Accelerating the decarbonization of carbonaceous gold ore by suspension oxidation roasting towards the improvement of gold leaching efficiency

Eliminating the gold preg-robbing effect of carbonaceous matter in carbonaceous gold ores is crucial for gold leaching. In this study, suspension oxidation roasting was proposed to accelerate the decarbonization of carbonaceous gold ore. The characteristics of oxidation reaction process and gas release were analyzed by TG-DTA-FTIR. The phase transformation and microstructure evolution of samples during roasting were analyzed by XRD, SEM and BET. The results show that the gold preg-robbing effect was eliminated after the gasification of carbonaceous matter, and the CaO generated by decomposition of carbonates can effectively capture the SO₂. After roasting for 75 min at 650 °C in a 20% O₂ atmosphere, the total carbon removal rate reached 99.42%, the distribution of exposed gold increased from 28.85% to 77.10% and the gold leaching efficiency increased from 4.55% to 84.83%. In addition, about 70% sulfur was mainly fixed in the roasted products in the form of sulfate. Therefore, the suspension oxidation roasting process is an efficient and clean pretreatment method for carbonaceous gold ores.     

Bimetallic platinum–ruthenium nanoparticles immobilized on reduced graphene oxide-TiO2 (RGO-TiO2) support for ethanol electro oxidation in acidic media

The present work addresses the potentialities of Pt–Ru nanoparticles deposited on a graphene oxide (RGO) and TiO₂ composite support towards electrochemical oxidation of ethanol in acidic media relevant for fuel cell applications. To immobilize platinum–ruthenium bimetallic nanoparticles on to an RGO-TiO₂ nanohybrid support a simple solution-phase chemical reduction method is utilized. An examination using electron microscopy and energy dispersive X-ray spectroscopy (EDS) indicated that Pt–Ru particles of 4–8 nm in diameter are dispersed on RGO-TiO₂ composite support. The corresponding Pt–Ru/RGO-TiO₂ nanocomposite electrocatalyst was studied for the electrochemical oxidation of ethanol in acidic media. Compared to the commercial Pt–Ru/C and Pt/C catalysts, Pt–Ru/RGO-TiO₂ nanocomposite yields higher mass-specific activity of about 1.4 and 3.2 times, respectively towards ethanol oxidation reaction (EOR). The synergistic boosting provided by RGO-TiO₂ composite support and Pt–Ru ensemble together contributed to the observed higher EOR activity and stability to Pt–Ru/RGO-TiO₂ nanocomposite compared with other in-house synthesized Pt–Ru/RGO, Pt/RGO and commercial Pt–Ru/C and Pt/C electrocatalysts. Further optimization of RGO-TiO₂ composite support provides opportunity to deposit many other types of metallic nanoparticles onto it for fuel cell electrocatalysis applications.     

Swapping catalytic active sites from cationic Ni to anionic F in Fe–F–Ni3S2 enables more efficient alkaline oxygen evolution reaction and urea oxidation reaction

Electrolysis of water for producing hydrogen instead of traditional fossil fuels is one of the most promising methods to alleviate environmental pollution and energy crisis. In this work, Fe and F ion co-doped Ni₃S₂ nanoarrays grown on Ni foam substrate were prepared by typical hydrothermal and sulfuration processes for the first time. Density functional theory (DFT) calculation demonstrate that the adsorption energy of the material to water is greatly enhanced due to the doping of F and Fe, which is conducive to the formation of intermediate species and the improvement of electrochemical performance of the electrode. The adsorption energy of anions (F and S) and cations (Fe and Ni) to water in each material was also calculated, and the results showed that F ion showed the most optimal adsorption energy of water, which proved that the doping of F and Fe was beneficial to improve the electrochemical performance of the electrode. It is worth noting that the surface of Fe–F–Ni₃S₂ material will undergo reconstruction during the process of water oxidation reaction and urea oxidation reaction, and amorphous oxides or hydroxides in situ would be formed on the surface of electrode, which are the real active species.     

Evaluation of physicochemical properties and microbial counts of raw and cooked low-fat patties added with eggplant powder prepared with different drying methods

Effects of different drying methods and different addition levels of eggplant (EP) on product quality of low-fat patties (LFPs) were investigated during storage. EP was dried in an oven dryer at 60 °C or a freeze dryer at −50 °C. LFPs were prepared by replacing with 1.5% soy protein isolate (SPI). Six treatments were used in this study: (1) control (CTL), without addition of EP; (2) reference (REF), 0.1% ascorbic acid; (3) O1, 0.25% oven-dried (OD) EP; (4) O2, 0.5% ODEP; (5) F1, 0.25% freeze-dried (FD) EP; and (6) F2, 0.5% FDEP. Redness (a*) and lightness (L*) values in LFPs added with EP were lower than those of others (p < 0.05) and decreased with increasing storage time. Yellowness (b*) values of cooked patties were increased during storage time (p < 0.05), with control having the highest value. The addition of EP or ascorbic acid into LFPs lowered microbial counts than control (p < 0.05). Thiobarbituric acid reactive substances (TBARS) was increased during storage, with REF having the lowest value, and patties added with EP had lower TBARS values than control during storage. Volatile basic nitrogen (VBN, mg%) contents of all patties also increased during storage time with O2 and F2 having lower values than control. Therefore, EP might have potential as a natural antioxidant in meat products during storage.     

Effects of structural parameters on water film properties of transpiring wall reactor

Corrosion and salt deposition problems severely restrict the industrialization of supercritical water oxidation. Transpiring wall reactor can effectively weaken these two problems by a protective water film. In this work, methanol was selected as organic matter, and the influences of vital structural parameters on water film properties and organic matter removal were studied via numerical simulation. The results indicate that higher than 99% of methanol conversion could be obtained and hardly affected by transpiration water layer, transpiring wall porosity and inner diameter. Increasing layer and porosity reduced reactor center temperature, but inner diameter's influence was lower relatively. Water film temperature reduced but coverage rate raised as layer, porosity, and inner diameter increased. Notably, the whole reactor was in supercritical state and coverage rate was only approximately 85% in the case of one layer. Increasing reactor length affected slightly the volume of the upper supercritical zone but enlarged the subcritical zone.     

Revealing the role of Ni2+ ions in inducing the synthesis of porous carbon balls: A novel substrate to enhance the Pt catalytic activity towards methanol-oxidation

Carbon-based materials have been often employed as electrocatalytic substrates because of their large surface area/highly porous structure. Similar to carbon substrates, the non-carbon related materials such as transition metals also play an important role in improving catalytic performance. However, the simultaneous synthesis and metallic functionalization of carbon substrates is a highly challenging issue. Herein, a hydrothermal method has been used for the preparation of Ni-functionalized porous carbon balls. The significant role of Ni²⁺ ions in the synthesis of porous carbon balls has been confirmed. The results of transmission electron microscopy indicate that, the as-prepared porous carbon balls were suitable for the dispersion of Pt nanoparticles with small particle size (less than 4 nm). In addition to providing the OH_ads species, the Ni can also modify the surface electronic structure of Pt. Electrochemical measurements results reveal that, under the strong interactions between Ni and Pt, the as-prepared porous carbon balls supported Pt nanoparticles (Pt/Ni-CB) catalyst possesses excellent electrocatalytic activity, stability and CO anti-poisoning capability towards methanol electrooxidation reaction (MOR). This work opens a novel idea for the construction of the metal functionalization of carbon substrates and their subsequent applications in other electrocatalytic reactions.     

Wavelength-dependent photoactivity of ZnxCd1−xS and ZnCo2O4/ZnxCd1−xS for H2 and H2O2 production

Zinc cadmium sulfide (Zn_xCd_1?xS) is a good photocatalyst for hydrogen evolution reaction (HER), but an optimum x (x_m) at which a maximum HER rate is reached varies from one report to another. In this work, we examine the effect of light wavelength, not only for the HER to H₂ in the presence of Na₂S and Na₂SO₃, but also for oxygen reduction reaction (ORR) without addition of any sacrifices. For the HER under a 365 and 420 nm LED lamp, the x_m were 0.9 and 0.7, respectively. For the HER under a 330 and 395–515 nm cut-off xenon lamp, the x_m were 0.7 and 0.5, respectively. For the ORR under a 420 nm cut-off halogen lamp, a maximum production of H₂O₂ was observed at x = 0.3. Furthermore, after 4% ZnCo₂O₄ loading, Zn_xCd_1?xS had an increased activity and stability, either for the HER or for the ORR. Through a (photo)electrochemical measurement, it is proposed that the photocatalytic activity of Zn_xCd_1?xS is determined by its light absorptivity and electron reactivity. The improved performance of n-type Zn_xCd_1?xS by p-type ZnCo₂O₄ is due to formation of a p-n junction, promoting the HER (ORR) on Zn_xCd_1?xS, and the sulfide (water) oxidation on ZnCo₂O₄. This work highlights that Zn_xCd_1-xS is a promising photocatalyst for H₂ and H₂O₂ production, respectively.     

Thermal and photon effects on the reaction of H2 and O2 to water over Ag–Pd/TiO2

The reaction of H₂ and O₂ to water are studied over a Ag–Pd/TiO₂ anatase catalyst, under dark and photo-irradiation conditions in the gas and liquid phases. The catalyst consisted of metal particles of mean size of ca.1 nm dispersed over 10–15 nm TiO₂ particles. Kinetic parameters including order of reaction (n), rate constant (k), and activation energy (E_a), were evaluated. E_a for the thermal reaction was found to be 49-47 kJ mol^?1. The oxidation reaction rate constant was found to be ca. 3 times higher in the presence of photons when compared to dark reaction at room temperature. The overall quantum yield of the reaction in the slurry phase was found to be 0.09. Considering the number of metal particles on TiO₂, the photon yield per metal particle was found to be 0.16. A possible explanation of the changes in kinetics with respect to experimental conditions is given.     

Ru-doped 3D porous Ni3N sphere as efficient Bi-functional electrocatalysts toward urea assisted water-splitting

Developing efficient, stable and ideal urea oxide (UOR) electrocatalyst is key to produce green hydrogen in an economical way. Herein, Ru doped three dimensional (3D) porous Ni₃N spheres, with tannic acid (TA) and urea as the carbon and nitrogen resources, is synthesized via hydrothermal and low-temperature treated process (Ru–Ni₃N@NC). The porous nanostructure of Ni₃N and the nickel foam provide abundant active sites and channel during catalytic process. Moreover, Ru doping and rich defects favor to boost the reaction kinetics by optimizing the adsorption/desorption or dissociation of intermediates and reactants. The above advantages enable Ru–Ni₃N@NC to have good bifunctional catalytic performance in alkaline media. Only 43 and 270 mV overpotentials are required for hydrogen evolution (HER) and oxygen evolution (OER) reactions to drive a current of 10 mA cm^?2. Moreover, it also showed good electrocatalytic performance in neutral and alkaline seawater electrolytes for HER with 134 mV to drive 10 mA cm^?2 and 83 mV to drive 100 mA cm^?2, respectively. Remarkably, the as-designed Ru–Ni₃N@NC also owns extraordinary catalytic activity and stability toward UOR. Moreover, using the synthesized Ru–Ni₃N@NC nanomaterial as the anode and cathode of urea assisted water decomposition, a small potential of 1.41 V was required to reach 10 mA cm^?2. It can also be powered by sustainable energy sources such as wind, solar and thermal energies. In order to make better use of the earth's abundant resources, this work provides a new way to develop multi-functional green electrocatalysts.