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Flocculation occurring in a feedwell plays a critical role in tailings slurry thickening process, which is complicated and significantly influenced by flow characteristics. This work presents a numerical approach to explore the effect of flow characteristics on flocculation performance. It combines an aggregation kernel and a breakage kernel, used to describe the polymer-bridging flocculation kinetics, with a conventional Computational Fluid Dynamics-Population Balance Model (CFD-PBM) coupling to model the complex flocculation-thickening behavior in a lab-scale gravity thickener. The solid-liquid phase interaction is described by an Euler-Euler approach with a modified Schiller-Naumann drag model. The turbulence of liquid phase is resolved by the RNG k-e turbulence model, while the solid kinematic eddy viscosity is described by a dispersed phase zero equation model. The capability of this proposed model is validated by a good agreement between experimental and predicted results in terms of single-liquid velocity and floc size distribution. The momentum and turbulence dissipation rates are investigated in and around the feedwell over a wide range of feed velocities, showing that the momentum and turbulence dissipation rates have a positive correlation with feed velocity. The momentum and turbulence dissipation rates decrease with the increase in scaled depth in the feedwell. The formation of large vortexes in the feedwell may cause a locally low turbulence dissipation rate. A reasonable increase of feed velocity favours the flocculation, however, an excessive feed velocity can cause a decrease in mean floc size. Modelling tailings flocculation is of great significance for understanding the flocculation behavior and revealing the effect of flow characteristics on flocculation performance.

The inlet design of hydrocyclones determines the flow field symmetry and facilitates the formation of vortices. In this study, an integrated multichannel inlet based on the Archimedes spiral is developed to improve particle classification by combining the advantages of existing designs. Hydrocyclones with conventional tangent or novel spiral inlets are comparably studied to evaluate the feasibility and superiority of this design using the validated volume of fraction model and two-fluid model. Numerical results show that this novel spiral inlet dramatically improves the flow field symmetry in terms of radial velocity and air core as well as reduces the short-circuit flow and circulation flow. In addition, it also provides strong diversion and pre-separation effects on particles. Consequently, this novel spiral inlet provides superior classification performance than the conventional design, appearing in smaller cut-size, higher cut sharpness, and higher capacity. Such advantages become less evident with increasing channel number, due to the increased turbulence intensity caused by the additional feed streams. The spiral inlet with two channels can largely resemble the design with two tangential inlets in all indices, which makes it the most suitable in this study. This design method can be easily extended to other types of hydrocyclones.

As a principal reason for the deterioration of separation accuracy, the bypass effect in hydrocyclones has received widely concerned. This paper presents a numerical study about the effect of flat bottom structure width on the bypass effect with the respect of flow field characteristics, separation efficiency, and particle spatial distribution with a verified TFM model. Numerical results demonstrate that wide flat bottom structure increases the cut size and reduces the fine particles misplaced in the underflow. However, the excessive flat bottom structure width increases coarse particles misplaced in the overflow causing by the superior turbulence intensity and the entrapment of the internal swirling flow. A wide flat bottom structure width reduces the turbulence dissipation rate, while the split ratio first decreases and then increases, indicating that the bypass effect is controlled by the turbulence dissipation and does not comply with the trend of the split ratio.

Reasonable numerical conditions are critical for the precision and accuracy of the numerical consequences of hydrocyclones. In this paper, the effects of resistance coefficient, wall roughness, and friction packing limit on particle velocity and distribution as well as the separation behaviors were studied in a cylindrical hydrocyclone using the two-fluid model. The results show that the friction packing limit and wall roughness can significantly influence the numerical results, whereas the effect of the resistance coefficient is negligible. As the friction packing limit increases from 0.4 to 0.55, the cut size gradually decreases with improving separation sharpness, and it reaches the minimum when the friction parking limit is 0.5. The wall roughness monotonously increases the cut size and reduces the separation sharpness. Simulation results were also compared with experimental data, and a reasonable prediction can be obtained with resistance coefficient, friction packing limit, and wall roughness height of 0.95, 0.5, and 50 μm, respectively.

In the present study, the thickening process of tailings slurry in a gravity thickener is modelled using Computational Fluid Dynamics (CFD), with a focus on the effects of particle size and feed velocity. A Two-Fluid Model (TFM) is employed to describe the particle-fluid and particle-particle interactions while turbulence is described by the ω-based Reynolds Stress Model (RSM). The validity of the model is demonstrated by close agreement between experimental measurement and simulation predictions of total solid mass of underflow, and particle cumulative mass distribution as a function of particle size in the underflow. The feedwell performance is evaluated in terms of kinetic energy dissipation and mixing performance. Particle size has a significant influence on the distribution of solid concentration. The increase of particle size leads to a higher critical settling height. For a given underflow discharging rate, solid concentration in the underflow increases with feed velocity only in a certain range, whereas increases continuously in the overflow. Large particle size corresponds to a higher critical feed velocity. Modelling the granular flow with a wide particle size distribution in a thickener helps explore the particle dynamic behaviors, thereby improving the thickening process.

The effects of rare earth elements (Ce, Eu, and Er) doping on the microstructure and gas sensing properties of ZnO nanowires were investigated. The Ce, Eu, Er-doped ZnO nanowires and pristine ZnO nanowires were synthesized via a solvothermal route. The structure of the prepared samples was studied and compared by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron microscopy. The gas sensors were fabricated by coating the prepared samples on aluminum oxides tube-based Au sensing electrode, with Ni-Cr heating wire to control the operating temperature. The operating temperature of all sensors was determined to be 300 °C with consideration of ethanol response. At this temperature, all sensors showed good ethanol sensing performance, with the 1%Ce-doped ZnO nanowires-based sensor exhibited the highest ethanol response over the other sensors. The mechanism for the microstructure and gas sensing behavior difference of various samples was discussed.

The misplacement of particles in the hydrocyclone is the primary reason for the deterioration of separation sharpness and has obtained extensive attention. This paper presents a study on the flow field characteristics and separation performance of cylindrical hydrocyclones with different spigot upper diameter by the TFM model. The numerical results indicate that the spigot upper diameter has a slight effect on the tangential velocity, while a smaller spigot upper diameter implies a higher turbulence intensity and an immense internal swirling flow region, causing more coarse particles misplaced in the overflow. However, an oversize spigot upper diameter denotes a superabundant circulating flow, reducing the fine particles misplaced in the underflow, and increasing coarse particles misplaced in the overflow. Under the combined action of the internal swirling flow and the circulating flow, both undersize and oversize spigot upper diameter generates a negative classification performance of the cylindrical hydrocyclone.

Maximizing separation sharpness is critical for the design and operation of hydrocyclones but remains difficult to achieve. This work presents a numerical study on the relationship between separation performance and the characteristics of axial velocity wave zone to understand the reasons for the limited separation sharpness. The results showed that this zone is featured as an inherent transition region, with extensive secondary vortices formed between inner and outer spiral flows. The presence of this zone adversely affects the fluid-solid momentum transfer, causing prolonged residence time and accumulation of intermediate-sized particles. The separation sharpness shows a strong dependence on the characteristics of axial velocity wave zone, which are further controlled by geometric parameters. Increasing the symmetry of flow field and optimizing the spatial distribution of this zone can help increase the separation sharpness while its size shows little effect.

Functionalized ionic liquids (FILs) as extractants were employed for the separation of tungsten and molybdenum from a sulfate solution for the first time. The effects of initial pH, extractant concentration, metal concentrations in the feed were comprehensively investigated. The results showed that tricaprylmethylammonium bis(2,4,4-trimethylpentyl)phosphinate ([A336][Cyanex272]) could selectively extract W over Mo at an initial pH value of 5.5; the best separation factor βW/Mo of 25.61 was obtained for a solution with low metal concentrations (WO3: 2.49 g/L, Mo: 1.04 g/L). The [A336][Cyanex272] system performed effectively for solutions of different W/Mo molar ratios and different metal ion concentrations in the feed. The chemical reaction between [A336][Cyanex272] and W followed the ion association mechanism, which was further proved by the Fourier-transform infrared (FTIR) spectra of loaded [A336][Cyanex272] and the free extractant. The stripping experiments indicated that 95.48% W and 100.00% Mo were stripped using a 0.20 mol/L sodium hydroxide solution. Finally, the selective extractions of W and Mo from two synthetic solutions of different high metal concentrations were obtained; the separation factor βW/Mo reached 23.24 and 17.59 for the first and second solutions, respectively. The results suggest the feasibility of [A336][Cyanex272] as an extractant for the separation of tungsten and molybdenum.

A novel ternary Ag/TiO2/clinoptilolite (ATC) nanocomposite was synthesized via a two-step synthesis strategy by combining the hydrothermal and in-situ reduction process. The obtained samples were characterized by a series of methods of XRD, SEM, TEM, N2 adsorption-desorption isotherms, XPS, FTIR, and UV-vis DRS. It is revealed that Ag and TiO2 nanoparticles were tightly bonded with the clinoptilolite and well-dispersed on its surface. Xanthates were employed as the target pollutants to evaluate the photodegradation efficiency of the as-synthesized samples. Particularly, the ATC photocatalyst exhibited an improved visible-light-induced photodegradation performance towards xanthates, which was much superior to those of binary Ag/TiO2 and Ag/clinoptilolite nanocomposites. The key influencing factors were also investigated to obtain optimal degradation conditions. The excellent photocatalytic performance of the ATC nanocomposites mainly benefited from the enlarged adsorption capacity, visible-light absorption region, and charge separation efficiency. The possible photodegradation mechanism was proposed according to the results of real-time spectral evolution, trapping experiment, and UV-vis DRS.

As flowing film gravity concentrators, spiral separators are extensively used in the processing of numerous minerals. Appropriate design of their cross-sectional geometries has been known as an eff...

Monohydric alcohols with varying chain lengths and isomeric structures, which had significant effects on improving the magnesite and dolomite flotation, were added separately to replace part of dodecylamine (DDA). The intensified effects of alcohols differ with different chain lengths and isomeric structures. Alcohols can enhance the adsorption of DDA and reduce the adsorption distance of DDA on both surfaces of magnesite and dolomite. And the adsorption energy of the mixed collector decreased with the increasing chain length of alcohol. The isomeric alcohols presented more significant effects on lowering the adsorption energy of the collectors. The co-adsorption of alcohol compressed the hydration layer and dilute the water concentration in the hydration layer. Changes of the hydration layer were greater with adding alcohol with a long carbon chain and isomeric structure. Thus, alcohols with long chain lengths and isomeric structures performed better in improving the flotation of magnesite and dolomite.

Ag- and Pt-doped WO3·0.33H2O nanorods with high response and selectivity to NH3 were synthesized from a tungsten-containing mineral of scheelite concentrate by a simple combined process, namely by a high pressure leaching method to obtain tungstate ions-containing leaching solution and followed by a hydrothermal method to prepare corresponding nanorods. The microstructure and NH3 sensing performance of the final products were investigated systematically. The microstructure characterization showed that the as-prepared WO3·0.33H2O nanorods had a hexagonal crystal structure, and Ag and Pt nanoparticles were uniformly distributed in the WO3·0.33H2O nanorods. Gas sensing measurements indicated that Ag and Pt nanoparticles not only could obviously enhance NH3 sensing properties in terms of response, selectivity as well as response/recovery time, but also could reduce the optimal operating temperature at which the highest response was achieved. The highest responses of 22.4 and 47.6 for Ag- and Pt-doped WO3·0.33H2O nanorods to 1000 ppm NH3 were obtained at 225 and 175 °C, respectively, which were about four and eight folds higher than that of pure one at 250 °C. The superior NH3 sensing properties are mainly ascribed to the catalytic activities of noble metals and the different work functions between noble metals and WO3·0.33H2O.

Interactive effects between feed flow rate and feed size distribution (FSD) are numerically investigated. The results show that, for too large or too small feed flow rate, when the FSD increases, the content of solid particles misplaced to the overflow or underflow increases, leading to a decrease in separation sharpness. These results can be explained by the multiphase flow pattern and solid particle spatial distribution. What's more, when the feed flow rate too small, the differences between the equilibrium radiuses of different sized particles are small, resulting in low separation sharpness. When the feed flow rate is too large, the regular distribution of different sized particles in the radial direction is severely destroyed. Based on the results from this study, in order to achieve the desired separation performance and the precise particle separation, it is recommended to adapt to changes in the FSD by appropriately increasing the feed flow rate.

The interaction effect between feed size distribution (FSD) and underflow orifice diameter (Du) is crucial for the adjustment of the hydrocyclone in plant but not clearly understood. This paper presents a numerical study on effects of FSD on separation performances of hydrocyclones at a wide range of Du. The numerical results show that both small or large Du will cause numerous particles being misplaced to the overflow or underflow products, resulting in poor separation performance. These results can be well explained using the predicted water flow pattern and particle distribution. Moreover, there are intense interaction effects between the Du and the FSD. It is pointed out that for an extremely small Du, the cut size explodes, and the separation efficiency and separation sharpness deteriorate rapidly with the increase of feed median size (d0.5). These behaviors are mainly due to the increase in the coarse particle content as d0.5 increases, resulting in an increase in the extent of particle accumulation near the spigot. Such accumulation causes a decrease in the tangential velocity and a break in the air core, which in turn leads to a decrease in the flow field stability. Thereby, regular distribution of the particle equilibrium radius along the radial direction is destroyed. As Du increases, the separation performance of the hydrocyclone is no longer affected by fluctuations in the FSD. Based on results from this study, it is recommended a moderate increase in Du is competent to mitigate the adverse effects caused by fluctuations in the FSD, to achieve the expected cut size, and relatively high separation precise for particles.

The metakaolin-based porous substrates were used as the growth substrate to synthesize SnO2 nanowires (SNWs) gas sensing materials via the gold-catalyzed vapor-liquid-solid growth mechanism. The porous substrates were fabricated by a pore-forming method with poly methyl methacrylate (PMMA) microspheres as the pore former. The effect of the porous structure of different as-prepared substrates on their product morphologies were characterized using X-ray diffraction and scanning electron microscopy. The resulting structural and morphological properties showed that all SNWs had a tetragonal rutile structure, and the aspect ratio of the SNWs enhanced with the increase in the apparent porosity or total pore area of substrates. The growth mechanism of the SNWs was discussed with respect to the effect of temperature gradient inside and outside the pores. The SNWs synthesized on the porous substrates with the PMMA content of 30 wt% exhibited the highest sensing performance towards 0.5–10 ppm H2S at the operating temperature of 85 °C, accompanying with the SNWs synthesized on a dense substrate and the substrate with the PMMA content of 20 wt% for comparison. It demonstrates that the porous structure of the metakaolin-based substrates significantly improves the aspect ratio and gas sensing properties of the SNWs.

WO3 porous films (WPFs) were synthesized by a non-hydrolytic sol-gel (NHSG) method using WCl6, C2H5OH, and C3H7NO as the precursors. The polyethylene glycol (PEG) was employed as a porogen to prepare the porous structure. The microstructures of WPFs were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Nitrogen adsorption-desorption isotherms were used to characterize the specific surface areas of the samples. The results indicated that the honeycomb-like WPFs were assembled by numerous WO3 nanoparticles with the diameter of 20–60 nm. Gas sensing measurements showed that the peak sensor response to NO2 was obtained at the operating temperature of 100 °C. The sensor based on WPFs showed excellent reversibility and fast response to NO2 at various operating temperatures and NO2 concentrations. The sensor also exhibited a significant NO2 selectivity compared with NH3, SO2, CH3OH, and C2H5OH, demonstrating a promising application in detecting NO2. The porous structure formation process of the WPFs was analyzed and gas sensing mechanism based on electron depletion theory as well as first principle calculations were discussed.

Various mono-noble metal nanoparticles (NPs) have been used to improve the functionalities of semiconducting sensing materials for high-performance gas sensors. However, understanding the effect of bimetallic noble NPs on their gas sensing behaviors is limited. In this work, the bimetallic Au/Pd-NPs decorated ZnO nanowires (ZNWs) were fabricated to study their NO2 sensing performance through comparing with their counterparts of pristine ZNWs, and mono Au- or Pd-NPs decorated ZNWs. The bimetallic Au/Pd-NPs decorated ZNWs were prepared by dipping the pristine ZNWs in a mixed solution of HAuCl4, PdCl2, Na2CO3, and absolute ethanol with heating evaporation. The bimetallic Au/Pd-NPs decorated ZNWs exhibited higher response of 94.2, faster response/recovery time of 35 s / 30 s, and lower optimal operating temperature at 100 °C towards 1 ppm NO2 than the performance of pristine ZNWs and mono Au- or Pd-NPs decorated ZNWs. Meanwhile, good selectivity and reproducibility have been achieved by bimetallic Au/Pd-NPs decoration. The mechanism on the enhanced sensing performance of the bimetallic Au/Pd-NPs decorated ZNWs has also been investigated systematically.

Immobilization has been regarded as one of the most effective technology to eliminate heavy metals contamination. However, the stability of immobilization products and the leakage of immobilized heavy metals impeded its further application. In order to depict the stability of chelating complexes C10H20MnN2S4, C10H20CuN2S4 and C10H20ZnN2S4, DSC-TG analysis, DFT calculation and leakage tests were carried out to reveal the stabilities and the potential leakage risks of immobilized heavy metals when sodium diethyl dithiocarbamate was used as soil amendments. The results indicated that the stability of these three chelating complexes was ranked in the order of C10H20CuN2S4> C10H20ZnN2S4> C10H20MnN2S4. Such precipitations as C10H20MnN2S4, C10H20CuN2S4 and C10H20ZnN2S4 were stable under the neutral and alkaline environment. Meanwhile, leakage of immobilized heavy metals decreased with the increasing leaching pH, whereas time and temperature had no significant impact on the leakage of immobilized heavy metals. And the maximum leakage of immobilized heavy metals was lower than the limited concentration.

One-dimensional (1D) ZnO nanorods (ZNRs) were synthesized by a facile and effective hydrothermal method using the mixture of sodium dodecyl sulfate (SDS) and polyethylene glycol 400 (PEG400) with a molar ratio of 1:1 as the complex surfactant. The microstructure and morphology were characterized using of X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results demonstrated that the ZNRs are of a single crystal hexagonal wurtzite structure, having a larger length-to-diameter ratio with more regular surface morphology compared with the ZnO products obtained in the presence of only SDS or PEG400. A possible growth mechanism was proposed based the mediation reaction of the complex surfactant. Gas sensing measurements indicated that the ZNRs assisted by the complex surfactant demonstrated excellent ethanol sensing properties at an optimal operating temperature of 300 °C, which could be ascribed to their large length-to-diameter ratio, one-dimensional structure, and numerous surface defects of oxygen vacancies.

A novel sensing material of polyethyleneimine-mediated WO3 nanoparticles was prepared by a simple and efficient one-pot hydrothermal method. The structure and morphology characteristics of the as-prepared WO3 nanoparticles were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results showed that the as-prepared WO3 nanomaterials were composed of highly dispersible WO3 nanoparticles, and these nanoparticles with the particle size in the range of 10–50 nm showed a monoclinic structure. NO2 sensing measurements demonstrated that WO3 nanoparticles-based gas sensor exhibited superior response, outstanding selectivity, excellent reversibility, and good long-term stability. The sensor response increased as NO2 concentration increased. The highest response value of 251.7 was achieved to 5 ppm NO2 at the optimal operating temperature of 100 °C. Especially, the sensor response could reach 3.2–50 ppb NO2. It also exhibited fast response and recovery times with a high sensor response even in a high-humidity environment. The excellent gas sensing properties of WO3 nanoparticles could be ascribed to their high effective surface areas as well as numerous oxygen vacancies, which foresee the great potential application for fast and effective detection of sub-ppm level NO2 under different humidity environments.

ZnO nanowires (ZNWs) and ZnO nanowires/Au nanoparticles hybrid (Au-ZNWs) with various Au concentrations were synthesized by a facile one-pot hydrothermal method and characterized by XRD, SEM, TEM, XPS, and FTIR. The structural characterization results exhibited that Au nanoparticles were self-assembled onto the surface of ZNWs and the c-axis growth of ZNWs is suppressed by the addition of HAuCl4 in the synthesis of Au-ZNWs hybrid. Gas sensing properties demonstrated the favorite sensing performance could be achieved for 1 mol% Au-ZNWs compared to pure ZNWs and Au-ZNWs with other Au concentrations. The maximum response of 1 mol% Au-ZNWs to 1 ppm NO2 was 31.4 at 150 °C, which was nearly 4 times higher than 8.2 of pure ZNWs. And the shortest response and recovery times could also be achieved by 1 mol% Au-ZNWs in a wide range of operating temperature. Au-ZNWs with various Au concentrations showed better selectivity to NO2 than pure ZNWs. The mechanism of enhanced NO2 sensing performance of Au-ZNWs was investigated by the combination of electronic and chemical sensitizations via Au nanoparticles functionalization.

High separation sharpness of hydrocyclones is an ultimate goal for the classification process and has attracted considerable attention. The existence of some special flow patterns, such as short-circuit flow and circulation flow, play an important role in the separation process and have not been clearly understood. This paper presents a numerical study of the effects of vortex finder wall thickness on the flow field and separation performance. More importantly, the formations and effects of short-circuit flow, circulation flow, and axial velocity wave zone (AVWZ) were investigated and understood. The simulation results were analyzed in terms of pressure drop, water velocity, separation efficiency, and particle distribution. The results indicate that a thicker vortex finder wall could reduce pressure drop, tangential velocity magnitudes, and the flow rates of both short-circuit flow and circulation flow but increase the fluctuations of axial and radial velocities especially beneath the vortex finder where the AVWZ is formed. The leakage effect of short-circuit flow on sub-coarse particles is less significant than the fluctuation effect of AVWZ. The circulation flow in pre-separation space is beneficial to re-separate the sub-fine and sub-coarse particles to improve the separation sharpness. Consequently, the hydrocyclone with a thin-walled vortex finder is more beneficial for efficient classification.

As motivated by the driving force of the urgent demand for high-performance nitrogen dioxide (NO2) sensor, in this work, a novel structure of Au@WO3 core–shell nanospheres (CSNSs) was designed and successfully prepared for NO2 detection. The techniques of X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller measurement, and elemental mapping analysis were used for the characterizations of the obtained samples. The results demonstrated that Au nanoparticles with 25–50 nm in diameter were successfully encapsulated by WO3 shells with the thickness of 30–50 nm. The NO2 sensing performance of the Au@WO3 CSNSs as well as the pure WO3 nanospheres were systematically investigated. Compared with the pure WO3 nanospheres, Au@WO3 CNNSs exhibited overall enhanced NO2 sensing performances in terms of response, detection limit, and response/recovery times. At the optimal operating temperature of 100 °C, Au@WO3 CSNSs showed excellent NO2 selectivity and long-term stability. Notably, the excellent NO2 sensing performance of Au@WO3 CSNSs was slightly affected by humidity. The possible sensing mechanism of the enhanced NO2 sensing properties of the Au@WO3 CSNSs was discussed.

Cu-doped ZnFe2O4 nanoparticles (Cu-ZFNPs) with spinel structure were synthesized by a facile hydrothermal route without using any surfactant. The structure and morphology of pure ZFNPs and Cu-ZFNPs with different Cu concentrations were characterized by XRD, SEM, TEM, XPS, and FTIR measurements. Microstructural characterizations showed that the diameters of both pure ZFNPs and Cu-ZFNPs with spinel structure were approximately 50 nm, which was not significantly affected by Cu doping. Gas sensing measurements showed that Cu-ZFNPs with proper Cu concentrations were favorable for enhancing H2S sensing performance especially at low operating temperatures compared to pure ZFNPs. Gas sensors based on pure ZFNPs and Cu-ZFNPs showed reversible response and excellent selectivity to H2S at the operating temperature of room temperature to 175 °C. The maximum response of 37.9 was obtained for the Cu-ZFNPs to 5 ppm H2S at room temperature. The sensing mechanism was discussed in accordance with the electron depletion theory and catalytic effect of Cu doping. It indicates that the prepared Cu-ZFNPs have potential application in H2S detection at low operating temperatures.

The reaction kinetics for the leaching of low-grade scheelite concentrate was investigated in an autoclave with sodium hydroxide in the presence of phosphate. The effects of stirring speed (300−600 r/min), reaction temperature (353−383 K), sodium hydroxide concentration (1.69−6.76 mol/L) and phosphate concentration (0.68−1.69 mol/L) on the WO3 dissolution ratio were studied. The results showed that the WO3 dissolution ratio was practically independent of stirring speed, while it increased with increasing the reaction temperature, and the concentrations of sodium hydroxide and phosphate. The experimental data were consistent with the shrinking core model, with a surface chemical reaction as the leaching rate-determining step. The apparent activation energy was calculated as 49.56 kJ/mol, and the reaction orders with respect to the concentrations of sodium hydroxide and phosphate were determined as 0.27 and 0.67, respectively. The kinetics equation of the leaching process was established.

A pore-forming agent method was adopted to fabricate a novel diatomite-based porous substrate used for preparing SnO2 nanowires (SNWs) as gas sensing materials. The optimal porous substrate with a cristobalite structure was obtained at a graphite content of 40 wt%, and the SNWs were synthesized on the porous substrate by the thermal evaporation method. Structural characterizations by X-ray diffraction and scanning electron microscopy demonstrated that the SNWs grown on the porous substrate had diameters of 20–100 nm and lengths of several hundreds of micrometers, which were thinner, longer and denser than those grown on the dense substrate. The SNWs grown on the porous substrate were found to exhibit a higher SO2 response (Ra/Rg = 33.5–50 ppm) and faster response and recovery times (3 s and 6 s) at a low operating temperature of 85 °C. It revealed that the porous surface of the as-prepared substrate was favorable for the growth of SNWs with a large length-to-diameter ratio and subsequently enhanced their SO2 sensing properties.

To improve the flotation efficiency while decreasing costs, mixed reagents composed of sodium oleate (NaOL) and monohydric alcohols were used as collectors for the flotation of magnesite and dolomite respectively. Single mineral flotation followed by measurements of surface tension and FTIR spectra were conducted to investigate the carbon chain length and isomeric effects of alcohols on the flotation and adsorption behavior of NaOL. Compared to NaOL alone, the mixed reagents of NaOL and monohydric alcohols, including butanol, isobutanol, octanol, and isooctanol, improved the recoveries of magnesite and dolomite. Additionally the recoveries increased as the carbon chains of the alcohols lengthened. The recoveries were enhanced in the case of mixed reagents consisting of NaOL and isomeric alcohols compared with those of the reagents composed of NaOL and the corresponding normal alcohols. The coadsorption of NaOL and monohydric alcohols on mineral surfaces could be verified by FTIR spectra. Alcohols could reduce the surface tension of NaOL solutions. Furthermore, the adsorption configurations of the NaOL alone and mixed reagents on the mineral surfaces were further investigated by DFT calculations. The bond population between the O atoms of NaOL and metal atoms of minerals increased with the lengthening carbon chains of the alcohols. When isomeric alcohols were added, the interaction intensities between NaOL and minerals were higher than those with corresponding normal alcohols. Hydrogen bonds formed between NaOL and monohydric alcohols, contributing to the dense hydrophobic layer on mineral surfaces. Additional hydrogen bonding between monohydric alcohols and mineral surfaces could also be observed when alcohols with long carbon chains were added. Finally, the flotation of magnesite and dolomite by NaOL were both enhanced by monohydric alcohols, especially those with long carbon chains and isomeric structures.

The application of NO2 sensor based on metal oxide semiconductor is limited due to high operating temperature and poor selectivity. In this work, a low-temperature and high-performance NO2 sensor based on Pd-functionalized ZnO nanowires (Pd-ZNWs) prepared by a facile one-pot hydrothermal method was reported. The Pd was formed and self-assembled onto the surface of ZnO nanowires (ZNWs) during this one-pot hydrothermal process. Microstructure characterization of Pd-ZNWs indicated that the obtained ZNWs with diameter of 100–250 nm and length of 2–10 μm had a single crystal hexagonal structure, and Pd/PdO nanoparticles of approximately 2–5 nm in diameter were distributed on their surface. Gas sensing measurement showed that Pd-ZNWs exhibited higher response, lower optimal operating temperature, and faster response/recovery speeds towards NO2 than those of pure ZNWs. The maximum responses of 1 mol%, 2 mol%, and 5 mol% Pd-ZNWs towards 1 ppm NO2 were 13.5, 9.4, and 9.4, respectively, which were obtained at a low operating temperature of 100 °C and 30% RH. Pd-ZNWs also showed a significant improvement in sensing selectivity towards NO2. At a high RH condition of 60%, the sensors based on pure and Pd-ZNWs still exhibited noticeable responses, fast response/recovery speeds, and good long-term stability to NO2 gas. The sensing mechanism of Pd-ZNWs towards NO2 was discussed by the combination of electronic and chemical sensitization.