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Size fractionation of brown fly ash: utilisation of grey fraction as a pozzolanic material in blended cement
No full textThe work aimed to classify a raw brown colour fly ash (RFA) into coarse grey fly ash (GFA) and fine brown fly ash (BFA) using a laboratory air classifier and to study the properties of grey fly ash-based blended cement. Portland cement (OPC) was partially replaced with 10–30% GFA by mass at 5% intervals to make blended cement. The physical and mechanical properties were determined as per Bureau of Indian Standards (BIS). The incorporation of GFA in cement mixes decreases the specific gravity, fineness, consistency, volume expansion and drying shrinkage while increases the setting time and flow-ability. The compressive strength of blended cement was observed lower than that of OPC at all ages, but the rate of strength development increases with the age. The replacement level up to 20% meets the BIS strength requirement of 33 MPa at 28 d for fly ash-based blended cement. The hydration studies were done using Isothermal Conduction Calorimetry (ICC) at 27 °C. The total heat of hydration was observed to decrease with the increasing GFA content. The microstructural characterisation of hardened cement pastes after 60 d using XRD, FTIR and SEM-EDS revealed the variations in mineralogical, structural and morphological propertie
Recycling of gold from waste electronic components of devices
No full textTremendous generation of e-waste and its illegal recycling are causing immense threat to environment as well as the loss of precious metals. The present research reports a novel hybrid process for the total recovery of gold from small depopulated components of e-waste. Connectors and integrated circuits (ICs) liberated from printed circuit
boards (PCBs) were pulverized and processed for gold leaching using 10 g/L sodium cyanide solution at 40 oC and
mixing time 15 min, where more than 95% gold was found to be leached out in single stage. From the obtained leach liquor, gold metal was recovered by charcoal adsorption followed by heat treatment. The raffinate left after adsorption of gold was found to contain ~10mg/L gold, which was also recovered using Amberlite IRA 400Cl at equilibrium pH 9.6 in 30 min maintaining aqueous/resin (A/R) ratio 25 mL/g. The raffinate solution was enriched to 882.41mg/L and the solution was further processed to get metal/salt using cementation/ evaporation. Obtained leached residue is processed for non-ferrous metals recovery and finally disposed-off after treatment and TCLP test. The effluent left after leaching could be easily decomposed and treated in ETP using standard environmental procedure
Novel approach for selective recovery of gold, copper, and iron as marketable product from industrial effluent
No full textGlobally, continuous R & D efforts are being made to recuperate precious metals from wastes in order to conserve the natural resources as well as minimize environmental pollution. Keeping in view of the above, a process has been developed to recover gold from industrial effluent using hydrometallurgical route. Initially, the effluent was pre-treated using precipitation and solvent extraction techniques to remove impurities, i.e., iron and copper as value added products. Iron was removed up to 99.99% at pH 3.5. Further, copper was extracted using 10% LIX 84IC maintaining phase ratio 1/1 in mixing time of 15 min and equilibrium (eq.). pH 2.2. Selective adsorption of gold was carried out using ionenaustauscher-II and resulted in 99% gold adsorption between pH 7 and 8 in contact time of 30 min. Experimental results obtained for the adsorption of gold was found to follow second order reaction and fitted well with the Freundlich isotherm. Gold from the loaded resin was eluted using a mixture of hydrochloric acid and thiourea. From the pure gold solution, metal could be produced using cementation/charcoal adsorption followed by heat treatment, respectively
Valorisation of waste galvanizing dross: Emphasis on recovery of zinc with zero effluent strategy
No full textGalvanizing dross-a waste product from steel industries but it can be a potential secondary resource for zinc through urban mining and recycling. In this concern, a novel and scalable recycling route with zero effluent strategy is developed for the recovery of zinc from galvanizing dross as high grade zinc salts along with value-added products through hydrometallurgical processing. In particular, as-such dross block was leached in 9% (v/v) sulphuric acid medium, wherein strong hydrogen gas effervescence results in alleviating the pulverization and stirring requirements; which are material and energy intensive. Leached zinc is purified and recovered as high purity ZnSO4.(H2O/7H2O) and Zn3(PO4)2.4H2O through controlled crystallization and phosphate precipitation respectively; which find application in fertilizers and anti-corrosive paints. Temperature difference method was opted for the crystallization of zinc sulfate salts, wherein 70 °C and 30 °C were found to be stability range of crystallization of ZnSO4.H2O and ZnSO4.7H2O respectively. ZnSO4-H2O phase diagram is developed using Factsage calculations to corroborate crystallization study. Moreover, exhaustive thermodynamic analysis of Zn2+-PO43--H2O system at 303 K on precipitation of zinc phosphate using di-ammonium hydrogen phosphate (80-240 g/L) is conducted and the results reveal that with increasing pH (3-6), intermediate hydrogen phosphate species (H3PO4, H2PO4- and H2PO42-) decompose to produce stable PO43- ions leading to zinc phosphate precipitation. Impurity like Iron and supernatant solution left after crystallization are recovered as hydrated iron-calcium sulfate mixture and ammonium sulfate salt respectively. This explored route is economical and easily adaptable with zero effluents, therefore, transcends serious challenges in terms of energy requirement, scale-up and effluent generation
Hall-Petch’ type of relationship between the extent of intergranular corrosion and grain size in a Ni-based superalloy
No full textThe present work elucidates the individual implication of wide spectrum of grain size on degree of sensitization (DOS) and intergranular corrosion in alloy 600H. Experimental evidences suggest that both the sensitization and desensitization phenomena are significantly delayed in the coarse-grained specimens. This is attributable to the lower driving force available in the coarser grains for the diffusion of Cr from the grain to the boundary. Interestingly, a Hall-Petch type relation has been observed between DOS (as well as weight loss) and grain size in which both the DOS and weight loss varied inversely proportional to the (grain size)1/4
Corrosion characteristics of vanadium micro-alloyed steel reinforcement bars exposed in concrete environments and industrially polluted atmosphere
No full textCorrosion resistance performance of rebars rolled from vanadium micro-alloyed (VMA) steel was evaluated vis-à-vis rebars rolled from steel having similar chemistry to the (VMA) steel without vanadium and subjected to thermomechanical treatment after hot rolling (TMT). Three test environments namely simulated concrete pore solution, mortars, and industrially polluted atmosphere were used to assess the performance of these rebars. Mass loss, electrochemical impedance spectroscopy, DC polarization and potential-time studies were employed to acquire quantitative data and explain the observed results. Raman spectroscopy was used to identify the corrosion products formed on the surface of the exposed rebars in different environments. The corrosion resistance of VMA rebars was better than TMT especially with increased duration of exposure in chloride contaminated concrete environments. However, under the industrially polluted atmosphere, both rebars exhibited comparative corrosion rates. Lesser detrimental effect of chloride present in concrete environment on the VMA steel rebars is attributed to the higher grain boundary per unit area in these rebars than in the TMT rebars. It is suggested that owing to the stronger tendency of the higher-grain-boundary- material to interact with oxygen and moisture, a thicker film of Fe(OH)3wasformed on its surface than on the surface of the TMT rebar, prior to their exposure to the test environments. This hydroxide film dissolved in alkaline environment of concrete, nucleated and grew as a protective FeOOH film on the surface of the rebars
Performance characterization and misplacement studies of liquid–solid fluidized bed density separator for coal beneficiation using Taguchi-ANOVA method
No full textCoal preparation plants commonly use density-based separators to remove high-density inorganic matter (rock) from low-density carbonaceous matter (coal). Liquid–solid fluidized bed separators (FBS), segregates particles with different size, shape, and density. Particles with different terminal velocities report to various heights of the fluidization column. This property has been used to beneficiate the low-grade coal particles. As the material systems in mineral processing vary broadly in physical characteristics, misplacement of particles to an undesired destination is a prevalent occurrence. The present work aims at understanding the influence of input variables on the separation performance and particle misplacement in FBS. Quantitative and qualitative analyses of the performance characteristics and misplacement have been studied using Taguchi statistical design and ANOVA. Misplacement and normalized misplacement indexes were calculated to quantify the extent of misplacement during segregation. The optimized mean separation efficiency was obtained at optimized combination of mean particle size of 400 µm, bed height of 20 cm, superficial velocity of 2.83 cm/s, and overflow tap height of 12 cm, whereas the optimized mean normalized misplacement index was obtained at mean particle size of 400 µm, bed height of 20 cm, superficial velocity of 2.12 cm/s, and overflow tap height of 12 cm
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An innovative environmental process for the treatment of scrap Nd-Fe-B magnets
No full textStrict environmental regulations as well as requirement of conservation of natural resources compelled the researchers to recycle the metal values from secondary resources. The scrap magnets found to be a potential
alternative resource to extract rare earth metal, Nd. Present paper reports a novel process flow-sheet for the
recycling of scrap Nd-Fe-B magnets to recover Nd as marketable salt and other valuable by-products. The Nd-Fe-B
magnets were demagnetized, crushed and charged to atmospheric leaching resulting in ~99.99% recovery of
REMs (Nd, Pr, Dy) and Fe using 1 M H2SO4 solution at room temperature for 90 min and pulp density 50 g/L. The
obtained leach liquor was subjected to acid extraction procedure by mixing the liquor with 70% TEHA diluted in
kerosene for 10 min, which requires five stages for complete extraction of acid from the liquor having O/A ratio
2:1. Ammonia solution was used to increase the pH of acid free leach liquor to 1.65 for the precipitation of Nd
(with minor amount of Pr and Dy) and above that to precipitate Fe. Further, processing of these valuables make
them industrially applicable. The leached residue was checked using Toxicity Characteristics Leachability Procedure (TCLP) test and found the remained metals within the permissible limit. This process offers a simple and
efficient means to reduce the toxicological effect by recovering Nd from magnets of computer hard disks
Effects of prior austenite grain size on impression creep and microstructure in simulated heat affected zones of boron modified P91 steels
No full textThe induction of this paper was to simplify the exaggeration effects of prior austenite size (PAG) size on microstructure, impression creep, creep-rupture life, creep-damage, and precipitate size in the sub-heat affected zones (sub-HAZs) of boron modified P91 steels. Simulation of sub-HAZs caused the manipulation in PAG size and microstructure. This manipulation reduced precipitate sizes (~50%) in P91B samples that lead to a 20% reduction in the non-homogeneous distribution of size of precipitates. Evaluation of minimum creep-damage rate (MCR) suggested FG (type-IV) and B-CG (type-III) as weakest links having a critical PAG size of 17 μm. But, creep-performance of B-CG was still better than most of the P91 samples. While PAG hardening limit was observed in CF/B-CF that made them the strongest links. Activation energy (AE) calculation showed that an increase in PAG size for P91 samples motivated MCR, inviting PAG embrittlement. While vice versa observed in P91B samples, inviting PAG hardening. P91B samples exhibited maximum creep-performance by the shrinking span of the creep-damage and increasing creep-rupture life. Mutual dependency between creep-rupture life and creep-damage showed that their relation was independent of microstructural features, thermal history, amount of deformation, and boron modifications. Whereas, limited creep-damage was found for samples having normalized creep-rupture life ≥ 2. This paper also discussed various diffusion mechanisms for sub-HAZs by simplifying inconsistency between calculated and actual AE that suggested both interstitial and substitutional nature of boron. Small-grained samples (PAG ≤ 17 μm) had lower AE, while big-grained samples (PAG > 17 μm) had higher AE