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Abstract <p>The cation exchange reaction 2RbAlSi<sub>3</sub>O<sub>8</sub> + BaCl<sub>2</sub>(aq) = BaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub> + 4SiO<sub>2</sub> + 2RbCl(aq) was studied under hydrothermal conditions (<i>T</i> = 650°C and <i>P</i> = 2 kbar). It was shown that Ba partitions preferentially into (Rb,Ba)-feldspar relative to fluid over the entire compositional range. The unit-cell parameters of (Rb,Ba)-feldspar solid solutions were refined. The excess mixing volume is negative and can be described by the two-parameter Margules model: <i>W</i><sup><i>V</i></sup>1 = –2.11 ± 0.05 and <i>W</i><sup><i>V</i></sup>2 = –1.85 ± 0.06 cm<sup>3</sup>/mol. Based on the distribution of Rb and Ba between feldspar and fluid, the excess mixing energy of the solid solution was estimated: <i>W</i><sup><i>G</i></sup>1 = 6.82 ± 0.54 and <i>W</i><sup><i>G</i></sup>2 = 12.25 ± 0.81 kJ/mol. The calculated excess mixing functions were compared with those of other feldspar solid solutions.</p>

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Experimental Study of RbAlSi3O8–BaAl2Si2O8 Solid Solutions: Cation-Exchange Equilibria with Fluid

  • 期刊论文

  • 发表日期：

    2026年2月1日

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  • A. R. Kotelnikov,
  • N. I. Suk,
  • Z. A. Kotelnikova,
  • G. M. Akhmedzhanova,
  • N. A. Drozhzhina

摘要

Abstract

The cation exchange reaction 2RbAlSi3O8 + BaCl2(aq) = BaAl2Si2O8 + 4SiO2 + 2RbCl(aq) was studied under hydrothermal conditions (T = 650°C and P = 2 kbar). It was shown that Ba partitions preferentially into (Rb,Ba)-feldspar relative to fluid over the entire compositional range. The unit-cell parameters of (Rb,Ba)-feldspar solid solutions were refined. The excess mixing volume is negative and can be described by the two-parameter Margules model: WV1 = –2.11 ± 0.05 and WV2 = –1.85 ± 0.06 cm3/mol. Based on the distribution of Rb and Ba between feldspar and fluid, the excess mixing energy of the solid solution was estimated: WG1 = 6.82 ± 0.54 and WG2 = 12.25 ± 0.81 kJ/mol. The calculated excess mixing functions were compared with those of other feldspar solid solutions.