Abstract: The presence of impurities in phosphoric acid hinders its application in downstream processes. The development of wet-process phosphoric acid deep purification technology enables the direct preparation of phosphate-based new energy materials through a simplified process, which represents the mainstream direction for industry advancement. The solvent extraction method was employed for the extraction and separation of Al and Fe impurities in wet-process phosphoric acid. The effects of different extractants, temperature, O/A ratio, time, and extractant content on the separation efficiency of Al and Fe impurities were investigated. Optimal conditions were determined as follows: N,N-N-octyl amine di (methylene phenylphosphonic acid) (OADMPPA) extractant, extractant content of 20wt%, time of 3 min, temperature at 25℃, O/A ratio of 1:1 and 3-stage cross-flow extraction. Under these conditions, the extraction rates for Al and Fe reached 54.5% and 99.6%. Consequently, the contents of Al and Fe impurities in phosphoric acid decreased from 0.857wt% and 0.175wt% to 0.717wt% and 0.015wt%. Additionally, the MER value reduced from 9.037% to 7.227%. Further optimization of stripping process of OADMPPA extractant loaded with Al and Fe was carried out, ammonium oxalate was identified as the optimal stripping agent. The optimized stripping conditions were as follows: 25℃, 5-stage cross-flow stripping, O/A ratio of 2:1, time of 15 min, and concentration of the stripping agent at 0.2 mol/L; the stripping efficiencies for loaded extractant Al and Fe reached 96.4% and 88.3%, effectively achieving their separation from the extractant phase. Finally, the mechanism behind Al or Fe extractants was investigated by stoichiometric calculation and Fourier infrared analysis during the extraction process. It was found that during this process, one molecule of Al combined with one-and-a-half molecules of OADMPPA extractant while one molecule of Fe combined with two molecules of OADMPPA extractant; functional groups involved in these interactions included P=O and P-O-H bonds. A competitive mechanism exists in the extraction process between Al and Fe, where Fe is more easily extracted.

Key words: wet-process phosphoric acid, aluminum and iron impurities, extraction, stripping, mechanism

摘要： 湿法磷酸工艺生产的磷酸产品杂质种类多、含量高，制约后端应用。湿法磷酸深度净化技术可以实现湿法磷酸短流程直接制备磷系新能源材料，是磷化工领域内的研究热点和前沿。本工作采用溶剂萃取法进行湿法磷酸中铝铁的萃取分离，研究了不同萃取剂、萃取剂含量、萃取时间、萃取温度、萃取O/A比(萃取相与磷酸体积比)和萃取级数对磷酸中铁铝杂质萃取分离效果的影响规律，筛选出最优条件：N,N-N-正辛胺二亚甲基苯基膦酸(OADMPPA)萃取剂、萃取剂含量20wt%、萃取时间3 min、温度25℃、单级O/A比1:1、错流3级萃取，最优萃取条件下，Al, Fe萃取率分别为54.5%和99.6%，磷酸中铝和铁含量分别由0.857wt%和0.175wt%降至0.717wt%和0.015wt%，MER值(磷酸中铝铁镁对应氧化物含量之和与五氧化二磷含量比)由9.037%降至7.227%。随后，针对O/A比1:1单级萃取条件下得到的负载Al, Fe的萃取剂，进行反萃工艺优化，筛选出草酸铵为最优反萃剂，优化的反萃条件：温度25℃、错流5级反萃、单级O/A比2:1、反萃时间15 min、反萃剂浓度0.2 mol/L，在优化反萃条件下，负载萃取剂Al, Fe的反萃效果分别达96.4%和88.3%，基本实现负载萃取剂Al, Fe有效反萃。最后开展了萃取剂铝铁萃取机理研究，通过对萃取过程中化学计量数计算、傅里叶红外分析，明确萃取过程中1分子Al和1分子Fe分别与1.5分子和2分子OADMPPA萃取剂结合，作用官能团为P=O和P-O-H键，同时，Al, Fe的萃取过程存在竞争机制，Fe更易被萃取。

关键词: 湿法磷酸, 铁铝杂质, 萃取, 反萃, 机理