Smelting process of ferrovanadium
The main raw material for ferrovanadium production in China is vanadium-titanium magnetite. After ore dressing and enrichment, vanadium-containing pig iron is smelted in a blast furnace, and vanadium slag is extracted during the blowing process of an atomizing furnace or a converter. After pulverization, the vanadium slag is added with sodium salt (soda ash, table salt or anhydrous sodium sulfate) for sodium oxidation and roasting, so that vanadium becomes soluble sodium metavanadate. After leaching and purification, ammonium sulfate is added to precipitate ammonium polyvanadate, and then deammoniation and melting are performed to cast into flake vanadium pentoxide. The required composition is vanadium pentoxide: 97-99%, P < 0.05%, S < 0.05%, Na2O + K2O < 1.5%. In addition, vanadium pentoxide is also extracted directly from vanadium-containing iron concentrate or vanadium-containing carbonaceous shale through chemical treatment. The main methods for smelting ferrovanadium are: Electrosilicothermic method. Flake vanadium pentoxide uses 75% ferrosilicon and a small amount of aluminum as reducing agents. In an alkaline arc furnace, qualified products are obtained through two stages of reduction and refining. During the reduction period, all the reducing agents of a furnace and 60-70% of the flake vanadium pentoxide are loaded into the electric furnace, and silicon thermal reduction is carried out under high calcium oxide slag. When the V2O5 in the slag is less than 0.35%, the slag (called lean slag, which can be discarded or used as building materials) is discharged and the refining period is entered. At this time, flake vanadium pentoxide and lime are added to remove excess silicon, aluminum, etc. in the alloy liquid. When the alloy composition meets the requirements, the slag and ferroalloy can be discharged. The slag discharged in the late refining period is called rich slag (containing 8-12% V2O5), which is returned for use when the next furnace starts to add materials. The alloy liquid is generally cast into cylindrical ingots, which are finished products after cooling, demolding, crushing and slag cleaning. This method is generally used for smelting ferrovanadium containing 40-60% vanadium. The recovery rate of vanadium can reach 98%. The electricity consumption for refining each ton of ferrovanadium is about 1600 kWh. Aluminothermic method uses aluminum as a reducing agent and adopts the bottom ignition method to smelt in the furnace tube of the alkaline furnace lining. First, a small part of the mixed furnace charge is loaded into the reactor and ignited. After the reaction starts, the remaining furnace charge is added successively. It is usually used to smelt high-vanadium iron (containing 60-80% vanadium), and the recovery rate is slightly lower than that of the electric silicon thermal method, about 90-95%.