The nature of ultramafic rocks from Sulawesi, Indonesia and their suitability for CO2 sequestration

Petrological and geochemical characterization of some ultramafic rock samples from Sulawesi has been conducted with the aim at deciphering physico-chemical properties in relation to their potential use as carbon dioxide storage. Mineralogical analysis was performed by means of optical microscopy and whole rock chemical compositions of the samples were determined by X-ray fluorescence (XRF) spectrometry. Results of analyses show that lizardite is predominant serpentine mineral present, followed by chrysotile and trace amount of magnetite. Remnants of olivine and pyroxene were detected in some samples but they have been pseudomorphically replaced by serpentine. Serpentinization of Sulawesi ultramafic rocks has led to transformation of olivine and lesser pyroxene become secondary phases mainly lizardite and minor chrysotile. This process also has changed the properties of rocks such as reduction in grain size and decreasing in density. Relatively higher MgO concentration combined with fine grained and porous rocks indicate that some Sulawesi ultramafic rocks are good candidate as the host for mineral carbonation. Fosteritic olivine and serpentine (lizardite) are the most soluble Mg-rich
minerals in acid. Carbonation may occurs where Mg2+ readily reacts with CO2 forming thermodynamicly stable magnesite (MgCO3)