Research On Collision Nucleation Rule Of NaCl And Crystallization Process Of KCl

Crystallization dynamics is the key process in a crystallization control process,it is relatively complex because of different research systems and crystallization condition varies.This work mainly has studied collision nucleation rule of the NaCl-H₂O system from fundamental research,simultaneously has researched the KCl crystallization process including the factors influencing crystal granularity and crystallization dynamics.The collision nucleation study of the NaCl-H₂O system was put in a crystallizer what volume is 2L.The influence of agitation speed and crystal granularity on nucleation rate and grain-size distribution and discussed the relations between collision nucleation process and agitation speed and particle size was studied in this work.The crystallization process of producing potassium chloride from carnallite which was produced in Qinghal Qarhan Salt was studied in a continuous system.The factors which affect the crystal size and size distribution were investigated.The effects of residence time and concentration of MgCl₂ in decomposition solution on crystallization process and product crystal size were also studied in DTB crystallizer what volume is 20L.The crystallization kinetics of potassium chloride was studied for the system and basic model of crystallization kinetics was established.The mainly conclusions as follows:1.In collision nucleation process,the nucleation rate increased with increasing stirrer speed and mother crystal size,and this tendency is more obvious when the mother crystal size is larger.2.In secondary collision nucleation process,for a fixed size of mother seed crystal,the dominant size decreases with increasing stirrer speed.The median size of broken crystal deceases with increasing stirrer speed.And for the low agitation speed (lower than 500 rpm).The size of broken crystal deceases with deceasesing the size of seed crystal for a fixed seed crystal,but not for the high agitation speed.3.The nucleation rate model of NaCl in this crystallization system was established by the experimental results:B⁰=1.624×10³V^0.3278L^2.002.4.For the system studies,the growth rate and nucleation rate can be represented by:B=6.65*10⁸*(ΔC)^1.464,G=10^1.5316*(ΔC)^0.4746;The relation between growth rate and nucleation rate are:B=10^3.6554*G^3.363.The result indicated that the nucleation rate and the growth rate were both proportional to the supersaturation in this crystallization process.This indicated that the low degree of supersaturation is advantageous to the crystal growth in the potassium chloride production process. 5.In the cooling crystallization process,long resident time and high density of MgCl₂ in circulation fluid is advantageous to the maintenance low degree of supersaturation,the crystal can grow in a good environment,thus the quality to be enhanced.The influence of impeller type on the product crystal size is not evident.