Basalt mineral surface charge and the effect of mineralization on its colloidal stability: Implications of subsurface CO2 storage

Abstract

Global concern over climate change caused by greenhouse gas emissions has received and is still receiving a lot of attention. Companies and nations have committed to reducing their carbon footprint to halt the consequences, and work is being done to create long-term strategies for CO2 usage. One of these goals is to use the CO2 that has been captured to make chemicals or to use it to make waste that can be buried or safely disposed of. One such endeavours is CO2 mineralization, which has been suggested as a method of CO2 utilization. It entails the creation of carbonates by the interaction of a fluid that contains CO2 with cations that are found in brines or rocks. However, the mineralization process is a protracted one, and until recently it was not believed that it could be completed in less than two years. Furthermore, little research has been done on how mineralization affects the electrokinetic and surface chemistry of cation-bearing rocks like basaltic rocks. Therefore, this study assesses how mineralization (carbonate precipitation) affects the colloidal and electrokinetic characteristics of basaltic rock.According to the study's findings, the electrical double layer (EDL) effect and protonation of the silanol group function as the two main controlling mechanisms of charge formation in the basaltic rock. More so, the rock sample is negatively charged over a range of pH and colloidally stable in freshwater. However, its colloidal stability is decreased in brines, and the EDL effect and potential determining ions (H+ and OH–) dominate its charge development. Additionally, different precipitates have distinct effects on the electrokinetic characteristics of basaltic rock, with the MgCO3 and FeCO3 precipitation having a more notable impact than the CaCO3 precipitation. Furthermore, at pH values of 3 – 4 (CO2 storage pH) in both freshwater and sweater environments, basaltic rocks exhibit near zero or low surface charge values indicating weak adhesion force. Thus, the question of if the near pH values of 2, can be considered as higher values of surface charge is observed in some cases. These findings raise questions about the structural integrity of basaltic rock, which has been touted as a prime candidate for the mineralization process due to its reactive nature, particularly in the case of colloidal stability after the mineralization process. The results of this study further provide new insight into the optimization of the mineralization process, which is dependent on the structural and petrophysical characteristics of the rocks and reservoirs that provide the cations for the process.