Reaction Engineering And Crystallization Behavior Of Preparation Of β-Ammonium Tetramolybdate In Concentric Continuous Crystallization Tanks

β-Ammonium tetramolybdate has coarse and uniform crystal structure and excellent thermal stability,the yield and various processing properties of molybdenum products produced from it are significantly improved.However,in the process of acid precipitation,the macroscopic factors of the solution lead to the change of the polymerization form of molybdenum,and there is co-crystallization of kinds of ammonium molybdate.Therefore,in this paper,the polymerization mechanism of molybdenum was studied,the crystallization environment ofβ-ammonium tetramolybdate was optimized,and a partitioned concentric circular crystallization equipment was designed to couple the reaction engineering with the various stages of acid precipitation and crystallization,and continuously prepared excellentβ-tetramolybdate.Ammonium tetramolybdate products.The main research contents and conclusions are as follows:（1）Study on the polymerization mechanism of molybdate ions during nitric acid precipitation and crystallization Microscopic:The structural map of Mo at a series of p H values during the crystallization process of nitric acid precipitation in the ammonium salt system was constructed from the molecular level.The results of ESI-TOF MS showed that:when the p H value was greater than 6.50,Mo existed as Mo O₄^2-;when the p H value was less than 6.50,Mo O₄^2-polymerized into Mo₇O₂₄^6-,in the coexisting solution of Mo O₄^2-and Mo₇O₂₄^6-,Mo O₄^2-disappears after acidification,and Mo₇O₂₄^6-transfers to Mo₈O₂₆^6-,which is most obvious at p H=2.44.Study on the influence of macroscopic factors on the crystallization of ammonium tetramolybdate.（2）Study on the influence of crystallization solution environment on the crystallization of ammonium tetramolybdate:The p H value is the key factor affecting the acid precipitation crystallization.During the crystallization process,a small amount of ammonia water must be added to adjust the p H value,dissolve the fine crystals,and promote the transformation of ammonium tetramolybdate.Properly increasing the temperature can obtain coarse crystals;reduce the contact energy between the crystals and the mother liquor.Improve product purity.After optimization,the crystallization environment ofβ-ammonium tetramolybdate was molybdenum concentration of 120 g·L^-1,acid precipitation temperature of 60°C,initial p H value of 7.50,stirring speed of 200 rpm,end point p H value of about 1.60,and holding time of 0（i.e.filter while hot）.（3）Design of concentric circular crystallization equipment and study of its reaction engineering:A partitionable concentric crystallization tank was designed,and the flow conditions in single tank liquid-liquid,liquid-solid and multi-tank liquid-liquid flow fields were studied,and the flow characteristics were greatly enhanced and improved by some control measures.Abnormal flow conditions and reducing the volume fraction of dead zone;in addition,Fluent software was used to establish the flow field distribution in the two-dimensional model of the single-tank reactor.The effect is much greater than the inlet and outlet flow rates.（4）Preliminary exploration of continuous production ofβ-ammonium tetramolybdate in concentric crystallization tanks:Coupling reaction engineering with ammonium molybdate acid precipitation crystallization,four methods were initially used to continuously prepare ammonium tetramolybdate products.The study found that the product obtained after adding fine crystals and back-dissolving+seed crystal back-slurry treatment isβ-（NH₄）₂Mo₄O₁₃based mixture with a small amount of hydrated ammonium tetramolybdate has a high purity and a large particle size elongated shape with uniform particle size distribution.There are 53 figures,29 tables,and 99 references...