Review of the Application of Ion Exchange Resins for the Recovery of Platinum-Group Metals From Hydrochloric Acid Solutions

Platinum-group metals (PGMs) have become one of the most sought after rare metals in this modern age of science and they will continue to increase in importance as a result of their advantageous use in clean-air technology. Due to the scarcity of these precious metals, the application of ion exchange processes to recover PGM ions from relatively uncontaminated aqueous solutions, such as produced by the leaching of secondary sources including used automotive catalytic converters and electronic scrap, is becoming an increasingly cost-effective option and hence an important topic for the PGM production industry. This paper provides a general overview of the basic principles and theories relevant to the hydrometallurgical recovery of PGMs using ion exchange resins, along with a review and discussion of the most important factors that affect the separation and purification of PGMs present initially in predominantly ionic state in an aqueous hydrochloric acid solution. It is shown that in these acidic chloride solutions, the current system of choice for the leaching of PGMs, the adsorption behavior of the PGM ions onto chelating ion exchange resins is strongly dependent on the anionic PGM chloro-complex species present. In addition, it is revealed that the main factors affecting this complexation are (i) acidity and chloride ion concentration of the contacting aqueous chloride solution, (ii) “ageing” of the solution, and (iii) temperature of the solution.     

Efficiency of high‐order elements for continuous and discontinuous Galerkin methods

To evaluate the computational performance of high‐order elements, a comparison based on operation count is proposed instead of runtime comparisons. More specifically, linear versus high‐order approximations are analyzed for implicit solver under a standard set of hypotheses for the mesh and the solution. Continuous and discontinuous Galerkin methods are considered in two‐dimensional and three‐dimensional domains for simplices and parallelotopes. Moreover, both element‐wise and global operations arising from different Galerkin approaches are studied. The operation count estimates show, that for implicit solvers, high‐order methods are more efficient than linear ones. Copyright © 2013 John Wiley & Sons, Ltd.     

Short Electrospun Fibers by UV Cutting Method

Short electrospun fibers were obtained by using UV cutting method. Either polymers with double bonds with a photocross‐linker (CL) and photoinitiator (PI) or known photochemistry of coumarin ([2 + 2] cycloaddition reaction) without the addition of CL and PI is utilized for making short electrospun fibers. The electrospun fibers were irradiated by UV light in the presence of a mask with a defined width of slits. The uncovered parts of fibers were cross‐linked and therefore became insoluble. The non‐cross‐linked parts were removed by immersion of the fibers into an appropriate solvent. The length of obtained short fibers can be controlled by changing the width of the slits of the employed mask.

     

Forward Adaptive Logarithmic Quantizer with New Lossless Coding Method for Laplacian Source

The aim of this paper is to improve the G.711 standard, which is widely used, especially in the public switched telephone network (PSTN). Two solutions are proposed. The first solution uses only lossless coder, achieving a bit-rate decrease of 0.82 bits/sample, compared to the G.711 codec. The second solution uses forward adaptation and a lossless coder, further decreasing the bit-rate (by 1.25 bits/sample) and achieving higher average signal-to-quantization noise ratio (SQNR) in comparison with the G.711 codec. Also, the second solution is more robust than the G.711 codec, which means that it has near constant SQNR for a wide range of input signal power. That is very important for signals whose input power varies with time, such as speech and video signals. Our solutions are compatible with the G.711 codec, they have little additional complexity and delay and therefore can be applied in real-time systems, such as PSTN or VoIP. They can also be used in many other systems, such as WiMax and OFDM, as a replacement or improvement of the G.711 codec. Standardization process of the G.711.1 standard (which is a wide-band extension of the G.711 standard) is largely present. Our solutions fulfill all the requirements for that new standard; therefore they can be implemented in its low-frequency part.     

Effect of preparation route on the microstructure and electrical conductivity of co-doped ceria

Dense Ce_0.8Sm_0.1Gd_0.1O_2?δ electrolytes were fabricated by sintering of CeO₂ solid solutions which were prepared from metal nitrates and NaOH using self propagating room temperature synthesis (SPRT). Three different routes were employed to obtain CeO₂ solid solution powders: (I) hand mixing of reactants, (II) ball milling of reactants and (III) ball milling of Ce_0.8Sm_0.2O_2?δ and Ce_0.8Gd_0.2O_2?δ solid solutions previously prepared by ball milling of corresponding nitrates and NaOH. Density measurements showed that ball milling, which is more convenient than hand mixing, is an effective way to obtain almost full dense samples after presureless sintering at 1550 °C for 1 h. These samples had larger grain size and consequently higher conductivity than the samples obtained by hand mixing. The highest conductivity of 2.704×10^?2 (Ω cm)^?1was measured at 700 °C in a sample prepared by route II. It was found that reduced grain size in samples obtained by hand mixing leads to a decrease in grain boundary conductivity and therefore decrease in the total conductivity. The results showed that mixing of single doped ceria solid solutions improved densification and inhibited grain growth.     

Investigation on thermal radiation spectra of coal ash deposits

This paper deals with thermal radiation properties of ash deposits on a pulverized coal boiler of an electric power plant. Normal emittance spectra in the 2.5–25 μm interval, and total normal emittance, were measured on 4 kinds of ash layers of a mm magnitude order thickness, at 560 → 1460 → 560 K in heating and cooling. It was found that ash powder layers are opaque for infrared radiation. The emittance increases with ash radiation wavelength and temperature. Ash powder is sintered and fused above 1200 K. The emittance of the sintered layer is above that of the unsintered layer. The authors propose, and explain by an example, correlating the experimentally obtained emittance spectra of ash deposits with a continuous curve, the formula of which defines the dependence of emittance on wavelength and temperature, i.e. ε = ε(λ,Т). Use of this formula, with parameter values determined by the proposed methodology, may greatly simplify the practical application of the experimentally determined emittances in the thermal design of existing and new steam boiler furnaces.     

Room-temperature synthesis of nanometric α-Bi2O3

Nanometric Bi₂O₃ powder was successfully synthesized by applying the method based on self-propagating room temperature reaction (SPRT) between bismuth nitrates and sodium hydroxide. X-ray powder diffraction (XRPD) and Rietveld's structure refinement method were applied to characterize prepared powder. It revealed that synthesized material is a single phase monoclinic α-Bi₂O₃ (space group P2₁/c with cell parameters a = 5.84605(4)Å, b = 8.16339(6) Å, c = 7.50788(6) Å and β = 112.9883(8)). Powder particles were of nanometric size (about 50 nm). Raman spectral studies conformed that the obtained powder is single phase α-Bi₂O₃. Specific surface area of obtained powder was measured by Brunauer-Emmet-Teller (BET) method.     

New nano-structured and interactive supported composite electrocatalysts for hydrogen evolution with partially replaced platinum loading

This work is concerned with preparation and characterization of nano-structured composite electrocatalytic material for hydrogen evolution based on CoPt hyper d-metallic phase and anatase (TiO₂) hypo d-phase, both deposited on multiwalled carbon nanotubes (MWCNTs) as a carbon substrate. The main goal is partially or completely to replace Pt as the electrocatalytic material. Four electrocatalytic systems were prepared with common composition 10% Me + 18% TiO₂ + MWCNTs, where Me = Co, CoPt (4:1, wt. ratio), CoPt (1:1, wt. ratio) and Pt. The structural changes and their influence on electrocatalytic activity were studied by means of XRD, TEM, SEM and FTIR. The electrocatalytic activity was assessed in aqueous alkaline and polymer acidic electrolytes by means of steady-state galvanostatic method. It was found that Co strongly affects the platinum particle size. The addition of Co reduces platinum particle's size from 11 nm (in pure Pt metallic system) to 4 nm (in both systems 4:1 and 1:1), i.e. almost by 3 times. The corresponding increase of the surface area and the number of the active catalytic centres improves the efficiency, despite the fact that the amount of used platinum was decreased up to 5 times. The catalyst based on CoPt (1:1) performed the best, while the activity of the pure platinum and CoPt (4:1) systems were very close. Generally, the studied electrocatalysts have shown good and stable performances for hydrogen evolution in PEM electrochemical cell. The influence of the hydrogen electrodes under investigation on the water electrolysis efficiency at current density of 0.3 A cm⁻² was assessed, using previous data oxygen evolution on IrO_x electrode. Related to the performances of commercial Pt (ELAT) electrode, when hydrogen electrodes with the prepared mixed electrocatalysts were used, the water electrolysis efficiency was only 5% lower for CoPt (1:1), nearly 10% lower for CoPt (4:1) and 13% lower in the case of pure Co-based electrocatalyst.