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A series of new green metallurgical processes have been proposed and developed to improve the recovery of vanadium and chromium in vanadium slag, and solve the environmental problems occurred in the traditional production process. The reactivity of three reaction media including sub-molten potassium hydroxide, sub-molten sodium hydroxide, and NaOH-NaNO3 binary molten salt medium has been examined and compared. In comparison with the traditional sodium salt roasting technology, which operates at 850 °C, the operation temperature in the new media can drop to 200~450°C, significantly decreasing the energy consumption. Chemical conversion ratio of vanadium and chromium using the new reaction media could reach to above 95% and 80%, respectively, superior to the traditional technology. For in the latter technology the data is 80% for vanadium and only 10% for chromium. Thus, the application of such reaction media in the processing of vanadium slag has been proven to be feasible and attractive, and the processes developed based on such media are expected to replace the traditional roasting process in the near future.

The redox behavior of vanadate ions at glassy carbon electrode in KOH solutions with concentration ranging from 0.1M to 1M had been studied using cyclic voltammetry method. It is found out that vanadate ions experience similar redox reactions in both NaOH and KOH solutions, which involve a single cathodic reduction and two oxidation reactions in one cyclic sweep. Nearly same currents are obtained under the same reaction conditions in both solutions. However, vanadate ions appear more difficult to be reduced in KOH solutions than in NaOH solutions, and the reduction reaction exhibits higher irreversibility. The reduction potential is influenced by vanadate ions concentration, and is more negative in KOH solutions. The reversibility of reduction reaction is greatly dependent on alkalinity, and the reduction potential obviously decreases with the increase of alkalinity in KOH solutions. However, only a slight decrease was observed in NaOH solution, which may be due to the fact that OH-exhibits higher activity in KOH solutions.