Dezhou Wei

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.

A new collector used for flotation of oxide minerals

A surfactant containing a mixed aliphatic structure, with a hydrocarbon chain and a diamine group, has proven to be collector for the flotation of quartz, calamine and calcite. And research about its collecting capability was carried out in laboratory. The test results show that the flotation recovery ascends sharply with increasing the concentration of collector. When the concentration of collector reaches 1.83×10^(-4)mol/L, the flotation recoveries of quartz, calamine and calcite get their maximum of 97.64%, 91.04% and 95.99%, respectively. The flotation recoveries of quartz, calamine and calcite rise sharply with the rise of pH. And in a wide range of pH, their flotation recoveries all exceed 90%. And in the whole flotation experiment, the flotation recovery of hematite rises with the increase of collector concentration and pH, while the maximal recovery is not more than 55%. Compared with dodecylamine, the N-dodecylethylenediamine has strong capability to quartz and calamine, while the flotation recoveries of calcite are closely. Hydrogen binding adsorption and electrostatic adsorption occur between the collector and the surface of quartz.

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.

Removing cadmium from electroplating wastewater by waste saccharomyces cerevisiae

The appropriate condition and scheme of removing cadmium from electroplating wastewater were investigated by adsorption-precipitation method using waste saccharomyces cerevisiae(WSC) as sorbent. Effect factors on biosorption of cadmium in cadmium-containing electroplating wastewater by waste saccharomyces cerevisiae and precipitation process of waste saccharomyces cerevisiae after adsorbing cadmium were studied. The results show that removal rate of cadmium is over 88% after 30 min adsorbing under the condition of cadmium concentration 26 mg/L, the dosage of waste saccharomyces cerevisiae 16.25 g/L, temperature 18 ℃, pH 6.0 and precipitation time 4 h. Biosorption-precipitation method is effective to remove cadmium in cadmium-containing electroplating wastewater by waste saccharomyces cerevisiae. The SEM, infrared spectroscopy and Zeta-potential of the cells show that chemical chelating is the main adsorption form; electrostatic attraction, hydrogen bonding and van der Waals force all function in adsorption process; and ―NH2―,―C=O―,―C=O―NH―,―CH3, ―OH are the main adsorption groups.

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.

Influence of sodium 2,3-dihydroxypropyl dithiocarbonate on floatability of chalcopyrite and galena

Abstract Sodium 2,3-dihydroxypropyl dithiocarbonate (SGX), which contains —OH and —CSS— in the molecule, was used to explore selective depression of galena from chalcopyrite in the flotation tests with ammonium dibutyl dithiophosphate (DDTP), and zeta potential and adsorption measurements were performed to study the interaction between SGX and minerals. The flotation tests of single minerals show that SGX has slight activation on chalcopyrite and strong depression on galena in the whole pH range. With SGX dosage increasing, the recovery of galena decreases rapidly, while that of chalcopyrite increases slightly. At pH=6, the copper grade and recovery of concentrate are 29.52% and 82.15% respectively when mixture of two minerals is tested. Zeta potential and adsorption measurements indicate that SGX has strong adsorption on galena and slight adsorption on chalcopyrite.

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.