Enhanced performance of extruded–spheronized carbide slag pellets for high temperature CO 2 capture

The pelletization of carbide slag is necessary for its practical application in the calcium looping process (CLP). In this work, CaO-based pellets were prepared from carbide slag waste via a novel method of extrusion–spheronization. However, this granulation method results in a loss of specific surface area and, consequently, inferior CO2 sorption performance of the carbide slag pellets. Two types of biomass-based pore-forming materials (microcrystalline cellulose and rice husk) were used for the first time to modify the pore structures of the pellets, and thus enhance their CO2 sorption performance. The addition of 20 wt.% microcrystalline cellulose is effective in improving the CO2 sorption of carbide slag pellets, displaying a high conversion of 52.64% in the 25th cycle. However, the additions of 10 and 20 wt.% rice husk both result in inferior cyclic CO2 capture performance owing to the aggravated sorbent sintering caused by the new eutectics, which are from the combination of aluminosilicate with the potassium contained in the rice husk. The pellets doped with 20 wt.% pre-washed rice husk (most potassium removed) display the highest 25th carbonation conversion of 51.02%, which is almost 1.46 times that of the pellets doped with raw rice husk. The addition of pore-forming materials weakens the pellets’ mechanical strength, and 5–10 wt.% addition of cement could enhance the mechanical strength and maintain the relatively good CO2 sorption performance of the pellets.