Yu. S. Krylov

Extraction methods in development of Gd-loaded liquid scintillators for detection of low-energy antineutrino: 1. gadolinium extraction with carboxylic acids

A comparison was made of the properties of solvents meeting the requirements posed on Gd-loaded organic liquid scintillators (transparency, light output, compatibility with the structural materials of the detector). The optical properties of the solvents were examined in relation to various factors (purity of the initial reagents, concentrations of Gd and scintillation additives). Extraction of Gd with C4 C8 carboxylic acids was examined. The composition of the extractable Gd complexes with 2-methylvaleric and 2-ethylhexanoic acids, GdR3·3HR·mH2O (where m = 1–2, depending on the solvents used), was determined. The solubility of water in 2-ethylhexanoic and 2-methylvaleric acids was examined. Scintillators based on Gd 2-methylvalerates have better parameters than those based on the other carboxylic acids tested. The instability of the optical properties of the Gd carboxylate solutions is presumably due to the presence of water in the scintillator. Possible methods of water removal from the organic phase were discussed.

Exhaustive removal of thorium and uranium traces from neodymium by liquid extraction

The Th content in commercially available Nd2O3 samples with the main substance content of 99.0–99.998% was found to be 2–8, and that of U, 3–230 ppb. Therefore, to obtain Nd meeting the requirements of the experiment on studying neutrinoless double β-decay, it should be purified to reduce the content of Th and U impurities by a factor of 103–104. To this end, the extraction of Nd, Th, and U from hydrochloric acid media with solutions of trioctylphosphine oxide (TOPO) in toluene was studied. The distribution ratios of Th increase with a decrease in the HCl concentration in the initial aqueous solution. With an increase in the Cl− concentration in the aqueous phase, the U distribution ratios decrease, probably because of a decrease in the concentration of the free extractant due to the extraction of Nd and HCl. On the contrary, the distribution ratios of Th increase with an increase in the Cl− concentration in the aqueous phase, with the slope of the straight line in the coordinates logDTh-log[Cl−]aq close to 7, which may be due to coextraction of Th with Nd in the form of the complex ThNdCl7. The enthalpies of formation of the extractable complexes of Th and U were determined from the temperature dependence of the extraction of Nd, Th, and U chlorides with a 0.1 M solution of TOPO in toluene. The optimal extraction system was chosen for Nd purification to remove traces of Th and U: organic phase, 0.1 M solution of TOPO in toluene; aqueous phase, 2.4 M NdCl3 + 0.1 M HCl. From the initial aqueous solution contaning 574 ppt Th and 2837 ppt U, by single extraction with an equal volume of 0.1 M TOPO in toluene, an aqueous solution containing <10 ppt Th and 31 ppt U (detection limit 10 ppt) was obtained. By semicountercurrent extraction, from the initial aqueous NdCl3 solution containing 200 ppb Th, the raffinate containing <10 ppt Th was obtained in one extraction step. The results obtained confirm the possibility of exhaustive removal of Th and U impurities (to the level of ≤1 ppt) from Nd by extraction with TOPO solutions from chloride solutions.

Scintillators Based on Ytterbium Chloride Adducts with Neutral Organophosphorus Extractants for Detecting Solar Neutrino for LENS (Low-Energy Neutrino Spectroscopy) Experiment

The main features of extraction of ytterbium chloride with dibutyl butylphosphonate (DBBP) and triisoamylphosphine oxide (TIAPO) were studied. The effects of temperature, DBBP and TIAPO concentrations in 1,2,4-trimethylbenzene (TMB), and concentrations of salting-out agents LiCl and NH4Cl and mineral acid (HCl) on the ytterbium distribution coefficient were determined. The isotherms of extraction of HCl and YbCl3 with 50% DBBP and TIAPO in TMB were obtained. The composition of the extractable complexes of ytterbium chloride with DBBP and TIAPO (S), YbCl3·3S, was determined by saturation and dilution methods. The saturation of 50% solutions of DBBP and TIAPO in TMB with ytterbium chloride was modeled. Two samples of scintillators with ytterbium concentration of 90 g l-1 were prepared, and their physical parameters were measured. The stability of sample properties was tested for 18 months.

Extraction methods in development of Gd-loaded liquid organic scintillators for antineutrino detection: 2. Scintillators based on solutions of gadolinium 2-methylvalerate

Complexes of Gd with carboxylic acids C4–C9 were prepared, and their properties were studied: solubility in water and organic solvents in relation to temperature, melting points, and decomposition points. A procedure was developed for removing water from gadolinium 2-methylvalerate Gd(2MVA)3 to a final content not exceeding 0.01%. To increase the solubility of Gd(2MVA)3 in low-polarity organic solvents and to stabilize the resulting organic solutions, it was suggested to add extractants such as 2-methylvaleric acid (H2MVA) or neutral organophosphorus compounds: triisoamylphosphine oxide (TIAPO) or trioctylphosphine oxide (TOPO). Liquid Gd-loaded organic scintillators based on Gd(2MVA)3 solutions with additions of H2MVA, TIAPO, and TOPO in trimethylbenzene (TMB), phenylxylylethane (PXE), and their mixtures with dodecane were prepared. Long-term tests (up to 2 years) of the stability of the optical properties of the scintillators obtained proved their stability at temperatures of up to 30°C. At elevated temperatures (40°C and higher), the scintillators degrade. The previously made suggestion that water in the scintillator negatively affects its optical properties in prolonged storage was confirm

Extraction of Sc from various media with triisoamyl phosphate: 2. Extraction of Sc from aqueous perchloric and hydrochloric acid solutions

The extraction of Sc from aqueous perchloric and hydrochloric acid solutions with triisoamyl phosphate (TIAP) was studied. The stoichiometry of the extractable complexes (ScA3 · 3TIAP, A = ClO4/− and Cl−) was determined by the saturation and dilution technique. The isotherms of extraction of Sc from aqueous HClO4 and HCl solutions were obtained. The extraction of impurity metals (Zn, Fe, Mo, Zr, Th, REE) was studied over wide HClO4 and HCl concentration ranges.

An indium-loaded organic liquid scintillator for solar neutrino detection

An organic liquid In-loaded scintillator based on a salt of carboxylic (2-methyl valeric) acid was developed. At an In loading of ∼50 g/l, the scintillator characteristics were as follows: the light yield was 9000 photons/MeV, and the attenuation length was ∼1.5 m. Operation of a 1-m-long optical module used as a detector prototype was demonstrated. The scintillator stability was tested under low-background conditions of an underground laboratory.

Extraction method for preparing indium-containing liquid organic scintillators for solar neutrino detection for LENS experiment, low-energy neutrino spectroscopy

Extraction of In with solutions of 2-methylvaleric acid (H2MVA) in trimethylbenzene (TMB) was studied. Depending on pH of the equilibrium aqueous phase, the extracted indium species are In(2MVA)3 · 3(H2MVA), In(2MVA)3, [In(2MVA)x(OH)3−x]n, etc., where 2MVA is the 2-methylvalerate anion and n is the degree of polymerization. By the extraction method, In-containing liquid organic scintillators (LOSs) with the following parameters were obtained: [In] = 50–96 g l−1, transparency 2–3 m, light output 68% relative to TMB. Long-term precision trials of the scintillators in the Gran Sasso underground laboratory (Italy) confirmed that the scintillator parameters were stable and met the requirements of the LENS experiment. A procedure was developed for preparing solid anhydrous indium hydroxycarboxylates, and their properties were studied. LOSs based on solutions of solid indium hydroxycarboxylates in TMB were prepared and subjected to long-term trials in which the transparency and light output were monitored. One of the major factors responsible for the instability of indium-containing LOSs is the presence of water in the organic phase.

Application of a semicountercurrent extraction method to waste solution treatment

General data and methods for calculations of the principal parameters of semicountercurrent extraction processes are presented. Examples of solving practical problems, based on application of the semicountercurrent extraction method to treatment of waste solutions containing various valuable components, are given. Deep purification of concentrated zinc chloride solutions to remove iron impurity with the aim of utilization of fluxing solutions was carried out. The process was performed in two semicountercurrent steps filled with VIK-II extractant in the form of zinc soap, through which the initial solution containing 250 g l−1 ZnCl2 and 0.25 g l−1 FeCl3 was passed (βFe/Zn ≥ 1500). The 100-fold amount of the solution relative to the working volume of the extractor was passed. The Fe concentration in the purified solution did not exceed 0.0025 g l−1 (<10−5%). A scheme of treatment of electrolytic chromic acid solution to remove iron was developed. Technical-grade HDEHP was used as extractant (βFe/Cr > 200). The process was performed in one semicountercurrent step filled with a solution containing 250 g l−1 chromic acid, 8.4 g l−1 Cr(III), and 13 g l−1 Fe(III), through which the extractant was passed in a volume equal to 0.66 of the initial aqueous solution volume. The Fe recovery was 98.5%. With Wo = Va, the Fe recovery was as high as 99.9%. A minor fraction of Cr (<8%) coextracted with Fe can be returned to the process.

Linear alkylbenzene (LAB) as diluent for extractants. Extraction of rare-earth elements with solutions of neutral organophosphorus compounds in LAB

Extraction of REE with solutions of neutral organophosphorus compounds (TBP, TIAP, DIOMP) in a new diluent, linear alkylbenzene (LAB), was studied. LAB exhibits significant advantages over known diluents: high flash point (+147°C), nontoxicity, absence of odor, low cost, availability, and good compatibility with polymeric structural materials. LAB is well compatible with TBP, TIAP, and DIOMP. Extraction of HNO3 and REE nitrates is not accompanied by precipitation of extractable complexes or by formation of a second organic phase in a wide concentration range, up to saturation of the extractant. The major extractable complex in extraction of REE nitrates is Ln(NO3)3·3NOPC, where NOPC = TBP, TIAP. The main parameters of extraction systems (distribution ratios, separation factors) with LAB are similar to those of the related systems with paraffin hydrocarbons as diluents. Experiments on group separation of REEs on a 56-step extraction installation gave results agreeing with the calculation data.

Extraction of Scandium from Various Media with Triisoamyl Phosphate: 3. Development of Extractive Refining of Scandium

Scandium refining to remove both more and less extractable impurity metals from hydrochloric acid solutions using semicountercurrent and countercurrent extraction with triisoamyl phosphate is modeled. A process for preparing high-purity scandium is developed, involving removal of more and less extractable impurity metals by semicountercurrent extraction and full countercurrent extraction, respectively, at a limited number of separation steps. From the initial scandium oxide (98% purity), 99.97% scandium oxide was prepared (99.995% purity with respect to REEs), i.e., the decontamination factors from both REEs and other impurity metals exceed 100.