Salinity-enhanced Release of Trace Metals from Sandstone and Variations in Mineral Compositions after Water-rock Interactions in the Presence of Supercritical CO2

Abstract

This research is aimed toward an understanding of the effects of the chemical characteristics and mineral compositions of sandstone and formation water based on saline water-rock-supercritical CO 2 interaction simulation experiments. These experiments were conducted to assess whether toxic trace elements could be dissolved and released in formation water from sandstone in a CO 2 storage layer after CO 2 geological sequestration, thus affecting groundwater quality. The experimental results reveal that the concentrations of Cd and Pb in the water under examination exceeded the national primary drinking standard as a result of saline/fresh water-rock-supercritical CO 2 interactions after 40 d of sandstone immersion in saline/fresh water and 20 d of interaction. In addition, the Mn concentration in the saline/fresh water exceeded the national secondary drinking standard after 40 d of sandstone immersion and 20-80 d of interaction. However, Cd, Pb, and Mn were released to a greater extent (in terms of concentration, 2-fold for Cd, 7-fold for Pb, and 1.7-fold for Mn) in the presence of salinity, revealing that salinity may enhance the dissolution of Cd, Pb, and Mn after 20 d of saline water-rock-scCO 2 interaction. After a long period of supercritical CO 2 -sandstone interaction, the trace metals previously mobilized can be immobilized again by an increase in alkalinity due to aragonite dissolution.