Ambient mineral carbonation of different lithologies of mafic to ultramafic mining wastes/tailings - A comparative study

Four lithologies of the Dumont nickel project were studied for assessing the carbonation capacity in ambient conditions of waste rocks and mineral processing tailings consisting of dunite, peridotite, gabbro, and volcanic materials. Mineral carbonation of these mine waste and tailing minerals is contemplated as a premium solution to permanently trap atmospheric CO2 into solid carbonates using a differential batch carbonation cell and carbonate precipitation columns. The different mafic to ultramafic lithologies of the Dumont nickel project were characterized before and after carbonation by means of X-ray diffraction and thermogravimetry analyses, Fourier transform infrared spectroscopy, optical microscopy, and quantitative evaluation of minerals by scanning electron microscopy. It was found that for identical size fractions, carbonation of rock wastes was quite limited as compared to the tailings. Brucite more abundant in dunite and peridotite substrates was found to be the main reactant involved in carbonation as compared to other less-reactive magnesium silicate minerals. Nesquehonite, the prevalent magnesium carbonate species formed in wet ambient carbonation, remained stable despite prolonged exposition in dry ambient air conditions. Finally, some design recommendations were formulated to overcome the dilemma due to separate storage of high-permeability brucite-poor (lowly reactive) waste rock stockpiles, and finely-ground low-permeability brucite-rich (highly reactive) tailings.