Abstract
Permanent geological storage of anthropogenic CO 2 and the development of low-carbon energy resources, including natural hydrogen (H 2 ), have become two key components of carbon-neutrality strategies. Ultramafic rocks are increasingly recognized as promising geological media because they can support both mineral carbonation and natural H 2 generation. However, the relationship between these processes, and the extent to which similar reactions occur in mafic rocks, remain poorly understood. Mafic and ultramafic rocks from the Charsk Ophiolite (eastern Kazakhstan) and the Kempirsai Ultramafic Massif (western Kazakhstan) were investigated under experimental conditions to evaluate their potential for CO 2 mineralization and natural H 2 generation. Serpentine-rich ultramafic rocks displayed the highest carbonation potential. Dissolution of lizardite released Mg 2+ ions that promoted secondary magnesite precipitation and efficient mineral trapping of CO 2 . Carbonation was substantially weaker in magnesiochromite-rich ultramafic rocks. Natural H 2 generation followed a different pattern. The highest H 2 concentrations were measured in ultramafic (0.872 mol%) and mafic (0.721 mol%) rocks from the Charsk Ophiolite, whereas only trace amounts were detected in samples from the Kempirsai Massif. CO 2 mineralization and natural H 2 generation were controlled by different mineralogical factors. Serpentine-rich ultramafic rocks were most favorable for long-term CO 2 immobilization through mineral carbonation, whereas Fe-bearing mafic and ultramafic rocks with high reaction potential were more favorable for natural H 2 generation. Kazakhstan’s ophiolitic complexes therefore represent promising geological targets for both permanent CO 2 storage and natural hydrogen exploration.