Geochemical characteristics of rare earth elements in different types of soils in China

The contents, distribution patterns, and specification of rare earth elements(REEs) in latosol(tropical zone), red earth(middle subtropical earth), yellow brown soil(northern subtropical earth), cinnamon soil(warm temperate zone), leached chernozem(temperate zone) and albic bleached soil(temperate zone) in China were determined with instrumental neutron activation analysis( NAA) and systematically studied. The results indicate that yellow brown soil, cinnamon soil, leached chernozem and albic bleached soil are characterized by light REEs(LREEs) enrichment and Eu-depletion, while latosol and red earth are characterized by LREEs enrichment and Ce-depletion, REEs exist mainly in a stable residual form in the six soils, and with increasing atomic number, the intermediate REEs(IREEs) of residual form have lower proportion than Light and heavy REEs. For the six unstable forms, the proportions of water-soluble, exchangeable, specific absorption, and carbonate forms are lower. Appearent zonal distribution patterns of REEs were found in the form of Fe-Mn oxides in different types of sails, and the general trend gradually decreases from southern to northern China. Proportions of REEs in bound organic matters are higher and follow the order: albic bleached soil > leached chernozem > red earth > latosol > yellow brown soil > cinnamon soil. Higher proportion of REEs exists in soils with higher proportion of organic matters. But their activation differs greatly with difference in relative proportions of loosely bound organic matter form and tightly bound organic matter form.