【作者】 常宏涛；

【导师】 涂赣峰； 吴文远；

【作者基本信息】 东北大学 ， 有色金属冶金， 2008， 博士

【摘要】 稀土元素具有特殊的物理与化学性能,因而在冶金、石油化工、玻璃陶瓷领域和各种功能材料中广泛应用。为了从混合稀土原料中获得单一稀土元素或某几种稀土元素,现工业上主要采用氨水或碳酸氢铵皂化的P204[二(2-乙基己基磷酸)]或P507[2-乙基己基膦酸单乙基己基脂]萃取剂分离稀土元素,但该方法产生含有很高浓度NH4+的废水,对环境污染严重。针对现有分离稀土的工艺和研究的不足,本论文通过在稀土氯化物溶液中加入配合剂柠檬酸(H3AOH),采用非皂化的P204萃取剂分离轻稀土元素。研究了该体系中P204萃取轻稀土元素的分配比、分离系数、萃取饱和容量与酸度、柠檬酸浓度和稀土浓度的关系,并对萃取轻稀土的机理及动力学进行了系统的研究。文中采用单级萃取实验方法研究了不同稀土料液、酸度和柠檬酸浓度条件下,在P204-HCl-H3AOH体系中轻稀土元素的分配比和萃取饱和容量,并采用回归分析法建立了以料液酸度、柠檬酸浓度和稀土浓度为变量的三元一次回归方程,分析了酸度、柠檬酸浓度和稀土浓度三因素对轻稀土的分配比和分离系数的影响。结果表明：当料液酸度pH值为1.0、柠檬酸浓度为0.25mol·L-1、稀土浓度为0.25mol·L-1时,轻稀土元素的分配比最大达到DLa=0.1767、DCe=0.7353.DPr=1.5221和DNd=2.4201,轻稀土元素间最大分离系数分别为βCe/La=4.16、βPr/Ce=2.07和βNd/Pr=1.59。同样工艺参数下,在串级萃取分离轻稀土的生产线上得到有效级平均分离系数分别是βCe/La=3.50、βPr/Ce=2.05和βNd/Pr =1.35,此值均高于该生产线皂化的P204萃体系中βCe/La=2.14、βPr/Ce=1.67和βNd/Pr=1.33。并且随着柠檬酸浓度的升高,P204萃取稀土的容量逐渐增大,最大可以达到29.71 g·L-1比盐酸体系提高近50%。通过实验结果得出P204在含有柠檬酸体系中与轻稀土离子的萃取平衡常数分别为：当pH>1时,1gKLa=-1.77、1gKce=-1.63、1gKPr=-1.26、1gKNd=-0.86；当0<pH≤1时,1gKLa=-0.61、1gKCe=0.13、1gKpr=0.40、1gKNd=0.80.轻稀土的萃取平衡常数随着原子序数的增加而增大规律说明,在P204-HCl-H3AOH体系中P204萃取轻稀土为“正序萃取”。P204分别萃取各轻稀土元素的萃取平衡常数间的差值比水相中柠檬酸与各轻稀土元素间配合稳定常数的差值大的现象,得出P204-HCl-H3AOH体系中轻稀土间的分离系数增大的原因。采用红外光谱分析方法从萃取剂分子结构的变化研究了P204-HCl-H3AOH体系萃取稀土离子的机理,结果表明：当pH>1时萃取反应是稀土离子与P204分子的P-OH基团H+置换,其属于阳离子交换机制；当0<pH≤1时反应过程复杂,P204分子中的P=O基团与P-OH基团同时参与了与稀土的配合,其萃取机制为阳离子交换和溶剂化配合双重机制；当pH<0时的萃取机制与0<pH≤1基本相同,但以P=O基团与稀土配合反应为主；0<pH≤1和pH≤0时,柠檬酸的存在阻碍了P204二聚体的形成,双重配合机理增强了P204的萃取能力,使萃取容量提高。配合不同稀土元素的P204红外光谱图发现,轻稀土离子与P204的配合能力依La→Nd顺序逐渐增强,并且P204-HCl-H3AOH体系中P204萃取相同稀土离子时P=O基团的频率和相对峰强的变化比P204-HCl体系的大,这进一步解释了柠檬酸作用下增大稀土分离系数的原因。采用恒界面法研究了P204-HCl-H3AOH体系萃取轻稀土的动力学,实验发现P204萃取轻稀土的速率随着搅拌速度、温度和比界面积的增大而增大,根据阿仑尼乌斯方程计算出P204-HCl-H3AOH体系中正向萃取轻稀土的表观活化能分别为ELa=19.11KJ-mol-1 ECe=13.13 KJ·mol-1、EPr=10.22 KJ·mol-1和ENd=8.39KJ·mol-1,表明此过程具有典型的扩散速度控制特征。通过研究酸度和萃取剂浓度对萃取速率的影响,确定P204-HCl-H3AOH体系中P204萃取轻稀土的正向反应速率方程式为：更多还原

【Abstract】 Since the rare earth (RE) products have particular physical and chemical properties, they are widely used in metallurgy, petrochemical industry, various functional materials and glass ceramic field etc. In order to obtain individual rare earth element or mixed several rare earth elements from mixed rare earth feed, P204 or P507 as extractant saponified by ammonia liquor or ammonium acid carbonate are used to separate rare earth elements, but this method produces drain water contained high concentration NH4+, which heavily give environment pollution.In this thesis, the coordination agent citric acid (H3AOH) is added to rare earth and the unsaponified P204 is used as extractant in order to improve the process of separating light rare earth. The distribution ratio of rare earth elements in rare earth chloride solution and P204 extractant, separation coefficient, saturated extraction capacity and acidity, citric acid concentration, rare earth concentration were studied. The mechanics and the kinetics of the light rare earth extraction were studied.Under the conditions of different rare earth feed, acidity and citric acid concentration, the distribution ratio of the light rare earths and extraction saturated capacity in P204-HCl-H3AOH system were studied by single stage extraction experiments. The ternary linear regression equation of feed acidity, citric acid concentration and rare earth concentration was obtained, and the effect of them on the distribution ratio and separation coefficient were analyzed. The results show that, when feed acidity pH 1.0, citric acid concentration 0.25mol·L-1 and rare earth concentration 0.25mol·L-1, the max distribution ratio(D) comes up to DLa=0.1767, DCe=0.7353, DPr=1.5221 and DNd=2.4201 respectively, the max separation coefficient(β) areβCe/La=4.16,βpr/Ce=2.07 andβNd/Pr=1-59 respectively. By continuous stage extraction, the average separation coefficient of areβCe/La=3.50,βpr/Ce=2.05 andβNd/Pr=1-35 respectively at the same experiments conditions as single stage extraction, which are higher compare to the saponified P204 systemβCe/La=2.14,βPr/Ce=1-67 andβNd/Pr=1-33. Moreover, the capacity of unsaponified P204 extracting rare earth increases with citric acid concentration, its maxium is 29.71 g·L-1, which increases nearly 50% compare to soaponified P204.The extraction equilibrium constants(K) of unsaponified P204 in the citric acid system are 1gKLa=-1.77, 1gKCe=-1.63, 1gKPr=-1.26, 1gKNd=-0.86 when pH>1; and 1gKLa=-0.61,1gKCe =0.13,1gKpr=0.40,1gKNd=0.80 when 0<pH≤1. The extraction equilibrium constants increase with atomic number, which indicates P204 extracting the light rare earth ions in P204-HCl-H3AOH system is "positive extraction". The difference value of extraction equilibrium constants between P204 and every light rare earth element is bigger than the difference value of the coordination equilibrium constants between of citric acid and every light rare earth element. This causes the separation coefficient of the light rare earths increase in P204-HCl-H3AOH system.The mechanics of extracting rare earth ion in P204-HCl-H3 AOH system were determined by infrared spectrum analysis. The results show that, extraction reaction are the replacement of H+of P-OH with rare earth ions according to cation exchange mechanics when pH>1. When 0<pH<1, the reaction process is complex, and P=O band and P-OH band participate the coordination with rare earths simultaneously, and its coordination mechanics is cation exchange and neutral complexation. When pH<0, the coordination mechanics is the same as that of 0<pH<l, but coordination reaction of P=O band and is primary. The above indicates that, when 0<pH≤1 and pH≤0, the existing of citric acid impeds the formation of P204 dipolymer, and double coordination mechanics strengthen the extracting ability of P204, therefore enhance extracting capacity. The infrared spectrogram of P204 coordinating with the different rare earth elements shows that the coordination ability increases gradually from La to Nd. Moreover, the variation of frequency and relative peak intensity of P=O band in P204-HCl-H3AOH system are bigger than that in P204-HCl system when extracting the same rare earth ion, which further explains the cause of the increase of rare earth separation coefficient when existing citric acid.The kinetics of extracting the light rare earth in P204-HCl-H3AOH system was investigated by constant interfacial area method. The results show that, the rate of P204 extracting light rare earths increases with stirring speed, temperature, specific interfacial area. According to Arrhennius equation, the apparent activation energy of extracting light rare earths are ELa=19.11KJ·mol-1, ECe=13.13 KJ·mol-1, EPr=10.22 KJ·mol-1 and ENd= 8.39 KJ·mol-1 respectively, which illustrates that this process has obvious diffusion velocity control characteristic. By studying the effect of acidity and extractant concentration on extraction rate, the positive reaction rate equations of extracting light rare earths in P204-HCl-H3AOH system are determined as fellows:更多还原