•HFM based NDSX process developed for Dy recovery.•Dy separated from NdFeB magnetic scrap with >97% purity and 94% recovery.•Separation behaviour of Nd, Dy and Pr under different hydrodynamic ...conditions were investigated.•The developed process for RE recovery from hard disk magnet has potential for scale up in RE recycling.
Hollow Fibre Membrane (HFM) operation in non-dispersive solvent extraction (NDSX) mode has been successfully employed for the separation of dysprosium from NdFeB magnetic scrap material using EHEHPA as an extractant. Effect of various hydrodynamic parameters including aqueous phase acidity, extractant concentration, Dy concentration in feed, phase ratio and flow rate were investigated to optimize the condition for quantitative recovery of dysprosium from the leach liquor obtained by the dissolution of hard disk drive (HDD) in nitric acid media. 0.5 M EHEHPA, 0.3 M HNO3 as aqueous feed phase, 100 ml/min flow rate and phase ratio of 1:1 were found to be optimum for both the cycle test runs. Taking the advantage of fast extraction kinetics of dysprosium, two cycle HFM-NDSX approach was adopted to concentrate Dy from 20 to 83% in first cycle while raising its purity >97% in the second cycle. The overall process also yielded neodymium rich by-product for its further purification.
Coal fly ash samples from different power plants of India have been collected and studied for their rare earth content and recovery. These samples were dissolved in nitric acid by (1) acid-digestion ...method and (2) by fusion with NaOH + NaNO3 mixture at 600 °C followed by successive hydrothermal treatment of the fused mass. The analysis of major and trace elements was done by ICP-AES.All the samples have similar element distribution with total rare earth content found in the range of 300 to 500 mg/kg and major elements as silicon, aluminum, iron, calcium and magnesium. Separation of bulk of the rare earth from matrix elements were carried out by using TEHDGA (N,N,N′,N′-tetrakis-2-ethylhexyldiglycolamide) impregnated XAD-7 resin. Quantitative separation of rare earth was obtained with no uptake of major elements. Simulated solution containing La, Nd, Y and Er, representing lighter and heavier rare earth, was prepared and studied for their adsorption behavior. The adsorption isotherm fitted well with Langmuir modelindicating monolayer adsorption of rare earth elements. Desorption of loaded rare earth elements was achieved by elution with 0.01 M nitric acid solution. The resin was recycled for 10 times and found to retain its extraction and elution properties.
•Samples of coal fly ash (CFA) collected from different power plants of India.•Dissolution of CFA by hydrothermal processes.•Total rare earth elements found in CFA are in the range of 300–500 mg/kg.•TEHDGA-XAD-7 resin was used to selectively separate rare earth elements.•High resin stability and recyclability observed.•Estimation, separation and recovery of rare earths effected from complex coal fly ash matrix.
The present work elaborates studies on samarium (Sm) extraction and transport behavior from aqueous stream by employing hollow fiber membrane. Percentage extraction and percentage transport of ...Sm(III) have been investigated under wide range of experimental parameters such as type of organic extractant, concentration of organic extractant, aqueous phase acidity, flow rate in the module, strip phase acidity and metal ion concentration. Taguchi method utilizing L-18 orthogonal array has been adopted to identify the most influential process parameters responsible for higher degree of extraction and transport of Sm(III) from nitric acid feed medium. A total of 18 experimental runs (each repeated thrice) were carried out under the combination derived from Taguchi array. In Taguchi analysis, the extraction of Sm(III) ions was directed into a precise signal-to-noise ratio for a "high is better" response. Analysis of variance indicated that the selection of organic extractant is the most influential factor controlling extraction and transport, followed by aqueous phase acidity. The experiment performed under the optimum conditions as predicted by Taguchi method resulted in 99.9% extraction of Sm(III) from the feed solution and 98.8% transport of Sm(III) across the membrane with minimum standard deviation.
The multi-faceted applications of rare earth elements (REE) in science and technology are not unknown. Scarcity in the primary sources of RE makes it necessary to explore different secondary sources ...available. Availability of REE in significant amount in spent NdFeB magnetic scrap makes the recycling of REE from this scrap, a lucrative option. In this work, synthetic solutions of 10 g/L (containing the rare earths Nd, Pr and Dy along with Fe) were equilibrated with the organic extractant N,N,N,'N'-tetra (2-ethylhexyl) diglycolamide (TEHDGA) encapsulated in polyethersulfone beads to study the extraction behavior of the REEs from nitric acid medium. Iron (Fe), the major component present in NdFeB scrap, poses the biggest challenge for rare earth extraction from the scraps. The TEHDGA impregnated polymeric beads were found to selectively extract the REEs, leaving Fe(III) in the feed solution. TEHDGA displayed higher selectivity towards the heavier rare earth Dy followed by Nd and Pr. The loading capacity of the beads was measured to be > 1700 ppm. The effect of different experimental parameters, such as contact time, solid-liquid ratio, TEHDGA concentration, feed acidity, were investigated. Contact time of 24 h, TEHDGA concentration of 0.75 M, solid-liquid ratio either 1:5 or 1:10 and feed acidity between 2 and 5 M have been found to suitable for quantitative extraction of REE particularly Dy(III). The recovery of the REEs from the loaded TEHDGA beads was > 90%. Furthermore, the experiment was carried out with higher quantity of beads and feed solution to study applicability of the same in bulk scale. A novel, easy and single-step separation of REE from Fe has been presented in this work.
Commercial purity aluminum sheets were anodized at 10–30V in 10% oxalic acid solution at room temperature. The anodized specimens were tested for its resistance against scratch damage using a ...microscratch adhesion tester operated in the progressive mode. The specimens were studied also for crystal structure, chemical composition, surface morphology, surface topography, microhardness and electrical resistivity by X-ray diffractometry, energy dispersive X-ray spectroscopy, field emission scanning electron microscopy, stylus based surface profilometer, Vickers microhardness tester and four point probe method, respectively. Microscratch test results showed improved adhesion of the anodic aluminum oxide coating with the untransformed bulk, as the anodizing potential decreased. During scratch test, the specimens showed formation of cohesive cracks at a load of 1N. Energy dispersive X-ray analysis showed that the concentration of oxygen increased marginally on increasing the anodizing potential. Field emission scanning electron microscopy showed comparatively less porous microstructure of the anodized specimens for anodizing conducted at potential 20V or lower. The results of profilometry showed formation of smooth coating surface at potentials lower than 25V. Microhardness test showed increased hardness of the anodized aluminum with increasing anodizing potential. The electrical resistivity of anodized aluminum was in the range of 106–109Ω·cm. X-ray diffraction measurements indicated amorphous structure of the so obtained aluminum oxide coating.
•Scratch resistance of anodic aluminum oxide coating evaluated•Coating thickness had a strong influence on roughness and adhesion.•The predominant coating failure mode during scratch testing was buckling.•The measured load for buckling agreed well with the calculated value.
The low temperature embrittlement behavior of duplex stainless steel 2205 was investigated on the basis of changes in mechanical and electrochemical properties after aging for 5000
h at 335, 365 and ...400
°C. Aging leads to increase in the hardness of δ-ferrite phase. The ferrite hardening was very rapid in the initial stages of aging; thereafter the hardness increase was more gradual at all the aging temperatures. Charpy impact test of the aged samples showed drastic decrease in impact toughness. The value of Charpy impact energy saturated after aging to 5000
h at all the aging temperatures. The embrittlement in the material is known to be caused by spinodal decomposition reaction in which the δ-ferrite decomposes into iron-rich α and chromium-enriched α′. For the purpose of non-destructive evaluation of thermal aging embrittlement, double loop electrochemical potentiokinetic reactivation (DL-EPR) test and anodic polarizations in acetic acid and HCl solution were carried out. The peak current density during the anodic scan in DL-EPR test and the peak anodic current density for secondary passivation during polarization in acetic acid increased with increase in aging time. A good linear correlation was observed between the peak anodic current density for secondary passivation during polarization in acetic acid and the microhardness of δ-ferrite phase.
•Studies on purification of low grade sodium diuranate (SDU) using DHOA.•High selectivity for uranium over rare earths and base metals observed.•Mixer settler studies and flow sheet development ...performed.•Uranium purity of more than 99.5% obtained.
A process is described for separation and recovery of uranium from low grade sodium diuranate (SDU) obtained from processing of phosphatic uranium with D2EHPA-TBP solvent. SDU containing impurities of rare earths mostly heavier fraction (Y, Dy, Er, Yb) and Fe, Al, Cr, Mn, Ca, etc. was dissolved in nitric acid and contacted with N,N-dihexyl octanamide (DHOA)/n-dodecane solvent for selective separation of uranium from rest of the impurities. The average separation factor of uranium with respect to the heavy rare earths and base metals was obtained was 30 and 1000 respectively. Effect of different experimental parameters like aqueous nitric acid concentration, DHOA concentration, uranium concentration, phase ratio of extraction, scrubbing and stripping was optimized to obtain high purity uranium product solution. The extraction of uranium by DHOA follows solvation mechanism, at low uranium loading the combining ratio of U to DHOA determined by slope analysis method suggests complex formation as UO2(NO3)2·2DHOA. A 8-stage counter current extraction of 70g/L uranium feed solution obtained on dissolving SDU in 3M HNO3 with 1M DHOA/n-dodecane solvent at O/A=1 and scrubbing with 80g/L pure uranium solution in 3M HNO3 at O/A=4:1 was found appropriate to obtain uranium of purity above 99.9%.
•Sensitization was dependent on grain fragmentation due to cold/warm rolling.•Depth of attack after DL-EPR test established by white light interferrometry.•Near boundary gradient zone established by ...electron backscatterd diffraction.•Near boundary gradient zone correlated with depth of attack.
The dependence of degree of sensitization on partially deformed (rolled and then sensitized) microstructure of 304L stainless steel was investigated. Structures with visible grain fragmentation, or clear reductions in grain size, showed a poor resistance to sensitization. However, non-fragmented deformed grains with clear presence of near boundary orientation gradients provided an improved resistance. Bulk statistical data were further corroborated through direct observations from electron backscattered diffraction (EBSD) and white light interferometry (WLI). EBSD quantified the near boundary gradient zones (NBGZ) while WLI characterized localized corrosion. Scaling between grain average depth of attack and dimension of NBGZ was established.
•IN-RAFMS corroded at 159.4 μm/y in molten Pb-Li (stirring conditions) for 10, 000 h via selective dissolution of Fe and Cr.•Incubation Period depicted low corrosion rate due to grain boundary attack ...and oxide dissolution.•Cr23C6 precipitates at the grain/lath boundaries weakens oxide layer leading to Pb-Li ingress.•CFD confirmed higher velocities at greater radial distance which reduce grain boundary attack but cause grain dropping.•Complete dissolution of oxide layer changes the mechanism to matrix dissolution.
The long-term corrosion behavior of IN-RAFM steel in molten Pb-Li upto 10, 000 h of exposure was studied in a rotating disc corrosion test facility at 823 K. As-received IN-RAFMS material possessed an air-formed surface layer containing oxides of Fe, Ce and W. Precipitation of chromium carbides at the grain/lath boundaries of as-received IN-RAFMS led to grain boundary attack by liquid Pb-Li during the initial “Incubation Period” which depicted slow dissolution of surface oxides and lesser corrosion rate. Complete dissolution of oxide layer altered the corrosion mechanism from grain boundary attack to matrix dissolution thereby increasing the corrosion rate.
Hollow fibre membrane (HFM) operation in supported liquid membrane mode has been successfully employed for the separation of terbium from lean aqueous media by using EHEHPA (PC88A) as an extractant. ...The effects of different process parameters such as aqueous-phase acidity, extractant concentration, phase ratio and flow rate were evaluated to optimize the condition for effective transport of terbium from a lean nitrate aqueous medium. Diffusional parameters were evaluated to establish the rate-determining step in Tb(III) transport from the feed side to the strip phase. Under optimized conditions of 1 M PC88A, 0.1 M HNO
3
as aqueous feed phase, 100 mL/min flow rate and phase ratio of 62:1, recovery of terbium was >95% from lean source. The process was successfully demonstrated in continuous mode of operation for concentrating the Tb(III) value from ppm to g/L under circulation mode while processing 30 L of aqueous phase. Considering the fast transport of terbium, three cycles HFM-SLM approach was proposed to concentrate Tb from 30% to 95%.
