Poster Presentation Australian Microbial Ecology 2019

Canga lake-edge field characterisation: inspiration for iron ore mine remediation (#155)

Alan Levett 1 , Emma J Gagen 1 , Anat Paz 1 , Paulo Vasconcelos 1 , Gordon Southam 1
  1. Univeristy of Queensland, St. Lucia, QLD, Australia

Iron ore provinces in tropical regions, including Brazil and Australia, are blanketed by an iron-rich duricrust, referred to as canga. To extract the iron ore, the canga must be removed, destroying the natural landscape and the associated biome. Iron ore remediation must therefore target the regeneration of the iron-rich blanket to provide a substrate for revegetation. Canga duricrusts are some of the longest-lived continuously exposed surfaces on Earth, evolving via the dissolution and precipitation of iron oxide minerals, mediated by the biome [1]. At a lake-edge near the S11D mine in the State of Pará, Brazil, canga appeared to form relatively quickly on a slope dipping 20 – 30°. Solutions flowing into the lake contained approximately 5 ppm Fe2+(aq) and supported abundant microbial biofilms associated with fresh iron oxide precipitates. This highlighted the role of microorganisms in the dissolution of otherwise stable iron oxide minerals and the importance of water to transport renewable iron. These canga cements also contained microfossils, demonstrating microbial involvement in the formation of the ferruginous cements. Inspired by this natural system, the ‘lake-edge’ environment was replicated in the laboratory to optimise the conditions for biogeochemical iron cycling, which was then used to accelerate iron oxide cementation. For the treatment experiment, microbially-driven iron oxide dissolution was promoted in a reactor and the solutions from the reactor were allowed to flow over crushed canga. Water chemistry and the microbial biome for the treatment were monitored and compared with the ultrapure water-only control for the duration of the six month experiment before substrate hardness was measured after a two week drying period. This experiment provides promising results that microbially-driven iron oxide cycling may provide a novel biotechnological tool for iron ore mine remediation, accelerating slope stabilisation and the regeneration of a substrate akin to natural canga for revegetation programmes.

  1. 1. Monteiro HS, Vasconcelos, PM, Farley (2018) A combined (U-Th)/He and cosmogenic 3He record of landscape armouring by biogeochemical iron cycling