The effect of hydrofluoric acid (HF) pretreatment on flotation of feldspar and quartz using dodecylamine (DDA) as collector was investigated by micro-flotation, zeta potential, pyrene fluorescence spectroscopy, attenuated total reflection flourier transformed infrared spectroscopy (ATR-FTIR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and bench scale flotation. The micro-flotation tests revealed that there was little difference in the flotation of feldspar and quartz at pH 2, using H₂SO₄ as pH regulator. After HF pretreatment, the floatability of feldspar significantly increased while the floatability of quartz showed no change. HF pretreatment resulted in leaching of SiO₂ and enrichment of Na, K and Al on the feldspar surface. Consequently, the negative surface charge of feldspar increased at pH 2, which allowed for the flotation separation of the feasible minerals. This took place via an increased electrostatic adsorption between DDA and Na, K, Al on the feldspar surface, which effectively increased its hydrophobicity and as a result, improved the floatability of feldspar. An alternative process which exhibited effective separation of quartz and feldspar while recycling the tailwater from the flotation was proposed.

ABSTARCT Wolframite is a series of minerals belonging to the isomorphic (Fe, Mn)WO₄ with varied Fe/Mn ratios, for which the floatability changes with its composition. In this work, the effects of composition on floatability were studied using micro flotation, collector adsorption tests, infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results showed that with an increasing Fe/Mn ratio, the flotation recovery of wolframite increased when using benzohydroxamic acid (BHA) as collector, but decreased when sodium oleate (NaOl) was applied. The chemisorption differences of these collectors were observed on the surface of wolframite, i.e., adsorption of BHA is greater at the surface of high-Fe wolframite, while NaOl is more easily adsorbed on high-Mn wolframite. Moreover, XPS analysis indicates that a new ferric product was generated on the surface of wolframite in the presence of BHA. In contrast, a new manganese product was formed after the addition of NaOl. These results demonstrate that Fe is the adsorption site for BHA, while Mn is the site for NaOl.

Using p-phenylene diamine (PPD) as a modifier and nitrogen resource, nitrogen-doping reduced graphene oxide was prepared by one-step refluxing method. The influence of PPD-GO (graphene oxide) mass ratio X on surface functional groups, layer structure, and electroconductivity of nitrogen-doping reduced grapheme oxide (NRGO-X) was investigated by Fourier Transform Infrared Spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV-vis absorption spectrum, and electrical measurement. The results showed that GO can be simultaneously reduced and nitrogen-doped by PPD. When PPD-GO mass ratio X ≤ 6, there existed three types of N configurations in NRGO-X, including pyridinic N, pyrrolic N, and graphitic N. However, when X > 6, the pyridinic N disappeared in a six-membered ring. Further, the reduction process of NRGO as well as the nitrogen doping level and type can be regulated by changing the mass ratio X. With the increase of X, the d-spacing of NRGO-X layers increased first and then decreased, while the electrical conductivity increased gradually.

Nano bubbles and films are important in theory and various applications, such as the specific ion effect of bubble coalescence, flotation and porous medium seepage; these rely greatly on the fundamental aspects of extended-DLVO surface forces. However, the origin and validation of the non-DLVO forces are still obscure, especially at the nano scale (1–5 nm). Herein, we report the first determination of the disjoining pressures of aqueous electrolyte nano-films using molecular dynamics (MD) simulations. Our results showed that adding salt does not lead to a decrease in the disjoining pressure. On the contrary, higher concentrations results in greater disjoining pressures. In addition, the temperature was found to significantly change the pattern of the disjoining pressure isotherm. These results aid the understanding of a number of underlying mechanisms, involving nano solid–liquid–gas surfaces.

The surface properties of coatings during deposition are strongly influenced by temperature, particle fluxes, and compositions. In addition, the precursor incident energy also affects the surface properties of coatings during sputtering. The atomistic processes associated with the microstructure of coatings and the surface morphological evolution during sputtering are difficult to observe. Thus, in the present study, molecular dynamics simulation was employed to investigate the surface properties of Au/Cu alloy coatings (Cu substrate sputtering by Au atoms) with different incident energies (0.15 eV, 0.3 eV, 0.6 eV). Subsequently, the sputtering depth of the Au atoms, the particle distribution of the Au/Cu alloy coating system, the radial distribution function of particles in the coatings, the mean square displacement of the Cu atoms in the substrate, and the roughness of the coatings were analyzed. Results showed that the crystal structure and the sputtering depth of Au atoms were hardly influenced by the incident energy, and the incident energy had little impact on the motion of deep-lying atoms in the substrate. However, higher incident energy resulted in higher surface temperature of coatings, and more Au atoms existed in the coherent interface. Moreover, it strengthened the motion of Cu atoms and reduced the surface roughness. Therefore, the crystal structure of coatings and the motions of deep-lying atoms in the substrate are not influenced by the incident energy. However, the increase in incident energy will enhance the combination of coatings and the base while optimizing the surface structure.

With the continuous development of rail transit industry and the acceleration of train speed, higher requirements are established for the operation quality of high-speed trains and the reliability of transmission system. In the process of train running, speed fluctuation and vibrations from various parts of the driving devices are common, which could be greatly affected by the traction torque. During traction transmission, the harmonic vibration torque exists in traction motor due to that the motor is connected with non-sinusoidal alternating current. In order to study the vibration influence of the electrical component of traction transmission system on the rail vehicles, i.e., bogie and car-body, an electro-mechanical coupling dynamic model for rail transit vehicles was established by explicitly incorporating the electric-induced traction into the transmission model. The dynamics responses of the vertical, lateral and longitudinal acceleration on vehicle components, such as axle box and car-body were quantitative analyzed. By comparison with field test, it was observed that there was a vibration peak of 12-times of the fundamental rotor frequency on the bogie frame and axle box, which existed at conditions of traction, uniform speed and braking. However, the vibration acceleration exhibit nearly little difference with or without traction force, especially at low frequency domain < 100 Hz.