Valorization of magnesium slag and CO2 towards a low carbon fiber reinforced cement board

Abstract

Pyrometallurgical extraction of magnesium from dolomite ores results in a large amount of magnesium slag discharge and CO2 emission, posing severe environmental hazards. This study introduces a new approach for the simultaneous upcycling of magnesium slag and CO2 by taking advantage of the high carbonation reactivity of magnesium slag. A CO2-solidified magnesium slag-based fiber cement board with high-strength and high-toughness (CHFCB) is developed, using magnesium slag as the binder, CO2 as the activator, and a mix of pulp and PAN fibers as the reinforcement. The optimal CHFCB preparation process was explored by adjusting the fiber ratio, molding pressure, and CO2 curing system, and the mechanisms underlying its strength and toughness were analyzed. The results indicated that with the optimal preparation, CHFCB exhibited a water-saturated flexural strength of nearly 20 MPa and a drying flexural strength of over 25 MPa. The ultimate deflection could be increased by up to 80 % or more during the bending deformation of CHFCB, while the tensile strain could be improved by over 50 % in the tensile fracture process of CHFCB. After 100 freeze-thaw cycles, the water-saturated flexural strength ratio of CHFCB reached 97.2 %, showing excellent durability. The microanalysis revealed that the dense stacking of calcite-type calcium carbonate and the presence of PAN fibers contributed to the high-strength and high-toughness of CHFCB. Additionally, the environmental and economic benefits of CHFCB were assessed, affirming its role as a sustainable building material that promotes energy efficiency and a green economy.