Numerical modelling of CO₂-water-basalt interaction

The effects of CO₂ on water-basaltic glass interaction have been simulated at 25°C. The calculations indicate that addition of CO₂ (2-30 bar) to water significantly changes the reaction path. Initially, the pH is buffered between 4 and 6 by CO₂ ionization, with dissolution of basaltic glass and the formation of secondary minerals with SiO₂, Mg-Fe carbonates and dolomite predominating. Upon the dissolution of additional basaltic glass and mineral fixation of CO₂, the pH increases to >8 and (Ca)-Fe-Mg smectites, SiO₂, Ca-Na zeolites and calcite become the dominant secondary minerals forming. The overall reaction path depends on the initial water composition, reactive surface area, and the composition of the phyllosilicates and carbonates forming. The key factors are the mobility of Mg²⁺, Fe²⁺ and Ca²⁺ and the competing reactions for these solutes among secondary minerals.