The process control of the crystallization of ammonium dimolybdate and the process conditions for the formation of single crystal

Ammonium molybdate is a typical homopolybdate with many types, mainly including ammonium dimolybdate, ammonium tetramolybdate, ammonium heptamolybdate, ammonium ocmolybdate, ammonium dodecolybdate and ammonium tetramolybdate. Ammonium molybdate used in the industry is mostly the mixture of the above ammonium molybdate in different proportions, which is easy to be hygroscopic and agglomerated, and not easy to disperse. Ammonium molybdate is the main raw material for preparation of molybdenum-based products, especially molybdenum powder. Its phase purity and chemical and physical properties have great influence on the quality of molybdenum powder. In addition, the crystal type, particle size, particle size distribution and dispersibility of ammonium molybdate can also greatly restrict the physicochemical properties and post-processing properties of molybdenum powder. Therefore, the preparation of non-agglomerated state, good dispersion, uniform particle size distribution, compared with pure ammonium molybdate products, has become a hot topic of scientific and technological research and development in recent years. The results confirmed that single crystalline ammonium molybdate with high purity, uniform particle size distribution, not easy to reunite and good viscosity, easy to store and other characteristics, in the process of roasting solution reduction of molybdenum powder, invulnerability to breakage and raw quantity is little, restore completely, uniform product, and roasting temperature easy to control, roasting the yield is higher, is expected to be the first choice of the reduction preparation of molybdenum powder with high quality raw materials. Therefore, it is of great application value and theoretical significance to study how to prepare high dispersive monocrystalline ammonium dimolybdate with large particle size. Firstly, the ammonium molybdate solution was prepared by the traditional acid pickling, ammonia leaching and chemical purification process using molybdenum calcined sand as raw material. With nitric acid sulfate instead of at the same time, has carried on the contrast experiment, analyzes the two kinds of acid treatment method of the ammonium molybdate solution obtained the change of the content of impurities, and the residues of sulfuric acid root, the sulfuric acid instead of nitric acid, the feasibility of the conclusion, the thesis, sulfuric acid for molybdenum industry by-products found in suitable way, and can effectively reduce the comprehensive cost of production. In order to prepare high-end ammonium molybdate products with less impurities, we have tried the deep impurity removal study of ammonium molybdate solution, and selected suitable cation exchange resin. The experimental results show that the cation metal impurities in ammonium molybdate solution can be better removed by using the ion exchange resin series method. Secondly, we use four ammonium molybdate as a raw material, preparation of two ammonium molybdate single crystal is studied in detail the technology route, examines the solution temperature, acidity and density, evaporation rate and the particle size and distribution of seed for two single crystal phase structure and morphology of ammonium molybdate, but also by adding additives, morphology of two ammonium molybdate single crystal implement effective control. The phase structure and morphology of ammonium dimolybdate single crystal were characterized comprehensively, and the precise XRD, FT-IR, Raman, TG-DSC and particle size analysis results were obtained, which provided relatively reliable basic data for further theoretical research in related fields. Finally, in order to further optimize the technological scheme for the preparation of ammonium dimolybdate single crystal, reduce the consumption of various materials and energy, and reduce the cost, we chose molybdenum berber as the raw material, and directly prepared ammonium dimolybdate single crystal without the traditional acid precipitation and crystallization intermediate step. The effect of temperature, concentration, acidity and seed on the product was investigated systematically, the purity and morphology of the product were all qualified, and the nucleation and growth mechanism of ammonium dimolybdate single crystal was also discussed.

Share this post