Circular utilisation of coal mine waste: enhancing geotechnical performance through biogenic stabilisation using...

Microbially induced calcite precipitation (MICP) is widely gaining popularity as a bio-mediated technique for soil stabilisation and recycling in an eco-friendly way. In the present study, MICP was employed to enhance the geotechnical properties of coal mine waste, a heterogeneous waste material unsuitable for engineering applications. To ensure the field-scale applicability of MICP and to address the shortcomings of the uniform distribution of calcite precipitations in high-fines-content matrices, a novel bacterial incorporation strategy was developed. This approach employed a native ureolytic bacterium, Sporosarcina pasteurii PS3A cells, for calcium carbonate precipitation through urea hydrolysis, resulting in the formation of mineral bridges that improved particle binding and reduced permeability. The chemical composition of the biogenic precipitate under different treatment conditions was probed by X-ray photoelectron spectroscopy, and its morphology was assessed using field-emission scanning electron microscopy. A ~ 17-fold increase in unconfined compressive strength in samples containing 22% fines was observed post-treatment. Optimisation of bacterial concentrations and cementitious solution molarity enabled precise control over volumetric shrinkage, which was reduced to 1-5%, improving dimensional stability across treated soils. The ultrasonic pulse velocity testing confirmed cementation, with a strong empirical correlation to unconfined compressive strength. These findings establish the necessity and effectiveness of targeted methodologies for applying MICP to fine-grained industrial wastes, advancing its viability as a sustainable alternative to conventional stabilisation techniques within the framework of the circular economy and low-carbon geotechnical engineering.