Study On Releasing Behavior And Control Of Potassium In Ammonia Leaching Process Of Molybdenum

Potassium is a harmful element in the application of ammonium molybdate and subsequent molybdenum products.It is hoped that the content of potassium is as low as possible.Ammonia leaching as a key step to prepare ammonium molybdate directly affects the quality of ammonium molybdate.Water washing as a pre-treatment link before ammonia leaching has a certain influence on the results of ammonia leaching.In this study,the process of water washing and ammonia leaching was studied,single factor simulation experiment was conducted on the influencing factors in the process of water washing and ammonia leaching,and XPS,ICP,MLA and other methods were used to study the kinetic law of potassium release in the production process of ammonium molybdate and its influencing mechanism,so as to explore the best production technology to further reduce the content of ammonium potassium molybdate,and the following conclusions were drawn:（1）The washing necessity test showed that the pretreatment of molybdenum calcine with washing could effectively reduce the leaching amount of potassium during the ammonia leaching process.The simulation experiment of washing and ammonia leaching showed that the higher the washing temperature,the better the potassium reduction,and the particle size had a certain effect on the potassium reduction after washing,among which the range of 150～178μm molybdenum calcine washing had the best effect.In the process of ammonia leaching,too small molybdenum baked sand will increase the release rate of potassium,and the release rate of potassium is the lowest when the particle size is in the range of 150～178μm.The most favorable leaching conditions for ammonium molybdate potassium reduction were as follows:temperature30℃,ratio of solid to liquid 1:5,particle size of molybdenum calcine ranging 150～178μm,ammonia concentration 20%.The leaching rate of potassium in ammonia leaching process of molybdenum calcine is affected by calcium and sodium.The results show that hydrated lime and sodium carbonate can promote the removal of potassium in water washing,but the addition of sodium carbonate leads to the release of more potassium in the ammonia leaching process.If only hydrated lime is added,the content of ammonium potassium molybdate can be effectively reduced.（2）Although most soluble potassium can be removed in the water washing process,the residual potassium will also be immersed in the ammonia leaching process as Mo O₃is immersed in the ammonia leaching process.Through XRF,XPS and MLA detection and analysis combined with Factsage 7.0 simulation,it is found that there are two forms of potassium in the ammonia leaching process of molybdenum calcine.One is ionic potassium in the form of KCl and K₂Si F₆,and the other is mineral potassium in the form of muscovite,orthoclase,anandite and illite containing potassium aluminum silicate.Thermodynamic analysis shows that ionic potassium in the form of KCl and K₂Si F₆has stronger potassium-releasing ability than mineral potassium.（3）The classical liquid-solid reaction kinetic model（shrinkage unreacted kernel model）can describe the potassium release process of molybdenum calcine at the early stage of ammonia leaching,but the fitting degree for the late stage of potassium release is not high.Parabolic diffusion model,two-constant model,Elovich model and first-order kinetic model were used to fit and compare the potassium-release process,and to fit the pre-later stages of potassium-release process under different conditions.The fitting degree of four kinetic models for potassium release in ammonia leaching process of molybdenum calcination was obtained as follows:Elovich model>double constant model>parabolic diffusion model>first-order kinetic model.Combined with the analysis of potassium leaching curve and kinetic equation parameters in ammonia leaching process of molybdenum calcine,the potassium release process can be divided into two stages.The activation energy required in the early stage of potassium release reaction is small,as low as 4.69 k J/mol,and the ionic reaction of KCl and K₂Si F₆is the main stage in the fast reaction period.The activation energy required for the late potassium-release reaction is 34.69 k J/mol,and the reaction is slow.The process is mainly dominated by the potassium-dissociation reaction between orthoclase and muscovite.（4）The Avrani equation was used to fit the potassium release data before and after ammonia leaching process of molybdenum calcine.It was found that the potassium release rate under different conditions had a good correlation with Avrani equation.The average reaction order before and after potassium release were 0.52 and 0.04,the influence indexes of molybdenum calcination sand size,solid-liquid ratio and ammonia leaching concentration on the early stage of potassium release were-0.059,0.333 and0.109,and the influence indexes on the late stage of potassium release were 0.323,-0.844 and 0.263,respectively.Therefore,the kinetic equation of potassium release before and after ammonia leaching process of molybdenum calcine was obtained as follows:Early potassium-release stage:-ln（1-x）=0.061D^-0.059P^0.333W^0.109exp（-2.51/8.314T）t^0.52Late potassium-release stage:-ln（1-x）=0.0029D^0.323P^-0.844W^0.263exp（-26.3/8.314T）t^0.04...