Bioleaching of ultramafic tailings by acidithiobacillus spp. for CO2 sequestration

Our plain-English summary of Bioleaching of ultramafic tailings by acidithiobacillus spp. for CO2 sequestration, by I.M. Power, G.M. Dipple, G. Southam (Environmental Science & Technology, 2010).

The study

• Authors: I.M. Power, G.M. Dipple, G. Southam
• Journal: Environmental Science & Technology
• Published: 2010;44(1):456-62
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Bioleaching experiments using various acid-generating substances, i.e., metal sulfides and elemental sulfur, were conducted to demonstrate the accelerated dissolution of chrysotile tailings collected from an asbestos mine near Clinton Creek, Yukon, Canada. Columns, possessing an acid-generating substance colonized with Acidithiobacillus sp., produced leachates with magnesium concentrations that were an order of magnitude greater than mine site waters or control column leachates. In addition, chrysotile tailings were efficient at neutralizing acidity, which resulted in the immobilization of metals (Fe, Cu, Zn) associated with the metal sulfide mine tailings that were used to generate acid. This suggests that tailings from acid mine drainage environments may be utilized to enhance chrysotile dissolution without polluting "downstream" ecosystems. These results demonstrate that the addition of an acid-generating substance in conjunction with a microbial catalyst can significantly enhance the release of magnesium ions, which are then available for the precipitation of carbonate minerals. This process, as part of a carbon dioxide sequestration program, has implications for reducing net greenhouse gas emissions in the mining industry.

In plain English

This laboratory study tested whether acid-producing bacteria could speed up the breakdown of chrysotile asbestos mine tailings, releasing magnesium that could later lock away carbon dioxide. It did not study human exposure or disease. The authors packed small columns with tailings from the closed Clinton Creek asbestos mine in Yukon, Canada. A one-month trial topped them with ground pyrite or elemental sulfur, with or without Acidithiobacillus bacteria. A one-year trial used bacteria-bearing sulfide tailings from Ontario's Kam Kotia mine or bacteria-colonized sulfur, plus controls without acid-generating material. In the one-month trial, bacteria-colonized sulfur columns released 100 mg of magnesium in total, versus 9.8 mg without bacteria. Over one year, the 8.5% sulfur column released 317 mg, or 14.3% of its magnesium. The year-long control columns averaged 13.7 mg. Metal levels draining from sulfidic-tailings columns were minimal, apart from occasional pulses in the 20% and 25% columns and rising levels late in the 30% column. The authors concluded that acid-generating substances with these bacteria greatly enhanced weathering of the tailings. They noted a drawback: carbonate already in the tailings dissolves during the process.

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 column leaching experiment in two phases (one month and one year)
• Who was studied: Chrysotile tailings and serpentinite collected from the closed Clinton Creek asbestos mine near Dawson City, Yukon, Canada, plus water samples from the mine site; no people were studied
• Exposure: Phase 1 (one month): ground pyrite or elemental sulfur layered onto chrysotile materials, in biotic (with Acidithiobacillus ferrooxidans or Acidithiobacillus thiooxidans) and abiotic versions. Phase 2 (one year): sulfidic tailings from the Kam Kotia mine or elemental sulfur, both containing viable Acidithiobacillus populations, compared with control columns that had no acid-generating substance.
• Main results:
  • Phase 1 (one month): biotic-pyrite columns released 52 mg of magnesium in total (0.26% of the magnesium present), versus 35 mg (0.18%) from abiotic-pyrite columns
  • Phase 1: biotic-sulfur columns released 100 mg (0.50%) of magnesium and abiotic-sulfur columns released 9.8 mg (0.05%)
  • Phase 1 control columns (chrysotile tailings, ground serpentinite, acid-washed tailings) released 1.1 mg, 0.2 mg and 0.03 mg of magnesium
  • Phase 1: drained liquid from all these columns had pH above 8.5, which the authors took as showing that the chrysotile materials neutralized the acid
  • The authors explained the faster dissolution, compared with a published rate model, as an effect of lower pH
  • Phase 2 (one year): columns with 20, 25 and 30% sulfidic tailings released 132 mg (5.96%), 139 mg (6.28%) and 224 mg (10.1%) of magnesium
  • Phase 2: columns with 6.5, 8.5 and 10.5% sulfur released 55 mg (2.48%), 317 mg (14.3%) and 261 mg (11.8%) of magnesium
  • Phase 2: the two control columns without acid-generating substance released an average of 13.7 mg (0.62%) of magnesium over the year
  • Iron, copper and zinc levels in drained liquid were minimal in the sulfidic-tailings columns
  • The 20% and 25% sulfidic-tailings columns showed no rising trend in metals but had occasional pulses of relatively high metal concentrations; the 20% column had pulses of 103, 4.8 and 7.2 mg/L (iron, copper and zinc combined) in weeks 4, 26 and 42
  • The 30% sulfidic tailings column showed declining pH and rising metal levels in later weeks
  • Magnesium concentrations in drained liquid from columns with bacteria and acid-generating substance were at least ten times higher than in controls and Clinton Creek site waters
  • Scaling up the 8.5% sulfur result, the authors estimated that 125 kt of carbon (458 kt CO2) could be stored in the first year if all leached magnesium were precipitated as hydromagnesite
• The authors' conclusion: The authors concluded that acid-generating substances used with Acidithiobacillus bacteria greatly enhanced weathering of the chrysotile tailings. They also concluded this could help ultramafic mine tailings serve as carbon sinks.
• Limitations the authors state:
  • Carbonate already present in the tailings is dissolved during leaching, a drawback for carbon storage
  • Iron-rich precipitates in sulfidic-tailings columns may coat surfaces and reduce magnesium silicate dissolution
  • The Clinton Creek tailings, with their accumulated secondary carbonate, may not be suitable for bioleaching
  • Irregular magnesium results may reflect uneven tailings and channelled water flow in the columns

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Clinton Creek property, northwest of Dawson, Yukon

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Tailings, Chrysotile, Carbonate Mineral.

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