TY - RPRT

T1 - Carbonation of Stapafell Basalt

T2 - An Experimental Study of the Mineral Dissolution and Precipitation Processes at Conditions Similar to that of the CarbFix Injection Site at Hellisheiði, Iceland

AU - Rasmussen, Maja Bar

N1 - Kemisk Institut

PY - 2015

Y1 - 2015

N2 - At the Hellisheiði Power plant just 25 km outside of Reykjavik, SW Iceland, injection of CO2 and water into a basaltic underground is performed. The purpose is to store CO2 by mineral carbonation. CO2 dissolved in water creates an acidic solution that dissolves reactive silicates in the basalt and precipitate carbonates from released Ca2+, Mg2+ and Fe2+ . The project was first launched in 2007 under the project name, CarbFix and fused with the similar project SulFix (that injected H2S into the undergound) in 2014 to create the CarbFix-SulFix project. This project covered the injection of 8 bar dissolved CO2 and H2S together at depths > 750 metres and temperatures between 200 and 270˚C. The aim of this study was to perform experiments at conditions, similar to those of the actual injection (270˚C, total pressure of 62 bar and a starting pressure of 8 bar CO2), to probe to what extend mineral carbonation of crystalline basaltic rock can be expected. The reacted material was analysed by X-Ray Diffraction (XRD) to identify the phases present after 5, 47, 155 and 244 hours of reaction. These patterns were then fitted to that expected for known minerals by Rietveld refinement to determine the relative abundances of the present phases. Furthermore, Scanning Elecetron Microscopy combined with Energy Dispersive X-ray Spectroscopy (SEM-EDXS) analysis were performed to identify any morphological changes in the mineral assemblage. The geochemical software, PHREEQC was deployed to model the kinetic dissolution of the basaltic minerals and to determine the secondary phase assemblage and their temperature dependence. The model suggested calcite precipitation occurring within the first hour while the first signs of calcite precipitation in the experimental data appeared after 5 hours of reaction. After 47 hours of reaction, peaks from calcite were clear in the XRD pattern and SEM-EDXS showed rhombohedral crystals with an elemental compositions consistent with calcite. After 244 hours of reaction, XRD and SEM-EDXS indicated that calcite had started to redissolve. Moreover, at that time, the analyses indicated a high degree of contamination originating from corrosion of the reactor vessel. This process undermined the robustness of the results, at least at longer reaction times. In SEMEDXS, forsterite showed a rim of reaction products, including hematite, which slowed down the process of forsterite dissolution. XRD analysis of two basalt samples from the injection depth at Hellisheiði showed peaks from calcite, showing that calcite is stable in the reservoir. The results of the experiments and the presence of calcite in the samples from Hellisheiði indicates that calcite most likely forms when CO2 is injected into the deeper subsurface of Hellisheiði.

AB - At the Hellisheiði Power plant just 25 km outside of Reykjavik, SW Iceland, injection of CO2 and water into a basaltic underground is performed. The purpose is to store CO2 by mineral carbonation. CO2 dissolved in water creates an acidic solution that dissolves reactive silicates in the basalt and precipitate carbonates from released Ca2+, Mg2+ and Fe2+ . The project was first launched in 2007 under the project name, CarbFix and fused with the similar project SulFix (that injected H2S into the undergound) in 2014 to create the CarbFix-SulFix project. This project covered the injection of 8 bar dissolved CO2 and H2S together at depths > 750 metres and temperatures between 200 and 270˚C. The aim of this study was to perform experiments at conditions, similar to those of the actual injection (270˚C, total pressure of 62 bar and a starting pressure of 8 bar CO2), to probe to what extend mineral carbonation of crystalline basaltic rock can be expected. The reacted material was analysed by X-Ray Diffraction (XRD) to identify the phases present after 5, 47, 155 and 244 hours of reaction. These patterns were then fitted to that expected for known minerals by Rietveld refinement to determine the relative abundances of the present phases. Furthermore, Scanning Elecetron Microscopy combined with Energy Dispersive X-ray Spectroscopy (SEM-EDXS) analysis were performed to identify any morphological changes in the mineral assemblage. The geochemical software, PHREEQC was deployed to model the kinetic dissolution of the basaltic minerals and to determine the secondary phase assemblage and their temperature dependence. The model suggested calcite precipitation occurring within the first hour while the first signs of calcite precipitation in the experimental data appeared after 5 hours of reaction. After 47 hours of reaction, peaks from calcite were clear in the XRD pattern and SEM-EDXS showed rhombohedral crystals with an elemental compositions consistent with calcite. After 244 hours of reaction, XRD and SEM-EDXS indicated that calcite had started to redissolve. Moreover, at that time, the analyses indicated a high degree of contamination originating from corrosion of the reactor vessel. This process undermined the robustness of the results, at least at longer reaction times. In SEMEDXS, forsterite showed a rim of reaction products, including hematite, which slowed down the process of forsterite dissolution. XRD analysis of two basalt samples from the injection depth at Hellisheiði showed peaks from calcite, showing that calcite is stable in the reservoir. The results of the experiments and the presence of calcite in the samples from Hellisheiði indicates that calcite most likely forms when CO2 is injected into the deeper subsurface of Hellisheiði.

M3 - Report

BT - Carbonation of Stapafell Basalt

PB - University of Copenhagen

ER -