Towards a sustainable geoliner construction in landfills by potential blending of fly ash with kaolin clay alternative: a review with an insight to Indian scenario

Abstract

Electricity generated through coal-based Thermal Power Plants (TPPs) has played a pivotal role in shaping modern civilization, revolutionizing industries, and improving the quality of life for billions of people worldwide. These TPPs contribute to about 37%–40% of the global energy requirements. Energy production, in turn, has a direct impact on the economy of any country. Apart from this boon to humankind, these TPPs combusting coal as their primary fuel also have specific environmental impacts, the major ones being water, air, and soil pollution due to unscientific disposal of high-quantity fly ash produced yearly. If we can put this ash to good use, it may assist us in mitigating the pollution caused by it. Although there are many conventional uses of fly ash, such as a pozzolanic material in the cement industry, more pathways need to be discovered to balance the high generation quantities with consumption. Therefore, a detailed description of its use in potential geoliner applications is presented in this article. A geoliner or a landfill liner acts as a virtually impenetrable layer to mitigate the leachate penetration into the underneath subsoil and groundwater, thus preventing contamination. There are presently some studies that support the use of only fly ash in such applications. Nevertheless, the properties of the geoliners using it are not so good to significantly mitigate environmental degradation owing to its high permeability and low densification tendency. The bentonite conventionally used has limited deposits and is mined intensively for its use as a natural sealant. Their deposits must also be conserved, and an alternative material that may serve similar application benefits, like bentonite, must be selected. The desired aim can be fulfilled if we blend this combustion residue with other suitable materials (such as kaolinite clay) with low permeability. Thus, the article focuses on the possibilities of blending fly ash with different clays for geoliner construction to improve the individual properties of fly ash. This will contribute to developing a scope for future scientific research in deploying these blends in natural membrane materials for various industries. Different types of geoliners that are designed to contain the disposed-off waste are also explained in detail. Additionally, a glimpse of the global fly ash market is put forward to depict its importance for various industries in this technologically advancing world. This article profoundly observes an overall environmental management aspect regarding waste utilization.

Graphical abstract