Microbially Accelerated Carbonate Mineral Precipitation as a Strategy for in Situ Carbon Sequestration and Rehabilitation of Asbestos Mine Sites

Our plain-English summary of Microbially Accelerated Carbonate Mineral Precipitation as a Strategy for in Situ Carbon Sequestration and Rehabilitation of Asbestos Mine Sites, by J. McCutcheon, S. Wilson, G. Southam (Environmental Science & Technology, 2016).

The study

• Authors: J. McCutcheon, S. Wilson, G. Southam
• Journal: Environmental Science & Technology
• Published: 2016;50(3):1419-27
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A microbially accelerated process for the precipitation of carbonate minerals was implemented in a sample of serpentinite mine tailings collected from the abandoned Woodsreef Asbestos Mine in New South Wales, Australia as a strategy to sequester atmospheric CO2 while also stabilizing the tailings. Tailings were leached using sulfuric acid in reaction columns and subsequently inoculated with an alkalinity-generating cyanobacteria-dominated microbial consortium that was enriched from pit waters at the Woodsreef Mine. Leaching conditions that dissolved 14% of the magnesium from the serpentinite tailings while maintaining circumneutral pH (1800 ppm, pH 6.3) were employed in the experiment. The mineralogy, water chemistry, and microbial colonization of the columns were characterized following the experiment. Micro-X-ray diffraction was used to identify carbonate precipitates as dypingite [Mg5(CO3)4(OH)2·5H2O] and hydromagnesite [Mg5(CO3)4(OH)2·4H2O] with minor nesquehonite (MgCO3·3H2O). Scanning electron microscopy revealed that carbonate mineral precipitates form directly on the filamentous cyanobacteria. These findings demonstrate the ability of these organisms to generate localized supersaturating microenvironments of high concentrations of adsorbed magnesium and photosynthetically generated carbonate ions while also acting as nucleation sites for carbonate precipitation. This study is the first step toward implementing in situ carbon sequestration in serpentinite mine tailings via microbial carbonate precipitation reactions.

In plain English

This laboratory study tested whether microbes could speed up magnesium carbonate formation in chrysotile asbestos mine tailings from the abandoned Woodsreef Asbestos Mine, New South Wales, Australia. The authors first soaked tailings in sulfuric acid at four strengths; the weakest, 0.04 M, released 1786 ppm of magnesium and alone ended near neutral (pH 6.3). Intact fibers remained in all leached samples.

In a column experiment, three acid-leached columns were inoculated with a cyanobacteria-dominated microbial community from a mine pit lake; one was left uninoculated as a control. After 4 weeks, inoculated columns formed a solid surface crust of magnesium carbonate minerals around the cyanobacteria. The control formed no consolidated crust and far fewer carbonates.

In what they called a simplified scenario, the authors estimated CO2 storage of 137 g/m2 (dypingite only) or 478 g/m2 (including biomass) for the inoculated columns. The control's 27 g/m2 was calculated for pyroaurite, which may have predated the experiment. The authors concluded this was a first step toward stabilizing chrysotile mine waste, expecting a crust to limit fiber transport by wind and water.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment: an acid leaching trial on tailings samples, followed by a reaction-column experiment comparing microbially inoculated columns with an uninoculated control
• Who was studied: Serpentinite (chrysotile and lizardite) mine tailings from the abandoned Woodsreef Asbestos Mine, New South Wales, Australia, a chrysotile mine operated 1971 to 1983. The leaching trial used five flasks of 5 g each. The column experiment used five columns of 90 g each: one sampled after leaching, three inoculated, and one uninoculated tailings control.
• Exposure: Leaching trial: tailings treated with dilute sulfuric acid (0.04, 0.08, 0.15 and 0.30 M) or deionized water. Columns: leached for 6 weeks with 0.022 M sulfuric acid, then three columns were inoculated with a cyanobacteria-dominated microbial consortium grown from pit Lake 4 at the mine and grown for 4 weeks.
• Main results:
  • In the leaching trial, 0.04, 0.08, 0.15 and 0.30 M sulfuric acid released 1786, 3407, 6848 and 9525 ppm magnesium, respectively. The deionized water control released 30 ppm.
  • Only the 0.04 M system reached a circumneutral final pH (6.3) suitable for the cyanobacteria.
  • All leaching systems still contained intact fibers at the end of the leaching experiment.
  • After 4 weeks, the inoculated columns showed extensive magnesium carbonate precipitation associated with filamentous cyanobacteria, forming a surface crust. Micro X-ray diffraction of the inoculated column surfaces identified chrysotile, dypingite and partially dehydrated hydromagnesite; white grains were confirmed as nesquehonite.
  • The uninoculated control column did not form a consolidated crust. Its magnesium carbonate precipitates were far less abundant than in the inoculated columns.
  • Water washed through the columns after the experiment contained 397 ppm magnesium (inoculated column) and 449 ppm (tailings control), compared with about 1786 ppm from the leaching trial. The authors suggested much of the leached magnesium was consumed by carbonate precipitation.
  • Estimated CO2 stored per unit area: 137 g/m2 for the inoculated column (dypingite only), 478 g/m2 for the inoculated column (dypingite plus biomass), and 27 g/m2 for the tailings control column (pyroaurite).
  • The authors stated that the pyroaurite identified in the control column may have been present in the tailings before the experiment, or alternatively may have formed during it.
• The authors' conclusion: The authors concluded that the study is a successful first step toward in situ stabilization of chrysotile mine waste using a microbial carbon sequestration strategy. They stated that cementing the tailings would limit transport of asbestos fibers offsite by wind and water; this was their expectation, not something measured in the experiment.
• Limitations the authors state:
  • Residual pore water could not be collected directly from the columns, so readily soluble material was recovered by washing water through one inoculated column and the control.
  • The CO2 storage values reflect a simplified scenario.
  • Leaching and reacting tailings at field scale would be challenging in the arid environment at Woodsreef.
  • Carbon stored in biomass does not last as long as carbon stored in minerals.

Topics

Medical terms in this study, explained in our Lexicon: Carbonate Mineral, Serpentinite, Tailings, Woodsreef Mine, Mineralogy, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM).

Related studies

• Direct gas-solid carbonation of serpentinite residues in the absence and presence of water vapor: a feasibility study for carbon dioxide sequestration — S.P. Veetil, L.C. Pasquier, et al. (2015)
• Modern carbonate microbialites from an asbestos open pit pond, Yukon, Canada — I.M. Power, S. Wilson, et al. (2011)
• Carbon dioxide sequestration using NaHSO4 and NaOH: A dissolution and carbonation optimisation study — A. Sanna, L. Steel, et al. (2017)
• Reaction mechanism for the aqueous-phase mineral carbonation of heat-activated serpentine at low temperatures and pressures in flue gas conditions — L.C. Pasquier, G. Mercier, et al. (2014)
• Lung mineral fibers of former miners and millers from Thetford-Mines and asbestos regions: a comparative study of fiber concentration and dimension — A. Nayebzadeh, A. Dufresne, et al. (2001)
• Investigative studies for the use of an inactive asbestos mine as a disposal site for asbestos wastes — E. Gidarakos, K. Anastasiadou, et al. (2008)

Browse more research in Environmental Science & Technology, or return to medical research.