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

Abstract

AbstractColumn tests were conducted to elucidate the pH neutralization and CO2 fixation behavior of alkaline recycled soils permeated with CO2. The ventilation period required for complete CO2 fixation (tEOF) was estimated from the test results of each column. The maximum amount of CO2 captured per gram of dry soil ((mCO2)max) was determined based on the inflow and outflow of CO2 for each specimen. The investigation into the effects of soil density, specimen height, CO2 gas concentration, and flow rate on tEOF and (mCO2)max revealed that tEOF increased with higher dry density (ρd) or specimen height (H), as a denser and larger specimen consumed more CO2 gas. Conversely, tEOF decreased with a higher CO2 gas concentration (C) or flow volume (Q) because a low C or Q resulted in an insufficient CO2 gas supply to match the consumption induced by the reaction. Lower C and Q tended to yield higher (mCO2)max, whereas higher ρd and H resulted in higher (mCO2)max. Furthermore, (mCO2)max increased with tEOF, with a slight reduction in pH after neutralization with increased tEOF. This phenomenon was attributed to the longer ventilation period enabling more Ca to react with the CO2 gas and maintain the equilibrium state of the reaction. Finally, the evaluation of the CO2 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 tEOF was associated with a higher CSR, although some variation was observed.