Process and Mechanisms for Extraction of Chromium and Vanadium from Vanadium Slag by Roasting with High Content of Mg(OH)2

Vanadium extraction from vanadium slag by roasting with CaO/MgO has been studied to alleviate furnace lining corrosion, and the reported Cr extractions were always < 10%, which was too low to meet the requirement of environmental protection. Mg(OH)2 instead of CaO/MgO was first reported to extract Cr and V simultaneously. It was found that the optimal roasting temperature, time, weight ratio of Mg(OH)2 to V slag powder and leaching pH for extraction of Cr and V were 1000°C, 2 h, 1.0 and 0.1, respectively, and the extractions of Cr and V were 63% and 98%, respectively. Thus, Cr extraction was increased by 530% compared to conventional CaO/MgO roasting. The addition of Mg(OH)2 to V slag significantly alleviated the powder sintering at 1000°C, which thus improved the oxidation kinetics of Cr3+ and increased Cr extraction. The molar ratios of Mg or Ca to V in the roasting samples of the previous works were always < 1.0, which was much lower than that of 10.6 in this work, which probably explains why the Cr extractions in the previous works were < 10%. The possible mechanism involved in the higher extraction of V than Cr was also explored.