Release Kinetics of Potassium during Ammonia Leaching of Molybdenum Calcine
In addition to being used as an additive for steelmaking,molybdenum is also widely used in petrochemical industry,electrical and electronic technology,metallurgical machinery,medicine,agriculture and other fields.With the wide application of low potassium molybdenum products in photoelectric information,medical and other fields,enterprises have put forward more and more stringent requirements for potassium content in ammonium molybdate.Ammonium molybdate,as the raw material for the production of low potassium molybdenum products,is the precursor for the production of molybdenum powder and molybdenum metal products,and is also widely used in chemical reagents,catalysts,flame retardants and other aspects.Its potassium content directly affects or even determines the quality of follow-up molybdenum products.Therefore,reducing the potassium content in ammonium molybdate is critical to the production of low potassium high-quality molybdenum products.Ammonia leaching,as the key process of ammonium molybdate production,has a very important impact on the release behavior of potassium and product quality.In this paper,the main factors affecting potassium leaching in the production of ammonium molybdate were analyzed in sections with molybdenum calcine as the experimental material,and the release kinetics of potassium in the production of ammonium molybdate and its influence mechanism were studied by means of inductively coupled plasma(ICP),X-ray photoelectron spectroscopy(XPS),mineral quantitative analysis system(MLA),scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).The main process of potassium release,the types of potassium bearing minerals and the transformation law in molybdenum calcine samples were systematically analyzed.Potassium containing minerals were bound in the mineral lattice by covalent bonds or are deeply bound by the lattice structure.The analysis results showed that although water washing could effectively remove most potassium ions in molybdenum calcine,a small part of potassium ions was still adsorbed on the surface of molybdenum calcine particles and released into solution during the ammonia leaching and dissolution of MoO3.The occurrence forms of potassium in the washed molybdenum calcine were potassium aluminosilicate,K2SiF6 and KCl.The total amount of potassium minerals decreased by 32.1％,which proved that potassium minerals also participated in the reaction.The main potassium minerals are orthoclase,illite,mica and barium ferrite mica.Potassium was released from the experimental samples through ion exchange and mineral decomposition.The mineral dissolution was mainly the release process of potassium in orthoclase and mica.Barite and illite released little potassium in ammonia,and orthoclase released more potassium than mica.In addition,the influences of leaching temperature,ratio of solid to liquid,particle size of raw materials and leaching time on the leaching process were discussed to obtain the best leaching conditions.The result showed that the release of potassium during ammonia leaching of molybdenum calcine could be divided into two stages:The first stage was the rapid dissolution reaction process of residual potassium ions in molybdenum calcine.At this time,the release reaction rate of potassium was fast,mainly concentrated in the first 35 min,and the release rate of potassium was large.The second stage was the release process of mineral potassium in molybdenum calcine.The release rate of potassium was relatively slow and the release amount was small.On the basis of analyzing the release behavior of potassium element,the optimum technological conditions of ammonia leaching of molybdenum calcine were determined.The results showed that the leaching time,temperature,solid-liquid ratio,raw material particle size,etc.would have a significant impact on the potassium leaching process.The most appropriate conditions for potassium reduction of ammonium molybdate were:temperature of 30 ℃,solid-liquid ratio of 1∶5,the particle size range of molybdenum calcine of 150～178 μm,and the concentration of ammonia water of 20％.In addition,the study of potassium release kinetics showed that the early stage of ammonia leaching of molybdenum calcine was a rapid dissolution process of ionic potassium,mainly the ion exchange reaction of KCl and K2SiF6.This stage conformed to Elovich model,and the leaching activation energy was 4.96 kJ·mol-1.The later stage of ammonia leaching of molybdenum calcine was mainly the release process of mineral potassium,especially potassium in orthoclase and mica.The release rate of potassium in this stage was slow,and it was greatly affected by temperature,solid-liquid ratio,particle size and other conditions.This process conformed to the double constant model,and the activation energy of leaching in this stage was 101.49 kJ·mol-1.The research results focused on the potassium leaching behavior of two stages in the ammonium molybdate leaching process,which could provide theoretical support for reducing the potassium content in ammonium molybdate products,so as to facilitate the preparation of ammonium molybdate with uniform particle size,intact grains and low potassium content,and effectively improve the product quality.
molybdenum calcineammonia leachingpotassium releasedynamicspotassium bearing mineral
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