Recovery of Zinc from Metallurgical Slag and Dust by Ammonium Acetate Using Response Surface Methodology.

Metallurgical slag and dust (MSD) are abundant Zn-containing secondary resources that can partially alleviate the shortage of zinc minerals, with hazardous characteristics and a high recycling value. In this work, the process conditions of recycling Zn from MSD materials leaching by ammonium acetate (NH3-CH3COONH4-H2O) were optimised using response surface methodology (RSM). The influences of liquid/solid ratio, stirring speed, leaching time, total ammonia concentration, and the interactions between these variables on the Zn effective extraction rate during the ammonium acetate leaching process were investigated. Additionally, the predicted regression equation between the Zn effective extraction rate and the four affecting factors was established, and the optimal process parameters were determined with a stirring speed of 345 r/min, leaching temperature of 25 °C, [NH3]/[NH4]+ of 1:1, total ammonia concentration of 4.8 mol/L, liquid/solid ratio of 4.3:1, and leaching time of 46 min. The Zn effective extraction rates predicted by the proposed model and the measured values were 85.25% and 84.67%, respectively, with a relative error of 0.58% between the two values, indicating the accuracy and reliability of the proposed model. XRD and SEM-EDS analysis results showed that Zn2SiO4, ZnS, and ZnFe2O4 were among the main factors affecting the low extraction rate of zinc from metallurgical slag dust. This work established a new technology prototype for the effective and clean extraction of zinc resources, which can provide new routes to effectively utilise Zn-containing MSD materials and lay a foundation for developing other novel techniques for recycling Zn from Zn-containing secondary resources.

Mechanism of microwave-assisted iron-based catalyst pyrolysis of discarded COVID-19 masks.

Inexpensive iron-based catalysts are the most promising catalysts for microwave pyrolysis of waste plastics, especially a large number of disposable medical masks (DMMs) with biological hazards produced by spread of COVID-19. However, most synthesized iron-based catalysts have very low microwave heating efficiency due to the enrichment state of iron. Here, we prepared FeAlOx catalysts using the microwave heating method and found that the microwave heating efficiency of amorphous iron and hematite is very low, indeed, these materials can hardly initiate pyrolysis at room temperature, which limits the application of iron-based catalysts in microwave pyrolysis. By contrast, a mixture of DMMs and low-valent iron oxides produced by hydrogen reduction at 500 °C can be heated by microwaves to temperatures above 900 °C under the same conditions. When the hydrogen reduction temperature was incerased to 800 °C, the content of metallic iron in the catalyst gradually increased from 0.34 to 21.43%, which enhanced the microwave response ability of the catalyst, and decreased the gas content in the pyrolysis product from 78.91 to 70.93 wt%; corresponding hydrogen yield also decreased from 29.03 to 25.02 mmolH2·g-1DMMs. Moreover, the morphology of the deposited solid carbon gradually changed from multi-walled CNTs to bamboo-like CNTs. This study clarifies the pyrolysis mechanism of microwave-assisted iron catalysts and lays a theoretical foundation for their application in microwave pyrolysis.

Deep Learning-Based Remaining Useful Life Estimation of Bearings with Time-Frequency Information.

In modern industrial production, the prediction ability of remaining useful life of bearings directly affects the safety and stability of the system. Traditional methods require rigorous physical modeling and perform poorly for complex systems. In this paper, an end-to-end remaining useful life prediction method is proposed, which uses short-time Fourier transform (STFT) as preprocessing. Considering the time correlation of signal sequences, a long and short-term memory network is designed in CNN, incorporating the convolutional block attention module, and understanding the decision-making process of the network from the interpretability level. Experiments were carried out on the 2012PHM dataset and compared with other methods, and the results proved the effectiveness of the method.

CNN-based neural network model for amplified laser pulse temporal shape prediction with dynamic requirement in high-power laser facility.

The temporal shape of laser pulses is one of the essential performances in the inertial confinement fusion (ICF) facility. Due to the complexity and instability of the laser propagation system, it is hard to predict the pulse shapes precisely by pure analytic methods based on the physical model [Frantz-Nodvik (F-N) equation]. Here, we present a data-driven model based on a convolutional neural network (CNN) for precise prediction. The neural network model introduces sixteen parameters neglected in the F-N equation based models to expand the representation dimension. The sensitivity analysis of the experimental results confirms that these parameters have different degrees of influence on the temporal output shapes and cannot be ignored. The network characterizes the whole physical process with commonality and specificity features to improve the description ability. The prediction accuracy evaluated by a root mean square of the proposed model is 7.93%, which is better compared to three optimized physical models. This study explores a nonanalytic methodology of combining prior physical knowledge with data-driven models to map the complex physical process by numerical models, which has strong representation capability and great potential to model other measurable processes in physical science.

A Study on the Mechanism and Kinetics of Ultrasound-Enhanced Sulfuric Acid Leaching for Zinc Extraction from Zinc Oxide Dust.

As an important secondary zinc resource, large-scale reserves of zinc oxide dust (ZOD) from a wide range of sources is of high comprehensive recycling value. Therefore, an experimental study on ultrasound-enhanced sulfuric acid leaching for zinc extraction from zinc oxide dust was carried out to investigate the effects of various factors such as ultrasonic power, reaction time, sulfuric acid concentration, and liquid-solid ratio on zinc leaching rate. The results show that the zinc leaching rate under ultrasound reached 91.16% at a temperature of 25 °C, ultrasonic power 500 W, sulfuric acid concentration 140 g/L, liquid-solid ratio 5:1, rotating speed 100 r/min, and leaching time 30 min. Compared with the conventional leaching method (leaching rate: 85.36%), the method under ultrasound increased the zinc leaching rate by 5.8%. In a kinetic analysis of the ultrasound-enhanced sulfuric acid leaching of zinc oxide dust, the initial apparent activation energy of the reaction was 6.90 kJ/mol, indicating that the ultrasound-enhanced leaching process was controlled by the mixed solid product layers. Furthermore, the leached residue was characterized by XRD and SEM-EDS, and the results show that, with ultrasonic waves, the encapsulated mineral particles were dissociated, and the dissolution of ZnO was enhanced. Mostly, the zinc in leached residue existed in the forms of ZnFe2O4, Zn2SiO4, and ZnS.

Porous carbon materials derived from discarded COVID-19 masks via microwave solvothermal method for lithium­sulfur batteries.

With the spread of COVID-19, disposable medical masks (DMMs) have become a significant source of new hazardous solid waste. Their proper disposal is not only beneficial to the safety of biological systems but also useful to achieve considerable economic value. The first step of this study was to investigate the chemical composition of DMMs. It is primarily composed of polypropylene, polyethylene terephthalate and iron, with fibrous polypropylene accounting for approximately 80% of the total weight. Then, DMMs were sulfonated and oxidised by the microwave-driven concentrated sulfuric acid within 8 min based on the fact that the concentrated sulfuric acid exhibits a good microwave absorption capacity. The co-doping of sulfur and oxygen was achieved while improving the thermal stability of DMMs. Subsequently, the self-activation pyrolysis of sulfonated and oxidised DMMs (P-SO@DMMs) was further realized in low-flow-rate argon. The specific surface area of P-SO@DMMs increased from 2.0 to 830.9 m2·g-1. P-SO@DMMs sulfur cathodes have promising electrochemical properties because of their porous structures and the synergistic effect of sulfur and oxygen co-doping. The capacity of the samples irradiated by microwave for 10 min at 0.1, 0.2, 0.5, 1, 2 and 5 C were 1313.6, 1010.9, 816.5, 634.4, 513.4 and 453.1 mAh·g-1, respectively, and after returning to 0.2 C and continuing the cycle for 50 revolutions, maintained 50.5% of the initial capacity. After 400 cycles, its capacity is 38.1% of the initial capacity at 0.5 C. It is slightly higher than the electrochemical performance of the sample treated by microwave for 8 min and significantly higher than the sample treated by 6 min. This work converts structurally complex, biohazardous DMMs into porous carbon with high specific surface area by clean and efficient microwave solvothermal and self-activating pyrolysis, which facilitates the development of carbon based materials at low cost and large scale.

Dielectric Properties of Silicothermic Reduction Chromite in the Microwave Field.

The microwave absorption properties of chromite and the feasibility of microwave reduction chromite have been discussed. The results show that as the density increases, the dielectric properties of materials increase. The dielectric properties are the best (the value around 4.2) when the silica ratio is 0.5. Microwave penetration depth shows that chromite and the mixture have good wave absorption properties.

Microwave Pyrolysis of Macadamia Shells for Efficiently Recycling Lithium from Spent Lithium-ion Batteries.

To reduce harm to the environment and human health and improve economic benefits, the large number of spent lithium-ion batteries that have been produced in recent years need to be reasonably recycled. The purpose of this article is to study a new method, microwave pyrolysis of the shells of macadamia nuts, for efficient recycling of lithium from spent lithium-ion batteries. XRD, SEM, and TGA analyses were used to observe the phase change during roasting. With the help of microwave heating and biomass pyrolysis, the decomposition temperature of Li(Ni1/3Co1/3Mn1/3)O2 was reduced to 300 °C. Carbonated water-soluble Li2CO3 was formed under the action of biochar. Accordingly, the effects of pyrolysis temperature (Pte), biomass dose (bio%), reduction roasting temperature (Rte) and reduction roasting time (Rti) on the leaching rate of lithium were studied, and the results indicated that 93.4% lithium could be leached under the following optimum conditions: bio% = 24, Pte = 500 °C, Rte = 750 °C, and Rti = 25 min. A lattice collapse model and coupling reaction theory explained the benefit of biomass pyrolysis on the decomposition of Li(Ni1/3Co1/3Mn1/3)O2. Finally, we designed a complete process for recycling the cathode powder of spent lithium-ion batteries. This study can guide industrial production to recover lithium-ion batteries in the future.

Microwave-absorbing properties of cathode material during reduction roasting for spent lithium-ion battery recycling.

As a hazardous material to the environment and human health, spent lithium-ion batteries need to be recycled in a reasonable way. To explore the effect of microwave heating on spent lithium-ion batteries (LIBs) recycling, the microwave-absorbing properties of a spent cathode powder (LiNixCoyMnzO2) were studied by measuring its dielectric properties from 25-900 °C at 2450 MHz under different conditions (temperature, carbon dose and apparent density). X-ray diffraction and thermogravimetric analysis (TGA) were used to study decomposition and reduction reactions in the heating process. The results indicated that the cathode material has good microwave-absorbing properties over the entire temperature range (25-900 °C), especially when mixed with carbon. As the reduction reactions proceed, the dielectric properties of the material increase rapidly from 600 °C, which means that microwave heating can promote a carbothermal reduction reaction. The effect of the carbon dose on the dielectric properties indicates that the carbothermal reduction reaction can fully occur when the carbon dose reaches 18%. Furthermore, the best microwave-absorbing performance can be achieved when the apparent density of the material is 1.41 g/cm3. These studies have established a basis for research towards the direct recovery of lithium from LIBs by microwave reduction roasting.

Microwave field: High temperature dielectric properties and heating characteristics of waste hydrodesulfurization catalysts.

The exploration of the dielectric properties of waste hydrodesulfurization catalysts has important guiding significance for the development of microwave heat treatment of waste hydrodesulfurization catalysts for the recovery of valuable metals. The resonant cavity perturbation technique was used to measure the dielectric properties of waste catalyst and the mixture of waste catalyst and Na2CO3 during roasting from room temperature to 700 °C at 2450 MHz. The heating properties of the waste catalyst and mixture of waste catalyst and Na2CO3 were determined in the microwave field. The results show that the waste catalyst and the mixture of waste catalyst and Na2CO3 exhibit strong microwave response capability, and the dielectric constant, dielectric loss factor, and dielectric loss tangent increase with increasing temperature; from 20 to 300 °C, the waste catalyst and the mixture of waste catalyst and Na2CO3 heated at a slower rate, while the material heated rapidly from 300 to 700 °C. In addition, the mechanism of microwave action has been proposed based on the study of dielectric properties and heating properties in the microwave field.

Thermodynamic, Structural and Thermoelectric Properties of AgSbTe2 Thick Films Developed by Melt Spinning.

Cubic AgSbTe2 compound is a metastable phase within Ag2Te-Sb2Te3 pseudo-binary phase diagram and theoretically rapid cooling molten elements to room temperature may be an effective way to obtain it. In this work, thick films composed of 5⁻10 nm fine grains were developed by a melt spinning technique. The formation mechanism of the nanostructure and its influences on the thermoelectric properties have been studied and correlated. Differential scanning calorimetry (DSC) analysis shows that the as-prepared films exhibit distinct thermodynamic properties when prepared under different cooling rates and doping element. A small amount of Se doping is effectively capable of inhibiting the emergence of the Ag2Te impurity and optimizing the electrical transport properties. All films have positive large Seebeck coefficient, but rather small positive or negative Hall coefficient, indicating a multicarrier nature of transport consisting of both holes and electrons. A power factor of ~1.3 was achieved at 500 K for Se-doped film for its excellent electrical conductivities. This result confirms that a combination of Se doping and melting spinning technique is an effective way to obtain high phase-pure AgSbTe2 compound and reveal its intrinsic transport properties routinely masked by impurities in sintering or slow-cooling bulk samples.

FSI-based non-cooperative target absolute distance measurement method using PLL correction for the influence of a nonlinear clock.

We propose a frequency swept interferometry (FSI)-based absolute distance measurement method that can be used to measure a noncooperative target located at a distance of 10s of m. In this method, an external cavity laser serves as the frequency tuning laser, and a single frequency laser and two acoustic optical modulators (AOMs) are used to measure the optical path difference (OPD) variation during the frequency tuning, which can correct the Doppler effect. A phase-locked loop (PLL) is introduced to synchronize the nonlinearities between the OPD variation measurement signal and the absolute distance measurement signal, improving the signal-to-noise ratio (SNR) of the OPD variation measurement signal. The distance to a noncooperative target located at 15 m is experimentally measured using this method, and a precision of 3.43 µm is obtained.

Combining sub-Nyquist sampling and chirp decomposition for a high-precision and speed absolute distance measurement method.

A high-precision and speed absolute distance measurement based on swept-wavelength interferometry is reported. A powerful method combining sub-Nyquist sampling and chirp decomposition for dispersion mismatch compensation is proposed. A standard deviation of 0.72 µm is obtained for the measurement of a target located at 3.9 m, which is better than the traditional method. The measurement can be completed in 1.9 s when the frequency range is 4.26 THz, which is much better than chirp decomposition without sub-Nyquist sampling.

Absolute distance measurement system with micron-grade measurement uncertainty and 24 m range using frequency scanning interferometry with compensation of environmental vibration.

We establish a theoretical model of the Doppler effect in absolute distance measurements using frequency scanning interferometry (FSI) and propose a novel FSI absolute distance measurement system. This system incorporates a basic FSI system and a laser Doppler velocimeter (LDV). The LDV results are used to correct for the Doppler effect in the absolute distance measurement signal obtained by the basic FSI system. In the measurement of a target located at 16 m, a measurement resolution of 65.5 µm is obtained, which is close to the theoretical resolution, and a standard deviation of 3.15 µm is obtained. The theoretical measurement uncertainty is 8.6 µm + 0.16 µm/m Rm (k = 2) within a distance range of 1 m to 24 m neglecting the influence of air refractive index, which has been verified with experiments.

Method based on chirp decomposition for dispersion mismatch compensation in precision absolute distance measurement using swept-wavelength interferometry.

We establish a theoretical model of dispersion mismatch in absolute distance measurements using swept-wavelength interferometry (SWI) and propose a novel dispersion mismatch compensation method called chirp decomposition. This method separates the dispersion coefficient and distance under test, which ensures dispersion mismatch compensation without introducing additional random errors. In the measurement of a target located at 3.9 m, a measurement resolution of 45.9 µm is obtained, which is close to the theoretical resolution, and a standard deviation of 0.74 µm is obtained, which is better than the traditional method. The measurement results are compared to a single-frequency laser interferometer. The target moves from 1 m to 3.7 m, and the measurement precision using the new method is less than 0.81 µm.

(3 + 1)-Dimensional commensurately modulated structure and photoluminescence properties of diborate KSbOB2O5.

Single-crystal diborate KSbOB2O5 has been prepared under a high temperature molten-salt method and its structure has been determined by single crystal X-ray diffraction analysis. The diffraction pattern shows strong main reflections and weak satellite reflections, clearly indicating a modulated structure. Using the four-dimensional superspace formalism for aperiodic structures, its reflections could be indexed as orthorhombic superspace group Pmn21(0ß0)s00 with the modulation vector q = 5/12b*, and then the structure solution and refinement reached a final commensurately modulated model that was refined extremely well and did not show any unusual features. On the other hand, the powder sample of KSbOB2O5 was synthesized by the high-temperature solid-state reaction method, and the powder X-ray diffraction pattern fits very well with the simulated from the single-crystal data. In addition, photoluminescence properties of diborate KSbOB2O5 activated by 4.5 mol% Dy(3+) have been studied, indicating an extraordinary phenomenon that the red emission at around 635 nm ((4)F(9/2) → (6)H(11/2)) is much stronger than the yellow emission at around 581 nm ((4)F(9/2) → (6)H(13/2)).

Temperature and moisture dependence of the dielectric properties of silica sand.

The major objective of this work was to investigate the effects of temperature and moisture content on the dielectric properties of silica sand. The dielectric properties of moist silica sand at five temperatures between 20 to 100 degrees C, covering different moisture content levels at a frequency of 2.45 GHz, were measured with an open-ended coaxial probe dielectric measurement system. The wave penetration depth was calculated based on the measured dielectric data. The results show moisture content to be the major influencing factor for the variation of dielectric properties. Dielectric constant, loss factor and loss tangent all increase linearly with increasing moisture content. Three predictive empirical models were developed to relate the dielectric constant, loss factor, loss tangent of silica sand as a linear function of moisture content. An increase in temperature between 20 to 100 degrees C was found to increase the dielectric constant and loss factor. The penetration depth decreased with increase in moisture content and temperature. Variation in penetration depth was found to vary linearly with decrease in moisture content. An predictive empirical model was developed to calculate penetration depth for silica sand. This study offers useful information on dielectric properties of silica sand for developing microwave drying applications in mineral processing towards designing better microwave sensors for measuring silica sand moisture content.

Optimization of hydrous ferrous sulfate dehydration by microwave heating using response surface methodology.

The work relates to assessing the ability of the microwave for dehydration of large amount of waste hydrous ferrous sulfate generated from the titanium pigment process industry. The popular process optimization tool of response surface methodology with central composite design was adopted to estimate the effect of dehydration. The process variables were chosen to be power input, duration of heating and the bed thickness, while the response variable being the weight loss. An increase in all the three process variables were found to significantly increase the weight loss, while the effect of interaction among the parameters were found to be insignificant. The optimized process conditions that contribute to the maximum weight loss were identified to be a power input of 960 W, duration of heating of 14 min and bed thickness of 5 cm, resulting in a weight loss of 31.44%. The validity of the optimization process was tested with the repeat runs at optimized conditions.

Alternating current impedance spectroscopy measurement under high pressure.

A microcircuit was designed and fabricated on a diamond anvil cell for alternating current impedance spectroscopy measurement under high pressure. Sputtered molybdenum film on a diamond anvil was used as an electrode, maintained the contact between the sample and the electrode stable, and reduced the electrode effect on the impedance measurement. By the empty cell and short circuit tests, the parasitic capacitive impedance from the sample chamber wall was observed to be larger than 10(5) Ω at a frequency lower than 1.0 MHz and could be ignored for samples with higher conductivity. The wire inductance was only 1.0 µH and just appeared at frequency higher than 20 kHz, which could be subtracted from measured impedance for the samples with higher impedance than several hundred ohms. Using this apparatus, the impedances of the II-VI group cadmium sulfide were measured. The pressure dependence of the grain interior conductance of CdS crystal was obtained, which reflected that the phase transitions of CdS under high pressure are the same as the single crystal measurement results.

High pressure effect on the ultrafast energy relaxation rate of LDS698 (C19H23N2O4Cl) in a solution.

Effects of high pressure in a range of up to 1.7 GPa on ultrafast energy relaxation of LDS698 (C(19)H(23)N(2)O(4)Cl) molecules in solution have experimentally been illustrated by a method of femtosecond time-resolved absorption spectroscopy. The rates of the intramolecular and intermolecular energy relaxations show quite different pressure dependences. The observed results are in good agreement with the theoretical interpretation based on the pressure influences on the molecular energy gaps, the intermolecular H-bond interaction, and the solution viscosity.