1. Recovery from vanadium slag: Vanadium slag is a raw material with high vanadium content, and the recovery technology is relatively mature. The current common process is the sodium roasting process. Different equipment is used: large enterprises generally use rotary kilns, while some enterprises use roasters. The process involves mixing vanadium slag with sodium salt (usually sodium carbonate or Glauber's salt), and roasting at a certain temperature to convert the vanadium into a soluble sodium salt. The roasted sand is then leached to dissolve the vanadate into solution, which is filtered to remove the residue, and then precipitated and refined to obtain vanadium pentoxide. Some foreign companies directly use vanadium-rich vanadium-bearing titano-magnetite to produce vanadium pentoxide. First, the ore is made into a concentrate, which is then mixed with a flux and roasted in a rotary kiln. The roasted sand is leached with water, the vanadium-containing solution is treated with ammonium salt, and finally ammonium metavanadate is precipitated.
2. Recovery from stone coal: The process of extracting vanadium from stone coal mainly involves the sodium roasting process, which involves the process flow of sodium roasting-oxidation roasting-leaching-hydrolysis-alkali solution-vanadium precipitation-thermal deamination-refined vanadium. This process is commonly used in China to extract vanadium from stone coal. It is characterised by its simplicity and makes full use of the thermal energy of stone coal. The disadvantage is that the recovery rate is relatively low, generally below 60%. The United States uses the above process, but uses dilute sulfuric acid leaching and solvent extraction technology, with a recovery rate of up to 70%.
The production process of the rotary kiln for vanadium pentoxide is as follows
waste catalyst → crushing → hydrochloric acid leaching → filtration → sodium hydroxide hydrolysis → vanadium precipitation → refining → calcination → product. The process is simple, and the recovery rate is above 90%. The rotary kiln roasting method is used to extract vanadium pentoxide. The high-temperature roasting section is 720–800°C. A certain amount of sodium carbonate is added to the vanadium slag to achieve the best conversion rate of the ore. The residence time of the ore in the high-temperature section of about 930°C should be maintained at 5–6 hours. The minimum high-temperature point of the rotary kiln for normal incineration should not be lower than 1100°C, and the melting point of the ore should not exceed 1000°C.
