Shuling Gao

Nitrogen dioxide sensing using tungsten oxide microspheres with hierarchical nanorod-assembled architectures by a complexing surfactant-mediated hydrothermal route

WO3 microspheres with hierarchical nanorod-assembled architectures were successfully synthesized by a complexing surfactant-mediated hydrothermal method in the presence of K2SO4 and H2C2O4 with a molar ratio of 1 : 1. Microstructural characterization by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy showed that WO3 microspheres with diameters ranging from 3 to 5 μm were assembled by 90 nm diameter nanorods and had a single crystal hexagonal structure. The analysis results of the elemental composition and chemical state demonstrated that the obtained WO3 microspheres were nearly stoichiometric. Based on the experimental results, a possible growth mechanism consisting of nucleation, Ostwald ripening, and self-assembly of WO3 crystals was proposed. Gas sensing properties demonstrated that WO3 microspheres exhibited not only a high response and excellent reversibility to NO2, but also a good linear relationship between the response and NO2 concentration in the range of 1 to 10 ppm. The response and recovery times significantly decreased as the operating temperature increased gradually. The highest response of 790 to 20 ppm NO2 was obtained at a relatively low operating temperature of 100 °C, which revealed that WO3 microspheres were very promising for fabricating low-consumption chemical gas sensors. The electron depletion theory was used for explaining the gas sensing mechanism by the chemical adsorption and reaction of NO2 gas molecules on the surface of WO3 microspheres.

Beneficiation of low-grade diasporic bauxite with hydrocyclone

Low-grade diasporic bauxite was treated with hydrocyclone of small cone-angle. The effects of apex diameter, feed pressure and feed concentration on separation indexes were tested, and then the separation process was discussed by hydrokinetics tentatively. The results show that the increase of apex diameter changes the spacial locality of the envelope of zero vertical velocity, resulting in decrease of the ratio of Al2O3/SiO2 in overflow and increase of the recovery of Al2O3 in underflow, while feed pressure and feed concentration have no remarkable effect on the spacial locality of the envelope of zero vertical velocity, however, the separation indexes are improved by the increase of feed pressure, but are worsened by the increase of feed concentration.

Selective depression effect in flotation separation of copper–molybdenum sulfides using 2,3-disulfanylbutanedioic acid

Abstract 2,3-disulfanylbutanedioic acid (DMSA) was found to be a selective depressant in the flotation separation of copper– molybdenum sulfides. The flotation results suggest that a low dosage of DMSA has a strong depression effect on chalcopyrite in the pH range between 4 and 12. At pH 6, the recoveries of molybdenum are up to 85%, 75%, and 80% while those of chalcopyrite are 15%, 5%, and 20% respectively when flotation tests are carried out with single minerals, mixed minerals and molybdenum-bearing copper concentrates. Adsorption isotherms measurement indicates that DMSA adsorbs more strongly on chalcopyrite than on molybdenite. The frontier orbital calculation reveals that the two S atoms of DMSA molecule are active centers for the adsorption of the DMSA molecule on chalcopyrite surface. Fermi level calculation shows that chalcopyrite can obtain electrons from the DMSA molecule while molybdenite cannot.

Numerical and experimental studies of flow field in hydrocyclone with air core

Abstract For the flow field in a d50 mm hydrocyclone, numerical studies based on computational fluid dynamics (CFD) simulation and experimental studies based on particle image velocimetry (PIV) measurement were carried out respectively. The results of two methods show that air core generally forms after 0.7 s, the similar characteristics of air core can be observed. Vortexes and axial velocity distributions obtained by numerical and experimental methods are also in good agreement. Studies of different parameters based on CFD simulation show that tangential velocity distribution inside the hydrocyclone can be regarded as a combined vortex. Axial and tangential velocities increase as the feed rate increases. The enlargement of cone angle and overflow outlet diameter can speed up the overflow discharge rate. The change of underflow outlet diameter has no significant effect on axial and tangential velocities.

Selective adsorption of bacteria on sulfide minerals surface

Abstract The adsorption of bacteria on sulfide minerals surface was studied, and the selective adsorption mechanism of cells on the sulfide minerals was investigated by means of FTIR, UVS and XPS. The results show that the three strains of bacteria adsorbed more preferentially on pyrite than on other two sulfide minerals surface at neutral and alkaline pH conditions. FTIR and UVS of three strains of bacteria indicate that there are more functional groups on their surface, such as O—H, C=O, N—H, C—O, and the content of saccharide is more than that of protein. The state of every element on sulfide minerals surface was analyzed by XPS. The empty orbital number of electronic shell of metal ions on minerals surface is important in selective adsorption process, and some stable constants of metal coordinates can be used to explain the contribution of some groups in saccharide of cell wall to the selective adsorption.

Selective depression of galena and chalcopyrite by O,O-bis(2,3-dihydroxypropyl) dithiophosphate

Abstract A novel synthesized reagent, O,O-bis(2,3-dihydroxypropyl) dithiophosphate (DHDTP), was investigated as depressant on the depression of chalcopyrite and galena, when ammonium dibutyl dithiophosphate (DDTP) was used as the collector in flotation tests. Zeta potential and adsorption measurement were performed to study the interaction between depressant and minerals. The flotation tests of two minerals show that DHDTP has slight depression on chalcopyrite in the whole pH range and strong depression on galena in the pH range of 6-10. When DHDTP dosage is increased, the recovery of galena decreases rapidly, while that of the chalcopyrite decreases slightly. The satisfied separation results of artificially mixed samples are that the copper grade and recovery rates of concentrate are 24.08% and 81%, respectively, when the pH is 6 with 278 mg/L DHDTP. Zeta potential and adsorption measurements show that DHDTP has more strongly adsorption capacity to galena than chalcopyrite.

Synthesis and characterization of single-crystalline SnO 2 nanowires

Tin oxide (SnO2) nanowires were synthesized on oxidized silicon substrates by thermal evaporation of tin grains at 900°C in Ar flow at ambient pressure. Structural characterization using X-ray diffraction and transmission electron microscopy shows that SnO2 nanowires have a single crystal tetragonal structure. Scanning electron microscopy observation demonstrates that SnO2 nanowires are 30–200 nm in diameter and several tens of micrometers in length. The surface vibration mode resulting from the nanosize effect at 565.1 cm−1 was found from the Fourier transform infrared spectrum. The formation of SnO2 nanowires follows a vapour-solid (VS) growth mechanism. The gas sensing measurements indicate that SnO2 nanowire gas sensor obtains peak sensitivity at a low operating temperature of 150°C and shows reversible response to H2 gas (100–1000 ppm) at an operating temperature of RT-300°C.

CFD numerical simulation of flow velocity characteristics of hydrocyclone

A CFD based numerical simulation of flow velocity of hydrocyclone was conducted with different structural and operational parameters to investigate its distribution characteristics and influencing mechanism. The results show there exist several unsymmetrical envelopes of equal vertical velocities in both upward inner flows and downward outer flows in the hydrocyclone, and the cone angle and apex diameter have remarkable influence on the vertical location of the cone bottom of the envelope of zero vertical velocity. It is also found that the tangential velocity isolines exist in the horizontal planes located in the effective separation region of hydrocyclone. The increase of feed pressure has almost no effect on the distribution characteristics of both vertical velocity and tangential velocity in hydrocyclone, but the magnitude and gradient of tangential velocity are increased obviously to make the motion velocity of high density particles to the wall increased and to make the cyclonic separation effect improved.

Synthesis and Characterization of Single-Crystalline SnO2 Nanowires

Tin oxide (SnO2) nanowires were synthesized on oxidized silicon substrates by thermal evaporation of tin grains at 900°C in Ar flow at ambient pressure. Structural characterization using X-ray diffraction and transmission electron microscopy shows that SnO2 nanowires have a single crystal tetragonal structure. Scanning electron microscopy observation demonstrates that SnO2 nanowires are 30–200 nm in diameter and several tens of micrometers in length. The surface vibration mode resulting from the nanosize effect at 565.1 cm−1 was found from the Fourier transform infrared spectrum. The formation of SnO2 nanowires follows a vapour-solid (VS) growth mechanism. The gas sensing measurements indicate that SnO2 nanowire gas sensor obtains peak sensitivity at a low operating temperature of 150°C and shows reversible response to H2 gas (100–1000 ppm) at an operating temperature of RT-300°C.

A low-temperature n-propanol gas sensor based on TeO2 nanowires as the sensing layer

TeO2 nanowires were synthesized on Au-coated glass substrates using a thermal evaporation method. Structural characterization showed that TeO2 nanowires with high surface-to-volume ratio and large mass production had a single-crystal tetragonal structure. A gas sensor based on TeO2 nanowires showed a quick response–recovery speed and a reversible response to n-propanol gas at low operating temperatures.