Study on the Influence of Carbide Slag Incorporation on the Carbon Sequestration Efficiency and Material Properties of Fly Ash-Based Carbon-Negative Filling Materials

Abstract

The number of abandoned mines in China is vast, and the resource conversion efficiency is relatively low. Industrial solid waste holds significant potential in the field of carbon sequestration, where alkaline activators play a crucial role in enhancing carbon capture performance. Fly ash, as a primary negative carbon filling material, exhibits low activity in its original state and limited carbon sequestration capacity. To improve its carbon sequestration performance, this study uses carbide slag as an alkaline activator to activate the latent pozzolanic activity of fly ash. The study further investigates the influence mechanism of carbide slag content on the workability, microstructure, and carbon sequestration efficiency of fly ash-based negative carbon filling material (Negative Carbon Filling Material, NCFM). The experiment uses low-calcium fly ash as the primary raw material and is conducted under two conditions: 2 MPa CO2 injection and atmospheric pressure without ventilation. The results showed that in the absence of CO2 infiltration, the addition of carbide slag led to a decrease in adsorption capacity. However, as the amount of carbide slag increased, the adsorption capacity first increased and then decreased, reaching a maximum value of 40.53 ml/g when the slag content was 20%. The pore size distribution of the samples with different slag contents was generally similar, showing a fluctuating downward trend. This was characterized by a single fractal dimension, which decreased with increasing slag content. Additionally, the total pore volume and specific surface area decreased, while the average pore diameter increased. In terms of carbon sequestration performance, the incorporation of carbide slag effectively increased the carbon content and efficiency of the fresh slurry, with both initially increasing and then decreasing as the incorporation level increased. Without the addition of carbide slag, the carbon content and efficiency were 13.02 mg/g and 28.87%, respectively. When the dosage was 40%, the carbon sequestration capacity and efficiency reached their highest values, with 1 g of carbon-negative material absorbing 26.06 mg of CO2 and an efficiency of 41.96%. The research findings indicate that carbide slag, as an alkaline activator, has significant potential for application in the carbon sequestration process. It provides a technical reference for the reutilization of abandoned mines, the resource utilization of solid waste, and CO2 mineral carbonation and sequestration. This contributes to advancing the goals of "carbon peak" and "carbon neutrality," and supports the achievement of sustainable development goals.

Keywords: Carbide slag, Fly ash, alkaline activators, negative carbon filling materials, CO2 mineralization sequestration, carbon sequestration efficiency