| Anthropogenic greenhouse gas emissions may be offset by sequestering carbon dioxide (CO2) through the carbonation of silicate minerals. In the natural environment, microbes can aid in silicate dissolution and carbonate precipitation, and therefore, can potentially be used to catalyze carbonation reactions. The hydromagnesite playas of Atlin, British Columbia, Canada provide a natural model to examine mineral carbonation on a watershed scale. At near surface conditions, microorganisms are involved in weathering of bedrock and precipitation of carbonate minerals, which results in CO2 sequestration. Regions with ultramafic bedrock, such as Atlin, represent the best potential sources of feedstocks for mineral carbonation. Experimental evidence demonstrates that microbial mats in the Atlin wetland create ideal conditions for biologically induced precipitation of dypingite [Mg5(CO3)4(OH) 2·5H2O] and have presumably played a significant role in the development of this natural carbonate playa. This biogeochemical process represents an important link between the biosphere and the inorganic carbon pool.;Leaching experiments were conducted using mine tailings from two active mines, Mount Keith nickel mine in Western, Australia and the Diavik diamond mine in the Northwest Territories, Canada. Experiments showed that phototrophs were able to cause alkalization and induce carbonate precipitation from waters produced from the leaching of tailings.;Keywords: carbon dioxide sequestration, mineral carbonation, mine tailings, carbonate, hydromagnesite, cyanobacteria, bioleaching, and microbialite;Bioleaching typically involves the extraction of metals from sulphidic ores using bacteria, but may also be applied to ultramafic tailings. Experimental columns, possessing ultramafic tailings collected from an abandoned mine near Clinton Creek, Yukon, Canada and an acid-generating substance, i.e., metal sulphides and elemental sulphur, colonized with Acidithiobacillus sp., produced leachates with magnesium concentrations that were an order of magnitude greater than mine site waters. These results demonstrate that bioleaching can significantly enhance the release of magnesium ions, which are then available for the precipitation of carbonate minerals. At the Clinton Creek site, carbonate structures, called thrombolites, were discovered in the open pit pond. The low sedimentation rate, high calcification rate, and noticeably low microbial growth rate appear to result in the formation of microbialites with a thrombolitic texture. These thrombolites are extremely young and have important implications for understanding microbialite formation in the geological past and carbonate precipitation at mine sites. |
