Carbon Sequestration Kinetic and Storage Capacity of Ultramafic Mining Waste

Mineral carbonation of ultramafic rocks provides an environmentally safe and permanent solution for CO2 sequestration. In order to assess the carbonation potential of ultramafic waste material produced by industrial processing, we designed a laboratory-scale method, using a modified eudiometer, to measure continuous CO2 consumption in samples at atmospheric pressure and near ambient temperature. The eudiometer allows monitoring the CO2 partial pressure during mineral carbonation reactions. The maximum amount of carbonation and the reaction rate of different samples were measured in a range of experimental conditions: humidity from dry to submerged, temperatures of 21 and 33 degrees C, and the proportion of CO2 in the air from 4.4 to 33.6 mol %. The most reactive samples contained ca. 8 wt % CO2 after carbonation. The modal proportion of brucite in the mining residue is the main parameter determining maximum storage capacity of CO2. The reaction rate depends primarily on the proportion of CO2 in the gas mixture and secondarily on parameters controlling the diffusion of CO2 in the sample, such as relative saturation of water in pore space, Nesquehonite was the dominant carbonate for reactions at 21 degrees C, whereas dypingite was most common at 33 degrees C.