Experiments and geochemical modelling of CO2 sequestration by olivine: Potential, quantification

Abstract

Aqueous solutions equilibrated with supercritical CO(2) (150 degrees C and total pressure of 150 bar) were investigated in order to characterize their respective conditions of carbonation. Dissolution of olivine and subsequent precipitation of magnesite with a net consumption of CO(2) were expected. A quantified pure mineral phase (powders with different olivine grain diameter [20-80 mu m], [80-125 mu m], [125-200 mu m] and [>200 mu m]), CO(2) (as dried ice) were placed in closed-batch reactors (soft Au tubes) in the presence of solutions. Different salinities (from 0 to 3400 mM) and different ratios of solution/solid (mineral phase) (from 0.1 to 10) were investigated. Experiments were performed over periods from 2 to 8 weeks. Final solid products were quantified by the Rock-Eval 6 technique, and identified using X-ray diffraction, Raman spectroscopy, electron microprobe and scanning electron microscopy. Gaseous compounds were quantified by a vacuum line equipped with a Toepler pump and identified and measured by gas chromatography (GC). Carbon mass balances were calculated. Olivine reacted completely with CO(2), trapping up to 57 +/- 2% (eqC of initial CO(2)) as magnesite; some amorphous silica also formed. Olivine grain diameter and solution/mineral ratios appeared to be the primary controls on the reaction, salinity acting as a second order parameter. During the experiments, fluid analyses may not be performed with approach adopted but, geochemical modelling was attempted to give information about the solution composition. This showed an interesting mineral matrix evolution. Under the experimental conditions, olivine appeared to be a good candidate for CO(2) trapping into a geologically stable carbonate, magnesite. The possible use of mafic and ultramafic rocks for CO(2) sequestration is discussed.