Bioleaching of Ultramafic Tailings by Acidithiobacillus spp. for CO 2 Sequestration

Application of acid-generating materials colonized by Acidithiobacillus spp. can dramatically enhance magnesium leaching from silicate minerals.

“One possibility is the application of acid-generating materials that are colonized by Acidithiobacillus spp., which can dramatically enhance magnesium leaching from silicate minerals [82,83] (Figure 3).”

Not all tailings will be suitable for passive carbonation acceleration strategies; for example, tailings that are highly carbonated or those that contain abundant sulfides.

“Importantly, not all tailings will be suitable for these strategies; for example, tailings that are highly carbonated [82] or those that contain abundant sulfides [98].”

In an active mining operation, it is possible to apply ex-situ carbonation to fresh tailings, which are more active for carbonation than weathered ones due to minimal authigenic carbonate content.

“In an active mining operation, it is possible to apply the ex-situ carbonation to fresh tailings, which are more active for carbonation than weathered ones due to minimal authigenic carbonate content [82].”

This biogeochemical process has potential to produce stable, long-term sinks for atmospheric CO2.

“This biogeochemical process has potential to produce stable, long-”

Carbonate minerals are stable and long-lived, making them an ideal sink for surplus atmospheric CO2.

“The stability and longevity of carbonate minerals make them an ideal sink for surplus atmospheric”

Biotic and abiotic acceleration strategies have proven effective in laboratory-scale studies.

“Although these strategies have proven effective in laboratory-scale studies (e.g., [13,15,19,28,32,33]), pilot projects are crucially needed to evaluate strategies for accelerating carbon mineralization, which if successful and cost effective could be incorporated into TSF design with the purpose of sequestering CO 2 .”

The Mg concentration of water draining from Clinton Creek chrysotile tailings is approximately 160 mg/L compared to the natural background Mg concentration in local creek water of approximately 70 mg/L.

“For example, the Mg concentration of water draining from Clinton Creek chrysotile tailings is ~160 mg/L in comparison to the natural background Mg concentration in local creek water of ~70 mg/L [13].”

Mg concentrations in leachates from columns containing metal sulfides generally declined over the year, likely owing to passivation of chrysotile surfaces by iron hydroxides, whereas Mg concentrations generally increased in columns using elemental sulfur, possibly owing to increasing populations of A. thiooxidans.

“Mg concentrations in leachates generated by those columns containing metal sulfides generally declined over the year, likely owing to the passivation of chrysotile surfaces by iron hydroxides [13], whereas Mg concentrations generally increased in columns using elemental sulfur, possibly owing to increasing populations of A. thiooxidans.”

In comparison to controls lacking microbes, leachate waters from biotic columns with ground pyrite had Mg concentrations up to 26% greater, and columns using elemental sulfur had Mg concentrations up to 580% greater.

“In comparison to controls lacking microbes, leachate waters from biotic columns with ground pyrite had Mg concentrations that were up to 26% greater, and in columns using elemental sulfur Mg concentrations were up to 580% greater (Figure 5b) [13].”

These same procedures could be applied to a bioleaching scenario to ensure that the neutralization potential of tailings is not exceeded.

“These same procedures could be applied to a bioleaching scenario to ensure that the neutralization potential of tailings is not exceeded [13].”

A potential strategy for cultivating acid-generating microbes in tailings storage facilities involves amending tailings with an acid-generating substance, such as waste sulfides or elemental sulfur.

“A potential strategy for cultivating these microbes in TSFs involves amending tailings with an acid-generating substance, such as waste sulfides or elemental sulfur [13].”

In year-long trials, 10% to 14% of the Mg contained within chrysotile was leached from columns using acid-generating substances colonized by Acidithiobacillus spp.

“In year-long trials (Figure 4c,d), 10% to 14% of the Mg contained within chrysotile was leached from the columns using acid-generating substances colonized by Acidithiobacillus spp.[13].”

Bioleaching columns amended with elemental sulfur have been shown to release up to 14% of the available Mg in the columns with leachate concentrations of up to about 9500 mg/L.

“Bioleaching columns amended with elemental sulfur have been shown to release up to 14% of the available Mg in the columns with leachate concentrations of up to ~9500 mg/L (Figure 4d) [13].”

Power et al. demonstrated that greater than 14% of the Mg in experimental bioleaching columns could be leached.

“Power et al. [13] demonstrated that greater than 14% of the Mg in experimental bioleaching columns could be leached, assuming that only a year's worth of tailings were leached and that the Mg was carbonated to form hydromagnesite, then 480 kt CO 2 or 124% of mine emissions could be offset.”

If only a year's worth of tailings were leached and the Mg was carbonated to form hydromagnesite, then 480 kt CO2 or 124% of mine emissions could be offset.

“Power et al. [13] demonstrated that greater than 14% of the Mg in experimental bioleaching columns could be leached, assuming that only a year's worth of tailings were leached and that the Mg was carbonated to form hydromagnesite, then 480 kt CO 2 or 124% of mine emissions could be offset.”