Study on the Classification Performance of a Novel Wide-Neck Classifier.

A novelty-designed wide-neck classifier (WNC) was proposed to enhance the passing ability and classification efficiency of fine particles. Using computational fluid dynamics (CFD), we studied the flow field and velocity distribution in the newly designed WNC. The velocity of the fluid gradually decreased from the wall to the center and from the cylinder to the cone, which facilitates particle classification and thickening. The Reynolds number (Re) and turbulent intensity (I) inside the WNC were discussed. The turbulent intensity increased with increasing feed velocity and overflow outlet diameter and decreased with increasing feed concentration and spigot diameter. The classification of coal slurry was performed to analyze the performance of WNC. The classification efficiency increased with increasing feed velocity but decreased as the feed concentration, spigot diameter, and overflow outlet diameter increased. The predictive models for classification efficiency influenced by the operational and structural parameters were constructed at high correlation coefficients, and the average error of these models was analyzed at 0.28%. Our results can provide valuable insights into the development of mineral classification.

Potential Evaluation for Preparing Geopolymers from Quartz by Low-Alkali Activation.

Alkali fusion of granite sawdust at a high alkali dosage can significantly improve geopolymerization activity, but also result in a high alkali consumption and a poor geopolymer performance. In this work, quartz, the most inert component in granite sawdust, was selected to explore the effect of low-alkali activation on its reactivity and the compressive strength of geopolymer. It was found that the amount of activated quartz is mainly determined by the amount of alkali used for activation. The surface of a quartz particle can be effectively activated by an alkali fusion process at a low alkali dosage of 5%. The metakaolin-based geopolymer synthesized with quartz activated by an alkali dosage of 5% shows a high compressive strength of 41 MPa, which can be attributed to the enhanced interfacial interaction between quartz and the geopolymer gel, suggesting that low-alkali activation is a potential way to improve the geopolymerization ability of granite sawdust.

Multiphase Flow Characteristics in the Classification Process of a Novel Wide Neck Thickener: Experiment and Simulation.

A novel thickening equipment known as a wide neck thickener (WNT) was designed to solve the problem of depending only on gravity settlement of the thickener. The computational fluid dynamics method with the Reynolds stress and the volume of fluid models and the particle image velocimetry experimental method were both applied to investigate the pressure and velocity variation and turbulent characteristics of the WNT under different parameter settings. The results indicate that experiments and simulations are consistent. Under four parameter settings, the axial and tangential velocities decrease to the minimum and then increase from the wall to the center. Under different feed velocity, cone angle, and spigot diameter settings, turbulent kinetic energy k and intensity I decrease from the cylinder to the cone and from the wall to the center; the max k and I correspond to the area near the inlet followed by the cylinder, and k and I in the cone are the smallest. When the classification overflow outlet (COO) diameter is 200 mm, k and I increase rapidly, the max k and I are transferred from near the inlet to near the cylinder wall at the COO, and the k and I near the wall decrease significantly.

DFT Study on the Adsorption of Monomeric Hydroxyl Aluminum on Fe(II)/Mg Replacement Kaolinite (001) Surfaces.

In the natural environment, Al and Si in the kaolinite crystal structure are likely to form lattice defects or be replaced by low-valence positive ions so that the base surfaces have permanent negatively charged sites. It is therefore very important to investigate the adsorption process and adsorption mechanism of adsorbates on the replaced surfaces. In this paper, two types of surface models formed by replacing Al atoms in the alumina octahedron of kaolinite (001) surface with Fe(II) and Mg were selected as the adsorption surfaces, these being the kaolinite Fe(II)Al-(001) and MgAl-(001) surfaces, respectively. Then, we used density functional theory (DFT) to simulate the adsorption of three monomeric hydroxy aluminum models (i.e., Al(OH)2 +, Al(OH)3, and Al(OH)4 -) on the two replaced surfaces. Results show that, when compared to the adsorption on the ideal kaolinite (001) surface, the adsorption energies of the three adsorbates adsorbed on the replaced surfaces are lower and the adsorption is more stable. When the three adsorbates are adsorbed on the kaolinite Fe(II)Al-(001) surface, adsorption stability increases with the number of hydroxyl groups, and hydrogen bonding and electrostatic adsorption play a major role. Conversely, when they were adsorbed on the kaolinite MgAl-(001) surface, the stability of the adsorption deteriorated as the number of hydroxyl groups increased. Moreover, the decisive roles are the interaction between the aluminum atoms in the adsorbates and the oxygen atoms on the replaced surface and the electrostatic adsorption.

Hierarchically porous biochar templated by in situ formed ZnO for rapid Pb2+ and Cd2+ adsorption in wastewater: Experiment and molecular dynamics study.

3D hierarchical porous biochar (HPBC) was synthesized by a thermally removable template without post-activation. Zn(NO3)2 decomposition produced gases and ZnO in situ to activate and expand the three-dimensional micro-and mesopores. Compared with pristine biochar (BC), the specific surface area and pore volume of HPBC were increased by 223 and 75 times, respectively. The abundant pore structure of HPBC significantly enhanced the diffusion rate of heavy metals. For example, compared to BC, the time required for HPBC to adsorb Pb2+ reach adsorption equilibrium was reduced by 87.5% (40 min vs 5min). Such an adsorption performance of HPBC was also insensitive to different background ions (K+, Na+, Ca2+, and Mg2+) with a much higher concentration than that of heavy metals. When applied to treat desulfurization wastewater from power plants, HPBC yielded 100% removal of Pb2+ and Cd2+, much higher than that by using commercial activated carbon (28%). Molecular dynamics simulation revealed different locations preferred by the adsorption of Pb2+ (micropores) and Cd2+ (mesopores) in the hierarchical pore structures. The adsorption of Pb2+ and Cd2+ on HPBC was mainly achieved by diffusion, oxygen functional group complexation, and precipitation. These results provided better knowledge to understand the microscopic adsorption mechanisms of heavy metals in hierarchical pores and a facile yet robust strategy to design such structures in biochar for efficient wastewater treatment.

Salt coagulation or flocculation? In situ zeta potential study on ion correlation and slime coating with the presence of clay: A case of coal slurry aggregation.

The aggregation state of mineral slurry by coagulant with the presence of clay nanosheets appears similar to a flocculation gel with the absence of flocculant. The interactions between particles in mixed clay and quartz minerals systems are influenced by the interactions of ion correlation and slime coating, which creates zeta potential variation. Particle concentration has a substantial effect on zeta potential, and coal slurry has a relative high particle concentration. To realize an in situ aggregation study, zeta potential measurement of coal slurry was performed using electrokinetic sonic amplitude (ESA) without dilution at different calcium ion concentrations and pH values. The zeta potentials of three minerals commonly occurring in coal slurry (quartz, kaolinite and montmorillonite) with similar particle concentrations were also measured. The result suggests that aggregation of coal slurry by calcium ions in the presence of clay minerals belongs to fluctuation. The ion correlation and slime coating could be detected by ESA with a decrease in zeta potential under high calcium ion concentration conditions. The face-face coagulated clay nanosheets were formed by ion correlation, acting as a "flocculant chain". The adsorption force between the "flocculant" and particles is described as a slime coating. This flocculation process is referred to as "salt-clay-coagulation-flocculation" (SCCF). During ion correlation, rearrangement of the electric double layer between face-face spaces causes a reduction of the zeta potential. The super-fine negatively charged clay nanosheets might coat onto the quartz particle surfaces under the effect of electrostatic attraction force and Ca2+ ion correlation. Quartz and clay minerals were oppositely charged because the special adsorption of calcium ions on the clay basal face was restricted in hexatomic rings.

Bifunctional polyaniline electroconductive hydrogels with applications in supercapacitor and wearable strain sensors.

In this article, bifunctional polyaniline/polyacrylamide (PANI/PAAm) hydrogel is fabricated. The hydrogel has capacitive performance and can be used for monitoring human motions. The effect of PANI doped with two different acids on the properties of hydrogels was researched. The first type of PANI hydrogel is doped with hydrochloric (HCl) and the second one with p-toluenesulfonic acid (PTSA). One application of these two kinds of hydrogels was prepared to serve as solid electrolytes in supercapacitors with sandwich structure. The sandwich structure was constructed by introducing two PANI film parts reinforced on both sides of the PANI hydrogel. Supercapacitors with sandwich structure possess areal capacitance of 635 mF/cm2 (HCl-PANI hydrogel) and 1022 mF/cm2 (PTSA-PANI hydrogel). In this structure, PANI hydrogel provides channels for ion transport as a solid electrolyte. In addition, the PANI hydrogel can be utilized as the sensitive sensors as well. By employing I-v curve and I-t curve to characterize the performance of the sensor, the hydrogel material can be used as a wearable sensor with sensitivity to slight deformation. This is a sensitive sensor that it can respond to the speed and amplitude of the bending movement of the arm. The effective bifunctional property results indicate that the hydrogel, capacitive and conductive PANI hydrogel has great piezoelectric sensitivity as the sensors, which has become promising materials for wearable sensors and solid electrolytes.

Density Functional Theory Study of Water Molecule Adsorption on the α-Quartz (001) Surface with and without the Presence of Na+, Mg2+, and Ca2.

Adsorption of the single water molecule on the α-quartz (001) surface with and without the presence of Na+, Mg2+ and Ca2+ was analyzed utilizing the density functional theory method. Our results demonstrate that the optimal adsorption configuration of the single water molecule on the α-quartz (001) surface lies in the bridge being configured with two formed hydrogen bonds. These were Os-Hw and Hs-Ow (s and w represent, respectively, surface and water molecules), while the main hydrogen bond is Hw-Os. Furthermore, the corresponding adsorption energy was ∼-72.60 kJ/mol. In this study, the presence of metal ions helped to deflect the spatial position of the water molecule, and the distance between Ow and Hs was altered significantly. Furthermore, the charge transfer between the interacting atoms increased in the presence of metal ions, wherein the effects of Ca2+ and Na+ proved to be significant compared to Mg2+. Finally, it emerged that metal ions interacted with the water molecule and were subsequently adsorbed on the α-quartz (001) surface. This occurred due to the electrostatic attraction, consequently impacting the hydration characteristics of the quartz surface.

Study on the aggregation behavior of kaolinite particles in the presence of cationic, anionic and non-ionic surfactants.

Aggregation behaviors of kaolinite particles with different surfactants were studied in this paper. Aggregation settling yield and fractal dimension analysis were used to determine the aggregation results. Zeta potential measurements, adsorption tests, Infrared spectroscopy analysis and scanning electron microscope measurements were conducted for further investigation into the mechanism. Experimental results showed that much better aggregation results was obtained in the presence of cationic surfactant than that in the presence of anionic and non-ionic surfactants. 98% aggregation setting yield was obtained in the presence of dodecylamine. Adsorption tests indicated that the adsorption capacity of dodecylamine on kaolinite surface was larger than that of sodium oleate and Tween80. Zeta potential measurements confirmed that dodecylamine was more beneficial to the aggregation of kaolinite particles. Infrared spectroscopy analysis revealed that the adsorption of dodecylamine on kaolinite surface was attributed to electrostatic and hydrogen-bonding interactions. Sodium oleate was adsorbed by chemical adsorption. However, Tween80 can hardly be adsorbed by kaolinite surface.

Hydrophobic aggregation of fine particles in high muddied coal slurry water.

The hydrophobic aggregation of fine particles in high muddied coal slurry water in the presence of four quaternary ammonium salts of 1231(dodecyl trimethyl ammonium chloride), 1431(tetradecyl trimethyl ammonium chloride), 1631(cetyl trimethyl ammonium chloride) and 1831(octadecyl trimethyl ammonium chloride) was investigated through the measurement of contact angles, zeta potentials, aggregation observation, adsorption and sedimentation. The results show that quaternary ammonium salts can enhance the hydrophobicity and reduce the electronegativity of particle surface, and thus induce a strong hydrophobic aggregation of slurry fine particles which promotes the settlement of coal slurry water. The adsorption of quaternary ammonium salts on slurry particles increases with the increase of alkyl chain length and reagent dosage, and will reach equilibrium when the dosage reaches a certain value. Weak alkaline conditions also can promote quaternary ammonium salts to be adsorbed on the coal slurry fine particles. In addition, reasonable energy input and a chemical environment of weak alkaline solution are conducive to hydrophobic aggregation settlement of high muddied coal slurry water with quaternary ammonium salts. The main mechanism of hydrophobic aggregation of coal slurry particles with quaternary ammonium salts is 'adsorption charge neutralization' and hydrophobic interaction.

Study of enhanced low-quality coal oxidative desulphurization and deashing by using HNO3 and microwave pretreatment.

In this paper, the effect of urea-hydrogen peroxide (UHP) solution on desulphurization and demineralization of coal with high sulphur and high ash by using HNO3 and microwave pretreatment was investigated. The oxidation process is strongly dependent on irradiation power and time for microwave pretreatment, UHP concentration, leaching time and temperature of the UHP solution. X-ray diffraction and Fourier transform infrared technique have been performed for the raw and treated coals. Compared with the UHP alone, successive treatments with HNO3 and microwave pretreatment resulted in the significant removal of total sulphur and mineral matter from the coal. The proposed experimental method has the meaning of practical guide to the desulphurization and deashing of coal by microwave.