Prospects for CO2 mineralization and enhanced weathering of ultramafic mine tailings from the Baptiste nickel deposit in British Columbia, Canada

The Baptiste deposit is located within the Decar nickel district in British Columbia, Canada and is a promising candidate for a CO2 sequestration demonstration project. The deposit contains awaruite (nickel-iron alloy) hosted in an ultramafic complex, which is dominated by serpentine [Mg3Si2O5(OH)(4); similar to 80 wt.%] and contains reactive brucite [Mg(OH)(2); 0.6-12.6 wt.%]. Experiments were conducted using metallurgical test samples and pulps from cores with the aim of determining the potential for this deposit to sequester CO2 via direct air capture of atmospheric CO2 and carbonation using CO2-rich gas. The experimental direct capture rate was 3.5 kg CO2/m(2)/yr and would sequester 17 kt CO2/yr based on year-round reaction and when extrapolated to the scale of the proposed tailings facility (5 km(2)). This rate can be increased by similar to 5 times (19 kg CO2/m(2)/yr) when aerating the tailings and would offset CO2 emissions by 95 kt CO2/yr (19-25% offset of projected CO2 emissions). Experimental carbonation rates with 10% CO2 gas could achieve offsets of up to 210 kt CO2/year (42-53% CO2 offset) based on 1 h reaction times and consumption of 0.8 wt% brucite if present. Targeting brucite-rich ore zones and optimizing CO2 delivery would likely lead to greater CO2 offsets.