海南岛西部非农用地土壤中的稀土元素地球化学特征

对海南岛西部发育典型的12个非农业土壤剖面REE的组成特征及其纵向变化规律进行研究发现,区内非农业土壤剖面不同层位之间的稀土元素具有一定的继承性,风化成土的基岩奠定了土壤中稀土元素的初始含量及土壤中呈现的LREE富集与Eu亏损的特点,而成土过程中稀土元素分异作用则进一步加剧土壤中LREE的富集和Eu亏损,土壤剖面浅部的氧化和水解作用致使Ce在浅层土壤中的富集,并导致由剖面深部至浅部,Ce呈现出正异常增大之趋势。区内稀土元素的赋存状态与稀土元素性质及其所处的土壤地球化学环境有密切联系,同一层中不同形态稀土元素含量总体上表现为残渣态>Fe-Mn结合态>有机态>可交换态(含水溶态)>碳酸盐态,而往土壤深部,残渣态所占比例逐步增大,Fe-Mn结合态、有机态与可交换态(含水溶态)所占比例逐步降低。

REE GEOCHEMICAL CHARACTERISTICS OF NON-CULTIVATED SOILS IN THE WESTERN AREAS OF THE HAINAN ISLAND

Various soil samples were collected from 12 non-cultivated soil profiles in western Hainan Province,and both the REE compositional features of these samples and their spatial variations in these non-cultivated soil profiles were analyzed.The results showed that the total REE contents in the soils are related to the basic rocks and the process of soil formation.The results also indicated that the LREE-enrichment and negative Eu anomaly which exist in the eluvial horizons,illuvial horizons and parent material horizons are due to both the material horizons and basic rocks.Moreover,LREE enrichment and negative Eu anomaly in the top soils tend to increase owing to REE fractionation during the process of soil formation.However,the increasing tendency of positive Ce anomaly from parent material horizons to eluvial horizons in the soil profiles is due to the enrichment of Ce resulting from the oxidation and hydrolysis of Ce3+ at the top of the soil profiles.The contents of REEs(in chemical form) are related to the properties of REEs and the geochemical environment where they are present.For each horizon,the contents of REEs follow the increasing order of residual form>Fe-Mn oxide form>organic form>exchangeable form(including water-soluble form)>carbonate form,and from top to deep soils,the percentage of residual form tends to increase while the Fe-Mn oxide form,organic form and exchangeable form tend to decrease.