氟硅酸制备高纯氟化铝新工艺研究

Study on new process of preparing high-purity aluminium fluoride from fluorosilicic acid

面对中国战略资源萤石日益匮乏的现状,开发了以磷肥副产氟硅酸为原料合成氟硅酸钠,经动态分解得到四氟化硅,四氟化硅纯化后和无水氯化铝发生气相沉积反应、提纯制备高纯氟化铝工艺路线,并对反应原理、工艺流程、关键点控制及产品质量和原料成本等进行研究。结果表明:氟硅酸钠软膏采用两级干燥方式进行干燥,干燥后水分≤0.05%(质量分数);氟硅酸钠热解采用动态分解方式,分解率>99%。粗四氟化硅气体采用浓硫酸洗涤、分子筛吸附、精馏提纯后纯度>99.5%;无水氯化铝以气体状态和提纯的四氟化硅反应,反应后产品纯度>99.5%,符合高端领域市场需求。该研究可为磷肥副产低品位氟资源的高效高值利用提供参考和借鉴。

Faced with the increasing shortage of fluorspar,a strategic resource in China,an industrial route for preparation of highpurity aluminium fluoride from fluorosilicic acid,a byproduct of phosphate fertilizer was developed.Fluorosilicic acid was used as raw material to synthesize sodium fluorosilicate,which was further dynamically decomposed to get silicon tetrafluoride.Silicon tetrafluoride was purified and then reacted with anhydrous aluminium chloride in vapour phase deposition to prepare highpurity aluminium fluoride.The reaction principle,process flow,key point control,product quality and raw material cost were also studied.The results showed that sodium fluorosilicate paste was dried by twostage drying method,and the moisture content after drying was≤0.05%(mass fraction).Dynamic decomposition method was adopted for sodium fluorosilicate pyrolysis with decomposition rate>99%.The purity of crude silicon tetrafluoride gas after washing with concentrated sulfuric acid,molecular sieve adsorption and distilled purification could reach 99.5%.Aluminium chloride reacted with purified silicon tetrafluoride in gas state,and the purity of the product after reaction was>99.5%,which met the market demand in highend field.This study could provide reference and guidance for the efficient and highvalue utilization of low grade fluoride resources as byproduct of phosphate fertilizer.