ASSESSING THE CARBON SEQUESTRATION POTENTIAL IN SOUTHWESTERN SWEDEN A comparative study of igneous rock from Greenland, Iceland, and Sweden to evaluate the carbonatization potential of the Billdal area, SW Sweden
Abstract
The main purpose of this study is to investigate the potential of geological Carbon Capture and
Storage (CCS) in SW Sweden using an innovative technique which mimics Earth's natural way of
regulating the global carbon cycle by turning CO2 gas into carbonate minerals. To achieve this,
comparative experiments on CCS potential were conducted using six different igneous rock samples.
These encompassed granite, gabbro, and dolerite of Proterozoic age from the Billdal area in
Gothenburg, Sweden, 1.3 Ga nepheline syenite and carbonatite from the Grønnedal-Íka alkaline
complex in SW Greenland, and a young basalt from the Holuhraun volcanic eruption in Iceland
2014 – 2015. Powdered rock samples of size 45 – 250 μm were subjected to carbonation reactions
with carbonated deionized water in closed systems at ambient temperature, 50°C, and 100°C,
respectively. The room temperature experiments lasted 63 days, while the 50°C ran for 32 days, and
the 100°C were conducted in a manner of three hours. The three experimental sets were monitored
daily by recording the pH of the solutions, showing gradual increases in pH with time until reaching
stable levels within the basic range. Among the rock samples, gabbro exhibited the highest pH value
(8.68) at room temperature, while syenite demonstrated the highest pH (9.01) at 50°C, and
carbonatite displayed the highest pH (8.42) at 100°C. After reaching a stable pH ~8, a weak NaHCO3 –
Na2CO3 solution of pH 9.2 was added to the solutions to enhance the potential of carbonate
precipitation.
Pre- and post- treated powdered rock samples were analysed using X-Ray Diffraction (XRD), Scanning
Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM – EDX), Circular Back Scatter
detector (CBS), and Everhart-Thornley Detector (ETD). Results using XRD showed no carbonate
precipitate while results of SEM-EDX found carbonate precipitates, most likely calcite, on basalt,
carbonatite, and nepheline syenite, but no precipitation on the granite, gabbro, and dolerite. The low
carbonatization rate of the latter three are ascribed to the lack of suitable divalent cations for
carbonate mineral formation. One surprising result was the degree of mineral alteration in these
Swedish rocks, which had turned pyroxenes into amphiboles. Pyroxenes would otherwise have been
ideal candidates for CCS. With these results at hand, the highly altered rocks of SW Sweden are
deemed unsuitable for CO2 sequestration through carbonate precipitation.
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Date
2023-08-18Author
Temmar, Alaël
Keywords
Climate change
carbon sequestration
rock – water geochemistry
petrology
carbonatization reaction
XRD
SEM
Series/Report no.
B1220
Language
eng