Applied Fundamental Research On The Cooling Crystallization Of Ammonium Metavanadate

Separation of ammonium metavanadate from ammonium salt solution is very important for the novel vanadium slag blank roasting-ammonium leaching process.Based on the crystal separation of ammonium vanadate leaching solution,solubility of ammonium metavanadate,metastable region of ammonium metavanadate,regulation of induction period and optimization of cooling crystallization separation process were investigated.The present study established a high-efficiency crystallization method.Besides,the best cooling crystallization and separation method was proposed.The product of ammonium metavanadate with uniform size and morphology was obtained.This research may provide theoretical support for the vanadium slag blank roasting-ammonium leaching cleaner production process.The main innovative achievements in this paper include:1.The solubility of ammonium vanadate in different ammonium salt solutions was studied.The effect of different anions on the solubility of ammonium vanadate in the ammonium salt solutions was obtained.The solubility of NH₄VO₃-H₂O and?NH₄?₂C₂O₄-NH₄VO₃-H₂O system was measured at the temperature from 313.15 to363.15 K.Furthermore,based on the solubility of ammonium vanadate in?NH₄?₂C₂O₄,?NH₄?₂SO₄,NH₄H₂PO₄ and NH₄HCO₃ systems,the different anions on the solubility of ammonium vanadate was compared.Results showed that most of the ammonium salts can greatly reduced the ammonium vanadate solubility in these systems.2.The influence of saturation temperature,cooling rate,stirring rate and different ammonium salts on the metastable region width of ammonium vanadate was studied.The temperature had a significant influence on the width of the metastable zone.The metastable region width of NH₄VO₃ gradually narrowed when the temperature increased.Different ammonium salt had different effect on the metastable region width.With increasing the addition amount of ammonium oxalate and ammonium bicarbonate,the metastable region width increased.3.The crystallization induction period of ammonium metavanadate was conducted by laser method.Based on the classical nucleation theory model,the relationship between the supersaturation coefficient S at different temperatures and the induction period t was fitted.According to the fitting equations,two nucleation mechanisms existed in crystallization process of ammonium metavanadate:one is homogeneous nucleation when the saturation is high,and the other is not nucleated when the saturation is low.4.The cooling crystallization rule of ammonium vanadate was studied systematically,and the optimum conditions were obtained.Further,the effect of crystallization temperature,cooling rate,agitation speed,seed load and different ammonium salt on crystallization rate,particle size and micro-structure of crystallized ammonium metavanadate was studied and discussed.