水热法处理磷石膏过程研究

【作者】 杨斌；

【导师】 罗康碧；

【作者基本信息】 昆明理工大学 ， 应用化学， 2006， 硕士

【摘要】 磷石膏是湿法磷酸生产过程中产生的副产物,每生产1吨湿法磷酸（按100%P₂O₅计）就会产生4.5～5.0t的磷石膏。在今后5年中世界磷肥需求量将以每年2.7%的幅度增长,其中中国的磷酸生产扩能将占全球一半以上,与此伴生的磷石膏的增长也将成了磷复肥生产企业实现可持续发展的负担。磷石膏中除了含有80%以上的CaSO₄·2H₂O以外,还含有少量磷酸盐、氟化物等杂质,这些杂质的存在极大地影响了磷石膏的综合性能,使其利用受到很大的限制。 在水热条件下晶体生长的各种参数能进行人为的调整,晶体的生长习性能够得到充分的显露;目前,利用水热法处理磷石膏的报道还比较少见;因此,本文用水热法对磷石膏的改性处理进行了探索。利用化学分析法和X—射线衍射对磷石膏的主要化学成分进行分析,利用光学显微镜和电子扫描电镜观察磷石膏的晶体形貌,利用差热分析仪初步确定磷石膏发生相变时的脱水温度。 在利用水热法处理磷石膏的过程中,水热工艺条件的改变和添加剂的加入改变了水热体系的性质,从而影响到磷石膏的溶解和结晶习性。实验主要以P₂O₅脱除率、CaO和SO₃的回收率、结晶水含量和磷石膏晶体形貌为主要考察指标。在实验中,利用单因素实验法系统地考察了影响磷石膏水热处理的水热温度、水热时间和固液比,确定了实验范围内的最佳水热时间、水热温度和固液比,并对磷石膏化学成分和晶体形貌有明显影响的添加剂进行了筛选。实验证明:在水热温度140℃、水热时间为4h、固液比为0.60、水热溶剂为酸性时,磷石膏水热产物能获得相对较高的P₂O₅脱除率和较高的CaO、SO₃回收率,同时磷石膏水热产物的晶体形貌也较为规整;而水热体系中加入添加剂后,在获得高的P₂O₅脱除率和CaO、SO₃回收率的同时,磷石膏水热产物的晶体也朝着更为规整的长柱状生长。 为了考察复合添加剂对磷石膏水热产物的影响,本文还利用正交优化实验法对添加剂组合进行筛选,确定了在最佳添加剂组合时磷石膏水热产物能够获得99.18%的P₂O₅脱除率、99.96%的CaO回收率和99.40%的SO₃回收率,同时磷石膏水热产物的结晶水含量接近半水石膏理论结晶水含量6.20%,水热产物的晶体也朝着细长柱状生长。 通过实验证明在进行水热处理前对磷石膏进行水洗不利于磷石膏的CaO和SO₃的回收,同时磷石膏晶体的生长也会受到影响。 通过对磷石膏水热处理过程的机理进行分析得知,通过改变水热体系的工艺更多还原

【Abstract】 Phosphogypsum is an by-product of wet-procedure for phosphoric acid production .producing 1 ton phosphoric acid（100% PA） will produce 4. 5⁵. 0 tons phosphogypsum. In the later five years, the market demand of phosphate fertilizer in the world will increase 2. 7% every year. Chinese phosphoric acid production ability will enlarge more than half of the global. Accompanying with the phosphoric acid production enlargement;the phosphogypsum increase will become burden of the phosphoric fertilizer manufacturing enterprises who expected to keep up a steady increase. Phosphogypsum contains not only more than 80% CaSO₄·2H₂O and but also a small amount impurities, such as phosphate and fluoride, etc. These impurities will largyly impair the properties of phosphogypsum and restrict the use of phosphogypsum.In the process of hydrothermal treating phosphogypsum, every parameter of crystal growth could artificially adjusted , crystal growth characteristics could be brought into full play also. The reports that used hydrothermal treating phosphogypsum did not appeared so for. The article explored modification of phosphogypsum with the help of hydrothermal method. By combination of chemical analysis and X-ray diffraction spectra（XRD）, the key chemical composition was analysed, using optical microscope and scanning electron microscope（SEM） observed crystal forms, and composition change dehydration temperature of phosphogypsum was determined by the differential thermal analysis（DTA）.In the process of hydrothermal treating phosphogypsum, changing the hydrothermal technological conditions and additives could transform the hydrothermal system properties and make further improve the dissolution and crystallize characteristics of the phosphogypsum. The primary experiment goals were separating rate of PA, recovery rate of CaO and S0;i, crystal water and crystal forms of phosphogypsum. In the experiment, using single factor test method studied systematically that the hydrothermal temperature, timeand proportions of solid and liquid had an effects on the process of hydrothermal treating phosphogypsum. The additives that distinctly affected the chemical composition and crystal form of phosphogypsum were chosen. The experiment showed that the phosphogypsum hydrothermal products could acquire relatively higher separating rate of P205, recovery of CaO and S0:) at 140°C hydrothermal temperature, 4 hour hydrothermal time, 0.60 proportions of solid and liquid and acid solvent. Simultaneously, crystal forms of the phosphogypsum hydrothermal products were relatively regular. When the additives were added to the hydrothermal system, higher separating rate of P205 and recovery of CaO and S03 were obtained, and the crystal forms of the phosphogypsum hydrothermal products were more regular long column form.For investigating the compound additives to influence the phosphogypsum hydrothermal products, using orthogonal optimize experiment in the article sifted combination additives and determined that when the experiment was carried out at the optimum combination additives, the phosphogypsum hydrothermal products acquired 99.18% separating rate P205, 99.96% and 99. 40 recovery of CaO and S0:(, at the same time, crystal water content of phosphogypsum hydrothermal products approached the hemihydrates gypsum theory crystal water 6. 20%, crystal forms were slender and longer.The experimental results showed that washing the phosphogypsum was harmful to recovering the CaO and S0;i, and the phosphogypsum growth were influenced.Analyzing the mechanism of the process of hydrothermal treating phosphogypsum knew that changing the hydrothermal system technological conditions and adding suitable additives could alter system supersaturation, improve phosphogypsum growth characteristic and promote the phosphogypsum crystal good growth.更多还原