Wencui Chai

A perspective of stepwise utilisation of Bayer red mud: Step two--Extracting and recovering Ti from Ti-enriched tailing with acid leaching and precipitate flotation.

The extraction and recovery of Ti from Ti-enriched tailing with acid leaching and precipitate flotation, as one of the critical steps, was proposed for the stepwise utilization of red mud. The factors influencing acid leaching and precipitate flotation were examined by factorial design. The leaching thermodynamics, kinetics of Ti(4+), Al(3+) and Fe(3+), and the mechanism of selectively Fe(3+) removal using [Hbet][Tf2N] as precipitating reagent were discussed. The extracting of Ti(4+), Al(3+) and Fe(3+) in concentrated H2SO4 is controlled by diffusion reactions, depending mainly upon leaching time and temperature. The maximum extracting efficiency of Ti(4+) is approximately 92.3%, whereas Al(3+) and Fe(3+) leaching are respectively 75.8% and 84.2%. [Hbet][Tf2N], as a precipitating reagent, operates through a coordination mechanism in flotation. The pH value is the key factor influencing the flotation recovery of Ti(4+), whereas the dosage of precipitating reagent is that for Al(3+) recovery. The maximum flotation recovery of Ti(4+) is 92.7%, whereas the maximum Al(3+) recovery is 93.5%. The total recovery rate for extracting and recovering titanium is 85.5%. The liquor with Ti(4+) of 15.5g/L, Al(3+) of 30.4g/L and Fe(3+) of 0.48g/L was obtained for the following hydrolysis step in the integrated process for red mud utilisation.

Probing acid/base chemistry and adsorption mechanisms of hydrolysable Al(III) species with a clay system in aqueous solution

The acid/base chemistry of hydrolysable Al(III) species with a clay (bentonite and kaolin) system was investigated at 35 °C in the expanded solution pH range from 1 to 9. The adsorption capacity (qe) and mechanism of Al(III) species on clays were examined by means of UV-Vis spectra, optical microscope, zeta potential testing, SEM, XPS and XRD analysis. The results demonstrate that the qe of Al(III) increases with increasing solution pH, and the maximum adsorptions of bentonite and kaolin are 13.64 mg g−1 and 1.06 mg g−1, respectively. Each Al(III) species offers a different contribution to the total adsorption capacity. The cation Al3+ is the dominant species below pH 4 and the anion Al(OH)4− is the main species above pH 6. The solution pH values change in the single clay or hybrid clay/Al(III) solution because of the acid–base dissolution and competitive adsorption of H+/OH− with Al(III) species. The particle sizes (d80) of the clays after adsorption at different pH were first associated with thermodynamics. The zeta potential variation of clays was first connected with the total charge numbers of Al(III) species in solution. Zeta potential, XPS and XRD studies indicate that charge neutralization and ion exchange dominate the adsorption process at lower pH and surface complexation and precipitation at higher pH.

Flotation Separation of Pyrite from Refractory High-Sulfur Bauxite

The existence of pyrite results in high soda consumption, iron pollution of alumina oxide and pipeline corrosion in the utilization of high-sulfur bauxite during the production of Bayer alumina. The flotation desulfurization of high-sulfur diasporic bauxite with modified 2-mercaptobenzimidazole (MBI) collector was studied in this work. The effects of pulp pH, collector dosage, activator dosage and frother dosage on flotation performance (the sulfur content in concentrate and Al2O3 recovery) were examined. The results indicate that the sulfur in bauxite was successfully decreased through the reverse flotation. With an optimal condition of 10% solid density, particle size of −74 µm of 75%, pulp pH 9, temperature 30 °C, collector dosage of 120 g/t, copper sulfate dosage of 20 g/t, and terpenic oil dosage of 120 g/t, the recovery of Al2O3 reached to 77.58%. The sulfur content of concentrate was decreased from 2.87 to 0.66%, with an aluminum to silicon ratio (A/S) increasing from 3.36 to 4.43.

Hydrothermal synthesis and electrochemical sensing properties of copper vanadate nanocrystals with controlled morphologies

Abstract Morphology-controlled synthesis of copper vanadate nanocrystals is of great significance in electrochemical sensing applications. A facile hydrothermal process for synthesizing copper vanadate nanocrystals with various morphologies (e.g., nanoparticles, nanobelts and nanoflowers) was reported. Phase, morphology and electrochemical performance of the as-synthesized copper vanadate nanocrystals were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and cyclic-voltammogram (CV) techniques. The results revealed that the morphologies of the Cu 3 V 2 O 7 (OH) 2 ·2H 2 O (CVOH) nanocrystals could be controlled by changing copper salts, surfactants and pH values. The CVOH samples showed enhanced electrochemical response to ascorbic acid. Comparatively, the CVOH nanobelts had the higher electrochemical sensing performance than those of CVOH nanoparticles and nanoflowers. The CVOH-nanobelts-modified GCEs had a linear relationship between the peak currents in their CVs and ascorbic acid concentration. The CVOH nanocrystals can be used as potential electrochemical active materials for the determination of ascorbic acid.

An Enhanced Study on Adsorption of Al(iii) onto Bentonite and Kaolin: Kinetics, Isotherms, and Mechanisms

ABSTRACT In order to remove aluminum ions in bauxite processing wastewater, two natural clay minerals (bentonite and kaolin) were used as adsorbents. The adsorption behaviors including kinetics and isotherms were studied at much broader pH range, higher temperature, and higher Al(III) concentration by batch experiments. The adsorption mechanisms were investigated by optical microscope, zeta potential testing, and XRD analysis. The results show that Al(III) adsorption is strongly pH dependent and increases clearly with increasing pH. The pseudo-second-order kinetic model can best describe the adsorption process, and the intra-particle diffusion was not the sole rate-controlling step. The Langmuir–Freundlich model can fit best the adsorption equilibrium data, and the maximum capacities of Al(III) adsorbed on bentonite and kaolin reach to 8.52 mg g–1 and 0.58 mg g–1, respectively, at 35°C. Thermodynamic studies display that the adsorption of Al(III) onto clay minerals is non-spontaneous. The adsorption of Al(III) onto bentonite is endothermic and causes an increase in the entropy, while kaolin is exothermic and causes a decrease in the entropy. The interaction mechanisms of Al(III) with bentonite and kaolin involve electrostatic attraction, cation exchange, surface complex, and precipitation. Bentonite as adsorbent has more potential to remove Al(III) than kaolin.

Research on the Interaction Between 1-Butyl-2-Mercaptobenzimidazole and Pyrite

The flotation desulfurization is generally used for the removal of sulfur impurities in the high sulfur bauxite. 1-butyl-2-mercaptobenzimidazole (DMBI) was synthesized and used as collector in the laboratory. The interactions between DMBI and pyrite with different adsorption time, solution pH, solution temperature and DMBI concentration were investigated in this work. Results show that the equilibrium adsorption time is 20 min, and the adsorption capacity decreases with increasing pH as well as temperature. With the increasing concentration, adsorption value increases and achieves the saturated adsorption. The adsorption of DMBI on pyrite is more consistent with Langmuir isothermal adsorption equation from 298.15 to 318.15 K. However, the adsorption is more fitted by the Freundlich isothermal adsorption equation at 288.15 K. Thermodynamic studies display that the adsorption of DMBI and pyrite is non-spontaneous and exothermic.

Pyrolysis of Active Fraction of Humic Substances-Based Binder for Iron Ore Pelletizing

The authors have developed a series of humic substances-based binders for iron ore pelletizing. This work was to gather information for the further industry application of humic substances-based binders in the field of iron ore oxidized pellets production. Pyrolysis of humic substances as the active fraction in the binders and its effects on fired hematite pellets was investigated in this study. Pyrolysis product of humic substances was focusing on four main gases (CO2, CO, H2and CxHy). The results demonstrated that effect of O2/N2atmosphere on weight loss of humic substances is obvious above 600 °C. Instantaneous concentration of gas products is increased with increasing pyrolysis temperature. Weight percentage of CO2 is increased obviously with increasing O2 concentration, while those of CO and H2 decreasing.