Optimizing carbonation reaction parameters of calcium carbide slag in acidic/alkaline environment enhancing CO2 mineralization efficiency

Abstract

Carbide slag (CS) is a typical alkaline solid waste with Ca(OH)2 as its main component, exhibiting a high capacity for CO2 mineralization. Currently, the methods for CS mineralization of CO2 include direct and indirect mineralization which the initial pH of the reaction system plays a crucial role in the mineralization process. In this study, we explored the effects of alkaline and acidic environments on the carbonation reaction between CS and CO2 and optimized the related reaction parameters. The alkaline system involved dissolving CS followed by introducing CO2, while the acidic system involved introducing CO2 first, followed by either one-time or intermittent addition of CS. We studied the dissolution behavior and reaction processes of CO2 and CS in both systems. The results showed that the carbonation reaction could be completed in the alkaline system. However, in the acidic system, the carbonation reaction is uncompleted with one-time addition of small amount of CS (solid–liquid ratio of 1:100) especially intermittent addition of CS. On the contrary, one-time addition of sufficient CS into acidic solution forming high solid-to-liquid ratio suspension (solid–liquid ratio of 5:100 and 10:100) resulted in thoroughly completion of the carbonation. More importantly, the CO2 fixation capacity, reaction rate, Ca2+ extraction, size distribution and phase structure of obtained calcite was superior to that of the alkaline system. This study demonstrates that although the acidic environment is unfavorable for the dissolution of CS and the leaching of Ca2+, the reaction can still proceed to completion at a faster rate under optimized conditions. This finding might promote the practical utilization of industrial solid waste for CO2 sequestration and enhance its scale-up application.