Abundances of rare earth elements in crude oils and their partitions in water

原油中の希土類元素の存在度及び希土類元素の水中での分配

中田 亮一*; 高橋 嘉夫*; Zheng, G.*; 山本 祐平; 清水 洋*

Nakada, Ryoichi*; Takahashi, Yoshio*; Zheng, G.*; Yamamoto, Yuhei; Shimizu, Hiroshi*

中国、新彊ウイグル自治区の泥火山より採取した原油及び共存する水の中の希土類元素の存在度を世界で初めて報告した。原油は軽希土類元素に富み、重希土類元素に枯渇した相対存在度パターンを示した。原油中の希土類元素濃度は共存水より百倍高かった。原油の疎水性と希土類元素イオンの性質を考慮すると、原油中の希土類元素は錯体として存在していると考えられる。C-NMRの分析によると、原油中にはフェノール基とカルボキシル基が含まれており、希土類元素はそれらの官能基に錯生成していると考えられる。原油中の希土類元素の相対存在度パターンは泥火山中の泥のパターンと類似しており、原油中の希土類元素は原油が発生した岩石もしくは堆積物から供給されたと考えられる。

Patterns of the entire range of REE in crude oils and coexisting water, collected from mud volcanoes in Xinjiang Province of China, are reported here for the first time. Crude oils show light REE enriched patterns with flat or depleted patterns in heavy REE, when normalized to chondrite. The REE concentrations in crude oils are larger than those in coexisting water by a factor of more than one hundred. Considering the hydrophobicity of oil and the high ionic characteristics of REE, it is strongly suggested that REE form complexes with ligands present in the crude oils. Based on the C NMR spectroscopy, it is found that small amounts of phenol and carboxyl groups are contained in the crude oil samples, which could possibly provide complexing sites for REE. REE patterns of crude oils are similar to those of coexisting mud samples collected from the same mud volcanoes, which suggests that the REE in crude oils are derived from rocks and sediments where crude oils were generated.