Activation of magnesium rich minerals as carbonation feedstock materials for CO 2 sequestration

Abstract

Mineral carbonation, the reaction of magnesium-rich minerals such as olivine and serpentine with CO 2 to form stable mineral carbonates, is a novel and promising approach to carbon sequestration. However, the preparation of the minerals prior to carbonation can be energy intensive, where some current studies have been exploring extensive pulverization of the minerals below 37 μm, heat treatment of minerals up to 650 °C, prior separation of CO 2 from flue gases, and carbonation at high pressures, temperatures and long reaction times of up to 125 atm, 185 °C and 6 h, respectively. Thus, the objective of the mineral activation concept is to promote and accelerate carbonation reaction rates and efficiencies through surface activation to the extent that such rigorous reaction conditions were not required. The physical activations were performed with air and steam, while chemical activations were performed with a suite of acids and bases. The parent serpentine, activated serpentines, and carbonation products were characterized to determine their surface properties and assess their potential as carbonation minerals. The results indicate that the surface area of the raw serpentine, which is approximately 8 m 2/g, can be increased through physical and chemical activation methods to over 330 m 2/g. The chemical activations were more effective than the physical activations at increasing the surface area, with the 650 °C steam activated serpentine presenting a surface area of only 17 m 2/g. Sulfuric acid was the most effective acid used during the chemical activations, resulting in surface areas greater than 330 m 2/g. Several of the samples produced underwent varying degrees of carbonation. The steam activated serpentine underwent a 60% conversion to magnesite at 155 °C and 126 atm in 1 h, while the parent sample only exhibited a 7% conversion. The most promising results came from the carbonation of the extracted Mg(OH) 2 solution, where, based on the amount of magnesium recovered in the precipitate after the 3.5 h reaction, the carbonation efficiency was estimated to be at least 53%. Reaction products included several hydrated magnesium carbonate compounds. The carbonation reaction was conducted at ambient temperature, 20 °C, and low pressure, 45 atm.