Preparation and characterization of high-strength insulating porous bricks by reusing coal mine overburden waste, red mud and rice husk

Coal mine overburden waste (MW) and Red Mud (RM), globally significant solid wastes posing substantial environmental challenges and inflicting ecological damage through leachates, have prompted industries to explore non-dumping alternatives; however, despite extensive research, economically viable solutions for efficient utilization and large-scale conversion remain elusive. The present research aims to explore the possibility of efficacious utilization and mass conversion of MW, RM, and rice husk (RH) to fabricate insulation bricks of IS:2042 standard. The study investigates the physical qualities of the bricks, considering variations in the particle size of MW and RH, the MW:RM ratio, sintering temperature, and the amount of RH used. The pH and conductivity tests validate the lower concentration of alkali metals present in the leachates of the insulation bricks. The fixation of alkali/heavy metals is achieved through the formation of phases like Albite, Iron silicate, and Pyrope during the sintering process, which entraps heavy metals within the spinel or silicate structure of the insulation brick. These phases along with in-situ formed mullite phase imparts better mechanical strength to the brick having porosity in the range of 16.4-57.2%, compressive strength 6.51-34.2 MPa, and thermal conductivity 0.37-0.67 W/mK. In conclusion, this study convincingly showcases the feasibility of producing high strength insulation bricks that adhere to the rigorous standards specified in IS:2042, with potential applications in refractory and other insulation-demanding sectors. The findings indicate that the majority of the bricks align with the IS:2042 standard. Moreover, this work highlights the substantial potential of utilizing MW as the primary ingredient, augmented by RM as an additive, in brick manufacturing. The study demonstrates that the insulating properties of these bricks can be effectively enhanced through the incorporation of RH. By incorporating waste materials into the manufacturing process, this approach promotes economic circularity in waste management and contributes to the advancement of sustainable development principles.