The purified vanadium- containing solution is mainly a Na 2 O-V 2 O 5 -H 2 O system, which may be acidic or basic depending on the leaching conditions. Since the solubility product of ammonium vanadate is less than sodium vanadate, NH 4 Cl, (NH 4 ) 2 SO 4 , etc. are added. 1. Weakly alkaline ammonium salt vanadium When the pH value is 8-9, the vanadium in the solution is mainly (1) According to Figure 1, the solubility of NH 4 VO 3 decreases with decreasing temperature, so the crystallization of NH 4 VO 3 should be carried out at 20 to 30 ° C; Fig.1 Relationship between solubility, density and temperature of NH 4 VO 3 in water 1-solubility and temperature; 2-density and density of saturated solution (two) (3) Stirring and seeding effect: The NH 4 VO 3 solution is easy to form a supersaturated solution. For this reason, seeding and stirring will accelerate the crystallization, as shown in Fig. 2. The crystal state under four conditions can be observed in the figure. It shows that stirring and seeding can significantly speed up the crystallization. Figure 2 NH 4 VO 3 crystal dynamic diagram 1-Standing; 2-Adding ammonium metavanadate seeds to stand; 3-stirring; 4-addition of vanadic acid according to seeding; Equilibrium concentration of metavanadic acid at 5-20~30 °C (4) After the weakly alkaline ammonium salt is vanadium, the residual liquid contains vanadium, which is about 1 to 2.5 g/LV 2 O 5 . The operation time is long and the energy consumption is high, and the obtained NH 4 VO 3 is calcined to obtain V 2 O 5 having a purity of 99%. The released ammonia is about 0.187 kg/kg V 2 O 5 and should be recovered. The weakly basic ammonium salt vanadium is often used in the red cake prepared by the purification hydrolysis method. Second, the weak acid ammonium salt vanadium At pH=4~6, vanadium mainly In the formula, x is generally between 0 and 2. In order to obtain a product containing no sodium, it is dissolved in hot water and recrystallized at a pH of 2, so that (NH 4 ) 2 V 6 O 16 crystals can be obtained. The residual solution of the weakly acidic ammonium salt vanadium reduces the V 2 O 5 content to 0.05-0.5 g/L. Third, acidic ammonium salt vanadium When pH = 2 to 3, vanadium in the solution is mainly precipitated as ammonium hexa-vanadate when ammonium ions are added. When vanadium is added, the pH is adjusted with sulfuric acid, and an appropriate amount of (NH 4 ) 2 SO 4 is added to precipitate vanadium at a temperature higher than 90 ° C. The product obtained by this method has high purity, fast vanadium precipitation, high vanadium precipitation rate, low ammonium salt consumption, about 0.06kg NH 3 /kgV 2 O 5 , only 1/3 of the ammonia consumption of ammonium metavanadate. The consumption of sulfuric acid is less than that of the hydrolysis precipitation method. Therefore, it has become the main method for producing V 2 O 5 with vanadium slag as raw material in China, and has been widely used abroad. 4. Calcination decomposition of ammonium vanadate The decomposition of NH 4 VO 3 and (NH 4 ) 2 V 6 O 16 is calcined at 450 to 600 ° C, and the reaction is as follows: 6NH 4 VO 3 =(NH 4 ) 2 V 6 O 16 +4NH 3 +2H 2 O (NH 4 ) 2 V 6 O 16 =3 V 2 O 4 +N 2 +4 H 2 O V 2 O 4 +1/2O 2 =V 2 O 5 The first step of the reaction releases a large amount of ammonia, which should be recovered. In the second step, the ammonium polyvanadate is further decomposed and reduced to tetravalent vanadium, but is oxidized to V 2 O 5 in a further oxidizing atmosphere. Calcination of ammonium vanadate is usually carried out in a rotary kiln. The kiln is divided into three zones, the first zone is a drying zone, 300-500 ° C; the second zone is a decomposition zone, 450-600 ° C; the third zone is above 450 ° C, air is introduced, and fully oxidized. Stainless Steel Tank,Centrifuge For Chemical,Three Foot Centrifuge,Hydraulic Motor Drive Wenzhou suote pharmaceutical and chemical engineering CO.,LTD , https://www.wzsuotejixie.com
The ions can form ammonium metavanadate or polyvanadate as precipitated. The conditions depend on the acidity of the solution. , which is Form exists. So join At the time, NH 4 VO 3 crystals were formed to precipitate. The factors affecting ammonium salt precipitation are as follows: The concentration should be larger than the stoichiometric number to promote complete precipitation by the same ion effect; Exist, join And precipitated as decavanadate. Since the purified liquid contains a large amount of sodium ions, the precipitation is generally:
December 02, 2024