Ferrugination of biocrusts grown on crushed ferricrete: Potential for slope stabilisation

Abstract

Bioremediation of degraded lands using biological soil crusts (i.e., biocrusts; complex association between soil, microorganisms, and extracellular polymeric substances) is an emerging biotechnological strategy to control surface erosion. Here, we examined the use of biocrusts for the stabilisation of iron ore mine waste. Simulating naturally occurring biomineralisation of microbial mats on ferricrete, we promoted the ferrugination of biocrusts on crushed iron-rich waste material, aiming to form iron biocement. The biocrusts on our 50-cm experimental slopes (comprised primarily of cyanobacteria, green algae, and fungi) aggregated crushed ferricrete fragments through the secretion of extracellular polymeric substances. Provided with an external source of ferrous iron, the biocrusts also acted as organic scaffolds for the precipitation of iron oxides. The mineralisation of the biocrusts led to the formation of biocemented aggregates that mechanically stabilised the crushed iron-rich waste material. The biocrusts, with and without biomineralisation, enhanced hydraulic conductivity and minimised erosion. The addition of ferrous iron without an organic framework resulted in a powdery coating of individual fragments, rather than consolidation of the substrate. Our findings demonstrate the potential of synthetic biocement as a long-term stabilisation strategy for waste rock stockpiles, engineered slopes, and mine remediation requiring the reformation of iron-rich duricrust.