Several fieldtrips were performed in the Troodos ophiolite, which included sampling of ultramafic and mafic rocks. A significant number of rock samples were collected and subsequently those with the highest potential for CO2 sequestration were selected for further investigation, based on petrographic analysis. Additionally, waste rock materials related to quarrying and/or mining activities were collected. The samples that were selected for further investigation are listed below:
Ultramafic rocks
• Dunite
• Harzburgite
• Pyroxenite
• Chromitite (sample from abandoned chromite mine)
Mafic rocks
• Olivine basalt
• Dolerite (quarry waste material)
Over 100 ball milling experiments were performed using the aforementioned rocks. The following methods were used for the characterization of the rock materials before and after ball milling: Powder X-ray diffraction (PXRD), BET, Scanning Electron microscopy (SEM) and Transmission Electron Microscopy (TEM) in combination with energy-dispersive X-ray spectroscopy (EDS), temperature-programmed desorption of CO2 (CO2-TPD). Based on the overall results, a methodology was developed for the creation of nanomaterials with high CO2 adsorption capacity.
Enhanced weathering experiments were also performed to assess the potential for the enhanced weathering of ultrafine rocks in seawater to facilitate the drawdown of CO2 directly from the atmosphere. Towards this goal, two peridotites (i.e. dunite, hurzburgite) and an olivine basalt (before and after ball milling) were reacted in artificial seawater in open system reactors. The pH and the concentrations of total dissolved inorganic carbon (DIC) were measured in all fluid samples. The dissolved Si, Mg and Ca concentrations were also determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Mineral saturation states of the reactive fluids were determined using the PHREEQC V3 software. The precipitation of carbonate minerals was studied by measuring the total inorganic carbon in the solids before and after the experiments. Furthermore, the solids were characterized by PXRD, SEM-EDS and TEM-EDS.
Additionally, the performance of building materials (i.e. lime-based mortars) modified by the addition of milled quarry waste material was studied. These were characterized using PXRD, SEM-EDS, mercury intrusion porosimetry, vacuum saturation, differential thermal analysis and thermogravimetry. The compressive and flexural strength values were also determined.
An overview of the CO2NOR project results is given below:
• The ball milling process substantially enhances the CO2 uptake of ophiolitic rocks (e.g. see Fig. 1).
• The highest CO2 uptake was acquired for the dunite, followed by the olivine basalt, harzburgite, pyroxenite and quarry wastes.
• Prolonged ball milling results in a reduction of specific surface area and CO2 uptake due to particle agglomeration that takes place after many hours of milling.
• The experimental results show that the CO2 uptake of waste materials from dolerite quarries can be substantially enhanced after ball milling, thus these materials can be potentially used as feedstock for the ex situ mineralization of CO2 (see Fig. 2).
• Lime-based mortars containing ball-milled waste material from dolerite quarries as additive show better performance compared to reference samples.
• The enhanced weathering of ball-milled peridotites in seawater can induce the drawdown of CO2 directly from the atmosphere and ultimately the precipitation of aragonite at ambient conditions, thereby promoting long-term and safe CO2 storage.
• The overall results of the CO2NOR project demonstrate that ball milling is a very promising technique for optimizing the carbon sequestration efficiency of ultramafic/mafic rocks and quarry wastes; thus, the proposed methodology could be a fundamental part of a future carbon sequestration strategy.
Outreach activities were performed according the predetermined plan in order to present the research results to society in a simple way. In addition, the results were presented to the scientific community through 4 publications in peer-reviewed international scientific journals and 3 presentations in national/international conferences.
