Red mud-based all-solid-waste cementitious materials: A review of synthesis, heavy metals immobilization and feasibility application

Abstract

As a supplementary cementitious material, red mud not only improves its utilization rate and alleviates environmental problems caused by large-scale stockpiling, but also mitigates CO₂ emissions and energy consumption associated with cement production. Developing red mud-based all-solid-waste cementitious materials with ideal bonding properties to completely replace cement presents both economic and environmental advantages. This paper took a novel perspective by focusing on red mud-based all-solid-waste cementitious materials, providing an informed delineation between red mud-based all-solid-waste alkali-activated cementitious materials and red mud-based geopolymer. We summarized the composition of raw materials, types of extra alkaline activator, and maximum compressive strength of the two cementitious materials, systematically classified the maximum amount of red mud added to different cementitious material systems, and revealed the synthesis mechanism of the two cementitious materials. The types of heavy metals contained in the two kinds of cementitious materials were analyzed and integrated, and the efficacy and mechanism of heavy metals fixation was revealed. The effects of key system components, such as alkaline, calcium and silicon-aluminum components, on the environmental-material properties of the cementitious materials have been elaborated in depth. The cementitious material is compared with conventional cement showing better sustainability. Feasible applications of the material covering different areas are also detailed. The summary and outlook of the current research work provides examples for the upcycling strategies and harmless valorization of red mud and solid waste, and provides guidance for the regulation of the properties of red mud-based all-solid-waste materials and their practical engineering applications.