Presented paper

IMWA2019 Students work

Carbonation Of Magnesium Silicates In Mine Waste: Field Scaled Testing Methods To Assess The Duel Opportunity For Carbon Capture And AMD Mitigation

Savage, Rhys (1); Pearce, Steven (2); Barnes, Andrew (1); Sapsford, Devin (3); Renforth, Phil (3)
1: Geochemic Ltd, United Kingdom; 2: Mine Environment Management Ltd, United Kingdom; 3: Cardiff University, United Kingdom

The mineral carbonation process, where magnesium carbonates can be formed from the weathering of silicates such as olivine in the presence of CO2, has been widely recognised as a potentially significant in the sequestering of large amounts of carbon dioxide into mine wastes.

Less-commonly studied but also of significance is the production of alkalinity from the process, which may offer significant mitigation of AMD discharges from these mine wastes. Because of the increasing need to consider carbon reduction as part of energy intensive processes such as mining, and the potential re-purposing of sites post closure, the concept of carbon capture within mine waste assessment has gained renewed emphasis. Previous authors have developed a number of novel methods to assess carbonation potential of the prospective materials, however, those are generally very site-specific and therefore not easily transferable between sites. To date, there has been limited effort to develop a standard method that can be widely used for the assessment of carbonation potential of mine waste at standard temperature and pressure. This makes such studies highly-specialist and prohibitively-expensive, limiting their implementation despite their potential benefit. To address this, we devised robust practical methods that can be carried out at the laboratoryscale, at relatively low-cost and with the potential to be readily standardised as well as scaled to field conditions.

Two main carbonation test experiments have been developed: bespoke column reactors to assess changes in pore water geochemistry as a result of the carbonation process and adjusted WTW Oxitop® consumption vessels to assess the kinetic rate of carbonation reactions. These tests have allowed both the rapid assessment of the carbonation rate of different material types; and the assessment of the key rate limiting factors of the process related to site conditions such as moisture content, particle size and temperature. The testing process has been used to determine both the potential sequestration rate and acidity buffering potential of the carbonation process within ultra-mafic sulfidic waste rock and tailings materials at a large nickel mine in Finland. The method has wider applicability to other sites given the low cost and relative simplicity of the testing process.