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.