Vanadium Recovery from Blast Furnace Slag
Vanadium is an important chemical element and important industrial metal with a wide range of applications. It is primarily extracted from ores and byproducts such as blast furnace slag. In this process, ore and slag are roasted at certain temperatures in order to reduce the iron oxide in them, followed by leaching and precipitation to recover the vanadium.
Vanadium recovery from slag is becoming increasingly important as the concentration of this element is increasing due to the increased use of blast furnaces and the increased efficiency of the operation. Furthermore, vanadium is gaining importance as it is becoming used more and more in alloys and catalysts.
The first step in recovering vanadium from slag is the crushing and grinding of the slag material. Crushing is often necessary in order to reduce the size of the particles to a size which is suitable for grinding. Grinding is then necessary in order to further reduce the size of the particles, to promote leaching, and also to increase the surface area of the slag material.
The next step is to roast the slag in order to reduce its iron oxide content. Roasting is necessary not only to remove the iron oxide but also to create an environment in which vanadium can be leached out. The most common approach is to use a fluidised bed roaster to heat the slag to temperatures in the region of 1000-1150°C.
Once roasted, the slag is leached in either an acid or alkaline solution. The type of leaching solution will depend on the type of ore and/or slag being processed as well as the targeted product. In the case of acid leaching, sulphuric acid is often used to promote leaching of the vanadium. In the case of alkaline leaching, either ammonia or sodium hydroxide are often used.
Once the vanadium has been leached, the next step is to precipitation and recovery. This involves adding a precipitant such as a carbonate or a sulphide to the leach liquors, which causes the vanadium to come out of solution. The precipitated vanadium is then recovered by either filtration or centrifugation.
Finally, the recovered vanadium needs to be purified in order to meet product specifications. This is usually done via a process of solvent extraction where the vanadium is extracted from other impurities such as iron, aluminium, and magnesium. The extracted vanadium is then further purified via crystallisation and/or distillation.
Vanadium recovery from blast furnace slag is an important and growing process. The process is not only seen as a way to recover valuable vanadium from a waste material but also as a way to reduce the environmental impact of these processes. The various steps involved are therefore becoming increasingly important, as they enable responsible and efficient recovery of this valuable element.
