Experiments on the simultaneous partitioning of divalent metal ions between phlogopite and 2M aqueous chloride solution under supercritical conditions

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 K_PN (Phl) for the ion exchange reaction between phlogopite (Phl) and aqueous chloride solution (aq) can be expressed as follows:

     K_PN (Phl) = (X_{1/6K2Me6Al2Si6O20(OH)4} / X_{1/6K2Mg6Al2Si6O20(OH)4})
     _Phl / (m_MeCl2⁰ / m_MgCl2⁰)_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.