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Co-precipitation reaction for Ba and Ra into calcite

方解石へのBa及びRaの共沈反応

吉田 泰*; 吉川 英樹; 中澤 俊之*; 佐藤 智文*

Yoshida, Yasushi*; Yoshikawa, Hideki; Nakazawa, Toshiyuki*; Sato, Tomofumi*

Caよりイオン半径の大きい2価の陽イオンについて方解石に対する共沈反応の傾向性を調べるために実験を行った。共沈反応は一般的に元素分配比で評価され、また、元素分配比は方解石の沈殿速度の影響を受けることが知られているため、幅広い沈殿速度の領域で元素分配比を測定する実験を行った。トレーサにはRa及びBaを用いた。実験の結果、Ra及びBaの元素分配比は、既往の報告値と同様に、沈殿速度の減少に伴い小さい値となった。RaとBaの元素分配比はともに小さく、結晶格子のひずみなどにより結晶内に取り込まれることが予想された。また、BaとRaでイオン半径が異なるにもかかわらず、元素分配比は同程度の値となり、RaとBaの共沈反応においては、イオン半径の大きさの違いは共沈反応に顕著な影響を与えないことが示された。

To evaluate incorporation behavior of Me$$^{2+}$$ larger than Ca in ion radius, co-precipitation experiment were implemented. Partition coefficient is generally used to estimate co-precipitation reaction and this parameter is reported to be affected by precipitation rate of calcite. Therefore, under the condition of variety of R, D for Me$$^{2+}$$ larger than Ca into calcite was measured. For trace elements Ra and Ba were used. As a result of experiment Partition coefficient for Ba (or Ra) are decreasing toward the slow R. This tendency is consistent with the reported data. The values of D of Ba and Ra which are low imply those large radius elements are difficult to incorporated into crystal lattice and inclusion is presumably induced by distortion of lattice structure. In addition there is no notable difference of D for Ra and Ba despite difference of radius length. It indicates an extent of inclusion does not depend on a difference of ion radius between Ra and Ba.

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