Research On Crystallization Control Mechanism Of Typical Strontium Compounds

Strontium compounds are widely used in electronic information,chemical industry,light industry,medicine,ceramics,glass,fireworks,metallurgy,military and many other fields.For many years,the strontium industry has formed an industrial pattern with the production of industrial strontium carbonate as the basic raw material?accounting for 80%of the industrial GDP?and the production of downstream products as the supplement?accounting for 20%of the GDP?.Especially after 2012 as the delisting of the CRT glass shell,production capacity of industrial strontium carbonate exceeded 50%,and competitive pressures increase sharply.At the same time,the country enhances the requirement of environmental protection,the industry urgently needs to develop environment-friendly production process and the structural adjustment.Strontium hydroxide is selected as the platform for developing downstream production and promoting the quality of products which is regarded as the key address this trouble.Aiming at these problems,a process for preparing high-quality strontium compound products has been designed(industrial strontium carbonate as crude material,and calcination,water-immersion,and recrystallization are formed as the method of producing strontium hydroxide as a platform,and further using it as raw material to prepare high-value and functional products such as larger-particle strontium hydroxide octahydrate,granular strontium chloride hexahydrate,and spherical strontium carbonate are prepared by crystallization.This thesis select cooling crystallization process of strontium hydroxide octahydrate,strontium chloride hexahydrate and strontium carbonate as the research object,using crystallization online-monitor machine such as online turbidity,two-dimesion probe,ultrasonic size analyzer and thermal polarizing microscope to analysis metastable zone,the kinetics of nucleation and crystal growth process,make a thorough inquiry of the crystallization mechanism and relevant operating conditions for appropriate particle size and morphology of the target products.Finally,a new crystallization regulation mechanism was established to guide the production process of these three strontium compounds.The specific research content included is as follows:?1?Studies on the metastable zone and nuclear kinetics of Sr?OH?₂·8H₂O.Equilibrium method and dynamic-temperature-changing method were used to obtain strontium hydroxide octahydrate in purified water and correlate with the general solubility model to obtain the solubility equation of 288.15?333.15K.Based on the measured data,vander Hoff equation is used to caculate the enthalpy and entropy of the solution.The turbidity system was used to measure the width of metastable zone under different crystallization operating conditions,and the change law of metastable zone with operating conditions was obtained.The nucleation theory was used to fit the metastable zone width of strontium hydroxide octahydrage,then nucleattion kinetics equations and related parameters are obtained to analyze the change of the metastable zone width with saturation temperature.Finally,based on the classical nucleation theory,a prediction model for the width of the metastable zone of strontium hydroxide octahydrate in purified water was established by fitting.?2?Studies on the growth process and seed control of Sr?OH?₂·8H₂O.Using polarizing microscope to investigate the growth of the self-made seeds after dissolving in a saturated solution at 298K.Crystallization operation conditions such as initial supersaturaton,cooling rate,stirring rate and crystal growing time,etc.are optimized by controlling single variate to otain strontium hydroxide octahydrate with D₅₀is about 400?m.To futher control the crystal size,larger crystals with D₅₀is about 1000?m can be obtained by adding extra seeds.Online-monitor platform consists of online turbility,ultrasonic particle analyzer,two-dimension probe was used to analyse the crystallization of strontium hydroxide octahydrate,and the mechanism of obtaining larger partical was proposed.?3?Studies on the metastable zone and nuclear kinetics of Sr Cl₂·6H₂O.Equilibrium method and dynamic-temperature-changing method were used to obtain strontium chloride hexahydrate in purified water and correlate with the general solubility model to obtain the solubility equation of 288.15?333.15K.Based on the measured data,vander Hoff equation is used to caculate the enthalpy and entropy of the solution.The turbidity system was used to measure the width of metastable zone under different crystallization operating conditions,and the change law of metastable zone with operating conditions was obtained.The nucleation theory was used to fit the metastable zone width of strontium chloride hexahydrate,then nucleattion kinetics equations and related parameters are obtained to analyze the change of the metastable zone width with saturation temperature.Finally,based on the classical nucleation theory,a prediction model for the width of the metastable zone of strontium chloride hexahydrate in purified water was established by fitting.?4?Studies on the growth process and ultrasonic control of Sr Cl₂·6H₂O.Using polarizing microscope to investigate the growth of the purified seeds in a saturated solution at 293K.Crystallization operation conditions such as initial supersaturaton,cooling rate,stirring rate and crystal growing time,etc.are optimized by controlling single variate to otain strontium chloride hexahydrate with D₅₀is about 931?m.Ultrasound is used to futher control the crystal size.Through ultrasound action,size of crystals and aspect ratio become smaller,and the morphology becomes granular.Crystals with D₅₀is about 236?m can be obtained by optimizing conditions.Online-monitor platform consists of online turbility,ultrasonic particle analyzer,two-dimension probe was used to analyse the crystallization of strontium chloride hexahydrate,and the mechanism of obtaining granular partical was proposed.?5?Studies on the morphology control of spherical strontium carbonate:strontium carbonate was prepared by the reaction of strontium hydroxide octahydrate with carbon dioxide and crystallization.Then investigated the effct of different morphology-control agentia on the mornology of strontium carbonate.Among them,EDTA-2Na was the best one.The effects of crystallization operation conditions such as the concentration of morphology-control agentia,the concentration of strontium hydroxide,carbonization aeration rate and temperature on the mornology were investigated.Useing EDTA-Sr instead of EDTA-2Na can get a better yield.Spherical strontium carbonate particles with good distribution can be obtained when the molar ratio is 1:1.The change of morphology versus time was obtained by sampling the carbonization process at different time intervals,and the growth mechanism of strontium carbonate is studied.In this dissertation,the growth model and spherical mechanism of spherical strontium carbonate were proposed.