Our journey in greenization of vanadium extraction from vanadium slag in China

China is the world's largest producer of vanadium products, whose major vanadium resource is vanadium slag obtained by smelting vanadium−titanium magnetite ores. The vanadium extraction techniques from vanadium slag have progressed stepwise toward greenization during the past 30 years in China. This review has systematically summarized these developments and classified the developments into three stages. The early stage is the efficient vanadium extraction techniques such as the sodium roasting−water leaching technique. The developed stage is the clean vanadium extraction techniques including the calcification roasting−acid leaching technique and sub-molten salt technique. The advanced stage is the green vanadium extraction techniques, for example the magnesiation roasting−acid leaching technique. The mechanisms, advantages and disadvantages of industrially applied and literature reported vanadium extraction techniques in each development stage are elaborated from multiple perspectives. Finally, future development directions are pointed out, aiming to inspire green extraction technique of vanadium worldwide.