Strategising the bioremediation of Brazilian iron ore mines

Iron ore mine remediation in Brazil presents a unique challenge, distinct from remediation efforts of other lateritic deposits, as a result of the lack of soil. These unique rupestrian (rock associated) ecosystems, including a suite of naturally rare and endemic plant species, are associated with the ironstone (canga) outcrops that commonly cap iron ore mines. To reinstate native ecosystems postmining, developing a substrate similar to the iron-rich cap rock is required. These iron-rich duricrusts have evolved by the ongoing dissolution and re-precipitation of iron oxide minerals, continuously forming new iron cements. Biological processes respond to fluctuating redox conditions that occur in micrometre-scale anoxic/reducing conditions within a broadly oxidizing environment. Reductive mineral dissolution is critical to the initiation of iron cycling that contributes to the evolution and stabilization of these duricrusts. Understanding the mechanisms that contributes to natural iron cement formation allows for the development of novel biotechnologies that aim to accelerate these processes. These biotechnologies would offer an environmentally friendly, circumneutral strategy for iron ore mine remediation. Successful remediation programmes would aim to accelerate the formation of iron cements necessary to stabilize crushed materials on hillslopes, restore a functional hydrology and regenerate a substrate similar to an iron-rich duricrust for revegetation using native species. Here, we review recent advances in understanding the biological processes that contribute to canga evolution and their implications for the remediation of iron ore mines in the future.