Abstract
Global efforts to combat climate change call for methods to capture and store CO2. Meanwhile, the global transition away from fossil energy will result in increased production of tailings (i.e., wastes) from the mining of nickel and platinum group metals (PGMs). Through carbon mineralization, CO2 can be permanently stored in calcium- and magnesium-bearing mine tailings. The Stillwater mine in Nye, Montana produces copper, nickel, and PGMs, along with 1 Mt of tailings each year. Stillwater tailings samples have been characterized, revealing that they contain a variety of mineral phases, most notably Ca-bearing plagioclase feldspar. Increases in inorganic carbon in the tailings and ion concentration in the tailings storage facilities suggest carbonation has taken place at ambient conditions over time within the tailings storage facilities. Two experiments were performed to simulate carbon mineralization at ambient temperature and pressure with elevated CO2 concentration (10% with N2), revealing that less than 1% of the silicate-bound calcium within the tailings is labile, or easily released from silicate structures at low-cost ambient conditions. The Stillwater tailings could be useful for developing strategies of waste management as production of nickel and PGM minerals increases during the global transition away from fossil energy, but further work is needed to develop a process that can realize their full carbon storage potential.
Highlights
Published: 5 August 2021Climate mitigation efforts are accelerating to avoid 2 ◦ C warming by 2100
Total inorganic carbon is presented as % C (g C/g sample)
Based on the observation of liquids from the two tailings storage facilities, it is clear that the Stillwater tailings are capable of dissolving and releasing alkaline cations that can react with dissolved CO2 at ambient conditions
Summary
Published: 5 August 2021Climate mitigation efforts are accelerating to avoid 2 ◦ C warming by 2100. Carbon-free power does not address “hard-to-avoid” emissions in the industrial and transportation sectors. The global energy transition will require increases in mineral production by up to 900% in the electric sector, coupled with sharp increases in the production of mine wastes [2]. To address the problem of “hard-to-avoid” emissions, technologies are being developed and deployed that can capture CO2 from industrial flue gases [3] or remove CO2 directly from the air [4]. Both of these technologies require a method of safe and reliable storage to prevent the CO2 from being re-emitted. Carbon mineralization is a process that reacts CO2 with alkaline material to produce solid carbonate minerals, satisfying the need for safe CO2 storage [5] that is permanent unless in low pH conditions
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