Mineral carbonation process for CO2 sequestration

Abstract

The most promising route for mineral carbonation is the aqueous process using naturally occurring silicate minerals. The overall carbonation reaction consists of the dissolution of MgO- or CaO-bearing silicates such as olivine, serpentine, and wollastonite, followed by the precipitation of carbonates such as magnesite and calcite. In this paper, we report the experiments to investigate both the dissolution and the precipitation processes, separately. Olivine dissolution kinetics has been studied under several temperature and CO2 pressure, and by varying the solution composition. The experiments were performed in a flow-through reactor at 90–120–150 ∘C. The pH was adjusted using either acids (e.g., HCl, citric acid) or LiOH, and by changing the CO2 pressure while the salinity was varied by adding NaCl and NaNO3. To estimate the dissolution rate for each experiment, a population balance equation (PBE) model coupled with a mass balance was applied. The obtained values were regressed over a pH range from 2 to 8, using a linear model of the form log(r)=−npH−B, where r is the specific dissolution rate (mol cm−2 s−1). The experiments to study the kinetics of magnesite precipitation were performed in batch using the H2O–CO2–Na2CO3–MgCl2 system at 90, 120, and 150 ∘C and at 100 bar of CO2 pressure. The solution composition and solid phases were monitored with insitu Raman spectroscopy. At the conditions applied, we observed two mechanisms: direct precipitation of magnesite and simultaneous precipitation of magnesite and hydromagnesite followed by the transformation of the latter into the former.