Preparation And Characterization Of High Purity Of Ammonium Vanadates

As an important strategic resource,vanadium and its compounds are widely used in steel,metallurgy,aerospace,chemical industry,medical treatment,battery and other fields.And the large application of vanadium in industy requires vanadium products with much higher purity.Vanadium metavanadate is an important ammonium vanadates,it not only an important raw material for the preparation of high-purity vanadium oxide,but also plays an irreplaceable role in chemical,pharmaceutical,catalyst and functional materials.The development of these fields puts higher requirements on the purity of ammonium metavanadate.Therefore,it is of great significance to study the preparation of high purity ammonium metavanadate by industrial grade ammonium poly-vanadate.At the same time,the preparation of ammonium vanadate precursors with good crystallization,uniform particle size distribution and controlled morphology was studied by controlling the deposition conditions.In this thesis,industrial grade ammonium poly-vanadate,used as raw material,was leached by NaOH solution,then purified and precipitated in alkalescence solution,and high purity ammonium metavanadate was prepared.In addition,the crystallization conditions of ammonium poly-vanadate and ammonium metavanadate were studied.The results show that with 70 g/L of NaOH,liquid-to-solid of ratio of 9.5:1(mL/g),leaching at 85℃ for 40 min,the leaching rate of ammonium poly-vanadate can reach 96.34%.The vanadium dissolution solution was purified by chemical precipitation method and solvent extraction method.The results show that the purification effect of the chemical precipitation method by magnesium chloride is better than by solvent extraction under alkaline conditions.The phosphorus and silicon impurities can be effectively purified by two-step purification method.The concentration of silicon in the vanadium-containing solution can be reduced to 1.56 mg/L,and the concentration of phosphorus can be reduced to 0.42 mg/L.The best process conditions for vanadium precipitated are as follows:the reaction time is 30 min,add ammonium coefficient K=1.6,reaction temperature is 40℃,initial pH is 9.0,the ratio of vanadium precipitated can reach above 98%.Finally,during the washing process of product ammonium metavanadate,it is effective to remove Na+ and K+ from ammonium metavanadate by 2 times of beating and washing plus ultrasonic treatment.The results show that the optimum conditions for washing ammonium metavanadate are as follows:washing water is 1%NH4Cl,solution liquid to solid ratio is 40:1(mL/g)and washing time is 30 min.The purity of ammonium metavanadate reaches 99.99%.The effects of concentration of vanadium,times of adding ammonium salt,pH,reaction temperature,aging time and dripping method on the on morphology and particle size of ammonium metavanadate crystal were investigated.The results show that the concentration of vanadium solution has a great influence on the crystal morphology.When the concentration of vanadium solution is low,the morphology is mainly columnar or square.When the concentration of vanadium solution is 60 g/L,the morphology is mainly rhomboid structure.The reaction temperature and aging time have no obvious effect on the crystal structure,but have a great influence on the particle size.It is beneficial to weaken agglomeration by adding polyvinyl alcohol(PVA),using ultrasonic treatment and adding vanadium in the vanadium precipitation process.In the process of vanadium precipitation by acidic ammonium salt,the effects of temperature,pH and reaction time on the morphology and particle size of ammonium poly-vanadate crystal were studied.The preferred process conditions for vanadium precipitated are as follows:concentration of vanadium is 60 g/L,adding acid and ammonium is at room temperature,reaction temperature is 90℃,add ammonium coefficient is 1.6,pH for vanadium precipitation is 3.0,reaction time is 3 h,and product is with hexagonal sheet and flower globular structure.It has full crystallization and uniform particle size distribution,and the average particle size is approximately 30 μm.