Yang Zhang

Effect of mechanical activation on alkali leaching of chromite ore

Mechanical activation was used to improve the extraction of chromium in molten NaOH. It is observed that the extraction ratio reaches 97% after leaching for 200 min when chromite ore is mechanically activated for 10 min, but only 34% if not activated. Mechanical activation can decrease the particle size, increase the surface area, and enhance the lattice distortion. Further, the mechanisms for mechanical activation were exposed. The results show that the mechanical activation mainly focuses on chromite ore particle size decrease and the lattice distortion. The formation of aggregation weakens the strengthening effect of mechanical activation for releasing high surface energy.

Solvent impregnated resin prepared using ionic liquid Cyphos IL 104 for Cr(VI) removal

Abstract Ionic liquid (IL) trihexyl (tetradecyl) phosphonium bis 2,4,4-trimethylpentylphosphinate (Cyphos IL 104) was impregnated on XAD–7 resin. The solvent impreganated resin (SIR) was prepared and applied in Cr(VI) removal. The morphology and the thermal stability of the resins were explored. The effects of equilibrium time and initial pH value on Cr(VI) adsorption were investigated. Adsorption isotherm, separation and desorption of the SIR, and selectivity of SIR were also explored. The results show that Cyphos IL 104 exists in the inner XAD-7 resin, and the optimum pH value range of the SIR for Cr(VI) extraction is 0 to 2. When NaOH used as desorption solution, the Cr(VI) can be effectively desorbed from the SIR.

Extraction mechanism of cerium(IV) in H2SO4/H3PO4 system using bifunctional ionic liquid extractants

The extraction of Ce(IV) in H2SO4/H3PO4 system was investigated systematically using bifunctional ionic liquid extractants (Bif-ILES) [A336][P507], [A336][P204] and [A336][C272] in n-heptane. The effects of H2SO4 concentration, extractant concentration and salting-out agent concentration were observed in detail. The extraction mechanism of Ce(IV) in H2SO4/H3PO4 system was obtained. The comparison with other extractants such as Cyanex923, TBP was also studied. Thermodynamic functions of the extraction reaction were calculated, showing that the extraction was an exothermic process. The separation of Ce(IV) from RE(III) and Th(IV) was also investigated. The result indicated that Ce(IV) could be selectively extracted in this system. CePO4 nanoparticles were obtained in the process of stripping using H2O2 in H2SO4/H3PO4 system. X-ray diffraction (XRD), scanning electron microscopy (SEM) and spectroscopy were adopted for the characterization of the sample.

A Clean and Efficient Method for Recovery of Vanadium from Vanadium Slag: Nonsalt Roasting and Ammonium Carbonate Leaching Processes

ABSTRACT A cleaner method has been developed for the extraction of vanadium from vanadium slag. Compared to the traditional alkaline salts roasting followed by the water leaching process, in the nonsalt roasting process because no additives are added, the chromium spinel in the raw vanadium slag will not be converted to carcinogenic chromate salts and exhaust gas will not be produced. The ammonium metavanadate is precipitated from the water leach solution. The wastewater from the vanadate precipitation process can be recycled into the leaching process. The leaching residue can be comprehensively utilized in conjunction with an iron-making process using blast furnace. The nonsalt roasting mechanism was systematically investigated in a laboratory study. The XRD and morphology analysis of roasted vanadium slag showed that the oxidation of vanadium spinel occurred in the following steps: (1) the destruction of vanadium spinel and the formation of solid solution of Fe2O3·V2O3; (2) the oxidation of solid solution of Fe2O3·V2O3 to Fe2O3·V2O4 and a portion of the V(IV) in the Fe2O3·V2O4 was reacted with basic oxide such as MgO to generate the low-valence vanadate Mg2VO4; (3) the formation by further oxidation of highest-valence vanadates Mn2V2O7 and Mg2V2O7. The effects of particle size, oxygen concentration, gas flow rate, and temperature on vanadium recovery were investigated. Simultaneously, the effects of leaching variables, including ammonium carbonate concentration and temperature, were examined. The thermodynamics of the system are also reported.

Leaching of chromite ore in concentrated KOH by catalytic oxidation using CuO as catalyst

Abstract CuO was used as a catalyst in the concentrated KOH solution to enhance the leaching of chromium from the chromite ore. The impacts of temperature, KOH-to-chromite ore mass ratio, CuO-to-chromite ore mass ratio, and gas flow rate on the chromium leaching rate were investigated. The results indicated that CuO played an important role in improving the chromium leaching rate. The leaching rate reached 98% after leaching for 6 h when CuO was applied, whereas it was only 60.8% without CuO under the same reaction conditions: temperature 230 °C, KOH-to-ore mass ratio 6:1, stirring speed 700 r/min, gas flow rate 1 L/min. According to the kinetics study, the catalytic oxidation was controlled by surface chemical reaction and the activation energy was calculated to be 15.79 kJ/mol when the temperature was above 230 °C. In contrast, without CuO, the rate-determining step was external diffusion and the apparent activation energy was 38.01 kJ/mol.