Fundamental Research On The Separation Of The Multiple Components In The Sub-molten Salt Method For Processing Vanadium-slag

There are many disadvantages in the traditional roasting technology for extracting vanadium, such as low vanadium and chromium extraction efficiency, serious environmental pollution and etc. The sub-molten salt clean production process for processing vanadium-slag was proposed by the Institute of Process Engineering, Chinese Academy of Sciences, which can achieve high efficiency extraction of vanadium and chromium at relatively mild reaction conditions, and eliminate the pollution of waste gas at the source. Based on the previous work on the conversion of vanadium-slag by sub-molten salt method, the gold of this research is to solve the following separation problem. As phase equilibrium is the foundation of crystallization separation, this dissertation studied the separation method of sodium chromate, sodium nitrate, sodium silicate in the sub-molten salt medium by using isothermal method to determine the solubility of the involved system, which can provide the theoretical basis for the process design and optimization of the sub-molten salt technology.This paper mainly studies the following contents:(1) For the separation of sodium vanadate, sodium chromateand sodium nitrate in the sub-molten salt process, the solubility of NaOH-NaNO₃-Na₃VO₄-Na₂CrO₄-Na₂SiO₃-H₂O system and its sub-systems were determined at 40℃and 80℃. Based on the solubility, a specific crystallization separation method was proposed, which is to separate sodium vanadate via cooling crystallization when the NaOH concentration is below 300g/L, then to evaporate the solution at 80℃to NaOH 400g/L, and then cooling to 40℃for sodium nitrate crystallization. Sodium chromate can be separated by evaporating the solution to NaOH about 500g/L and separating at 80℃.(2) The proposed crystallization process for sodium vanadate, sodium chromateand sodium nitrate was simulated to verify its feasibility by determining the concentration changes in the evaporating and cooling process.(3) The interaction between various substances and its effects on the separation process were analyzed on the basis of the above-determined solubility.(4) Hydration effects of the NaOH-H₂O, NaOH-NaNO₃-H₂O and NaOH-Na₃VO₄-H₂O were simulated, and the hydration radius and hydration numbers of the ions were obtained, which can explain the decreasing tendency of the solubility of sodium nitrate and sodium vanadate as the NaOH concentration increasing.