红壤中稀土元素结合形态的分布及分配

红壤剖面中稀土元素结合形态的分布研究表明，稀土元素的各种结合形态中以残渣态为主，其次为铁锰氧化物结合态，大部分稀土元素的可交换态、碳酸盐结合态、有机质结合态及酸溶态含量较为接近。稀土元素结合形态在剖面层中的分布大致可分为两类，一类以表层含量较高，如有机质结合态；另一类以深层含量较高，如可交换态、碳酸盐结合态、残渣态（大部分稀土元素表现为C层＞A层＞B层）和酸溶态（主要表现为C层＞B层＞A层），而铁锰氧化物结合态变化较复杂，但主要集中在深层。不同母质对不同稀土元素各种结合形态的分布有一定的制约作用．表现为某些稀土元素的一些结合形态在一种或几种母质的红壤中占主导地位。稀土元素结合形态的分配研究表明，元素Pr、Tb、Tm、Yb、Lu的分异普遍比较显著，在不同结合形态中呈现富集或亏损，而Ce、Sm、Eu等元素则主要在某一种结合形态中发生分异。从稀土元素的各种结合形态与红壤的硅酸盐成分及其有机质含量、pH值间的相关分析认识到结合形态与红壤本身成分间的密切关系。

DISTRIBUTION AND THEIR PATTERNS OF CHEMICAL FORMS OF REE IN RED SOILS

Research on the distribution of chemical forms of REE in the profiles of red soils shows that the main chemical form of REE is the residual form, coming next is the form of combination with oxides of Fe and Mn. The contents of REE of various chemical forms (e.g. exchangeable, combined with carbonate or organic matter and acid soluble) are almost the same. According to the distribution patterns, the chemical forms in soil profiles can be divid-ed into two groups: one is high in the upper horizons, for example the chemical form of com-bination with organic matter and the other is high in the deeper horizons. The contents of REE in the form of Fe, Mn oxides are highly variable, they are mainly concentrated in the deeper horizons. Different parental materials have some constraints on the distribution of dif-ferent chemical forms of REE. Research on the distribution patterns of REE in different chemical forms indicates that obvious differentiation occurred for the elements Pr, Tb, Tm,Yb and Lu in all chemical forms, and the differentiation of Ce, Sm and Eu mainly occurred in one chemical form. Correlation analyses between the contents of chemical forms and silicate composition, the contents of organic matter and pH values revealed a close relationship. of chemical forms with soil composition.