Accelerating microbial iron cycling promotes re‐cementation of surface crusts in iron ore regions

Abstract

Accelerating microbial iron cycling is an innovative environmentally responsible strategy for mine remediation. In the present study, we extend the application of microbial iron cycling in environmental remediation, to include biocementation for the aggregation and stabilization of mine wastes. Microbial iron reduction was promoted monthly for 10 months in crushed canga (a by-product from iron ore mining, dominated by crystalline iron oxides) in 1 m 3 containers. Ferrous iron concentrations reached 445 ppm in treatments and diverse lineages of the candidate phyla radiation dominated pore waters, implicating them in fermentation and/or metal cycling in this system. After a 6-month evaporation period, iron-rich cements had formed between grains and 20-cm aggregates were recoverable from treatments throughout the 1-m depth profile, while material from untreated and water-only controls remained unconsolidated. Canga-adapted plants seeded into one of the treatments germinated and grew well. Therefore, application of this geobiotechnology offers promise for stabilization of mine wastes, as well as reformation of surface crusts that underpin unique and threatened plant ecosystems in iron ore regions.

Hydrologic Alteration and Enhanced Microbial Reductive Dissolution of Fe(III) (hydr)oxides Under Flow Conditions in Fe(III)-Rich Rocks: Contribution to Cave-Forming Processes

“…While the Fe(III)-rich rocks of this region were generally considered to be resistant to weathering (Schuster et al, 2012;Monteiro et al, 2014), it is becoming increasingly clear that microbiological activities may induce extensive transformations to these rocks, especially canga (Parker et al, 2013(Parker et al, , 2018Levett et al, 2016Levett et al, , 2020Gagen et al, 2018Gagen et al, , 2019Paz et al, 2020). Previous work has focused on the transformations of canga-Fe as a mechanism of canga permanence, whereby the weathering resistance of canga is owed to the alternating reductive dissolution of Fe(III) (hydr)oxides and abiotic or microbiological reoxidation of Fe(II) back to Fe(III) (Levett et al, 2016(Levett et al, , 2020Gagen et al, 2018Gagen et al, , 2019Gagen et al, , 2020Paz et al, 2020). In this way, canga appears to be continuously weathering and reforming.…”

Ten principles for restoring campo rupestre, a threatened tropical, megadiverse, nutrient‐impoverished montane grassland

“…The challenges for campo rupestre restoration are especially high for mining sites, where soil and topsoil removal for mineral extraction dramatically changes the landscape and makes full ecological restoration unrealistic. Emerging technology including the reformation of ironrich duricrusts (Gagen et al 2020), cementation of residual minerals promoted by root exudates (Paz et al 2020), and successful species reintroduction using different methods (Figueiredo et al 2021;Gastauer et al 2021;Onésimo et al 2021) constitute reasons for optimism and higher levels of restoration aspirations than previously thought (Guedes et al 2021). Our principles are not exhaustive and should be viewed as an initial attempt to integrate the limited scientific evidence into a conceptual framework to steer both restoration policy and practice in campo rupestre, one of the most iconic grasslands worldwide (Bond 2019).…”

Acquiring Iron-Reducing Enrichment Cultures: Environments, Methods and Quality Assessments

“…These formations support a unique vegetation [ 5 , 6 ] containing 38 plant species of edaphic endemism [ 7 ] endangered by mining [ 8 ]. The restoration of lateritic crusts in the post-mining landscape may be a viable strategy to maintain this biological heritage in the region, reconciling the conservation of biodiversity with the sustainable exploitation of natural resources in one of the most important mineral provinces of the world [ 8 , 9 ].…”

“…To accelerate the biocementation in post-mining landscapes, the inoculation with iron-reducing bacteria may be necessary to restore cangas , especially in environments where such organisms are naturally scarce or lacking [ 22 ]. As iron reduction requires anaerobic conditions, effective iron-reducers are expected to inhabit aquatic ecosystems such as pools, lakes and crevices of natural iron-rich canga environments, often characterized by intense iron cycling [ 9 ]. Further iron-rich habitats, specifically those that present cycles of anaerobic and aerobic conditions promoted by flooding and drought regimes, may harbor candidate enrichment culture to induce the biocementation of substrates rich in iron oxides, enabling the large-scale restoration of lateritic crusts in the post-mining landscape.…”