Giga Metals is actively pursuing carbon sequestration through mineral carbonation.
Introduction to Mineral Carbonation
The Turnagain deposit host minerals include olivine – Mg2SiO4, serpentine - Mg3Si2O5(OH)4, and brucite – Mg(OH)2. These minerals naturally carbonate, as shown below in simplified form for serpentine and brucite. The actual reaction pathways involve many intermediate compounds; kinetic limitations at lower temperatures favour intermediates on shorter timescales.
Serpentine: Mg3Si2O5(OH)5 + 3 CO2 → MgCO3 + 2 SiO2 + 2 H2O
Brucite: Mg(OH)2 + CO2 → MgCO3 + H2O
Carbonation in natural river basins in northern climates has been shown to proceed at up to 0.1 t/ha/y, while the tailings from existing and past ultramafic mines have shown dramatically elevated carbonation rates of up to 62 t CO2/ha/y in similar climactic areas. The increase is due to both reduced particle size and deposition methods providing greater surface areas exposed to atmospheric exchange.
The ultimate absorption capacity of commercial mine tailings is dependent on many factors, including mineralogy, particle size, deposition methodology, tailings management practices, and strength of CO2 source (ambient vs enriched). Many active carbonation schemes have been proposed which could possibly sequester up to 0.4 t CO2/t mineral, such as thermal activation and operation at elevated CO2 pressure and temperature. Another approach is injection of CO2 into underground rock formations, such as the CarbFix process operating in Iceland today, which has permanently sequestered over 65,000 tonnes of CO2.
A side benefit of carbonation of tailings is an increase in physical strength of the material through the cementation resulting from reactions with carbon dioxide which can bind mineral grains together, adding stability and dust suppression to the deposited tailings. This has been shown to be potentially significant, with unconfined compressive strength increasing measurably indicating a reduction in risk from ultramafic tailings management facilities which are operated to maximize carbon sequestration. Reduced tailings risk is a welcome benefit in today’s tailings-conscious world.
Sequestration at Turnagain
Giga Metals continues to fund research at the University of British Columbia to explore the carbon sequestration potential of Turnagain materials. Without a high concentration CO2 source in the area, achieving near total carbonation at Turnagain will be impossible. However, passive carbonation provides a low-cost approach to achieving increased carbonation rates from available materials. Passive carbonation mimics natural processes but increases the exposure of the minerals to the reactive CO2. The research that Giga Metals is supporting is focused on understanding the passive carbonation better, including opportunities to maximize the benefits.
Initial test results on Turnagain host mineral samples have been positive, with stable sequestration rates of 27 to 34 t/ha/y. These values are in the range demonstrated for other similar commercial mines and are of the right scale to provide a pathway to net-zero nickel mining at Turnagain. Coupled with an electric mine haul fleet using clean BC hydroelectric power, Turnagain’s tailings management facility could absorb enough CO2 to completely offset its Scope 1 and 2 emissions.
Giga Metals continues to support the broader activities of the research being led by Dr. Greg Dipple at the CarbMinLab. This research is mapping the distribution and volume of ultramafic rocks in British Columbia and assessing their potential to capture and store the greenhouse gas (GHG) carbon dioxide (CO2) through a naturally occurring chemical reaction that removes CO2 from the atmosphere and safely stabilizes it long-term in benign carbonate minerals. British Columbia has large quantities of the active materials that could potentially support large-scale sequestration activities.
Watch the project update below to see a video demonstration of actual CO2 reduction:
Please get in touch if you would like more information on our carbon sequestration efforts.