Calcined vanadium pentoxide

After filtration, the precipitate is calcined to produce red calcined vanadium pentoxide or further melted and crushed to produce flakes of black vanadium pentoxide, both having a purity greater than 99.5 wt.% V Oj. Liquors produced as byproduct during operations... 

The red cake can be further purified by dissolving it in an aqueous solution of Na2C02- The iron, aluminum, and silicon impurities precipitate from the solution upon pH adjustment. Ammonium metavanadate then precipitates upon the addition of NH Cl and is calcined to give vanadium pentoxide of greater than 99.8% purity. 

The active phase, which is soHd at room temperature, is comprised of mixed potassium and sodium vanadates and pyrosulfates, whereas the support is macroporous siUca, usually in the form of 6—12 mm diameter rings or pellets. The patent Hterature describes a number of ways to prepare the catalyst a typical example contains 7 wt % vanadium pentoxide, 8% potassium added as potassium hydroxide or carbonate, 1% sodium, and 78 wt % siUca, added as diatomaceous earth or siUca gel, formed into rings, and calcined in the presence of sulfur dioxide or sulfur trioxide to convert a portion of the alkah metal salts into various pyrosulfates (81,82). 

Vanadium is stripped from the organic solution with 1.5 mol dm sulfuric acid to a concentration of about 50gdm V. After an iron removal step with strong sulfuric acid, the organic solution is washed with water and recycled. From the vanadium strip liquor, ammonium polyvanadate (APV) is precipitated by oxidation and addition of ammonia. The APV slurry is thickened and pumped to a vacuum belt filter, where the APV cake is carefully washed with fresh water. The APV filter cake is dried and then calcined to vanadium pentoxide. 

Vanadium pentoxide is an intermediate in recovering vanadium from minerals (See Vanadium). Sodium polyvanadate, obtained as a red cake in one of the steps in extracting vanadium from its ores is calcined at 700°C in air to form a melt of vanadium pentoxide. Pentoxide is prepared in purified form by dissolving red cake in sodium carbonate solution followed by addition of an aqueous solution of ammonia and ammonium chloride. Ammonium metavanadate is precipitated which on decomposition at 320 to 430°C forms vanadium pentoxide. 

AIPO4-5 molecular sieve (BET surface area, 299 m g ) used in this study was prepared by the method of Wilson et al. [1j. VjOg/AIPO -S samples were prepared by impregnating with aqueous solutions of ammonium vanadate after removing templating agent in the AIPO -S by calcining at 530°C. The samples were dried at 110 C for 24 h then calcined in air at 550°C for 2 h. VAPO -S was prepared from gel mixture of phosphoric acid, pseudoboehmite, vanadium pentoxide, tri-propylamine and water (1.3 PrjN x AljOj PjOj 40 HjO) by crystallization at 165°C for 3 - 7 days [7. ... 

Impregnation has been used to prepare a number of catalysts having different metal support combinations. Highly loaded nickel catalysts supported on alumina, titania, silica, niobia and vanadium pentoxide were prepared by adsorption of nickel nitrate from an ammoniacal solution onto the support material. The supported salts were dried at 120°C and calcined at 370°C before reduction to the supported metallic nickel. It was found that the ease of reduction depended on the crystallinity of the support. Amorphous or poorly crystalline supports made the reduction of the nickel oxide more difficult than on crystalline supports. As examples of its generality, this procedure was also used to prepare... 

Fig.3. The XRD pattern of vanadium pentoxide layer with calcination conditions.

Stratcor process (Durango, CO). In Durango, US Vanadium Corp. recovers vanadium as a coproduct with uranium by leaching the ore concentrate for 24 h with hot sulfuric acid and an oxidant such as sodium chlorate (NaClOj). After removal of solids, the leachate is fed into a solvent-extraction circuit, where the uranium is extracted in an organic solvent consisting of 2.5%-amine-2.5%-isodecanol-95%-kerosene. Vanadium remains in the raffinate, which is fed into a second solvent-extraction circuit. There vanadium in turn is extracted in the organic phase, stripped with a 10 wt.% soda-ash solution, and precipitated with ammonium sulfate. The ammonium metavanadate precipitate is filtered, dried, and calcined to yield flakes of black (fused) vanadium pentoxide. 

Because vanadium pentoxide, V Oj, which coprecipitates simultaneously with sodium uran-ate, is always present in the impure yellow cake, at levels ranging from 5 to 6 wt.%, it must be removed by roasting the impure yellow cake with sodium carbonate at S60°C for 30 min, and after cooling the solid calcinated mass is leached with water to extract the soluble sodium vanadate, NaVOj. The leached product is filtered and the washed yellow cake is dried, while the solution from which vanadium can be recovered is stored. 

With sulfuric acid a vanadium hydroxide is precipitated that can be redissolved in soda to a pure soluhon of sodium vanadate. Addition of ammonium chloride precipitates white crystalline ammonium vanadate NH VO. This can be calcined to give orange vanadium pentoxide, suitable for production of pure vanadium and of fer-rovanadium. 

Vanadium-zirconia is another blue stain used often. A mixture consists of zirconia ZrO, silica SiO, and vanadium pentoxide (vanadium in + oxidation state, which is colorless). The blue color is due to the formation of in the calcination process. The V atom in is in the -hIV oxidation that has a characteristic blue color. The formation of scans to be facilitated by the addition of... 

General Chemical Co. Developed by Joseph. A mixture of caustic soda, potash, and vanadium pentoxide added to wet mix of fine kieselguhr, potassium sulfate, and tragacanth gum. Dilute sulfuric acid added to neutralize alkalis. Mixture evaporated before granulation and extrusion. Calcined 600°C. 

---