磷石膏常压盐溶液法制备α-半水硫酸钙研究

发布时间：2018-01-20 19:15

  本文关键词： 磷石膏 α-半水硫酸钙 常压盐溶液法 转晶速率 溶解动力学　出处：《华东理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：为实现磷石膏有效资源化利用,本研究选取盐溶液为介质在常压下对磷石膏进行转晶制备αα-半水硫酸钙。通过对磷石膏进行浸取除杂,对比了不同条件下水洗、硫酸浸取工艺对磷石膏中P_2O_5、F-的去除率;以磷石膏为原料在Ca-Mg-K复合盐溶液中进行转晶反应制备αα-半水硫酸钙,采用FESEM、XRD、TG-DTA等分析方法对不同Ca~(2+)浓度及pH值条件下反应体系中的产物进行了表征;对各反应体系在不同反应时间内固、液两相组成及含量的变化进行测定,计算得到了相应Ca~(2+)浓度以及pH条件下的转晶速率;建立了磷石膏溶解动力学模型,对溶质饱和度C*以及磷石膏溶解速率R_s进行拟合,得到了不同反应条件下的反应动力学方程。主要研究内容和结论如下:(1)研究了磷石膏除杂工艺,结果表明,单一水洗除杂能够有效去除磷石膏中水溶性P_2O_5、F-,在水洗60min,温度65℃的条件下,磷石膏中可溶性P_2O_5含量下降了66.54%,F-含量下降了 64.33%;硫酸浸取除杂过程中,随着浸取液H_2SO_4质量分数的增大、反应温度的升高,浸取液的除杂效率相应提高,在55℃下,质量分数为35%的硫酸溶液中浸取2h后,磷石膏样本中P205含量降低了 75.6%,F-含量降低了 78.4%。(2)考察了不同pH以及Ca~(2+)浓度的反应条件下产物晶体微观结构及晶体形貌的影响。通过FESEM对不同初始反应体系中的产物晶体形貌进行表征后发现,当体系中Ca~(2+)浓度较高时,其产物晶体尺寸较大,长径比低,此时产物结构较为理想,当Ca~(2+)浓度大于4.2M时将严重延缓磷石膏的转晶速率;pH对产物长径比有显著影响,在pH=7.0～8.0的中性-弱碱性条件下,产物长径比低,产物晶体呈短柱状或棒状;而当体系中pH值降低,产物晶体长径比增加,向细针状晶型生长。(3)pH值以及Ca~(2+)浓度对产物含水率以及转晶速率有重要影响。产物含水率反映了产物中半水相所占比例,在Ca~(2+)浓度高的体系当中,二水硫酸钙的溶解速率较慢,因而其转晶速率也变慢;而当体系中pH值下降,磷石膏溶解速率变快,溶液中的游离态SO42-离子浓度增加,反应速率加快。(4)建立了磷石膏溶解动力学模型,研究了不同Ca~(2+)浓度下磷石膏的溶解动力学特征。通过测定溶解阶段液相硫酸根离子浓度随时间的变化,对溶质饱和度C*及瞬时溶解速率Rs进行拟合,得到了反应动力学参数。结果表明,磷石膏的溶解过程属于表面反应控制,在Ca~(2+)浓度2.5M-3.5M的范围内的中性环境中,溶解反应的表观反应级数相差不大,平均值为1.533。
[Abstract]:In order to realize the effective utilization of phosphogypsum, a 伪 伪 -hemihydrate calcium sulfate was prepared by transprystallization of phosphogypsum in salt solution under atmospheric pressure, and the impurity removal was carried out by leaching phosphogypsum. The removal rate of P _ S _ 2O _ 5 F- in phosphogypsum by water washing and sulfuric acid leaching under different conditions was compared. Calcium 伪 -hemihydrate was prepared by transprystallization of phosphogypsum in Ca-Mg-K complex salt solution. The products in the reaction system were characterized by TG-DTA and other analytical methods under different Ca~(2 concentration and pH value. The changes of the composition and content of solid and liquid in different reaction time were determined. The corresponding Ca~(2) concentration and the transgranular rate at pH were calculated. The dissolution kinetics model of phosphogypsum was established, and the solute saturation C * and the dissolution rate of phosphogypsum R _ s were fitted. The reaction kinetics equations under different reaction conditions were obtained. The main contents and conclusions are as follows: 1) the impurity removal process of phosphogypsum is studied, and the results show that. The water soluble P _ 2O _ 5F in phosphogypsum can be effectively removed by single washing and removing impurity under the condition of water washing for 60 min and temperature 65 鈩，

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