Dialkylmethyl-2-(N,N-diisobutyl)acetamidoammonium iodide as a ruthenium selective ligand from nitric acid medium
Graphical abstract
Introduction
Ruthenium is one of the most hazardous fission products contained in the highlevel radioactive waste (HLW) due to high fission yield and relatively shorter half lives of its isotopes (103Ru: 39.27 d, 106Ru: 1.02 y) resulting in high specific activity [1]. It is also the most difficult fission product to separate from high level radioactive waste due to its variable valences at different nitric acid concentrations. Ru is of particular interest because it contributes largely to beta and gamma activity of the waste and its tendency to form volatile tetroxide during vitrification [2]. Due of these reasons, ruthenium needs to be separated from the waste to make it amenable for disposal.
Certain problems usually encountered during treatment of nuclear waste solutions due to the presence of ruthenium. It forms a series of nitro–nitrato complexes at different concentrations of nitric acid which are partially extractable by tributyl phosphate (TBP) during purex process and are difficult to strip. This results in residual radioactivity in the spent solvent [3], [4]. During vitrification of the HLW, ruthenium gets oxidized to volatile tetroxide RuO4 which gets deposited as RuO2 on contact with steel surface leading to hot spots on the wall of the inner surface. This also causes corrosion at the inner steel surface [5]. One of the isotopes of ruthenium, 106Ru, also has application in radiotherapy of tumors [6], [7], [8], [9].
Solvent extraction is a well known practice for separation of radionuclides from waste solution. The success of the process mainly depends on the efficiency of the solvent. Suitable solvents for ruthenium are scantly reported specially from nitric acid medium. Two solvents, namely, TBP and tetrahexyl ammonium iodide (THexI) have been reported for this purpose [10], [11]. These solvents have different extraction behavior and have been reported with lower distribution ratio (D) values as ∼1.0 (1.0 M HNO3) and 0.5 (1.5 M HNO3) for 30% TBP/kerosene and 0.2 M THexI/methylisobutylketone, respectively. Tertiary amines and quaternary ammonium salts are widely used for extraction of ruthenium [11], [12], [13], [14], [15]. Maeck et al. [11] have reported the extraction of ruthenium from nitric acid medium using THexI, where iodide ion enhanced the extraction process among halides. Considering this fact, we have chosen a quaternary ammonium iodide in our designed principle. A specially designed alkyl appendage, 2-(N,N-dialkyl) acetamide was incorporated in to the quaternary ammonium center to increase the solubility of the metal-ligand complex in the organic phase as well as to enhance extractability at higher acidity utilizing the buffering property of the dialkyamido group [16], [17], [18], [19]. This paper describes the synthesis and extraction behavior of a new class of quaternary ammonium iodide based ligands 1–3 with 2-(N,N-diisobutyl)acetamide as an alkyl appendage (Fig. 1).
Section snippets
Chemicals
Nitric acid, n-dodecane and isodecyl alcohol (IDA) were obtained from local sources. Diisobutylamine, dioctylamine, dihexylamine, dipropylamine, ruthenium nitrosyl nitrate, methyl iodide and other chemicals used were of analytical grade. The solvents were dried and distilled from the indicated drying agents: THF from sodium/benzophenone; triethyl amine from CaH2 and then stored over calcium metal. Analytical thin layer chromatography was performed using silica gel plates (about 0.5 mm) and
Determination of organic phase composition
Considering the polar nature of ligand, metal-ligand complex and their poor solubility in n-dodecane, IDA has been chosen as a phase modifier to mitigate the third phase formation [20], [21]. In order to find out the most suitable solvent composition, extraction studies were carried out at different concentrations of IDA in n-dodecane at 1 M HNO3. The ligand 1 was initially chosen to optimize the extraction conditions. The solubility of ligand was very poor in n-dodecane and low when the IDA
Conclusions
In conclusion, trialkyl-[2-(N,N-diisobutyl)acetamido]ammonium iodides, have been designed and synthesized as a new class of quarternary ammonium based ligands to extract ruthenium selectively from nitric acid medium. Ruthenium was extracted in the form of an iodide complex only. Stoichiometry of extracted complex as determined by slope analysis method showed 1:1 ratio for metal to ligand. The role of anionic part of the ligand was found to be very new and interesting in this study. The ligand
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Cited by (9)
Ruthenium speciation in radioactive wastes and state-of-the-art strategies for its recovery: A review
2021, Separation and Purification TechnologyCitation Excerpt :The change in the order of extraction by with the aqueous phase acidity can be rationalized by considering steric hindrance and ligand protonation. The quaternary ammonium amide ligands viz. 2-(N,N-diisobutyl)acetamido ammonium iodide/nitrate (XVI-XIX)were also investigated for Ru uptake from nitric acid solutions and the results were quite encouraging [118]. Maximum Ru extraction was seen with XVI into 0.2 M extractant solution giving a DRu value of 13.38 at 1.5 M HNO3.
Ruthenium recovery from alkaline radioactive feeds using an extraction chromatography resin containing Aliquat 336
2021, Separation and Purification TechnologyCitation Excerpt :Also, due to the good solubility of RuO4 in organic diluents, there is a possibility of partitioning of Ru into the organic phase in solvent extraction operations [7,8]. There is a recent spurt in research activity related to Ru separation from radioactive feeds [9–12]. Though most of the recent reports are focused on Ru separation from acidic feeds, mainly those concerning high level waste (HLW), there is very little work reported on the separation of Ru from alkaline feeds, which can be an intermediate level waste (ILW) or a low level waste (LLW).
Recovery of Ru(III) from hydrochloric acid by cloud point extraction with 2-Mercaptobenzothiazole-functionalized ionic liquid
2017, Chemical Engineering JournalCitation Excerpt :However, the scarce availability of Ru(III) could not meet the continually expanding demand, and the spent Ru(III) containing materials also pose potential environmental risk [10]. In this context, recovery and separation of Ru(III) from spent catalysts or waste liquor using high-efficiency extractant is urgently required [11]. Recently, huge research efforts have been devoted to recover and separate Ru(III) with conventional extractants (e.g., TBP [12], N,N′-Dimethy-N,N′-Dicyclohexylmalonamide [13], tertiary, quaternary [14], n-paraffin hydrocarbon [15], Cyanex 923 [16], o-methoxyphenyl thiourea [17], etc.).