Commentary: Ex Situ Aqueous Mineral Carbonation

Abstract

CO2 conversion to calcium and magnesium carbonates has garnered considerable attention since it is a thermodynamically downhill pathway to safely and permanently sequester large quantities of CO2. This seminal work performed at The National Energy Technology Laboratory in Albany (NETL-Albany) reports the conversion of calcium-and magnesium-bearing silicate minerals, such as olivine [(Mg, Fe)2SiO4], wollastonite (CaSiO3), and serpentine [Mg3Si2O5(OH)4], as they are reacted with CO2 in an aqueous environment to form magnesium or calcium carbonates. This paper discusses various pretreatment methods of the starting materials, such as grinding or heat treatment of hydroxylated Mg silicates, to enhance the reaction kinetics. The effects of various chemical additives (e.g., NaCl and NaHCO3), and reaction parameters, such as temperature, pressure, and reaction time, on the conversion are investigated. Feasibility assessments and energy and economic analyses of the direct carbonation of calcium-and magnesium-bearing minerals are presented.The key contributions of this study are the identification of the optimal conditions for the carbonation of olivine (185°C, P 15 atm, distilled water), and heat-treated serpentine (155°C, P 15 atm CO 2 0 = , 1.0M⋅NaCl + 0.64M⋅NaHCO3). High extents of carbonation of 49.5, 81.8, and 73.5% of olivine, wollastonite, and heat-treated serpentine, respectively, achieved within an hour of reacting with CO2 in an aqueous environment are reported. The identification of the optimal reaction conditions to achieve the rapid conversion of calcium-and magnesium-bearing silicate minerals to carbonates has spurred a significant global scientific interest in mineral carbonation as a promising technology for CO2 conversion and storage with the potential reuse of carbonates.In particular, this work has found unique relevance for ex situ and in situ carbon mineralization. In ex situ mineral carbonation, CO2 is converted to carbonates in engineered processes where there is considerable control over the reaction conditions. In in situ mineral carbonation, CO2 is injected into geological formations containing calcium-and magnesium-bearing minerals and rocks with the aim toward natural carbon mineralization over time. Predicting the fate of CO2 injected into geological formations containing these rocks and minerals and developing chemical processes for converting CO2 to carbonates require a fundamental understanding of the kinetics of mineral carbonation and the corresponding morphological changes in materials. Thus, more recent studies have focused on understanding the carbon mineralization behavior via direct carbonation (Bonfils et al., 2012;Gadikota et al., 2014a; Eikeland et al., 2015) and indirect carbonation, which involves the dissolution of minerals (Park et al

Quantitative Review of Olivine Carbonation Kinetics: Reactivity Trends, Mechanistic Insights, and Research Frontiers

“…Olivine, ranging from the magnesium-rich end-member forsterite (Mg 2 SiO 4 ) to the iron-rich end-member fayalite (Fe 2 SiO 4 ), is a primary source of carbonation potential within these host rock lithologies. In particular, forsterite is a key constituent of upper mantle and lower crustal rocks, and given its relatively fast dissolution rate, forsterite has received a considerable amount of attention for its geologic and ex situ , carbon mineralization by reaction with CO 2 /H 2 O fluids to form magnesium carbonates.…”

Direct Olivine Carbonation: Optimal Process Design for a Low-Emission and Cost-Efficient Cement Production

“…Several experimental studies have determined beneficial operating conditions for the direct mineral carbonation of olivine. ,,− These studies assessed the conversion rates depending on the temperature, pressure, additives, and particle size of the feedstock material. According to Gerdemann et al, optimal operating conditions for direct olivine carbonation are at a temperature and pressure of 185 °C and 150 bar, respectively .…”

“…Therein, we formulated dynamic mole balances and applied nonideal thermodynamics for the species interaction. Hence, the influence of the operating conditions of the reactor, i.e., temperature, pressure, particle size, and residence time, is extensively evaluated with respect to the reactor performance, both experimentally and computationally. ,,− However, these process design choices require consideration of the overall mineral carbonation process to obtain (1) favorable operating conditions for (2) a low-emission and cost-efficient process configuration.…”

Carbon Dioxide Fixation by Precipitating NaHCO3 via Carbonation of NaOH-Dissolved Ethanol Aqueous Solution

“…Although chemical absorption and pressure swing adsorption are traditionally used technologies to capture CO 2 , mineral carbonation is more advantageous compared to these processes since it can ensure CO 2 fixation. − Mineral carbonation or CO 2 mineralization technology that converts CO 2 into stable solid materials, such as in the form of (bi)­carbonate mineral, can be applied to one of the efficient CCUS technologies. , Many types of CO 2 mineralization processes including the accelerated carbonation have recently been developed with various minerals. , There are a variety of kinds of (bi)­carbonate minerals to fix CO 2 , and they have various features in terms of CCUS technologies. − Wet-based mineral carbonation to produce carbonates by the reaction between CO 2 and alkali (earth) metal hydroxide in water is a process that is easily seen in nature, and its mechanism is well-known through previous works. − Generally, in wet-based mineral carbonation using alkali metal hydroxide as a raw material, it is difficult to precipitate the alkali metal bicarbonate as a reaction product, due to its high solubility in water, , unlike the case of using an alkali earth metal hydroxide as a raw material. However, if the solid form of sodium bicarbonate can be simply obtained by wet carbonation, which is the material that fixes CO 2 , as well as being widely used for various purposes, such as antacids, medicine, baking powder, and carbon dioxide gas generators, − the wet-based mineral carbonation using alkali metal hydroxide might be very efficiently applied to one of the many CCUS options.…”