Shaona Wang

Kinetics analysis of decomposition of vanadium slag by KOH sub-molten salt method

A novel process was developed for the decomposition of vanadium slag using KOH sub-molten salt under ambient pressure, and the effects of reaction temperature, alkali-to-ore mass ratios, particle size, and stirring speed on vanadium and chromium extraction were studied. The results suggest that the reaction temperature and KOH-to-ore mass ratio are more influential factors for the extraction of vanadium and chromium. Under the optimal reaction conditions (temperature 180 °C, initial KOH-to-ore mass ratio 4:1, stirring speed 700 r/min, gas flow 1 L/min, and reaction time 300 min), vanadium and chromium extraction rates can reach up to 95% and 90%, respectively. Kinetics analysis results show that the decomposing process of vanadium slag in KOH sub-molten salt can be well interpreted by the shrinking core model under internal diffusion control. The apparent activation energies for vanadium and chromium are 40.54 and 50.27 kJ/mol, respectively.

Tuning α-Fe2O3 nanotube arrays for the oxygen reduction reaction in alkaline media

The oxygen reduction reaction plays a crucial role in alkaline fuel cells. Herein, an α-Fe2O3 nanotube array material was fabricated via a facile two-step electrochemical anodization method and employed as an efficient ORR catalyst in alkaline media. Due to its highly ordered open top architecture, the α-Fe2O3 nanotube array electrode exhibits excellent ORR catalytic activity with an onset potential of −0.39 V (vs. Hg/HgO) and high current density of 6.95 mA cm−2. Results show that the ORR exhibits quasi-reversible diffusion-controlled reaction characteristics and a well-defined four electron pathway. Moreover, as the crystalline structure transforms from α-Fe2O3 to Fe3O4 or as the alkaline concentration increases, the ORR activity is disturbed and the electron transfer number decreases. The as-prepared electrodes possess favorable alkaline tolerance as indicated from their chronoamperometric curves and Raman spectra. Accordingly, this novel α-Fe2O3 nanotube array material can be employed as efficient and low cost non-noble metal electrodes for electrochemical energy applications.

Research and prospect on extraction of vanadium from vanadium slag by liquid oxidation technologies

A series of innovative green metallurgical processes using novel reaction media including the NaOH/KOH sub-molten salt media and the NaOH-NaNO3 binary molten salt medium, for the extraction of vanadium and chromium from the vanadium slag have been developed. In comparison with the traditional sodium salt roasting technology, which operates at 850 degrees C, the operation temperatures of these new processes drop to 200-400 degrees C. Further, the extraction rates of vanadium and chromium utilizing the new approaches could reach 95% and 90%, respectively, significantly higher than those in the traditional roasting process, which are 75% and approximate zero, respectively. Besides, no hazardous gases and toxic tailings are discharged during the extraction process. Compared with the conventional roasting method, these new technologies show obvious advantages in terms of energy, environments, and the mineral resource utilization efficiency, providing an attractive alternative for the green technology upgrade of the vanadium production industries.

Alumina recovery from spent Bayer liquor by methanol

Decomposition of sodium aluminate solution is the key step for alumina production; however, approximately only 55% alumina yield is obtained by seeded precipitation. So, it is difficult to obtain sodium aluminate solution with high caustic ratio. In this study, a method was explored to recover alumina from spent Bayer liquor by deep decomposition with methanol. A variety of conditions, including reaction temperature, reaction time, methanol amount and seed coefficient were elaborately investigated. The results showed that the appropriate conditions were 1:1 in volume ratio of methanol to spent Bayer liquor, more than 1.0 seed coefficient and in a 40 degrees C water bath for 24 h. By characterizing through XRD, the crystal products were found to be Al(OH)(3). With this method, the molar ratio of Na(2)O to Al(2)O(3) of the spent liquor can be increased from about 3.0 to 10.0 due to the recovery of alumina, which is beneficial for the treatment of red mud.

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.

High-Rate and Long-Term Cycle Stability of Li–S Batteries Enabled by Li2S/TiO2-Impregnated Hollow Carbon Nanofiber Cathodes

The high theoretical energy density of lithium-sulfur (Li-S) batteries makes them an alternative battery technology to lithium ion batteries. However, Li-S batteries suffer from low sulfur loading, poor charge transport, and dissolution of lithium polysulfide. In our study, we use the lithiated S, Li2S, as the cathode material, coupled with electrospun TiO2-impregnated hollow carbon nanofibers (TiO2-HCFs), which serve as the conductive agent and protective barrier for Li2S in Li-S batteries. TiO2-HCFs provide much improved electron/ionic conductivity and serve as a physical barrier, which prevents the dissolution of lithium polysulfides. The Li2S/TiO2-HCF composite delivers a discharge capacity of 851 mA h gLi2S-1 at 0.1C and the bilayer TiO2-HCFs/Li2S/TiO2-HCF composite delivers a high specific capacity of 400 mA h gLi2S-1 at 5C.

Hollow carbon nanofiber as a stabilizer for in situ TiO2/VO2 co-impregnation with high rate performance and ultra-long cycling life as lithium-ion battery anode

TiO2 and VO2 were first co-impregnated in the shell of electrospun hollow carbon nanofibers. The hierarchical porous structure enabled fast electron transfer and electrolyte penetration, resulting in high power rate and ultra-long cycling life, which makes the structure a promising anode for lithium ion batteries.

Thermal hydrolysis synthesis and characterization of monoclinic metahewettite CaV6O16·3H2O

Monoclinic metahewettite CaV6O16·3H2O has been fabricated via thermal hydrolysis of calcium vanadate (Ca10V6O25). High purity calcium vanadate precipitate, featuring column structure with surface area of 8.61 m2/g, can be obtained by reacting sodium orthovanadate (Na3VO4) with calcium oxide at 90 °C for 2 h. By acidification of calcium vanadate in hot water at pH of 1.0–3.0, the monoclinic metahewettite crystals with uniform particle distribution, layered structure and nonporous structure can be fabricated. With the well crystallized layered structure, CaV6O16·3H2O may be a potential cathode material for secondary batteries as well as super capacitor materials.

Vapor Pressure Determination of the KOH + K2CrO4 + H2O System

The evaporation crystallization of K2CrO4 from KOH aqueous solution is one of the key units of the chromate cleaner production process developed by the Chinese Academy of Sciences. The vapor pressure of the KOH + K2CrO4 + H2O system was determined so as to optimize the evaporation operation. On the basis of the experimental results, the relationship between the vapor pressure and the temperature as well as the concentrations of KOH and K2CrO4 were determined as log(P/kPa) = 7.52−3.62 × 10-2(C KOH/mol·L-1) − 7.83 × 10-2(C K 2 CrO 4 / mol·L-1) − 2055.74 K/T wherein C KOH ranges from (0.8 to 10) mol·L-1, C K 2 CrO 4 ranges from (0 to 2) mol·L-1, and T ranges from (328.15 to 368.15) K.