Chemical Beneficiation of Low Grade Coal - A Review

India is having large reserves of low grade coals. The use of low-grade coal in various industries like power plants, metallurgical plants, cement units etc. leads to environ-mental pollution because of generation of large amount of solid and gaseous pollutants. Therefore, it is of impor-tance paramount to clean the coal before its utilization. There are a number of upgrading technologies to produce clean coal. The current paper reviews demineralization aspects by physical and chemical beneficiation of high ash and/ sulfur containing coal.Physical beneficiation of coal is not very effective in separation of the finely dispersed minerals, whereas chemical beneficiation uses expensive reagents and leads to generation of large amount of waste-water which needs to be purified before discharge. Thus, a combined approach consisting of physical and chemical cleaning of coal appears to have a potential for. signifi-cant reduction of ash with less investment while generat-ing less polluting wastewater

Solvent Extraction and Separation of Trivalent Lanthanides Using Cyphos IL 104, a Novel Phosphonium Ionic Liquid as Extractant

Solvent extraction of trivalent lanthanides from chloride solution using a novel ionic liquid Cyphos IL 104 (trihexyl(tetradecyl)phosphonium bis-2,4,4-(trimethylpentyl) phosphinate or [R4PA]) has been investigated, while comparing the results with that of its precursors trihexyl(tetradecyl)phosphonium chloride [R4PCl or Cyphos IL 101], Cyanex 272 [HA] and their equimolar mixture. The results also indicate very high extractability of Cyphos IL 104 toward trivalent lanthanides. Unlike the conventional acidic extractants, extraction of trivalent lanthanides with Cyphos IL 104 increases the equilibrium pH of the aqueous phase due to the preferential extraction of acid over the lanthanide ions. Extraction mechanism has been established by studying the extraction of neodymium(III) with the ionic liquid as a function of the concentrations of Cyphos IL 104 and chloride ions. Separation studies of trivalent lanthanides from a mixed solution containing 1 × 10−4M each of La, Nd, Gd, and Lu with Cyphos IL 104 or Cyanex 272 indicate that Cyphos IL 104 is a better extractant in terms of extraction coefficient, but Cyanex 272 exhibits better selectivity toward heavier lanthanides. The prospects of stripping and regeneration of ionic liquid (Cyphos IL 104) have also been discussed in the present study

Recovery of Rare Earth Oxide from Phosphor Powder of Spent Fluorescent Lamp

Phosphor powder contained inside fluorescent tubes is a rich source of rare earths. Phosphor used in fluorescent lamps is of tricolour type that emits visible light of three different colours, i.e., red, green and blue. Among three phosphors, europium-doped Y2O3 is a typical red phosphor that is used predominantly in triband phosphor for displays and fluorescent lamps. In view of above, the present work was focussed on optimising conditions to recover yttrium and europium selectively and synthesizing highly pure Y2O3:Eu3+ (red phosphor) from the liquor arising from leaching of a phosphor powder of spent fluorescent lamps in chloride medium and using oxalic acid as precipitant. The typical composition of the leach liquor obtained at optimum leaching conditions was (g/L): 26.9 Y, 1.6 Eu, with slight impurities of Al and Ca. Process parameters, including acidity, concentration of oxalic acid and temperature, were optimized to produce yttrium oxalate. Under the optimum conditions, the recovery of yttrium and europium as oxalates was quantitative. The synthesised yttrium-europium oxalate was calcined at 600°C to convert it into Y2O3:Eu3+. The yttrium-europium oxalate/oxide powder so formed was characterized by thermogravimetric differential thermal analysis, X-ray diffraction, scanning electron microscopy and chemical analysis, all of which confirmed the presence of pure Y-oxalate and oxide. The microscopy image of the synthesised Y2O3:Eu3+ exhibited flaky particles of 5 μm size; the purity of synthesized red phosphor was >99%, as determined by chemical analysis and energydispersive spectroscopy

Atmospheric water vapor condensation on engineered interfaces: Busting the myths

Condensing atmospheric water vapor on surfaces is a sustainable approach to potentially address the potable water crisis. However, despite extensive research, a key question remains: what is the physical mechanism governing the condensation from humid air and how significantly does it differ from pure steam condensation? The answer may help define an optimal combination of the mode and mechanism of condensation as well as the surface wettability for best possible water harvesting efficacy. Here we show that this lack of clarity is due to the differences in heat transfer characteristics during condensation from pure vapor and humid air environments. Specifically, during condensation from humid air, the thermal resistance across the condensate is non-dominant and the energy transfer is controlled by vapor diffusion and condensate drainage. This leads to filmwise condensation on superhydrophilic surfaces, offering the highest water collection efficiency. To demonstrate this, we measured condensation rate on different sets of superhydrophilic and superhydrophobic surfaces in a wide degree of subcooling (10 - 26 C) and humidity-ratio differences (5 - 45 g/kg of dry air). The resulting condensation rate is enhanced by 57 - 333 % on the superhydrophilic surfaces as compared to the superhydrophobic ones. The findings of this study challenges the nearly century-old scientific ambiguity about the mechanism of vapor condensation from humid air. Our findings will lead to the design of efficient atmospheric water harvesting systems

Preferred Mode of Atmospheric Water Vapor Condensation on Nanoengineered Surfaces: Dropwise or Filmwise?

Condensing atmospheric water vapor on surfaces is a sustainable approach to addressing the potable water crisis. However, despite extensive research, a key question remains: what is the optimal combination of the mode and mechanism of condensation as well as the surface wettability for the best possible water harvesting efficacy? Here, we show how various modes of condensation fare differently in a humid air environment. During condensation from humid air, it is important to note that the thermal resistance across the condensate is nondominant, and the energy transfer is controlled by vapor diffusion across the boundary layer and condensate drainage from the condenser surface. This implies that, unlike condensation from pure steam, filmwise condensation from humid air would exhibit the highest water collection efficiency on superhydrophilic surfaces. To demonstrate this, we measured the condensation rates on different sets of superhydrophilic and superhydrophobic surfaces that were cooled below the dew points using a Peltier cooler. Experiments were performed over a wide range of degrees of subcooling (10–26 °C) and humidity-ratio differences (5–45 g/kg of dry air). Depending upon the thermodynamic parameters, the condensation rate is found to be 57–333% higher on the superhydrophilic surfaces compared to the superhydrophobic ones. The findings of the study dispel ambiguity about the preferred mode of vapor condensation from humid air on wettability-engineered surfaces and lead to the design of efficient atmospheric water harvesting systems

Solvent extraction and separation of copper and zinc from a pickling solution

Solvent extraction studies of copper and zinc have been carried out using Versatic 10 acid and Cyanex 272 separately from a model brass pickle liquor. Various parameters for the extraction and separation of copper and zinc such as effect of pH, extractant concentration, phase ratio etc. have been optimized. It was observed that copper was almost completely extracted into the organic phase comprising of 30% Versatic 10 acid at the equilibrium pH of 5.0 using the phase ratio of 1:1 whereas, zinc extraction was noticed at above pH 5.0. On the other hand the pH0.5 values were 3.5 and 4.6 for zinc and copper respectively with 20% Cyanex 272. The difference in pH0.5 value of 1.10 indicated the possible separation of Zn and Cu. By McCabe Thiele diagram number of stages required for the counter current extraction of copper and zinc has been determined for both the solvents. The stripping study showed that 1 mol/L H2SO4 was sufficient to strip metal ions in a single contact from each of the extractant

Processing of a Waste Stream for Separation and Recovery of Copper and Zinc

Solvent extraction studies of copper and zinc have been carried out using Cyanex 272 and LIX 984N separately from a model waste stream of brass pickling. Various parameters for the extraction and separation of copper and zinc such as effect of pH, extractant concentration, phase ratio etc. have been optimized. The results show that extraction of copper and zinc from solution after acid extraction increased with increase in pH and their pH0.5 values were found to be 3.5 and 4.6, and 2.5 and 5.5 with Cyanex 272 and LIX 984N, respectively; LIX 984N showed greater selectivity for copper compared to zinc. By McCabe Thiele diagram number of stages required for the counter current extraction of copper and zinc has been determined for each of the solvents. The stripping study showed that 1 mol/L H2SO4 was sufficient to strip metal ions from both the extractants. An attempt was made to prepare high value products such as copper powder and zinc oxide from the loaded or stripped solution which could be imminently suitable for various P/M and other application

Enhancement of spatiotemporal regularity in an optimal window of random coupling

We investigate the spatiotemporal dynamics of a lattice of coupled chaotic maps whose coupling connections are dynamically rewired to random sites with probability p, namely at any instance of time, with probability p a regular link is switched to a random one. In a range of weak coupling, where spatiotemporal chaos exists for regular lattices (i.e. for p = 0), we find that p > 0 yields synchronized periodic orbits. Further we observe that this regularity occurs over a window of p values, beyond which the basin of attraction of the synchronized cycle shrinks to zero. Thus we have evidence of an optimal range of randomness in coupling connections, where spatiotemporal regularity is efficiently obtained. This is in contrast to the commonly observed monotonic increase of synchronization with increasing p, as seen for instance, in the strong coupling regime of the very same system.Comment: 10 pages, 6 figure

Extractive separation of La and Nd using Ionic Liquid as extractant

Significant amount of Rare Earth Metals (REMs) are used in magnets, batteries, tube lights, catalyst etc. due to their unique features. Therefore, it is necessary to develop a process which can extract and separate the individual REMs efficiently. The present investigation deals with the solvent extraction and separation of light rare earth elements such as La and Nd from the chloride medium using an ionic liquid(IL), [R3N+.Cy272-] as an extractant. Various parameters were investigated to optimize the condition for separating La(III) and Nd(III) of 10-4M concentration each. At pH 4.0, 90% Nd(III) and 20% La(III) were extracted from the chloride solution. The pH0.5 values for La(III) and Nd(III) were found to be 4.5 and 3.7 respectively. Extraction of La(III) and Nd(III) increased with the increase in IL concentration. At pH 4.5 and IL concentration of 0.01M separation factor (βNd/La) Nd(III) over La(III) was found to be 49. This shows that synthesized ionic liquid has sufficient potential to separate lighter lanthanides (e.g. La and Nd) from their mixed solutions generated during the processing of the REMs from primary or secondary resources