The protracted weathering of banded iron formations (BIFs) results in giant supergene iron ore deposits. An indurated iron duricrust known as canga covers these lateritic profiles making it extremely resistant to erosion and protecting the friable ore underneath (Dorr, 1964). Canga is the ultimate weathering product of BIF and is mostly composed of detrital BIF and iron ore, cemented together by goethite. Geochemical evidence suggests that the goethite in canga has undergone repeated dissolution and reprecipitation and that biogeochemical processes are important in the ongoing cycling of iron in canga (Monteiro et al. 2014).
Effective post-mining rehabilitation strategies for tropical iron ore areas will rely on the re-formation of canga. We expect that enhancing natural biogeochemical cycling of iron in canga is an ideal platform for re-formation of canga and thus the accelerated remediation of iron ore sites. In the present study, we enriched iron reducing consortia from various canga ecosystems and attempted to promote reductive dissolution of highly crystalline iron oxides (goethite, hematite). Interestingly, fermentative processes (e.g., Paenibacillus, Clostridium spp., coupling incomplete oxidation of glucose to iron reduction) were much more effective at reducing the iron oxides in canga than dissimilatory iron reduction processes (e.g., complete oxidation of lactate coupled to iron reduction by Shewanella spp.). Lab-scale experimental models to promote canga re-formation using this fermentative approach for reductive dissolution of iron oxide are underway and are being coupled with several approaches to promote subsequent cementation of canga fragments using key microbial groups (i.e., cyanobacteria, iron oxidising bacteria and fungi).