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3 分离过程从天然存在的稀土混合物中分离单一稀土的不同方法实质上是利用碱性的较小差别,而这个差别又是由于从镧到镥的离子半径逐渐减小而引起的.碱性的差异会影响盐的溶解度、离子的水解作用和络合物的形成.这些性质构成了用分级结晶、分级沉淀、离子交换和溶剂萃取等分离方法的基础.除了三价的氧化状态外,铈、镨和铽还能以四价状态出现,钐、铕和镱以二价状态出现.在有效地分离过程中,选择性地氧化或还原这些元素是很有用的,因为二价状态、四价状态比起二价状态这些元素在化学性质上有很大的差别.
3 The separation process The different methods of separating a single rare earth from a naturally occurring rare earth mixture essentially make use of a small difference in alkalinity, which in turn is due to a gradual decrease in ionic radius from lanthanum to neptunium. Differences affect the solubility of salts, the hydrolysis of ions and the formation of complexes, which form the basis of separation methods such as fractional crystallization, fractional precipitation, ion exchange and solvent extraction.In addition to the trivalent oxidation state, cerium, Praseodymium and terbium also appear in the tetravalent state, and samarium, europium and ytterbium appear in the divalent state.It is useful to selectively oxidize or reduce these elements in an efficient separation process because the divalent state, the tetravalent state The chemical properties of these elements are quite different from the bivalent state.