Abstract
Experiments on the simultaneous partitioning of divalent metal ions were carried out in the system K2Mg6Al2Si6O20(OH)4 (phlogopite) − KCl - (Ni2+,Mg2+,Co2+,Zn2+,Fe2+,Mn2+,Ca2+,Sr2+) Cl2 - H2O 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 Mg2+ and Fe2+. Zn2+ shows the same negative anomaly in the partition coefficients as observed in other minerals with 6-fold sites. Co2+ 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 Co2+ may be related with polymerization of Si tetrahedra.
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