Guihong Han

A facile disposal of Bayer red mud based on selective flocculation desliming with organic humics

Humics flocculant was applied in the disposal of Bayer red mud based on selective flocculation desliming process. The parameters affecting selective flocculation behavior such as flocculant dosage, slurry pH and agitation intensity were studied. For flocculating mechanism analysis, the iron mineral and the flocs product were characterized by ζ-potential testing, settling experiments, optical microscope and SEM imaging. The results show that humics exhibits a good selective flocculation performance in the high alkaline pH range. With an optimal condition of 2% solid density, flocculant dosage 30 mg L(-1), Na2SiO3 dosage 200 mg L(-1), slurry pH 10.0 and agitation speed 1000 rpm, the recovery of iron minerals of 86.25±1.31%, the iron grade of concentrate of 61.12±0.10%, the separation index of 0.69±0.02 can be obtained in the selective flocculation. It is found that the adsorption bridging of humics polymer dominates the selectively flocculating the iron minerals. Large flocs or aggregates with a better settling capacity are generated because of humics occurring. The maximum settling velocity of 38.23±1.51 m h(-1) is reached at pH 10. This work brings the easiness in directly recovering fine particle size of iron-bearing minerals from red mud.

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.

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.

Experimental Investigation on Desiliconization of Low-Grade Bauxite by Flotation Process

Low-grade bauxite resources are abundant in China. However, the high content of silica can not meet the production requirments of alumina. Desiliconization experiments were carried out during the process of one roughing-one cleaning direct flotation in this work using diasporic high-silica bauxite as experimental ore samples, sodium oleate as collector and humic acid as depressant. The effects of flotation parameters on the alumina-silica ratio (A/S) and Al2O3 content from Henan province were investigated. The optimum conditions for roughing stage are obtained as follows: humic acid dosage of 20 g/t, sodium oleate dosage of 700 g/t, particle size (content of particles below 0.074 mm) of 85%, pH 9.0. And the dosage of humic acid and sodium oleate for cleaning-stage was a third of that in roughing-stage. The alumina content in the concentrate increases from 58.91 to 65.05%, while A/S rises from 3.27 to 7.97. This research can show a promising application of low-grade bauxite for alumina production.

Research on the Interaction of Humic Acid with Iron Minerals

Binder is indispensable in the production of iron ore pellets and the quality of pellets seems to be related to the interactions between binders and iron minerals. Humic acid is proved a suitable binder for iron ore pelletizing. In this paper, the interactions between humic acid and iron minerals were investigated by adsorption experiments and molecular dynamic simulations. Adsorption experimental results show that the adsorption of humic acid on hematite is easier than that on magnetite, and the maximum adsorption capacities of humic acid on hematite and magnetite reach 17.1, 7.39 mg/g, respectively. The results of adsorption isotherms indicate that the Langmuir model provides the best correlation of the experimental data, while the thermodynamics results demonstrate that the adsorption process is a spontaneous exothermic process. Molecular dynamic simulations reveal that the interaction between hematite and humic acid is stronger than that between humic acid and magnetite.

Research on Impurity Removal of Low Grade Bauxite

An acid leaching method was adopted to remove the impurities of potassium and iron from the DI (diaspore-illite) type low grade bauxite acquired from Dengfeng city of Henan province, in order to provide a higher quality raw material for the refractories industry. The effects of sulfuric acid concentration, leaching temperature, reaction time and sulfuric acid to bauxite ratio on removal efficiency of impurities were investigated. The optimum experiment conditions were: sulfuric acid concentration of 7 mol/L, reaction temperature of 90 °C, reaction time of 4 h and sulfuric acid to bauxite ratio of 6 mL/g. Under these conditions, the removal efficiency of potassium and iron were 19.2 and 94.0%, respectively. The approach presented in this work is a promising process of comprehensive utilization of low grade bauxite.

Investigation of Flotation Behaviors of Refractory High-Silica Bauxite

High content of silica results in high soda consumption, which limits the use of high-silica bauxite in the production of Bayer alumina. In this work,the main flotation parameters of high silica bauxite (A/S 5.0) including particle size, pulp pH, collector dosage and dispersant dosage were studied. With an optimal condition of 33% solid density, particle size of -74 μm above 93%, sodium oleate dosage 2200 g•t−1, Na2CO3 dosage 2000 g•t−1, sodium hexametaphosphate dosage 30 g•t−1, slurry pH 9.4 and agitation speed 2280 rpm, the recovery of aluminum minerals of 56%, the A/S of concentrate of 12.2, and the separation index of 0.4 can be obtained.