LEACHING OF LANTHANOIDS FROM ANDESITIC ROCKS BY ACIDIC AQUEOUS-SOLUTIONS

Laboratory experiments on leaching of lanthanoids (Ln's) from andesiti c rocks by acidic aqueous solutions were carried out in order to find some clue to better elucidation of Ln patterns of acidic hot spring wa ters in nature. Ln's are different from major elements but phosphorus (P) in behavior upon leaching: While leaching of the major elements co ntinued even at the reaction time (t(R)) of 64 h, that of Ln's seeming ly finished by t(R) = 2 or 4 h. The behavior of P upon leaching was di ssimilar to that of other major elements but rather resembled that of Ln's. This indicates that a part of each Ln may exist as phosphates in rocks. Light Ln's were found to be leached out by acidic waters more easily than heavy Ln's. This could be due to the difference in ionic r adii of Ln's and/or be attributed to the difference in resistance to d issolution by acidic waters among various Ln-containing minerals in th e rocks used in the present experiments. The results obtained are succ essfully applied to the elucidation of the Ln patterns of the waters f rom the Kusatsu-Yubatake hot spring, the Kusatsu spa, Gunma and from t he Obuki hot spring, the Tamagawa spa, Akita.