In situ redox control and Raman spectroscopic characterisation of solutions below 300 °C
I‐Ming Chou, Ruoheng Wang, Jiann‐Neng Fang
Abstract
Redox reactions often occur and significantly affect many geological processes. To simulate redox reactions in low temperature (T < 400 C) hydrothermal experiments, fused silica was used as a hydrogen membrane to impose an externally fixed H 2 pressure (P H 2 ) on a fused silica capillary capsule (FSCC; 150 m inner diameter, 375 m outer diameter and 6 mm long) to define the redox state of the sample in the FSCC. At 300 C, it required less than 7 hours to reach osmotic equilibrium. In this study, a constant P H 2 was imposed on an FSCC, which originally contained a 0.5 m (mole/kg H 2 O) SnCl 4 0.5 m HCl aqueous solution, at 300 C and vapour saturation pressure. In situ Raman spectra of the sample solution collected at 300 C show that the reduction rate of Sn IV to Sn II species increased substantially with an increase of 1.1 bar of P H 2 . We characterised precipitation and dissolution of cassiterite under various P-T-pH-P H 2 conditions and greatly increased our capabilities for performing rigorous hydrothermal experiments at temperatures below 400 C, in which redox control is difficult to ensure without in situ approaches.