Application of diffusion dialysis for reduction of acidity of real pregnant leach solutions containing Ni and Co ions

ABSTRACT

Diffusion dialysis (DD) was proposed as a pretreatment step to reduce the acidity of real sulfate/chloride pregnant leach solutions containing cobalt(II) and nickel(II). Optimum DD conditions that enable reduction of acidity in the feed while maintaining a high rejection level of metal ions present in PLS were proposed, e.g. for 0.06 dm³/min flow of both aqueous phases H⁺ concentration in the dialysate reached 3.8 and 2.99 M for PLS1 and PLS2, respectively. Acid diffusion coefficients varied from 0.32 ?10 ^?6 to 3.15?10^?6 m/s and decreased with increasing phase flow rates. Moreover, dialysate neutralization was beneficial for the H⁺ reduction in the feed.     

Adsorption of urea,creatinine, and uric acid from three solution types using spherical activated carbon and its recyclability

In this paper, we propose that the urinary toxins from the wastewater be adsorbed on an adsorbent such as spherical activated carbon and the latter be regenerated by subjecting it to high temperatures to recycle activated carbon and also to recycle the water used in dialysis. We studied the adsorption of artificial waste dialysate, which is a mixed solution of urea, creatinine, and uric acid, and the separate solutions for each of these and found that their extents of adsorption onto the spherical activated carbon material were nearly identical. The amount of adsorption was approximately 1.4 mg·g⁻¹ for urea, 18 mg·g⁻¹ for creatinine, and 20 mg·g⁻¹ for uric acid. The urea, creatinine, and uric acid adsorbed onto the spherical activated carbon decomposed on heat treatment at 500 °C, and the adsorption capacity of the spherical activated carbon was regenerated. Our study successfully demonstrated that the spherical activated carbon can be recycled in the waste dialysate treatment process.     

Electron emission from CVD diamond p-i-n junctions with negative electron affinity during room temperature operation

We successfully observed electron emission from hydrogenated diamond p-i-n junction diodes with negative electron affinity during room temperature operation. The emissions started when the applied bias voltage produced flat-band conditions, where the capacitance-voltage characteristics showed carrier injection in the i-layer. In this low current injection region, the electron emission efficiency (η) of the p-i-n junction diodes (p is top layer) was about 5 × 10^− 5, while that of the n-i-p diodes (n is top layer) was about 10^− 8. With increasing diode current, both diodes showed an increase in η and a nonlinear increase in emission current. In the high current injection region with high diode current of 5-50 mA, both diodes had an emission current of almost 10 μA, where η of a p-i-n junction diode was 0.18%, while that of a n-i-p junction diode was 0.02%.Note that η, which corresponds to the electron emission mechanism, depended on the diode current level.     

Synthesis of zinc oxide nanostructures on graphene/glass substrate by electrochemical deposition: effects of current density and temperature

The electrochemical growth of zinc oxide (ZnO) nanostructures on graphene on glass using zinc nitrate hexahydrate was studied. The effects of current densities and temperatures on the morphological, structural, and optical properties of the ZnO structures were studied. Vertically aligned nanorods were obtained at a low temperature of 75°C, and the diameters increased with current density. Growth temperature seems to have a strong effect in generating well-defined hexagonal-shape nanorods with a smooth top edge surface. A film-like structure was observed for high current densities above -1.0 mA/cm² and temperatures above 80°C due to the coalescence between the neighboring nanorods with large diameter. The nanorods grown at a temperature of 75°C with a low current density of -0.1 mA/cm² exhibited the highest density of 1.45 × 10⁹ cm^-2. X-ray diffraction measurements revealed that the grown ZnO crystallites were highly oriented along the c-axis. The intensity ratio of the ultraviolet (UV) region emission to the visible region emission, I_UV/I_VIS, showed a decrement with the current densities for all grown samples. The samples grown at the current density below -0.5 mA/cm² showed high I_UV/I_VIS values closer to or higher than 1.0, suggesting their fewer structural defects. For all the ZnO/graphene structures, the high transmittance up to 65% was obtained at the light wavelength of 550 nm. Structural and optical properties of the grown ZnO structures seem to be effectively controlled by the current density rather than the growth temperature. ZnO nanorod/graphene hybrid structure on glass is expected to be a promising structure for solar cell which is a conceivable candidate to address the global need for an inexpensive alternative energy source.     

Invariance with pH of enthalpies of activation for O2 reduction at Pt electrodes in acid solutions

The apparent enthalpies of activation, ΔH^*_a, for O₂ reduction at Pt electrodes are determined in acid solutions of different pH. In the high current density region, characterized by a Tafel slope close to − 120 mV, ΔH^*_a,h is lower than ΔH^*_a,l in the low current density region characterized by a Tafel slope close to − 60 mV. Although ΔH^*_a,l > ΔH^*_a,h it is concluded that at every pH the enthalpies of activation at the zero Galvani potential difference are the same in both current density regions. Therefore, irrespective of the different Tafel slopes, the same mechanism is operative in both regions. In all solutions, ΔH^*_a for either current density region are independent of pH when they are determined at constant potentials vs rhe. This invariance with pH is unexpected in view of the suggested variance of the Galvani potential difference with pH. Alternative causes for the invariance are discussed.     

Electroreduction of dioxygen (ORR) in alkaline medium on Ag/C and Pt/C nanostructured catalysts—effect of the presence of methanol

Ag/C catalysts with different loading were prepared using a colloidal route to obtain well dispersed catalysts on carbon, with a particle size close to 15 nm. An amount of 20 wt.% Ag on carbon was found to be the best loading in terms of current density and mass activity. The 20 wt.% Ag/C catalyst was then studied and the kinetics towards ORR was determined and compared with that of a 20 wt.% Pt/C catalyst. The number of exchanged electrons for the ORR was found to be close to four with the rotating disk electrode (RDE) as well as with the rotating ring disc electrode (RRDE) techniques. From the RDE results, the Tafel slopes b, the diffusion limiting current density inside the catalytic film (j_l^film) and the exchange current density (j₀) were evaluated. The Tafel slopes b and diffusion limiting current densities inside the catalytic film (j_l^film) were found to be in the same order for both catalysts, whereas the exchange current density (j₀), which is a suitable estimation of the activity of the catalyst, was at least 10 times higher at the Pt/C catalyst than at the Ag/C catalyst. The behavior of both catalysts in methanol containing electrolyte was investigated and it was found that at a low methanol concentration, the Pt/C catalyst was quasi-tolerant to methanol. But, at a high methanol concentration, the ORR at a Pt/C was affected. However, the Pt/C catalyst showed in each case better activity towards ORR than the Ag/C catalyst, even if the latter one was less affected by the presence of methanol than the former one.     

Ruthenium based DSA® in chlorate electrolysis—critical anode potential and reaction kinetics

Ruthenium based DSA®s have been investigated in chlorate electrolyte using rotating discs made from commercial electrodes. Measurements of the voltammetric charge, q*, and of iR-corrected polarisation curves up to current densities of 40 kA/m² were recorded on new anodes and on aged anodes from 3 years of production in a chlorate plant. Anodic polarisation curves in chloride containing electrolytes bend towards a higher slope at approximately 1.2 V versus Ag/AgCl, likely due to oxidation of ruthenium. The potential and current density at which the curves bend have been defined as the critical potential, E_cr, and the critical current density, i_cr. New anodes that operate at a relatively high potential, >E_cr, obtain an increase in real surface area and thereby a decrease in anode potential and in the selectivity for oxygen formation during the first months of operation. Experiments at constant ionic strength under chlorate process conditions showed that E_cr decreased with increasing chloride concentration with a factor of −0.09 V/log Cl⁻, whereas i_cr increased with increasing chloride concentration. The chlorine evolution reaction was of the first order with respect to chloride concentration. A possible reaction mechanism for chlorine formation is suggested.     

Electrical and light-emitting properties from (111)-oriented homoepitaxial diamond p–i–n junctions

We have succeeded in fabricating a (111)-oriented diamond p–i–n junction with high crystalline quality intrinsic layer and with low series resistance. The series resistance of this diamond p–i–n junction was improved by decreasing the resistivity and specific contact resistance of n-type layer, which is allowed to inject higher current while maintaining lower junction temperature. Current density–voltage characteristics showed a rectification ratio of 10⁶ at ± 15 V at room temperature. A clear ultraviolet emission at around 235 nm due to free exciton recombination was observed at a forward current, while the broad visible light emission from deep levels was significantly suppressed. Moreover, stronger excitonic emission by two orders of magnitude than that of (001)-oriented diamond p–i–n junctions with high series resistance was realized.     

Electrocatalytic and thermal activation of anodic oxygen- and cathodic hydrogen-evolution in alkaline water electrolysis

In micro-electrolysis cells (4 cm² electrode area) which possess a sandwich-configuration as used in advanced water electrolysis[1] different anodic and cathodic electrocatalysts, which did not contain noble metals were investigated over the current density range from 10^?4 to 1.0 A cm^?2 and a temperature range from 30 to 130°C (electrolyte: 50 wt% caustic potash). Mechanically activated nickel electrodes, RuO₂ doped anodes and Pt-black covered cathodes served as comparison standards for H₂ and O₂ evolution.IR-drop connections were not applied. Nonetheless the measuring-method used allowed to keep IR-induced mistakes in voltage-reading in single-electrode voltages below 40 mV even at the highest current densities of 1.0 A cm^?2.Plots of voltage vs log current densities for anodic oxygen evolution possess slopes between 40 and 70 mV (100°C) dec^?1 of current density which in some cases—especially at low temperatures—increased up to a value of 2 RT/F at higher current densities. By increasing the temperature these steeper parts of the anodic current—voltage curves very often disappear.The current-voltage curves of anodic oxygen evolution for different temperatures unexpectedly run nearly parallel to each other ie with a slope which is nearly independent of temperature and thus cannot be described according to the Butler—Volmer equation with a constant value of the formal charge-transfer coefficient βⁱ.The effective activation energies obtained from dln i_o/d(1/T) range from 70 to 100 kJ mole^?1.O₂ overpotentials at current densities around 1 A cm^?2 are most efficiently decreased by (i) application of mixed oxides containing cobalt in at least two different valency states (Co^II/Co^III or Co^III/Co^IV) and (ii) by use of higher working temperatures; roughened surfaces, however, are only of limited value in this respect.Voltage vs log current curves for cathodic hydrogen evolution show a pattern which is in agreement with the Butler—Volmer equation. The effective charge-transfer coefficient is close to 0.5 and increases slightly above this value for Raney-metal activated cathodes.The effective activation energies lie between the limits of 40 and 55 kJ mol^?1. Hydrogen evolution overpotentials are most efficiently decreased by (i) preparation of cathode surfaces with high roughness factors, (ii) using Ni, Co or Fe as cathode material and (iii) by increasing the working temperatures.     

Emission characteristics of planar field electron emitters containing carbon nanotubes operating in the high current density mode

Planar field electron emitters containing carbon nanotubes that demonstrate stable emission currents with densities about 1 A/cm² have been fabricated using the chemical vapor deposition method. The analysis of field emission characteristics based on Fowler-Nordheim theory allowed one to calculate not only the field amplification coefficient β, but also the total emission area A of all the emitting nanotubes. Using the value of A and an estimate of the emission area of an individual nanotube fulfilled in this work, the approximate number of emitting nanotubes N before and after the flow of the high density emission current, has been calculated. It has been found that the concentration of the emitting nanotubes N in such field emitters after the high density emission current flow was about 10⁵ cm⁻². Besides this, the location of light radiating nanotubes heated by high density emission currents has been investigated. This has revealed the regions of the emitter surface that gave the main contribution to the electron emission.     

Nucleation and surface morphology of aluminum-lanthanum alloy electrodepsited in a LaCl3-saturated AlCl3-EtMeImCl room temperature molten salt

The cathodic polarization curve on a tungsten disk electrode was measured in a LaCl₃-saturated AlCl₃-EtMeImCl [1-ethyl-3-methylimidazolium chloride] melt (N=0.667: N is molar fraction of AlCl₃) at 298 K. The deposition overpotential of aluminum increases compared with the curve obtained before adding LaCl₃. It was found that the nucleation/growth process is instantaneous nucleation from chronoamperometric data. When galvanostatic electrolysis was performed in the LaCl₃-saturated melt, the strong orientation of (200) for the electrodeposits is observed at low current densities (≤7.5 mA cm⁻²). On the other hand, the normalized integrated intensity of XRD for (200) and (220) reflections has similar strength at high current densities (≥10.0 mA cm⁻²). The electodeposits become denser than those obtained in the original melt. In particular, very smooth surface is obtained in the case of 15.0 mA cm⁻² with stirring the bath.     

A new polarised hot filament chemical vapor deposition process for homogeneous diamond nucleation on Si(100)

A new hot filament chemical vapor deposition with direct current plasma assistance (DC HFCVD) chamber has been designed for an intense nucleation and subsequent growth of diamond films on Si(100). Growth process as well as the I=f(V) characteristics of the DC discharge are reported. Gas phase constituents activation was obtained by a stable glow discharge between two grid electrodes coupled with two sets of parallel hot filaments settled in-between and polarised at the corresponding plasma potential. The sample is negatively biased with a small 10–15 V extraction potential with respect to the cathode grid. Such design allows to create a high density of both ions and radicals that are extracted and focussed onto the surface of the sample. The current density onto the sample can be finely tuned independently of the primary plasma. A homogeneous plasma fully covering the sample surface is visualized. Consequently, a high-density nucleation (⩾10¹⁰ cm⁻²) occurs.     

Electroformed iron and FeCo alloy

Iron and FeCo alloys were electroformed from additive-free acidic chloride baths. Film stress and magnetic properties were strongly influenced by deposition current density and operating temperature. In general, low film stress and low coercivity (H_C) was achieved with low current density and high operating temperature baths. SEM micrographs indicated that these conditions promote large grain growth. Coercivity of electroformed iron films linearly increased with increasing film stress, indicating that magnetoelastic energy is a dominant anisotropy. The addition of 0.25 M CaCl₂ improves current efficiency while maintaining low film stress. The lowest iron film stress of 5 MPa was achieved from 1.5 M FeCl₂ in the absence of CaCl₂ at 20 mA cm⁻² with a current efficiency of 91%. A “normal” codeposition of FeCo was observed in acidic chloride baths, where the deposition rate of Co²⁺ was faster than Fe²⁺. Film compositions also played an important role in magnetic properties of FeCo films in addition to film stress. Magnetic saturation (M_S) of FeCo films increased linearly with an increase in deposited Fe content. High magnetic saturation with low-stress (M_S of 2.3 T and σ=70 MPa) were achieved from 71Fe29Co films.     

Energy storage and release properties of Sr-doped (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics

Pb_0.94−xLa_0.04Sr_x[(Zr_0.6Sn_0.4)_0.84Ti_0.16]O₃ (x=0,0.02,0.04,0.06) antiferroelectric ceramics were fabricated via conventional solid-state reaction. The increase of Sr content enhanced the stability of antiferroelectric phase, which resulted in the rise of phase transition fields and energy density. When x=0.06, the releasable energy density was 1.52 J/cm³ and the efficiency was 93.3% under 129 kV/cm. The pulsed discharge current was also measured to evaluate the energy release properties. Under 129 kV/cm, the obtained current density could be as high as 165.5 A/cm². The pulsed discharge energy density was 1.21 J/cm³ and 90% of that could be released in less than 200 ns. The high energy density, high efficiency and fast energy release time indicate that the obtained AFE ceramics are very promising for pulsed power capacitors.     

Achieving high comprehensive energy storage properties of BNT-based ceramics via multiscale regulation

It is difficult to obtain high polarization strength and high breakdown strength synchronously, resulting in the drawback of lower energy storage density, which inhibits commercial application of energy storage materials. We have successfully prepared (1-x)(0.93Bi_0.5Na_0.5TiO₃-0.07CaSnO₃)-xSrTiO₃ (BNT–CS–xST) ceramics by solid-state method. The presence of polymorphic nanodomains and the large electric displacement generated by the high charge Sr²⁺-Sr²⁺ ion pairs help to delay saturation polarization (P_m ∼ 48.64 μC/cm² at 315 kV/cm). In addition, the breakdown field strength (E_b) is increased by grain refinement and increasing the band gap. It is noteworthy that a high recoverable energy storage density (W_rec = 4.2 J/cm³) and a great efficiency (η = 88%) were achieved simultaneously in BNT–CS–0.5ST ceramic. Moreover, excellent charge-discharge performance was also achieved, with a discharge energy density W_d of 2.2 J/cm³, a current density C_D of 1724 A/cm² and a power density P_D of 250 MW/cm³. The study demonstrates that the great potential of BNT–CS–xST ceramics in power storage devices and provides an effective strategy for designing ceramics dielectric capacitors with excellent performance.     

Steroid-Functionalized Imidazolium Salts with an Extended Spectrum of Antifungal and Antibacterial Activity

It is established that high rates of morbidity and mortality caused by fungal infections are related to the current limited number of antifungal drugs and the toxicity of these agents. Imidazolium salts as azole derivatives can be successfully used in the treatment of fungal infections in humans. Steroid-functionalized imidazolium salts were synthesized using a new, more efficient method. As a result, 20 salts were obtained with high yields, 12 of which were synthesized and characterized for the first time. They were derivatives of lithocholic acid and 3-oxo-23,24-dinorchol-4-ene-22-al and were fully characterized by ¹H and ¹³C nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and high resolution mass spectrometry (HRMS). Due to the excellent activity against bacteria and Candida albicans, new research was extended to include tests on five species of pathogenic fungi and molds: Aspergillus niger ATCC 16888, Aspergillus fumigatus ATCC 204305, Trichophyton mentagrophytes ATCC 9533, Cryptococcus neoformans ATCC 14116, and Microsporum canis ATCC 11621. The results showed that the new salts are almost universal antifungal agents and have a broad spectrum of activity against other human pathogens. To initially assess the safety of the synthesized salts, hemocompatibility with host cells and cytotoxicity were also examined. No toxicity was observed at the concentration at which the compounds were active against pathogens.     

The effect of temperature on limiting current density and mass transfer in electrodialysis

This study focuses on a high-temperature operation in electrodialysis of salt solutions and studies the effect of temperature on limiting current density and mass transfer. Experiments were conducted under various conditions of temperature (T), varying from 15 to 90°C; of dialysate concentration (C_d), varying from 5 × 10^?3 to 3 × 10^?2M ; and of dialysate velocity (u_d), varying from 0.206 to 2.44 cm s^?1. A least squares fitting of the experimental data on limiting current density (I_lim) yields an Arrhenius equation as follows: The molar flux N? (mol cm^?2 s^?1), initial concentration (C₀; M ) and temperature (T; °C) were found to have the following relationship: N?/C₀ is slightly increased with increasing temperature ranging from 25 to 70°C.     

The stability of the CNT/Ni field emission cathode fabricated by the composite plating method

A novel composite plating method has been developed for the fabrication of carbon nanotube/Ni (CNT/Ni) field emission cathode. The field emission properties of the initial CNT/Ni field emitter show a low turn-on electric field E_on of about 1.1 V/μm with an emission current density of 1 μA/cm², and a low threshold electric field E_th of about 1.7 V/μm with an emission current density of 1 mA/cm². After performing a stability test with a high emission current density in high vacuum, the corresponding microstructure and the degree of graphitization of the CNT/Ni field emitter were measured by using scanning electron microscopy and Raman spectroscopy. We found that the degree of graphitization slowly decreases with the duration time t_FE of the stability test, the size of small rod-like CNT/Ni composite structures in the film increases with t_FE, and obvious cracks appear in the film as t_FE is larger than 60 h. The degradation of the field emission properties may be explained by the Joule heating effect on the CNT/Ni field emitter under high emission current density.     

Structure-design strategy of 0–3 type (Bi0.32Sr0.42Na0.20)TiO3/MgO composite to boost energy storage density,efficiency and charge-discharge performance

A novel 0–3 type (Bi_0.32Sr_0.42Na_0.20)TiO₃/MgO composite is investigated in this work, which possesses a high stored energy storage density w_s˜2.50 J/cm³, recoverable energy storage density W_R˜2.09 J/cm³ with high efficiency η˜84% under low electric field (20 kV/mm). The excellent performance is owning to the increase of breakdown strength (BDS) value and the intrinsic mechanism for enhanced BDS value by MgO incorporation is disclosed by numerical simulations (COMSOL). Moreover, the studied composite exhibits excellent charge-discharge performance, the current density (C_D) and power density (P_D) are 1671 A/cm² and 150 MW/cm³, respectively, which are much superior to that of other ceramics. Besides, most of the stored energy is discharged within ˜0.15 μs via charge-discharge tests. This work not only provides a novel technique to designing bismuth-based ceramic capacitors with simultaneously high W_d, η and excellent charge-discharge performance, but also deepens the understandings of the role for the metallic oxide in the composite.     

Phase evolution during reactive flash sintering of Li6.25Al0.25La3Zr2O12 starting from a chemically prepared powder

Reactive flash sintering (RFS) of a chemically prepared multiphase precursor powder was performed to fabricate Li_6.25Al_0.25La₃Zr₂O₁₂ (Al-LLZO) ceramics. This approach allowed for obtaining single-phase dense samples in a remarkably short processing time of 30 s, at a furnace temperature of 600 °C, with an electric field of 50 V cm^?1 and a current limit of 150 mA mm^-2. The ceramics display high bulk conductivity of 0.18 mS cm^?1 at room temperature. Furthermore, phase evolution is studied by in-situ X-ray diffraction during: i) conventional heating and ii) RFS under current rate mode. As expected, the intermediate phases progressively dissolved into the Al-LLZO matrix by conventional heating. On the other hand, RFS promoted the growth of the intermediate La₂Zr₂O₇, an effect that was overcome by the thermally driven formation of Al-LLZO at higher temperatures. The observed different reaction pathway suggests that RFS can be used for stabilizing phases that are not thermodynamically favored upon conventional heating.