Subarctic Weathering of Mineral Wastes Provides a Sink for Atmospheric CO₂

Abstract

The mineral waste from some mines has the capacity to trap and store CO(2) within secondary carbonate minerals via the process of silicate weathering. Nesquehonite [MgCO(3)·3H(2)O] forms by weathering of Mg-silicate minerals in kimberlitic mine tailings at the Diavik Diamond Mine, Northwest Territories, Canada. Less abundant Na- and Ca-carbonate minerals precipitate from sewage treatment effluent deposited in the tailings storage facility. Radiocarbon and stable carbon and oxygen isotopes are used to assess the ability of mine tailings to trap and store modern CO(2) within these minerals in the arid, subarctic climate at Diavik. Stable isotopic data cannot always uniquely identify the source of carbon stored within minerals in this setting; however, radiocarbon isotopic data provide a reliable quantitative estimate for sequestration of modern carbon. At least 89% of the carbon trapped within secondary carbonate minerals at Diavik is derived from a modern source, either by direct uptake of atmospheric CO(2) or indirect uptake though the biosphere. Silicate weathering at Diavik is trapping 102-114 g C/m(2)/y within nesquehonite, which corresponds to a 2 orders of magnitude increase over the background rate of CO(2) uptake predicted from arctic and subarctic river catchment data.

Strategizing Carbon-Neutral Mines: A Case for Pilot Projects

“…These mines have formed the basis of field, laboratory, and geochemical modeling studies aimed at developing the capacity to better utilize mine wastes as carbon sinks [11,13,[15][16][17][18][19][20][21]28,[37][38][39][40].…”

“…Most of the residual kimberlite waste (2 Mt/year; dominantly lizardite and forsterite) is piped as slurry into a natural basin used as a TSF [17]. The tailings are partially submerged in a pond in the center of the basin (Figure 1b).…”

“…We refer to this process as passive carbonation because it occurs without human mediation and is not an intended outcome of the TSF design. Passive carbonation has been documented at Clinton Creek [18,20], Diavik [17,21], and Mount Keith [11,19] as well as other abandoned and active mine sites in Canada, United States, Australia, and Norway [24,26,30,42].…”

“…Specifically, numerous studies have explored the use of ultramafic mine wastes as a potentially valuable feedstock for carbon mineralization [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Ultramafic and mafic mines generate vast quantities of mine tailings that offer a readily available, fine-grained feedstock for carbonation.…”

“…Ultramafic and mafic mines generate vast quantities of mine tailings that offer a readily available, fine-grained feedstock for carbonation. As an indication of their reactivity, passive carbonation of ultramafic tailings has been documented at several sites under normal mining conditions [11,17,18,20,21,24,26,30]. Tailings storage facilities (TSFs) for ultramafic and mafic mine wastes are typically designed solely to hold tailings and recycle process water.…”