Abstract

The objective of this study is to investigate the geochemical change of feldspar minerals by supercritical CO₂, which exists at CO₂ sequestration sites. High pressurized cell system (100 bar and 50^oC) was designed to create supercritical CO₂ in the cell and the surface change and the dissolution of plagioclase and orthoclase were observed when the mineral surface reacted with supercritical CO₂ and water (or without water) for 30 days. The polished slab surface of feldspar was contacted with supercritical CO₂ and an artificial brine water (pH 8) in the experiments. The experiments for the reaction of feldspar with only supercritical CO₂ (without brine water) were also conducted. Results from the first experiment showed that the average roughness value of the plagioclase surface was 0.118 nm before the reaction, but it considerably increased to 2.493 nm after 30 days. For the orthoclase, the average roughness increased from 0.246 nm to 1.916 nm, suggesting that the dissolution of feldspar occurs in active when the feldspars contact with supercritical CO₂ and brine water at CO₂ sequestration site. The dissolution of Ca²⁺ and Na⁺ from the plagioclase occurred and a certain part of them precipitated inside of the high pressurized cell as the form of amorphous silicate mineral. For the orthoclase, Al³⁺, K⁺, and Si⁴⁺ were dissolved in order and the kaolinite was precipitated. In the experiments without water, the change of the average roughness value and the dissolution of feldspar scarcely occurred, suggesting that the geochemical reaction of feldspars contacted with supercritical CO₂ at the environment without the brine water is not active.

Keywords CO₂ sequestration, supercritical CO₂, feldspar dissolution, geochemical reaction, brine aquifer