Abstract:
The invention relates to a method for the extraction of vanadium from various sources in the form of vanadiumpentoxide, V 2 O 5 , from a source containing vanadium. The method includes the steps of: providing a source of V 2 O 5 , heating the source to a temperature of at least 1000° C., evaporating V 2 O 5  from the heated source and recovering the evaporated V 2 O 5 .

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a method for the extraction of vanadiumpentoxide, V 2 O 5 , from a source containing vanadium. 
       BACKGROUND ART 
       [0002]    Vanadiumpentoxide, V 2 O 5 , is mainly used as a catalyst in the chemical industry and for the production of ferrovanadium. 
         [0003]    In the past there has been a great interest to recover vanadium or vanadium oxide from different sources. In particular, different routes for selective pre-oxidation of vanadium from raw iron has received much attention and e.g. EP 235 291, EP 134 351, U.S. Pat. No. 4,071,355 and GB 1 281 203 discloses recovery of vanadium oxide from molten metal. 
       SUMMARY OF THE INVENTION 
       [0004]    The general object of the present invention is to provide an alternative production route for the extraction of vanadium from various sources in the form of vanadium pentoxide. This and other objects are achieved by means of a method as defined in claim  1 . Preferred embodiments of the invention are specified in the dependent claims. 
         [0005]    The present inventors have found that it is possible to extract vanadium in the form of in the form of vanadium pentoxide, V 2 O 5 , by evaporation of this oxide. To be specific, the claimed method includes the steps of:
       providing a source containing vanadium,   if necessary, converting at least part of the vanadium in said source to V 2 O 5 , thereby providing a source of V 2 O 5 ,   heating the source to a temperature of at least 1000° C.,   evaporating V 2 O 5  from the heated source and   recovering the evaporated V 2 O 5 .       
 
         [0011]    The invention is defined in the claims. 
     
    
     DETAILED DESCRIPTION 
       [0012]    Basically any vanadium containing source can be used in the claimed method. However from a practical point of view the vanadium containing source is suitably selected from the group of: ore, slag, ash and V 2 O 5  formed by roasting vanadium-sulphide from spent petroleum refining catalysts since these are the most important sources. If the vanadium in said source is not in the form of vanadium pentoxide, V 2 O 5 , then it is necessary to convert at least part of the vanadium to V 2 O 5  In most cases all vanadium is converted to V 2 O 5  This is done by roasting the sulphide or by oxidation of the lower oxides (V 3+/ V 4+ ) to pentoxide (V 5+ ). 
         [0013]    Preferably the ore is selected from the iron sands, magnetite, hematite, titani-ferrous magnetite and vanadium-titanium magnetite; the slag is selected from converter slag, submerged arc furnace slag, ladle slag and slag obtained by selective oxidation of vanadium from raw iron; and the ash is selected from petroleum coke ash, in particular fly ash and boiler ash. 
         [0014]    The evaporation is promoted by an oxidizing atmosphere and the evaporation increases with increasing partial pressure of oxygen such that oxygen-enriched air and pure oxygen results in higher evaporation ability than in air. 
         [0015]    Evaporation can take place from a solid and/or a liquid V 2 O 5 —containing source. A major source of supply is slag from the steel industry. In this case the slag should be liquid and an oxidizing gas is preferably blown into or through the liquid slag bath held at 1200° C. to 1900° C., preferably 1450° C. to 1700° C. The slag normally comprises at least three of the following components CaO, MgO, MnO, SiO 2 , TiO 2 , FeO x  and VO x , wherein x indicates that the oxides need not be stoichiometric and that more than one valence state may present. Vanadium can have three valence states: V 3+ , V 4+  and V 5+ . High slag basicities stabilizes higher vanadium oxidation states such that one should expect V 4+ /V 5+  to be the predominant redox-pair. 
         [0016]    Ash, such as petroleum coke ash can optionally be mixed with one or more of components selected from CaO, MgO, MnO, SiO 2 , TiO 2 , Al 2 O 3  and FeO x  and subjected to at least partly melting wherein the ash/slag mixture is liquid or solid-liquid mixture and held at 1200° C. to 1900° C., preferably 1450° C. to 1700° C. and wherein oxygen or oxygen enriched air is blown through the slag bath for generation and evaporation of V 2 O 5 . 
         [0017]    Evaporation of V 2 O 5  from a solid vanadium-containing source is a feasible alternative, in particular when using ore. The Swedish magnetite ore for instance contains about 1.5% V. In one preferred embodiment magnetite ore is roasted to hematite at a temperature in the range of 1100-1300° C. by using oxygen as a carrier gas in a fluidized bed reactor. In this case, the temperature should be adjusted to lay just under the softening temperature of the vanadium containing iron ore in order to avoid problems with sticking. As an alternative to oxygen, air or oxygen enriched air containing 22-99% oxygen may be used. 
         [0018]    As a precursor for the source of V 2 O 5 , it is possible use vanadium-sulphide, V 3  S 4 , from spent catalysts. V 3   5   4  is deposited in high amounts on petroleum refining catalysts for desulphurization. When these catalysts are spent said sulphide can be converted to oxide by a roasting treatment and thus provide a source of V 2 O 5 . The roasting can be performed by conventional methods known in the art. The roasting of V 3  S 4  and the evaporation of V 2 O 5  may be performed in a single step by oxidizing the V 3  S 4  at temperatures of at least 1000° C., so that V 2 O 5  is evaporated as it is formed. 
         [0019]    The evaporated V 2 O 5  is recovered by subjecting the V 2 O 5  containing gas to condensation. Any type of condensation can be used. A conventional cold trap may be used. 
       EXAMPLE 1  
       [0020]    Vanadium containing slag from the production of high alloyed tool steels was treated according to the invention. The slag had the following composition in weight percent; 5% V 2 O 5 , 37.5% CaO, 20% FeO, and 37.5% SiO 2 . 
         [0021]    The slag was split in two samples. The samples were heated in air under laboratory conditions in a platinum crucible at 1853K respectively 1873K during 120 minutes. The exit gas from the furnace was cooled, filtered and formed oxide particles were collected. For the sample heated to 1823K 80% by weight of V 2 O 5  was recovered. For the sample heated to 1873K 90% by weight of V 2 O 5  was recovered. The purity of the vanadium pentoxide was over 95% by weight. 
       EXAMPLE 2 
       [0022]    Pet coke slag was heated in an alumina crucible and melted in an electric arc furnace. The slag had the following composition expressed in weight percent; 42.8% V 2 O 3 , 12.5% CaO, 10.7% FeO, 7.4% Al 2 O 3  and 26.6% SiO 2 . 
         [0023]    The slag was heated in the furnace from room temperature to a temperature of 1480° C. Air was blown into the liquid slag. This resulted in an oxidation of FeO to Fe 2 O 3  and of V 2 O 3  to V 2 O 5 . The slag was kept liquid under oxidizing conditions for 400 minutes. The reaction was found to be faster with oxygen blowing. The exit gas was condensed in a cold trap. 
         [0024]    The amount of V 2 O 5  found in the cold trap was equivalent to 92% by weight of the original amount in the pet coke slag. The purity of the vanadium pentoxide was over 98% by weight. 
       EXAMPLE 3 
       [0025]    A Swedish magnetite ore containing 95% Fe 3 O 4 , 1.5% V 2 O 5  and the residual mainly SiO 2  was heated in an alumina crucible for two hours at 1623K under a flow of oxygen enriched air containing 50% oxygen. The content of V 2 O 5  in the magnetite ore decreased after 2 hours processing from 1.5% to 0.3%. The purity of the vanadium pentoxide was 95% by weight.