Enhanced CO2 Sequestration Strategy Using CO2 Capturing Material Synthesized from Spent Railway Tie Concrete

Lots of railway tie concrete waste are produced which needs appropriate treatment for disposal. This study introduces a novel strategy for converting railway tie concrete waste into a highly efficient CO₂ capturing material (RTC). To enhance the CO₂ capturing capabilities, a CaCl₂ solution was employed as a modifying agent (Ca-RTC). The introduction of a 0.001 M CaCl₂ solution increased the Ca content in Ca-RTC by only 0.08% compared to unmodified RTC, yet it significantly enhanced porosity and surface area. This modification led to an 11.57% of excellent CO₂ capturing ability, which is 2.5 times greater than that of the original RTC. Even though the Ca content is similar in RTC and Ca-RTC, the significant increase in BET surface area led to a notable improvement in CO₂ capturing ability. However, increasing the CaCl₂ concentration beyond 0.005 M resulted in a reduction of CO₂ capturing ability, attributed to the inhibitory effect of Cl⁻ ions. The kinetics of the CO₂ capturing reaction and the impact of CO₂ pressure on Ca-RTC were systematically investigated. Finally, the CO₂ capturing mechanism of Ca-RTC was elucidated.