Guangye Wei

Activation pretreatment of limonitic laterite ores by alkali-roasting using NaOH

Activation pretreatment of Cr-containing limonitic laterite ores by NaOH roasting to remove Cr, Al, and Si, as well as its effect on Ni and Co extraction in the subsequent pressure acid leaching process was investigated. Characterization results of X-ray diffraction (XRD) and scanning electron microscopy/X-ray energy dispersive spectroscopy (SEM/XEDS) show that goethite is the major Ni-bearing mineral, and chromite is the minor one. Experimental results show that the leaching rates of Cr, Al, and Si are 95.6wt%, 83.8wt%, and 40.1wt%, respectively, under the optimal alkali-roasting conditions. Compared with the direct pressure acid leaching of laterite ores, the leaching rates of Ni and Co increase from 80.1wt% to 96.9wt% and 70.2wt% to 95.1wt% after pretreatment, respectively. Meanwhile, the grade of acid leaching iron residues increases from 54.4wt% to 62.5wt%, and these residues with low Cr content are more suitable raw materials for iron making.

Dechromization and dealumination kinetics in process of Na2CO3-roasting pretreatment of laterite ores

A novel process was proposed for the activation pretreatment of limonitic laterite ores by Na2CO3 roasting. Dechromization and dealumination kinetics of the laterite ores and the effect of particle size, Na2CO3-ore mass ratio, and roasting temperature on Cr and Al extraction were studied. Experimental results indicate that the extraction rates of Cr and Al are up to 99% and 82%, respectively, under the optimal particle size of 44-74 mu m, Na2CO3-to-ore mass ratio of 0.6:1, and temperature of 1000 degrees C. Dechromization within the range of 600-800 degrees C is controlled by the diffusion through the product layer with an apparent activation energy of 3.9 kJ/mol, and that it is controlled by the chemical reaction at the surface within the range of 900-1100 degrees C with an apparent activation energy of 54.3 kJ/mol. Besides, the Avrami diffusion controlled model with on apparent activation energy of 16.4 kJ/mol is most applicable for dealumination. Furthermore, 96.8% Ni and 95.6% Co could be extracted from the alkali-roasting residues in the subsequent pressure acid leaching process.

Preparation of Cr2O3 precursors by hydrothermal reduction in the abundant Na2CO3 and Na2CrO4 solution

Precursors of chromium oxide (p-Cr2O3) were prepared by reducing hexavalent chromium in the presence of sodium carbonate solution under hydrothermal conditions. Methanal was used as the reductant, and carbon dioxide was the acidulating agent. The influences of reaction temperature, initial pressure of carbon dioxide, isothermal time and methanal coefficient on Cr(VI) reduction were investigated. Experimental results showed that Cr(VI) was reduced to Cr(III) with a yield of 99%. Chemical titration, thermogravimetry (TG), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) were used to characterize the p-Cr2O3 and Cr2O3. The series of p-Cr2O3 were found to be multiphase even if they presented different colors, from gray green to lavender. After these p-Cr2O3 samples were calcined, the product of rhombohedral Cr2O3 with a purity of 99.5wt% was obtained.

Crystallization behaviors of bayerite from sodium chromate alkali solutions

In order to clean production of chromium compounds, it is a critical process to remove aluminates and utilize aluminum compounds from artificial chromate alkali solutions. The effects of Na2CrO4 on the neutralization curve, Al(OH)(3) precipitation efficiency and induction period of bayerite were investigated. The results indicate that the neutralization curve of the artificial chromate alkali solutions shows three distinct regions and its induction period is longer than that of pure sodium aluminate solutions at the same aluminum concentration. And the decreased temperature and volume fraction of CO2 enhance the particle size of bayerite beta-Al(OH)(3). Bayerite composed of agglomerates of rods and cone frustums was obtained from alkali metal chromate solutions with 28.5% CO2 (volume fraction) at temperatures ranging from 50 degrees C to 70 degrees C. Coarse bayerite with particle size (d(50)) from 24.2 mu m to 29.3 mu m extremely has few impurities, which is suitable for comprehensive utilization.

Influence of Na2CO3 as Additive on Direct Reduction of Boron-bearing Magnetite Concentrate

Boron-bearing magnetite concentrate is typically characterized by low grade of iron and boron (wTFe = 51% – 54%, wR2O3 = 6%–8%), as well as the close intergrowth of ascharite phase and magnetite phase. A promising technology was proposed to separate iron and boron by coupling the direct reduction of iron oxides and Na activation of boron minerals together. The influence of Na2CO3 as additive on the direct reduction of boron-bearing magnetite was studied by chemical analysis, kinetic analysis, XRD analysis and SEM analysis. The results showed that the addition of Na2CO3 not only activated boron minerals, but also reduced the activation energy of the reaction and promoted the reduction of iron oxides. Besides, the addition of Na2CO3 changed the composition and melting point of non-ferrous phase, and then promoted the growth and aggregation of iron grains, which was conducive to the subsequent magnetic separation. Thus, the coupling of the two processes is advantageous.

Crystallization of gibbsite from synthetic chromate leaching solution in sub-molten salt process

Abstract For the clean and economical production of chromium compounds, it is crucial to remove aluminates from chromate alkali solutions and utilize aluminum-containing compounds. In this work, carbonization was used to remove aluminates from a synthetic chromate leaching solution containing a high K2O/Al2O3 mole ratio. The influence of reaction temperature, carbonization time, flow rate of carbon dioxide, and seed ratio on the precipitation of Al was investigated. The optimal output was obtained under the following experimental conditions: a reaction temperature of 50 °C, a carbonization time of 100 min, a carbon dioxide flow rate of 0.1 L/min, and a seed ratio of 1.0. Gibbsite was obtained following carbonization. The structure and morphology of the gibbsite were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and laser particle size analyzer. The particle size distribution and morphology of the gibbsite were significantly influenced by the experimental conditions. The gibbsite had a mean particle size (d50) of 16.72 μm. The thermal decomposition of the gibbsite was analyzed by XRD and the decomposition path was determined. The obtained coarse α-Al2O3 precipitate, which contains 0.08% Cr2O3 and 0.10% K2O, was suitable for subsequent utilization.