Extraction of vanadium from converter slag by two-step sulfuric acid leaching process

•A mechanical activation - calcification roasting - two step leaching vanadium extraction process is proposed.•The re-utilization of the leaching liquor was investigated for economic and environmental consideration.•Vanadium in the leaching liquor can be concentrated by the recycle of the leaching liquor.•Recycle of the leaching liquor significantly decreased the leaching solution consumption and wastewater discharge.

Because of its potential to achieve a high recovery rate of vanadium, the mechanical activation pretreatment of vanadium-bearing converter slag followed by calcification roasting at low temperature and a two-step leaching process may be a viable alternative to the present roasting and one-step leaching process for vanadium extraction. The object of this study is to enhance the leaching efficiency of vanadium by mechanical activation and two-step leaching methods. The effects of solution acidity, liquid/solid ratio, particle size of the roasted slag, stirring speed, leaching temperature and time were investigated. The first stage leaching liquor was recycled in order to improve vanadium content in the leaching solution and reduce leaching solution consumption and wastewater discharge. Experimental results showed that approximately 81.8% vanadium was dissolved in the first stage of the leaching process with a solution pH of 2.5, and approximately 8.1% vanadium was dissolved in the second stage of the leaching process with a solution pH of 0. In the first stage, the vanadium leaching efficiency was significantly hindered by long recycle times, though this property also increased the content of vanadium in the leaching solution and greatly decreased the water consumption. In addition, mineralography and microstructures of the solid samples were studied by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) to help understand the mechanism.