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Flotation of low-grade graphite ore using collector derived from low density polyethylene waste
No full textThe increasing wide range of applications of graphite for electrode, lubricants, refractory applications especially the recent surging electric automobile industry, resulting in significant need of graphite in future. Graphite demand in the energy storage industry is expected to grow 15 times faster than today's demand by 2030. Due to depleting high-grade ore, utilization of low-grade ore by beneficiation becomes utmost importance for sustainable development and resource management. In this work, low-grade graphite ore from Tamil Nadu, India with 86.84% ash was beneficiated by flotation technique for recovering graphite with lower ash content. Flotation, a surface phenomena, based on the surface hydrophobicity of the mineral surface to be separated and since graphite is naturally flotation mineral, this technique is adopted for beneficiation. The mostly commonly used collector in graphite flotation is diesel. In view of continuous cost escalation of diesel, an alternate collector was developed utilizing the low-density polyethylene (LDPE) waste paving way for plastic waste utilization. The flotation efficacy of this new collector (Collector PE) derived from LDPE waste was compared with that of diesel in graphite flotation. The run-of mine graphite ore was initially size reduced for liberation of values from its associated impurities, followed by flotation. The mesh-of-grind, dosages of collector (diesel and PE) and frother (Methyl Isobutyl Carbinol, MIBC) were optimized for better process efficiency for increasing the surface hydrophobicity of graphite particles leading to better separation efficacy. The ore characterization by x-ray diffraction revealed that graphite was accompanied predominantly by quartz with minor fractions of pyrites and several other phyllosilicates such as kaolinite and muscovite. Exfoliated morphology of graphite with thick layers were observed from SEM images. Flotation reagents such as diesel, collector PE and MIBC were characterized by FTIR to analyze their functional groups that enhances the efficiency of the separation process. A graphite float (rougher concentrate) with 15.2% weight recovery and 17.7% ash content was obtained after 10 minutes of grinding (d80: 240.5µm) with 0.85kg/t of collector (diesel) and 0.07kg/t of frother (MIBC) dosages and on two-stage cleaning, a final concentrate with 12.66% weight recovery and 8.70% ash content was obtained. A graphite final concentrate with 13.04% weight recovery and 8.90 % ash was achieved with two-stage cleaning, when treated with 0.57 kg/t of collector PE and 0.07 kg/t of MIBC. These results indicate that the flotation efficiency of the collector PE derived from LDPE wastes is comparable with that of diesel and would be economical when used in large scale industrial graphite flotation
Electrochemical treatment of spent NdFeB magnet in organic acid for recovery of rare earths and other metal values
No full textThe spent Neodymium-Iron–Boron (NdFeB) magnet is potential secondary resource of rare earth elements. Conventional hydrometallurgical processing of spent NdFeB magnet requires energy intensive steps viz. crushing, grinding, roasting etc. and is associated with the discharge of acidic effluents in the environment. The chemical dissolution of waste magnet using biodegradable organic acids is also associated with the major drawback of poor leaching efficiency. The present study is focused on the electrochemical dissolution of spent NdFeB magnet in organic acid for the recovery of rare earths and other metal values. The electrochemical dissolution studies were carried out using citric acid as an electrolyte. The dissolution of spent NdFeB magnet in citric acid was studied with and without electrochemical effect. It was found that the dissolution of NdFeB magnet in citric acid enhanced significantly under electrochemical effect as compared to chemical dissolution. The reaction mechanism of electrochemical dissolution was also determined. The effect of various parameters such as citric acid concentration, current density, stirring speed, bath temperature etc. were studied for electrochemical dissolution of spent NdFeB magnet. The anodic dissolution efficiency and energy consumption were also evaluated. A solvent extraction method using 1M di-(2-ethylhexyl) phosphoric acid (D2EHPA) as an extractant was developed to extract rare earths selectively and quantitatively from the electrolytic liquor. From the loaded organic, mixed oxalates of rare earths were recovered quantitatively by precipitation stripping using oxalic acid solution as stripping agent. Mixed oxides of neodymium, praseodymium and dysprosium of purity 99.9% were obtained by calcination at 1073 K. Iron oxide (98.6% pure) was also produced as by-product of the process. The solid products were characterized by chemical analysis, XRD, SEM and TG-DTA. Enhanced dissolution of metals in citric acid under electrochemical effect is the main advantage of this electrochemical process. The developed process is clean and avoids energy intensive steps viz. crushing, grinding and roasting
Temperature dependent deformation behavior and stacking fault energy of Fe40Mn40Co10Cr10 alloy
No full textThe variation in stacking fault energy (SFE) with the change in temperature has been evaluated experimentally for Fe40Mn40Co10Cr10 high entropy alloy. The distance between partial dislocations was measured using transmission electron microscopy (TEM) based weak-beam dark field (WBDF) technique. SFE of the system was found to be 37.7 (±7) mJ/m2 and 19.5 (±5) mJ/m2 at room temperature (RT) and -100°C, respectively. Owing to the decrease in SFE, a transition in the deformation behavior occurred from limited twin formation and slip dominance at RT to mixed-mode consisting of FCC→HCP transformation and twinning at -100°C. Simultaneous occurrence of twins and deformation-induced martensitic transformation led to superior strength-ductility combination in the specimen deformed at -100°C. SFE of the studied alloy at RT was 42% higher than that of the equiatomic FeMnCoCrNi alloy. This increase in SFE, despite removal of Ni can be understood by considering the effect of the alloy chemistry re-adjustment on
Conducting-Polymer-Based Supercapacitors
No full textCPs are known for their astonishing electrical and electrochemical properties. Characteristic features are tunable conductivity, structural flexibility, mild synthesis and processing conditions; chemical and structural diversity makes them excellent candidate for different fields of interest. Since the first introduction of CPs, it still remains relevant to discuss and grow rapidly in different fields of applications with various modern advancements. This chapter aims to revisit the journey and recent advancements of CPs in the field of energy storage systems like supercapacitors. Supercapacitors are one of the popular modern energy storage systems as they have many advantages like high power density, long cycle life, moderate to high capacitance, tunable rate capability, simple construction and low processing cost. Despite many advantages, supercapacitor is still facing many major challenges such as limited potential window, low energy density and sluggish rate kinetics. CPs have been considered as one of the excellent candidates for supercapacitor as they show miscellaneous redox nature, amazing electrical conductivity, good flexibility and many others. Therefore, substantial discussion is required to discuss the supercapacitors and its advantages and disadvantages, recent advancements, future challenges and new possibilities. This review focuses on the synthesis, processing and chemical modifications of various CPs with various interesting properties and their electrodes used for the advancements of supercapacitors which is the need of the hour
Nonlinearity in the propagation of acoustic waves: Simulation and experimental validation in a creep damaged material
No full textA 3-Dimensional mathematical model has been developed to understand the nonlinear characteristics of an acoustic wave propagating in a creep-damaged medium. Nonlinearities were assumed to be originated from the material due to creep damage in terms of change in precipitate size, nucleation, and growth of micro voids. For carrying out mathematical simulation in this research, a nonlinear material model has been used and the dynamic value of second order elastic constants as well as density measured for the specimen after each creep interruption were incorporated into it. For studying acoustic wave propagation inside the model of Inconel 600 alloy, a common excitation and acquiring point (pulse-echo mode) has been selected via the acoustoelastic effect. The signal received has been used for calculating the acoustic nonlinearity parameter (β) which is the indicative parameter for expressing progression of damage in the material. This parameter β can be calculated as the ratio of the amplitude of the transmitted signal to the square of the amplitude of the second harmonic and is dependent on the elastic constants of the material. The simulation results obtained through the model were validated experimentally. A drastic increase in β was observed at the transition region from secondary to tertiary stage of creep in the studied material, which is due to the increase in the volume fraction of precipitates as well as micro void initiation and are the dominating cause of material failure. So, this technique can be used for assessment of localized deformation in any material much prior to failure
Development of Hydrometallurgical Process for Recovery of Rare Earth Metals (Nd, Pr, and Dy) from Nd-Fe-B Magnets
No full textNon-availability of rich primary resources of rare earth metals (REMs) and the generation of huge amounts of discarded magnets containing REMs, compelled the researchers to explore the possibilities for the recovery of REMs from discarded magnets. Therefore, the present paper
reports the recovery of REMs (Nd, Pr, and Dy) from discarded Nd-Fe-B magnets. The process consists of demagnetization, pre-treatment, and hydrometallurgical processing to recover REMs as salt. Leaching studies indicate that 95.5% Nd, 99.9% Pr, and 99.9% Dy were found to be dissolved at
the optimized experimental condition i.e., acid concentration 2 M H2SO4
, temperature 75 ◦C, pulp
density 100 g/L, and mixing time 60 min. Solvent extraction technique was tried for the selective extraction/separation of REMs and Fe. The result indicates that 99.1% (24.42 g/L) of Nd along with 90% (1.08 g/L) of Pr and total Fe were co-extracted using 35% Cyanex 272 at organic to aqueous
(O/A) ratio 1/1, eq. pH 3.5 in 10 min of mixing time. It requires multistage separation and therefore, not feasible in view of economics. Thus, direct precipitation of REMs salt and iron oxide as pigment was studied using two stages of precipitation at different pH. The obtained precipitate of REMs and Fe hydroxides were dried separately to remove the moisture and further treated at elevated temperature to get pure REMs oxide and red oxide
Influence of quenching strategy on phase transformation and mechanical properties of low alloy steel
No full textThe energy-efficient quenching and nonisothermal partitioning process has been shown to engender an excellent strength-ductility combination in low alloy steels. Conventionally, these steels are quenched to a specific temperature in the martensite region, i.e. between Ms and Mf, followed by slow cooling to room temperature. However, in the present study, an attempt has been made to investigate the behaviour of low alloy steel quenched in the bainite region, i.e. temperature between Bs and Ms, followed by slow cooling to room temperature. For comparison, the same steel was also quenched to two different temperatures in the martensite region as well as direct quenched to room temperature. The XRD results showed the maximum austenite retention for a lower quench temperature in the martensite region. Both the direct quenching and the quenching and nonisothermal partitioning from the martensite region led to a microstructure dominated by the presence of auto-tempered martensitic laths. However, the sample quenched in the bainite region and subsequent slow cooling gave rise to bainite-ferrite laths containing coarse carbides. An interlath precipitation of carbides was observed for the bainite, in contrast to the intralath carbide precipitation in martensite. The austenite remained at the quench temperature decomposed to bainite during slow cooling from the bainite region, whereas M-A constituents were formed during slow cooling from the martensite region. The microstructural constituents were observed to be finest for the direct-quenched sample due to a lower quench temperature. Interestingly, the sample quenched in the bainite region showed a significant improvement in ductility, in contrast to the sample quenched in the martensite region and direct-quenched to room temperature that showed higher strength
Role of air pollutant for deterioration of Taj Mahal by identifying corrosion products on surface of metals
No full textDeterioration of metallic and non-metallic structures and monuments is largely controlled by their surrounding environment. The Taj Mahal, a UNESCO (United Nations Educational, Scientific and Cultural Organization) world heritage situated in Agra of India built in seventeenth century using white marbles, is famous for its aesthetic look. Gradual yellowing and blackening of the monument are matter of great concern, and if not controlled, the heritage structure may lose its glaze and beauty. Extensive studies available on deteriorating effect of the monument miss a vital point related to the pollutants coming from severely polluted River Yamuna which flows very close to the Taj Mahal. To ascertain the possible effects of the pollutants carbon steel, copper and zinc samples were exposed for four years at the premise of Taj Mahal. The surface characterization of the exposed metals with electrochemical impedance spectroscopy, Raman spectroscopy and X-ray diffraction reveals the formation of respective sulphides of the studied metals. The findings suggest that the hydrogen sulphide from the polluted Yamuna River had damaging effect. The wind rose diagram developed at site of exposure further supports the above findings. The corrosion rate of copper was found to be 2.46 mu m/year. This observation as well as identification of corrosion products formed on the metal surface (strong peaks of copper sulphide) provided strong evidences that the hydrogen sulphide evolved from the polluted river accelerated the deterioration of the metal
Excitation dependence and independence of photoluminescence in carbon dots and graphene quantum dots: insights into the mechanism of emission
No full textExcitation-dependent, multicolor emission from different varieties of 0D carbon systems has attracted immense research attention. It is generally accepted that some variants of 0D carbon exhibit excitation dependent emission, while other variants do not. A third variant exhibits both excitation dependent as well as excitation independent emission. In this work we investigate the structure, composition, steady-state emission-excitation and photoluminescence decay dynamics of three distinctly different variants of 0D carbon - amorphous carbon dots (aCDs), graphene quantum dots (GQDs) and nitrogen-doped GQDs (NGQDs). We find that despite significant differences in the structure and composition there is a striking similarity in the excitation energy dependence of the emission characteristics of these three different dots. All of them exhibit excitation energy independent emission below some threshold wavelength (lambda(th)), and above this threshold the emission becomes excitation dependent. We also demonstrate that a similar trend is apparent for nearly all variants of 0D carbon reported in the literature. The threshold wavelength correlates well with the excitation wavelength for the most intense emission and the photoluminescence excitation peaks, suggesting a common origin of light emission in these carbon dots. The findings provide important clues for developing a unified general picture for understanding the light emission mechanism in 0D carbon nanostructures
Rheological behavior of coal-water slurries of Indian coals using carboxymethylcellulose as dispersant- a comparative study
No full textThe rheological nature of coal-water suspensions of two Indian coal samples (namely coal 1 and coal 2) was reported and compared in the shear rate range of 60-160 s(-1) at constant pH of 8. Proximate and ultimate analysis were used to characterize the coal, and zeta potential and turbidity measurements were carried out to test the suitability and selection of carboxymethylcellulose (CMC) as a dispersant for the Coal Water Slurry (CWS). The effects of percentage solid loading, dispersant dosage on the rheological nature were studied. The rheological data was fitted for the power law model to categorize the slurry flow nature with reference to the calculated flow behavior index of the model. At lower solid loadings (10%, 20%), the shear stress-shear rate relation did not alter with the dispersant dosage and the slurries exhibited shear thickening behavior. The effects of the slurry parameters were quite predominant at 30%, 40%, and 50% solid loadings as they exhibited the shear thinning behavior. The slurry with 30% solid loading showed transition from shear thickening to shear thinning with the increase in dispersant dosage. For a given percentage of solids, a lower magnitude of shear stress versus shear rate, a wider distribution of flow behavior index and favorable pumpable characteristics were seen for coal 1 in comparison to coal 2 owing to their chemical nature and amount of ash-bearing mineral constituents