Nitric Acid Medium Research Articles

Highly selective separation of 99TcO4−/ReO4− with rapid liquid-liquid two-phase disengagement by amine-diamide ligands

Efficient and selective extraction of pertechnetate (TcO4−) from nitric acid medium has become a significant challenge, especially in the presence of a large excess of interfering anions. By employing a combined strategy involving H-bonding and electrostatic interaction, a highly selective extraction of TcO4− can be achieved. The present work reports three homologous amine-diamide ligands with different alkyl chain lengths on the amine N atom of 2,2′‐(metylimino)bis(N,N‐dioctylacetamide) (MIDOA), 2,2′‐(butylimino)bis(N,N‐dioctylacetamide) (BIDOA) and 2,2′‐(octylimino)bis(N,N‐dioctylacetamide) (OIDOA), and their extraction behaviors for TcO4−/ReO4− in HNO3 solution are also investigated by using n-dodecane as a diluent. It has been shown that all of them exhibit excellent extractability and high selectivity to TcO4−/ReO4−. Their extractability and phase disengagement follow the order of OIDOA > BIDOA > MIDOA, revealing a greater extractability and rapider phase disengagement for the amine-diamide ligand with longer chain substituents on the amine N atom. Both slope analysis and loading capacity test indicate the formation of 1:1 metal/ligand extracted complex, which is also confirmed by the analyses of single-crystal X-ray diffraction (SC-XRD), electrospray ionization mass (ESI-MS), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). The extraction of TcO4−/ReO4− by the amine-diamide ligand follows the anion exchange extraction model and is a spontaneous and endothermic process. Furthermore, a competing extraction test was also conducted and demonstrates excellent extractability and high selectivity to TcO4−/ReO4−.

Application ICP-OES to Multielement Analysis on Plastic Waste and Blends with Vacuum Gas Oil: Developing a Sample Preparation Protocol

This paper introduces a new methodology for a routine metal analysis of plastic waste (PW) and PW blended with petroleum feedstock such as vacuum gas oil and VGO (PW/VGO). For such purposes, recycled polyethylene and polypropylene plastic were selected to mimic the potential feeds to be integrated at the Fluid Catalytic Cracking unit (FCC) to produce valuable products. Elements such as P, Ca, Al, Mg, Na, Zn, B, Fe, Ti, and Si were included in the method development. Different sample preparation methods were evaluated, such as microwave-assisted acid digestion (MWAD) and dry/wet ashing, followed by a fusion of the ash with lithium borate flux. Some PW homogenization pretreatments, such as cryogenic grinding and hot press molding, were also covered. The finding of this work suggests that MWAD with HNO3 and H2O2 is adequate for both types of samples and is the quickest sample preparation; however, the sample needed to be homogenized, and recoveries for Si and Ti may be biased for PW due to the limited solubilities of these elements in the nitric acid media. Carbon removal is required before fusion sample preparation and analysis due to the amount of carbon in PW samples. The sample needed to be homogenized for wet ash fusion but not for the pre-ash (dry) method. A benefit to the damp ash pretreatment is that the ash for the sample was created in the same crucible used for fusion digestion, avoiding material loss during sample management. Fusion from wet ash or carbon removal allowed for better acid solubility for Si and Ti in PW. The results of the PW samples evaluated matched well with those of both sample preparation methodologies. For most elements, precision was <10% regardless of the sample preparation; however, Fe and P had some variation using wet ash fusion, possibly due to contamination in an open digestion system or variation due to being close to the method limit of quantification (LOQ). The methodology reported here is robust enough to be implemented as routine analysis in any laboratory facility.

Styrene divinyl benzene beads (SM-2) functionalized with triisobutylphosphine sulfide for selective uptake of palladium(II) from nitric acid medium

Resins impregnated with organic extractants regarded as effective adsorbent materials due to their ability for selective sorption. These resins consist of a polymeric material that is infused with accessible organic extractants. Furthermore, these resins merge the unique properties and the distinctive characteristics of both liquid-liquid extraction and solid-liquid sorption processes. In this work, the impregnation of Styrene divinyl benzene beads (SM-2 beads) with triisobutylphosphine sulfide (TIBPS = CYANEX 471X) was prepared. A SM-2 bead functionalized with CYANEX 471X (SM-2-TIBPS beads) was characterized using scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FT-IR) techniques and investigated for recovery and separation of palladium ions from a 3 M nitric acid solution. Various parameters were studied, as shaking time effect, nitric acid concentration, SM-2-TIBPS beads weight, Pd(II) concentration and temperature. The Pd(II)/SM-2-TIBPS sorption system has an endothermic nature and was fitted with a Langmuir isotherm model with a 0.9860 regression factor. The kinetics modeling was fitted with PSO and IPD models with regression factors of 0.9889 and 0.9959, respectively. The maximum monolayer sorption capacity of SM-2-TIBPS was found to be 17.47 ± 0.9 mg/g. The sorption of Pd(II) from different media at 3 M takes the following sequence: HNO3 > HCl > H2SO4. Desorption of about 76.38 ± 2.4% was achieved with (1 M + 1 M) of thiourea + HCl after one desorption stage. Effect of other interfering ions, as Pt(II), Pb(II), Eu(III), Cu(II), Mo(VI), Co(III), Zr(IV), Fe(III), Cd(II), and Ce(III), indicates high separation factors between Pd(II) and other investigated metal ions, which ranged from 9.4 to 35.

Study on the adsorption performance of Eu(III) in nitric acid medium by TODGA-C resin

Study on the adsorption performance of Eu(III) in nitric acid medium by TODGA-C resin

Understanding the role of alloying elements Cr, Ni in erosion–corrosion process of nuclear grade austenitic stainless steel 304 L by total reflection X-ray fluorescence

Stainless steel (SS) has gained an indispensable position as one of the most widely used industrial material. In nuclear industry, it is one of the technologically most important structural materials used in pressure tube, containment vessel and reprocessing-related applications. In fact, SS 304 L is the workhorse material of the reprocessing plant which faces the hostile conditions of acid, temperature as well as high radiation dose. These conditions can affect the erosion-corrosion behavior of the material and can lead to poor mechanical properties. This also affects the life of the reactor components. In the present study, a systematic work has been carried out to develop an in-depth understanding of the Corrosion Rates (CRs) with respect to the loss of major and minor elements from SS into the corrosive nitric acid medium using Total reflection X-Ray Fluorescence (TXRF). The effect of acid molarity as well as temperature, on the erosion-corrosion behavior of SS304L was studied. The TXRF studies have revealed that the CR was maximum in 2 M HNO3 and minimum in 8 M, showing that as the nitric acid molarity has an important role to play in the corrosion and as the molarity increases, the passivation of SS 304 L also increases. This observation was further corroborated with the concentrations of Fe, Cr and Ni, which had leached into the nitric acid medium. The role of alloying elements, Cr and Ni, in the passivation of SS was also studied. The effect of temperature showed that at 45 °C, the rate of corrosion was minimum, as compared to at 25 °C and 90 °C which reveals that the formation of chromium oxide passive layer was thermodynamically most favorable at this temperature.

Extraction and Separation of zirconium using Aliquat 336 from Egyptian black sand

A solvent extraction method has been employed to extract and separate zirconium from the nitric acid medium using 6% tri-caprylmethylammonium chloride (Aliquat 336) [CH3(CH2)7]3N+(CH3) Cl- dissolved in kerosene as diluent. The relevant factors controlling the extraction process of zirconium using Aliquat 336 were studied. These factors include Aliquat 336 concentration, A:O phase ratio, contact time and diluent type. More than 99.6% of Zr was extracted by 6% Aliquat 336 at contact time 10 minutes, phase ratio O:A (v: v) 2:1 and the diluent were kerosene. Third phase formation was studied and dissolving it by using decanol as modifier was also done. Stripping of zirconium from loaded Aliquat 336 has been carried out using 4M H2SO4 as an effective stripping agent. The feasibility of using Aliquat 336 for separation of zirconium was assisted by stripping studies. The loaded zirconium onto Aliquat 336 has been stripped by stripping efficiency 94.18% when using 4M H2SO4 as an efficient eluting agent at 10 minutes contact time and phase ratio O:A (v: v) 1:1.

Cyphos Nitrate Selectively Separates Y(III) from Sr(II) Present in Acidic Feed Solution: An Efficient Ionic Liquid based Extraction Process

AbstractMutual separation of Y(III) and Sr(II) from their waste solution has been an emerging research domain due to their various industrial applications. In this investigation, we emphasize the feasibility of selective separation of Y(III) from Sr(II) present in nitric acid medium using undiluted cyphos nitrate ionic liquid (IL): trihexyl(tetradecyl)phosphonium nitrate ([P66614][NO3]) as the ligating phase. The set experimental parameters were the feed phase acidity, initial nitrate ion concentration, initial feed metal ion concentration, equilibration time and temperature to unveil the efficacy of the proposed system. Efficient extraction of Y(III) selectively in presence of Sr(II) using only a salting agent in aqueous phase without additional extractant in IL phase was highlighted. A remarkable separation factor (SF) obtained for Y(III) over Sr(II) explored the efficacy of the proposed IL system. Y(III) loading in IL phase both in unirradiated and irradiated conditions was compared to evaluate the coordination behavior of irradiated moieties. In addition, a most important advantage of the proposed system is that it employs Milli‐Q water for the back extraction (stripping) of the loaded Y(III) from IL phase and does not demand any complexing agent (water soluble). This undoubtedly corroborates the economic and environmental benefits of the proposed IL system.

Study of the inhibitory properties of 2-((benzylthio)methyl)-1H-benzo[d]imidazole with respect to the corrosion of aluminum in a nitric acid medium

Due to its massive use, the behavior of aluminum in a 1 M nitric acid solution was studied in this work; this study which is mainly based on the inhibitory properties of 2-((benzylthio)methyl)-1H-benzo[d]imidazole (2-BTM1HBI) was carried out using the mass loss technique of temperature varying from 298 to 338 K and concentration of 10-3 mM at 5 mM. The inhibitory efficiency of 2-BTM1HBI increases with the increase of the concentration and this up to 96.09% but decreases with the increase of the temperature. The study of isotherms shows that the adsorption of the molecule studied on the surface of aluminum obeys the modified Langmuir isotherm (villamil model). The thermodynamic adsorption quantities were determined and discussed. They show that the adsorption of 2-BTM1HBI is spontaneous and exothermic with an increase in disorder. Adsorption is done in two modes: physisorption and chemsorption with a predominance of physisorption. The thermodynamic quantities of activation have shown that the dissolution process is endothermic with an increase in disorder.

Corrosion Behavior of Ferritic 12Cr ODS and Martensitic X46Cr13 Steels in Nitric Acid and Sodium Chloride Solutions.

This paper presents corrosion resistance results of a 12Cr ferritic ODS steel (Fe-12Cr-2W-0.5Zr-0.3Y2O3) fabricated via a powder metallurgy route as a prospective applicant for fuel cladding materials. In a spent nuclear fuel reprocessing facility, nitric acid serves as the primary solvent in the PUREX method. Therefore, fundamental immersion and electrochemical tests were conducted in various nitric acid solutions to evaluate corrosion degradation behavior. Additionally, polarization tests were also performed in 0.61 M of sodium chloride solutions (seawater-like atmosphere) as a more general, all-purpose procedure that produces valid comparisons for most metal alloys. For comparison, martensitic X46Cr13 steel was also examined under the same conditions. In general, the corrosion resistance of the 12Cr ODS steel was better than its martensitic counterpart despite a lower nominal chromium content. Potentiodynamic polarization plots exhibited a lower corrosion current and higher breakdown potentials in chloride solution in the case of the ODS steel. It was found that the corrosion rate during immersion tests was exceptionally high in diluted (0.1-3 M) boiling nitric acid media, followed by its sharp decrease in more concentrated solutions (>4 M). The results of the polarization plots also exhibited a shift toward more noble corrosion potential as the concentrations increased from 1 M to 4 M of HNO3. The results on corrosion resistance were supported by LSCM and SEM observations of surface topology and corrosion products.

Extractive Mass Transfer of Zr(IV) into a Hydrophobic Ionic Liquid Medium Containing Diglycolamide Extractant: Solvent Extraction and Spectroscopic Analysis.

Solvent extraction of Zr(IV) in ionic liquid (IL) medium is less known and Zr(IV) - IL chemistry indeed needs exploration to realize the coordination approach of Zr(IV) in IL phase. In view of this, in the present work, a strongly hydrophobic imidazolium based IL: 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide ([C8mim][NTf2]) as the medium containing a diglycolamide (DGA) extractant: N,N,N',N'-tetra-n-octyldiglycolamide (TODGA) was opted to understand the extraction behavior of Zr(IV) from nitric acid medium. Different experimental parameters such as the concentration of initial nitric acid, initial feed metal concentration, equilibration time and ligand concentration were tuned to unravel the extraction efficiency of the proposed IL phase towards Zr(IV). The extraction scenario was completely dependent on the hydrophobicity of IL diluent and increasing extraction trend with an increase in feed acidity along with the coordination of two TODGA molecules ensured Zr(IV) - complex formation in a neutral solvation mechanistic pathway. The extraction trend of Zr(IV) was compared with molecular diluent (n-dodecane (n-DD)) containing TODGA and a phase modifier: N,N-dihexyloctanamide (DHOA). The coordination aspect of Zr(IV) with ligand in IL phase was ascertained spectroscopically to validate Zr(IV) loading in IL phase. Thermodynamics of Zr(IV) extraction revealed the nature of the extraction process and the complex formation.

Comparison of the corrosion behaviour of 10Cr and 17Cr Al added ODS steel in simulated reprocessing nitric acid medium

It is imperative to comprehend the corrosion behavior of different Cr containing Al-added ODS steel reactor clad materials in nuclear reprocessing simulating conditions, as high dissolution of clad material is not desirable. In this present work, the effect of varying HNO3 concentrations (3, 6, 11.5 M HNO3) and with oxidizing (Cr6+, Ce3+) and non-oxidizing (Fe3+) ions in 6 M HNO3 on 10Cr (10Cr-5Al-0.5Ti-0.5Y2O3-Fe) and 17Cr (16.78Cr-4.46Al-0.5Ti-0.45Y2O3-Fe) Al-ODS steels are investigated. The potentiodynamic anodic polarization studies revealed an ennoblement of corrosion potential by elevated cathodic current resulting from increased oxidizing conditions in HNO3 by concentration and oxidizing ions. Through various electrochemical techniques like open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), the 17Cr Al-ODS steel exhibited improved corrosion resistance with lower Ecorr, increased passivation range (Epass range), lower corrosion current density (icorr) and increased charge transfer resistance (Rct). The SEM studies revealed variation in corrosion morphology as shallow corrosion cavities and deeper corrosion pits in 17Cr Al-ODS and 10Cr Al-ODS steel, respectively, at high oxidizing environment. The enhanced corrosion resistance of 17Cr Al-ODS is associated to the improved passivation with the high Cr level in the steel compared to 10Cr-ODS steel, which is corroborated by XPS analysis. New knowledge on nitric acid corrosion mechanism on the Cr in Al-ODS steels and the influences of oxidizing ions in reprocessing environments are described.

Characterization of arsenic species by liquid sampling-atmospheric pressure glow discharge ionization mass spectrometry

A liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source operating at a nominal power of 30 W and solution flow rate of 30 µL min−1 and supported in a He sheath gas flow rate of 500 mL min−1 was interfaced to an Orbitrap mass spectrometer and assessed for use in rapid identification of inorganic and organic arsenic species, including As(III), As(V), monomethylarsonic acid, dimethylarsinic acid, and arsenobetaine in a 2% (v/v) nitric acid medium. Mass spectral acquisition in low-resolution mode, using only the ion trap analyzer, provided detection of protonated molecular ions for AsBet (m/z 179), DMA (m/z 139), MMA (m/z 141), and As(V) (m/z 143). As(III) is oxidized to As(V), likely due to in-source processes. Typical fragmentation of these compounds resulted in the loss of either water or methyl groups, as appropriate, i.e., introducing DMA also generated ions corresponding to MMA and As(V) as dissociation products. Structure assignments were also confirmed by high-resolution Orbitrap measurements. Spectral fingerprint assignments were based on the introduction of solutions containing 5 µg mL−1 of each arsenic compound.

Synthesis, Characterization and Dissolution behavior of Nitrides of U-Zr and U-Pu-Zr metallic alloy fuels for Aqueous reprocessing

The aqueous based PUREX process is an alternate choice to pyro-reprocessing of metallic alloy fuels (U-Zr/U-Pu-Zr). Direct dissolution of metallic alloy fuels in a nitric acid medium is not feasible due to vigorous reaction exhibited by the alloys when exposed to this medium. Conversion of metallic alloys into their oxides is a challenging method due to poor dissolution of oxides in nitric acid. Excellent dissolution of nitrides compared to oxides of metallic alloy fuels lead to exploit the nitride route for aqueous reprocessing. Hence, a novel method was adopted to prepare the nitrides of unirradiated U-Zr and U-Pu-Zr alloys via hydridation using UH3, as source-cum-getter instead of hydrogen cylinder. In this context, nitrides of unirradiated U-Zr/U-Pu-Zr metallic alloys were prepared by nitridation via hydridation. Initially, nitrides of U and Zr metals were synthesized and the formation of ZrN and U2N3 and UN phases were confirmed by powder X-ray diffraction measurements. Subsequently, nitrides of unirradiated U-Zr and U-Pu-Zr alloys were synthesized and characterized by X-ray diffraction, scanning electron microscopy and particle analyzer. The dissolution behavior of nitrides of Zr, U, U-Zr and U-Pu-Zr alloys were examined in nitric acid (12 M) medium under reflux conditions at 383 K for 8 h. The present study highlights the potential of the nitride route for efficient dissolution of actinides (U and Pu) and it is very important to develop flow sheets for the aqueous reprocessing of metallic alloys fuels.

A novel bidentate diamide ligand DODQ for the separation of uranium and rare earth ions in nitric acid medium

High efficiency extractants play a necessary role in the selective removal of uranium from rare earth minerals. In this paper, a novel cyclic bidentate diamine extractant, 1, 4-dioctyl-1, 4-dihydroquinoxaline-2, 3-dione (DODQ), was synthesized, and the complexation and extraction of UO22+ in nitric acid medium were systematically studied. The results indicate that DODQ exhibits a unique combination of properties in removing UO22+, with an extraction capacity 132 times higher than that of DODPhOA (acyclic structure). Extraction isotherm experiments and slope analyses illustrate the formation of a 1:1 DODQ/UO22+ regime during the extraction process. Electrospray mass spectrometry, fluorescence spectroscopy, and X-ray crystal diffraction analyses further corroborated its stoichiometric properties. In addition, DODQ can remove UO22+ from rare earth solutions containing UO22+ with high selectivity. This study provides an alternative method to separate uranium from the leaching solution of rare earth ore and has a new understanding of the coordination and complexing behavior of UO22+ with bidentate oxygen-containing ligands.

Gamma radiation synthesis of hydroxyethyl cellulose/acrylic acid/CYANEX 471X hydrogel for silver ions capture from acidic nitrate medium

The current novelty in this study is to recover silver ion with selective extractant such as cyanex 471X (triisobutylphosphine sulfide) through a clean and green method with high efficiency. Herein, a sustainable hydrogel (HEC/AAc/CX3) was fabricated from triisobutylphosphine sulfide, hydroxyethyl cellulose (HEC), and acrylic acid (AAc) using gamma irradiation polymerization and implanted for the sorption of silver Ag (I) ions from a nitrate acidic medium. Different techniques were employed for characterization of HEC/AAc/CX3 hydrogel such as FT-IR, SEM, XRD, and EDX, before and after the sorption process of Ag(I) ions. Gel content and swelling kinetics ratio of hydrogels at different irradiation doses (10, 20, 30, 40, and 50 kGy) were studied. The Fickian diffusion model results indicate that HEC/AAc/CX3 hydrogel is non-Fickian diffusion, which confirmed that the diffusion and relaxation rates are compatible and were selected for further sorption of Ag(I). The irradiated HEC/AAc/CX3 hydrogels, which contain 0.1 g of cyanex 471X, were employed for batch sorption of 100 mg/L Ag(I) from an acidic solution, and the suggested conditions were pH = 1, time = 60, and v/m = 0.05 L/g, which gives a sorption percentage of 75%. The values of thermodynamic parameters ΔH, ΔG, and ΔS were evaluated as—62.80 kJ/mol, 5 kJ/mol, and -227 J/mol, which indicate that the sorption system was exothermic and nonspontaneous in nature. The maximum adsorption capacity of irradiated HEC/AAc/CX3 for Ag(I) was found to be 12 mg. g−1 at 298 K. Furthermore, the maximum desorption percent of Ag ions from HEC/AAc/CX3 was found to be 70% and achieved with 0.5 M NH4SCN after one desorption cycle. The prepared hydrogel proved its selectivity towards silver ions with facile desorption steps and reusability cycles.Graphical

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

In order to realize the effective separation of palladium from high-level liquid waste (HLLW), a ligand-supported adsorbent (NTAamide(C8)/SiO2-P) was prepared by the impregnation method in a vacuum. The SiO2-P carrier was synthesized by in situ polymerization of divinylbenzene and styrene monomers on a macroporous silica skeleton. The NTAamide(C8)/SiO2-P adsorbent was fabricated by impregnating an NTAamide(C8) ligand into the pore of a SiO2-P carrier under a vacuum condition. The adsorption performance of NTAamide(C8)/SiO2-P in nitric acid medium has been systematically studied. In a solution of 0.2 M HNO3, the distribution coefficient of Pd on NTAamide(C8)/SiO2-P was 1848 mL/g with an adsorption percentage of 90.24%. With the concentration of nitric acid increasing, the adsorption capacity of NTAamide(C8)/SiO2-P decreases. Compared to the other 10 potential interfering ions in fission products, NTAamide(C8)/SiO2-P exhibited excellent adsorption selectivity for Pd(II). The separation factor (SFPd/other metals > 77.8) is significantly higher than that of similar materials. The interference of NaNO3 had a negligible effect on the adsorption performance of NTAamide(C8)/SiO2-P, which maintained above 90%. The adsorption kinetics of Pd(II) adsorption on NTAamide(C8)/SiO2-P fits well with the pseudo-second order model. The Sips model is more suitable than the Langmuir and Freundlich model for describing the adsorption behavior. Thermodynamic analysis showed that the adsorption of Pd(II) on NTAamide(C8)/SiO2-P was a spontaneous, endothermic, and rapid process. NTAamide(C8)/SiO2-P also demonstrated good reusability and economic feasibility.

Graft Copolymerization of Acrylonitrile onto Banana Cellulose Fiber

The graft co-polymerization of acrylonitrile monomer (AN) onto banana cellulose fiber (BCF) was carried out using ceric ammonium nitrate (CAN)/oxalic acid (OA) as redox pair in the aqueous nitric acid medium at 90 ºC. The effect of different reaction conditions on the grafting has been studied by determining the grafting parameters, i.e. concentration of acrylonitrile, ceric ammonium nitrate, oxalic acid, nitric acid, reaction time and temperature were carefully optimized to achieve the highest rate of grafting polymerization (RG), highest percent grafting yield (%GY) and grafting efficiency (%GE). All the reagents enhanced the RG%, GY% and %GE, with an increase of concentration up to a certain extent and then found to decline, except for the concentration of nitric acid. The grafting parameters were also increased with time/duration and temperature. The water retention value (WRV) of the grafted co-polymer was also measured. Activation parameters such as energy of activation (Ea), enthalpy change (ΔH), entropy change (ΔS) and free energy change (ΔG) can also be reported by using the Arrhenius plot. The evidence of grafting can also be predicted by the FTIR spectral analysis, moreover, the organic reaction mechanism has been proposed.

Microstructural evaluation and corrosion behaviour of Inconel 82 and Inconel 625 overlays on 304L stainless steel weld used in nuclear fuel reprocessing plant

Weld overlays are considered the most cost-effective surface modification technique to mitigate corrosion in the nuclear industry. Considering this, an attempt to overlay the 304L weld metal at some critical weld locations of the nuclear fuel reprocessing plant with Inconel alloy was initiated. The work focuses on the microstructural evaluation and corrosion behaviour of Inconel 82 and Inconel 625 weld overlays on 304L stainless steel (SS) weld metal in a nitric acid and chloride medium. Scanning electron micrographs of the 304L SS weld metal revealed a duplex microstructure containing δ-ferrite as a minor phase in the austenite matrix. The microstructure of the Inconel 82 and Inconel 625 weld overlays was found to be fully austenitic, with Nb-rich laves phases at the inter-dendritic region. The hardness of the Inconel weld overlays was found to be higher than that of the 304L SS weld metal. X-ray diffraction measurements showed austenite and δ-ferrite in the 304L SS weld metal and a single austenite phase in the Inconel weld overlays. Potentiodynamic anodic polarization experiments carried out in 4M and 8M nitric acid indicated superior passive film stability in the Inconel weld overlays when compared to the 304L SS weld metal. Comparatively, Inconel 625 weld overlay was found to be much superior to Inconel 82 weld overlay in nitric acid medium. The 304L SS weld metal exhibited inferior pitting resistance in chloride medium by virtue of the high δ-ferrite present in the weld fusion zone. The pitting resistance of the Inconel 82 weld overlay marginally improved, while a substantial enhancement occurred in the Inconel 625 weld overlay.

Estimating the corrosion rate of stainless steel R-SUS304ULC in nitric acid media under concentrating operation

The amount of corrosion of the austenitic stainless steel was evaluated considering the changes in solution composition and boiling during actual concentration operations. Austenitic stainless steel R-SUS304ULC is the structural material of the highly radioactive liquid waste concentrator in Japanese spent fuel reprocessing plant, which treats highly corrosive nitric acid solutions during enrichment operations. The study results show that it is necessary to focus on nitric acid concentrations, oxidizing metal ion concentrations, and decompression boiling as factors that accelerate the corrosion rate of stainless steel because of cathodic reaction activation.

Separation of rare earth elements from waste NdFeB magnets: The influence of hematite seeds and agents on the hematite precipitation in nitric acid medium

ABSTRACT Nowadays with the evolution of technology and rare earth elements (REE) are raw materials for a multitude of products, especially in technological applications. Large amounts of electronic waste rich in REE are produced, and this can be utilized as a valuable resource. For these reasons, efforts and research are focusing on secondary production, which is recycling and recovery of REE and specifically neodymium (Nd) from end-of-life components. In this study, the recovery of REE from NdFeB was investigated based on Box-Behnken experimental design technique. The effect of the experimental parameters in the hydrolysis of Fe3+ to hematite in a nitric acid medium in the hydrothermal reactor was examined in detail. Afterwards, the influence of the temperature, time, and hematite precipitation agents including starch (C6H10O5) n, sucrose (C12H22O11), and hematite seeds (Fe2O3) on the recovery of REE, and hematite precipitation were analyzed by statistical analyses. The optimal parameters for maximum REE recovery and iron removal under pressure and temperature were determined to be a process temperature of approximately 145°C, a process time of approximately 6 hours with the starch addition. The optimum parameters are in harmony with the validation experiments.