稀土萃取分离过程中四价铈成因探究

Study on origin of tetravalent cerium in extraction and separation of rare earth

稀土冶炼分离企业在采用串级萃取工艺分离提纯镨钕系列化合物的过程中普遍存在组分铈超标的问题,通常认为导致上述问题的主要原因为四价铈的生成,在萃取生产线铈/镨分离段引入还原剂可以确保产品质量,但对于导致其质量波动的原因尚未能给出合理解释。通过对萃取分离过程中萃取体系温度、反应时间、搅拌强度、空气引入量、皂化剂种类等因素的研究来查找要因。研究结果表明:随着萃取体系温度的升高、反应时间的延长、搅拌强度的增大、空气引入量的增加,萃取剂P507有机相中负载的四价铈含量呈上升趋势;不同镁盐皂化剂对P507有机相中四价铈的生成量影响显著。实验室模拟生产过程数据显示:采用氧化镁作为皂化剂,在反应温度为50℃、反应时间为10 h、P507有机相皂化值为0.50 mol/L、通入一定量空气且搅拌桨直径为10 cm的条件下,硫酸体系萃取转型后的有机相中四价铈质量浓度高达0.123 g/L,盐酸体系萃取转型后的有机相中四价铈质量浓度高达0.386 g/L;在同等反应条件下,采用碳酸氢镁作为皂化剂时,P507有机相中仅生成微量的四价铈,质量浓度仅为0.005 1 g/L,该研究成果为后续工艺改进提供指导。

Rare earth smelting and separation enterprises generally have the problem that the component cerium exceeds the standard in the process of separating and purifying praseodymium and neodymium series compounds by the cascade ex-traction process.It was generally believed that the causes of the above problems is cerium quadrivalent,and usually reduc-ing agents were added to the cerium/praseodymium separation section of the extraction line to ensure product quality.But the main reasons for its fluctuations were unexplained fully.The extraction system temperature,reaction time,stirring inten-sity,amount of air introduced,different saponification agent types and other factors in the process of extraction separation were studied to find the origin of cerium tetravalent.The results showed that the load of cerium in P507 extractant organic phase showed an increasing trend with the increase of extraction temperature,reaction time,stirring intensity and air intro-duction,and different magnesium salt saponification agents had a significant effect on the cerium production in P507 ex-tractant organic phase.Laboratory simulation production process data showed that when magnesium oxide was used as a sa-ponification agent,the saponification value of P507 organic phase was 0.50 mol/L,quantitative air was injected,the reaction temperature,time and the diameter of stirring paddle respectively were 50℃,10 h,10 cm,the mass concentration of cerium in the organic phase after the transformation of sulfuric acid system could reach 0.123 g/L,and the mass concentration of ce-rium in the organic phase after the transformation of hydrochloric acid system could reach 0.386 g/L.Under the same reac-tion conditions,using magnesium bicarbonate as a saponification agent,P507 organic phase only generated a trace of ce-rium,the mass concentration was only 0.0051 g/L.The research results provided guidance for the subsequent process imrium,the mass concentration was only 0.0051 g/L.The research results provided guidance for the subsequent process im⁃provement.