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.