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Abstract
Bauxite residue (red mud) is a solid waste resulting from the aluminum production industry. Disposal or landfill of the red mud (RM) poses irreversible environmental problems; therefore, it is compelling to find practical solutions that can mitigate the negative environmental problems of RM stacking storage. In the past decades, although the recycling of RM has achieved significant progress, challenges remain from both academic and practical perspectives. Previous studies have demonstrated that all the aluminosilicate-based solid wastes have pozzolanic activity, and thus can be considered as resources to manufacture eco-friendly cementitious materials to relieve the carbon emission burden. Therefore, combining RM and other solid wastes to manufacture green cementitious materials has become a promising route to alleviate the burden of environmental pollutions. However, challenges from the fluctuation of the chemical compositions, inert activity, heavy metals stabilization, efflorescence, the side effects of the second pollutions from solid wastes, the hydration process, and mutual interaction mechanisms between the various types of solid wastes are still unclear, especially for multi-components RM-based cementitious materials. This review article summarizes the state of the art of mechanical properties, microstructure characterization methodologies, and hydration process and mechanisms of RM along with other solid wastes. The main challenges and future research trends are discussed. This article attempts to summarize the details of the RM recycling technologies that are beneficial to readers in understanding the background knowledge and research methodologies of eco-friendly cementitious materials.
Highlights
Introduction of BauxiteResidue (Red Mud)Bauxite residue, called red mud (RM), is the main solid waste in the aluminum production process
RM has been considered as solid waste, from the perspective of materials chemistry, it is a promising raw material for manufacturing cementitious materials due to the fact that the main chemical compositions of RM are primarily composed of iron oxides (5–30%), titanium dioxide (2–15%), calcium oxide (0–20%), silicon oxide (5–50%), and undissolved alumina (0–20%) [4,5], which ensure the potential pozzolanic activity of the RM
Alkali-activation is still the main approach to realize the solidification of the RM solid waste systems
Summary
Called red mud (RM), is the main solid waste in the aluminum production process. The bauxite residue (red mud) was a high pH value material due to the high concentrations of calcium and sodium hydroxide along with a complex chemical composition, and it has become one of the main solid wastes that pose significant environmental problems. RM has been considered as solid waste, from the perspective of materials chemistry, it is a promising raw material for manufacturing cementitious materials due to the fact that the main chemical compositions of RM are primarily composed of iron oxides (5–30%), titanium dioxide (2–15%), calcium oxide (0–20%), silicon oxide (5–50%), and undissolved alumina (0–20%) [4,5], which ensure the potential pozzolanic activity of the RM. For the pore size distribution, it was claimed that the replacement of RM in cement could increase the volume of the pores with sizes smaller than 100 nm due to the pozzolanic activity of the RM and the filling effect of the fine RM particles [6]
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