CO2 mineralization of high-calcium fly ash: Synthesis of spindle-like aragonite whiskers on fly ash surfaces to lower nucleation barrier and enhance its performance as a supplementary cementitious material

초록

Utilizing carbonation fly ash (FA) as a supplementary cementitious material (SCM) to replace cement is a crucial approach for reducing carbon emissions in the cement industry. Currently, typical carbonation products, high-aspect-ratio aragonite whiskers, can effectively enhance the mechanical properties of cement. However, aragonite whiskers adversely affect the workability of cement paste, thereby limiting the content of aragonite that can be incorporated into the cement. To address this limitation, this study proposes a novel method for synthesizing spindle-like aragonite whiskers on FA surfaces via wet carbonation, aiming to simultaneously achieve carbon sequestration and morphological control. Additionally, CFA-Aragonite used as an SCM improved both the workability and mechanical performance of cement pastes. The effects of Mg2 +/Ca2+ ratio, Mg2+ concentration, and reaction temperature on aragonite formation were systematically investigated, and the heterogeneous nucleation mechanism was explored in conjunction with a kinetic model. The results showed that under the conditions of Mg2+/Ca2+ molar ratio of 2:1, Mg2+ concentration of 0.3 M, and temperature of 80 degrees C, spindle-like aragonite with a length of 3 mu m and an aspect ratio of 3-4 was synthesized on the FA surface. The FA substrate can provide heterogeneous nucleation sites and synergistically reduce the nucleation energy barrier with Mg2+, resulting in 62-87% reductions compared to homogeneous nucleation and thereby promoting the controlled growth of aragonite. CFA can achieve a CO2 sequestration of 76.43 kg CO2/t FA. With a 30% replacement level of spindle-like CFA, the mechanical properties of the cement pastes were significantly increased while maintaining the workability.

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