Xuzhong Gong

Sticking behavior caused by sintering in gas fluidisation reduction of haematite

Abstract The sticking of haematite and iron powder during the fluidisation process was investigated using a visual fluidised bed reactor. The results showed that the amount of iron needed to stick decreased with increasing fluidisation temperature. Owing to no iron whisker formation in the experiments, the sticking phenomenon was discussed in the special case where iron morphology was dense or porous, and much attention should be paid to the effect of sintering of iron–iron contact on sticking, especially, surface nano-/microstructures of fresh iron that caused an increase in particle cohesiveness and sticking tendency. It was assumed that haematite covered with iron transformed into cohesive particles that self-agglomerated above minimum sintering temperature. Owing to the interface reaction induced, the sticking temperature of haematite was always lower than that of iron powder in the same size ranges. On the basis of sintering with surface diffusion mechanism, the tendency of sticking was enhanced by reduction reaction through reinforcing mass transfer on particle surface. Therefore, when iron whiskers were suppressed, sticking phenomenon was viewed as the agglomeration fluidisation among cohesive particles under sintering action.

Sulfur removal from bauxite water slurry (BWS) electrolysis intensified by ultrasonic

Effects of ultrasonic on desulfurization ratio from bauxite water slurry (BWS) electrolysis in NaOH solution were examined under constant current. The results indicated that ultrasonic improved the desulfurization ratio at high temperatures because of the diffusion and transfer of oxygen gas in electrolyte. However, due to the increase in oxygen gas emission, ultrasonic could not improve the desulfurization ratio obviously at low temperatures. Additionally, the particle size of bauxite became fine in the presence of ultrasonic, indicating that the mass transfer of FeS2 phase was improved. According to the polarization curves, the current density increased in the presence of ultrasonic, indicating that the mass transfer of liquid phase was improved. The apparent activation energy (AAE) of electrode reaction revealed that ultrasonic did not change the pathway of water electrolysis. However, ultrasonic changed the pathway of BWS electrolysis, converting indirect oxidation into direct oxidation. The AAE of BWS electrolysis in the presence of ultrasonic was higher than that in the absence of ultrasonic. And the low AAEs (less than 20 kJ/mol) clearly indicated the diffusion control during BWS electrolysis reaction.

Hierarchically 3D porous films electrochemically constructed on gas–liquid–solid three-phase interface for energy application

Hierarchically porous films as catalysts or supports are fascinating electrode materials for the electrochemical conversion and storage of energy due to the short transportation paths of electrons and ions. A novel and feasible method to construct 3D porous films is developed by direct electrodeposition on a gas–liquid–solid (GLS) three-phase interface. The formation mechanism of the porous structure is discussed based on bubble behavior and electrocrystallization. The progress toward the preparation of porous metals/alloys on cathodes and metal oxides/polymers on anodes is reviewed. The surface decoration of porous metal films by noble metals or non-metal compounds is summarized. The promising energy applications of porous films are highlighted.

Sulfur removal from ionic liquid-assisted coal water slurry electrolysis in KNO3 system

Abstract Ionic liquid-assisted coal water slurry (CWS) electrolysis was carried out in KNO3 system with constant current. The effects of ionic liquids including structure, concentration, temperature and time on the removal of sulfur were investigated to intensify desulfurization ratio from CWS electrolysis. Given the organic structure of imidazole, the influence of anions on the desulfurization was in the following order: Br− >BF4− >Cl−. Given the same anion of Br−, imidazole showed better performance than pyridine in terms of sulfur elimination. With increasing N-butylpyridinium bromide ([BPy]Br) concentration, the desulfurization ratio increased at the initial stage, and then decreased after 0.30 mol/L. Additionally, the desulfurization ratio continuously increased with time and temperature. Finally, the organic sulfur occurrences in coal before and after experiments were characterized by XPS technique. Results showed that the removal of thiophene was improved due to the extraction-oxidation effects and others (i.e. thioethers and sulfoxide) were removed mainly via enhanced oxidation and hydrolysis reactions.

Roles of Electrolyte Characterization on Bauxite Electrolysis Desulfurization with Regeneration and Recycling

The recycling of NaCl used as supporting electrolyte for bauxite electrolysis was carried out in this study. The electrolyte was regenerated by adding anhydrous CaCl2 into the solution after filtration, and effects of electrolyte characterization on bauxite electrolysis were examined by observing the change in desulfurization ratio and cell voltage. The results indicated that the desulfurization ratio increased with increasing recycling times of electrolyte. In the meantime, the increase in recycling times has led to the decrease in pH value as well as the increase in Fe ion concentration in the electrolyte, which were the main reasons for the increase in the desulfurization ratio with increasing recycling of electrolyte. The pH value of electrolyte after second electrolysis was lower than 1.5, and the desulfurization ratio increased obviously due to the increase in Fe3+ concentration and suppression of jarosite formation. The increase in Ca2+ concentration did not apparently change desulfurization ratio and anode surface activity. However, with Ca2+ addition, the cathode surface was covered by CaSO4·nH2O, thus resulting in the increase of cell voltage.

Effects of electrolyte recycling on desulfurization from bauxite water slurry electrolysis

Abstract To lower the cost of bauxite electrolysis desulfurization using NaOH solution as the supporting electrolyte, effects of electrolyte recycling on bauxite electrolysis desulfurization were investigated. The results indicate that electrode corrosion, cell voltage, the desulfurization rate and the pH value of the electrolyte have no obvious changes with the increase of cycle times. Additionally, there were some transitive valence S-containing ions in electrolyte after the electrolysis, such as SO32−, S2O32−. However, most of the sulfur in bauxite was eventually oxidized into SO42− into the electrolyte, and these S-containing ions did not affect the recycling utilization for electrolyte.

Desulfurization from Bauxite Water Slurry (BWS) Electrolysis

Feasibility of high-sulfur bauxite electrolysis desulfurization was examined using the electrochemical characterization, XRD, DTA, and FTIR. The cyclic voltammetry curves indicated that bauxite water slurry (BWS) electrolysis in NaOH system was controlled by diffusion. Additionally, the desulfurization effect of NaCl as the electrolyte was significantly better than that of NaOH as an electrolyte. As the stirring rate increased, the desulfurization ratio in NaCl system was not increased obviously, while the desulfurization ratio in NaOH system increased significantly, indicating further that electrolysis desulfurization in NaOH solution was controlled by diffusion. According to XRD, DTA, and FTIR analysis, the characteristic peaks of sulfur-containing phase in bauxite after electrolysis weakened or disappeared, indicating that the pyrite in bauxite was removed from electrolysis. Finally, the electrolytic desulfurization technology of bauxite was proposed based on the characteristics of BWS electrolysis.

Insight of Iron Whisker Sticking Mechanism from Iron Atom Diffusion and Calculation of Solid Bridge Radius

The sticking temperatures of three kinds of iron particles with different morphologies were examined at an inert atmosphere in a fluidized bed, indicating that the sticking temperature of a fresh reduction iron particle was lower than that of reagent iron particles, and that the sticking temperature of an iron particle with a whisker was lower than that of an iron particle without a whisker. Cavity defects on the surface of an iron particle with different morphologies were examined by positron annihilation spectroscopy. The results indicated that cavity defects on the surface of an iron particle with an iron whisker were higher than with others, which resulted in an easier surface diffusion of Fe atoms. From the calculation of a critical solid bridge radius, the critical solid bridge radius lowered with the decreasing of gas velocity and particle size. And when an instantaneous solid bridge radius was bigger than a critical solid bridge radius, sticking of the iron particle happened. The iron whisker made the surface diffusion rate of Fe atoms occur more quickly, which resulted in a faster growth rate of the instantaneous solid bridge radius. Therefore, the iron whisker supported the sticking.

Effects of ash/K2CO3/Fe2O3 on ignition temperature and combustion rate of demineralized anthracite

Abstract The effects of ash/K2CO3/Fe2O3 and their interactions on the ignition temperature and combustion rate of acid-washed anthracite were examined. The coal ashes from combustion of anthracite at different temperatures showed very different properties such as chemical compositions, color and morphology. Reactivities of demineralized anthracite with and without catalysts were measured by thermo-gravimetric analyzer (TG-DTG). The results indicate that ash itself has no catalytic effects on ignition temperature while the combustion rate is improved, especially by the ash prepared at high temperatures. The use of ash with K2CO3 (or Fe2O3) together as combustion catalysts reveals that the interactions (i.e. sintering reactions) between them have caused the reduction in combustion rate, compared with the cases when K2CO3 or Fe2O3 was employed individually. Similarly, the synergistic effect between K2CO3 and Fe2O3 was also observed to lower the combustion rate of demineralized anthracite.

The Importance of Slag Structure to Boron Removal from Silicon during the Refining Process: Insights from Raman and Nuclear Magnetic Resonance Spectroscopy Study

Slag structure plays an important role in determining the relative ease of boron removal from silicon. Correlation between slag structure and boron removal thermodynamics was experimentally studied by Raman and nuclear magnetic resonance (NMR) spectroscopy using CaO-SiO2-Na2O slags with different optical basicities (0.6 to 0.71). Optimization of slag depolymerization leads to efficient removal of boron. The extent of nonbridged oxygen content (NBO/T) and boron removal gradually increased with an increase in optical basicity from 0.6 to 0.66: B2O3 derived from boron oxidation captured nonbridging oxygens of Q0(Si), Q1(Si), and Q2(Si), and was incorporated into the silicate network in the form of Q3(Si and B). When optical basicity increased to 0.71, NBO/T rapidly increased and boron removal decreased considerably. Quick depolymerization of Q3(Si and B) deteriorated the stability of boron. Various structural forms of boron in the silicate network were successfully detected: the BO3 trihedrons [3]B-3Si, [3]B-2Si-1NBO, and BO3 (nonring), and the BO4 tetrahedrons BO4 (1B, 3Si) and BO4 (0B, 4Si). BO4 (1B, 3Si) was the main structure contributing to the increase of boron capacity; BO3 (nonring), detected under higher optical basicity conditions, may cause deterioration of boron removal by suppressing its oxidation.