Experiments on the simultaneous partitioning of divalent metal ions were carried out in the system K
2Mg
6Al
2Si
6O
20(OH)
4 (phlogopite) − KCl - (Ni
2+,Mg
2+,Co
2+,Zn
2+,Fe
2+,Mn
2+,Ca
2+,Sr
2+) Cl
2 - H
2O in the temperature range of 500 to 800 °C at 100 MPa, using the pressure vessel of a cold seal type.
The partition coefficient
KPN (Phl) for the ion exchange reaction between phlogopite (Phl) and aqueous chloride solution (aq) can be expressed as follows:
KPN (Phl) = (
X1/6K2Me6Al2Si6O20(OH)4 /
X1/6K2Mg6Al2Si6O20(OH)4)
Phl / (
mMeCl20 /
mMgCl20)
aq where Me designates divalent metal ion,
m: molality, and Xi: mole fraction of end-member i in biotite solid solution. The partition coefficient - ionic radius (PC-IR) curve marks a peak between Mg
2+ and Fe
2+. Zn
2+ shows the same negative anomaly in the partition coefficients as observed in other minerals with 6-fold sites. Co
2+ also represents such a negative anomaly as was previously found in tremolite and hedenbergite. Based on the previous and present experimental results, it is considered that the anomaly of Co
2+ may be related with polymerization of Si tetrahedra.
抄録全体を表示