Neutralization and CO2 fixation behavior of alkaline recycled soil using column tests with CO2 ventilation

Abstract Column tests were conducted to elucidate the pH neutralization and CO 2 fixation behavior of alkaline recycled soils permeated with CO 2 . The ventilation period required for complete CO 2 fixation ( t EOF ) was estimated from the test results of each column. The maximum amount of CO 2 captured per gram of dry soil (( m CO2 ) max ) was determined based on the inflow and outflow of CO 2 for each specimen. The investigation into the effects of soil density, specimen height, CO 2 gas concentration, and flow rate on t EOF and ( m CO2 ) max revealed that t EOF increased with higher dry density ( ρ d ) or specimen height ( H ), as a denser and larger specimen consumed more CO 2 gas. Conversely, t EOF decreased with a higher CO 2 gas concentration ( C ) or flow volume ( Q ) because a low C or Q resulted in an insufficient CO 2 gas supply to match the consumption induced by the reaction. Lower C and Q tended to yield higher ( m CO2 ) max , whereas higher ρ d and H resulted in higher ( m CO2 ) max . Furthermore, ( m CO2 ) max increased with t EOF , with a slight reduction in pH after neutralization with increased t EOF . This phenomenon was attributed to the longer ventilation period enabling more Ca to react with the CO 2 gas and maintain the equilibrium state of the reaction. Finally, the evaluation of the CO 2 consumption rate ( CSR ) for each column specimen revealed that a higher C and Q resulted in a lower CSR , whereas a higher H resulted in a higher CSR . Additionally, a longer t EOF was associated with a higher CSR , although some variation was observed.