.44×10−4 M palladium thus conforming to above stoichiometry of metal to ligand. Acid uptake studies have shown that 1:1 stoichiometry exists between T(2EH)TDGA and HNO3 at nitric acid concentration above 3.5 M. The effect of various diluents on the extraction of palladium was studied and it was found that there is quantitative uptake irrespective of the nature of diluents. More than 99% of palladium was back extracted in single contact using 0.01 M thiourea in 0.1 M nitric acid. Extraction studies with HLLW elements showed negligible uptake of U, Am, Eu, Sr, Cs and Ru.

Abstract

DTDGA solvent system was evaluated for hydrolytic and radiolytic stabilities to ascertain its application in separation and recovery of palladium from High Level Liquid Waste (HLW) solutions. Hydrolysis of DTDGA solvent system was not observed when it was kept in contact with 3.0 M nitric acid solution for two weeks. Moreover, contrary to other ‘S’ donor extractants used for the said purpose, the oxidation of thioetheric sulphur to sulphoxide or sulphones was also not observed. On the other hand, radiolysis of DTDGA solvent system was notably observed, which was found to increase with increase in absorbed dose. At gamma radiation dose of 0.2 MGy, no significant loss of DTDGA was observed. Aliphatic diluent namely n-dodecane was found to have sensitization effect on degradation of DTDGA. The degradation products were identified by GC-MS, the major ones were found to be formed by cleavage of thioetheric and amidic bonds of DTDGA molecule. The liquid–liquid extraction studies of palladium with irradiated solvent indicate that there was no significant change in D Pd up to an absorbed dose of 0.2 MGy above which it decreases gradually. Further, the radiolysis does not affect the stripping behavior of palladium. Extraction studies of Simulated High Level Liquid Waste (SHLW) elements with irradiated solvent system showed that, except palladium, any other element is hardly extracted thus retaining its remarkable selectivity.

Abstract

Hydrolytic and radiolytic stability of T(2EH)TDGA solvent system has been investigated to establish its application in separation and recovery of palladium from High Level Liquid Waste (HLW) solutions. Hydrolysis of T(2EH)TDGA solvent system with nitric acid was not observed. Moreover, unlike other “S” donor extractants used for the said purpose, the oxidation of thioetheric sulphur to sulphoxide or sulphones was also not observed. However, radiolytic degradation was notably observed and found to increase with increase in absorbed dose. n-dodecane was found to sensitize the degradation of T(2EH)TDGA. At gamma radiation dose of 0.2 MGy, no significant loss of T(2EH)TDGA was observed. The degradation products were identified by GC-MS. The major products were found to be formed by cleavage of thioetheric and amidic bonds of T(2EH)TDGA molecule. The extraction studies of palladium with irradiated solvent indicate that with 0.025 M T(2EH)TDGA/n-dodecane, there was no significant change in D Pd up to an absorbed dose of 0.2 MGy above which it decreases significantly. However, with 0.05 M T(2EH)TDGA/n-dodecane, there is gradual decrease in D Pd with increase of absorbed dose. Further, the radiolysis does not affect the stripping behavior of palladium. Extraction studies of Pd(II) and other fission products from simulated high level liquid waste (SHLW) solutions to irradiated solvent system showed that, except palladium, any other element is hardly extracted thus retaining its remarkable selectivity.

Abstract

This paper presents the results of investigations carried out on processing and characterization of CrB2-based novel composites. Niobium metal powder was used as additive to form new composites. Hardness and fracture toughness of chromium boride increased by addition of niobium. CrB2 composites were prepared by addition of 2.5, 10 and 20 wt.% Nb. Density of higher than 95% ρ th was achieved in all the samples. Hot pressed samples were analyzed to contain reaction products of NbB2, Cr2B3 and Cr3B4 phases along with CrB2. Hardness of CrB2 composite was increased from 18.46 GPa to 21.89 GPa by increasing the Nb content from 2.5 to 10 wt.%. Fracture toughness of composites prepared by addition of 2.5 and 10% was measured as 3.11 and 3.38 MPa.m1/2 respectively. Addition of 20% Nb resulted in increased fracture toughness of 4.32 MPa.m1/2 .