In the current research, P25 TiO2 materials sealed in quartz vacuum tubes were subject to annealing and ice-water post-quenching, with the effects on TiO2 structures, morphology, and photocatalytic activity being studied. It is shown that the vacuum-sealed annealing can lead to a decrease in the crystallinity and temperature of anatase-to-rutile phase transition. A disorder layer is formed over TiO2 nanoparticles, and the TiO2 lattices are distorted between the disorder layer and crystalline core. The ice-water post-quenching almost has no effect on the crystalline structure and morphology of TiO2. It can be seen that the vacuum-sealed annealing can generate more defects, and the electrons are mainly localized at lattice Ti sites, as well as the percentage of bulk oxygen defects is also increased. Although further ice-water post-quenching can introduce more defects in TiO2, it does not affect the electron localization and defect distribution. The vacuum-sealed annealing process can increase the photocatalytic acetone oxidations of the anatase phase TiO2 to some extent, possibly because of the defect generation and Ti3+ site formation; the further ice-water quenching leads to a decrease in the photocatalytic activity because more defects are introduced.
The seepage characteristics of sand affect its strength, mechanical deformation characteristics, and find safety and stability. The drag coefficient is a dimensionless physical quantity expressing the interaction between fluid and particles, it is also an important parameter that characterizes the permeability of granular soils. Through the seepage test of standard sand with single particle sizes and different grades, analyze the seepage laws of standard sand with different particle sizes in the Darcy and non-Darcy seepage. The relationship between parameters a and b in the seepage equation and porosity (n), average particle size (d50), nonuniformity coefficient (CU), and curvature coefficient (CC), and their influence degree were studied. An empirical formula for determining the permeability coefficient of standard sand is established. By adding a correction factor and verifying its rationality, the empirical formula of standard sand permeability parameters is finally obtained.
Tailings sand is the dam-building material of the tailings dam accumulation sub-dam, and its mechanical properties directly affect the safety and stability of the whole tailings dam. With the improvement of mineral sorting technology, the content of fine and ultrafine particles in the tailings gradually increases, which will affect the mechanical strength of tailings accumulation sub-dam. To improve the settling effect of tailings accumulation in the Chengchao iron ore mine (China), the effect of iron tailings flocculation and settling law on the mechanical properties of tailings sand was studied. Polymerized iron sulfate (PFS) as an inorganic polymer flocculant, compared with the traditional flocculant, has a stronger flocculation and adsorption capacity, is widely used in drinking water, industrial wastewater, and domestic sewage treatment, is an anionic polyacrylamide (APAM-800) for polymer compounds, mainly divided into nonionic, cationic, and anionic three, and is commonly used mine flocculant at home and abroad. Through different flocculants, PFS, and APAM-800 compound flocculation and settling experiments, the effect of the flocculant-dosing scheme on the settling rate and turbidity of clarified liquid was determined, and the change in tailings consolidation shear strength of the best dosing scheme was measured. The experimental results showed that the settling rate of iron tailings was the fastest when PFS was used in combination with APAM-800 at 1.2 g L−1 and 0.20 g·L−1 dosages, respectively. The direct shear test results showed that the internal friction angle of tailings sand increased by 2.18°, the cohesion increased by 5.814 kPa, and the shear resistance of flocculated settled tailings increased, which can effectively improve the safety factor of tailings sand pile sub-dam.
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