Carbon mineralization technology has emerged as a promising method for permanently sequestering CO2 by transforming it into a thermodynamically stable solid carbonate material. Recently, alkaline industrial waste, particularly from steel and iron-making processes, has been identified as a proper feedstock due to its high potential for CO2 storage and the ability to reduce landfill strain significantly. In this context, this review focuses on the possibilities and challenges associated with the carbon mineralization of steel and iron-making slag. Given that the composition and characteristics of feedstock play crucial roles in carbon mineralization, in-depth examinations of the generation of by-products and the corresponding physicochemical properties were conducted. In the context of the carbon mineralization process, our primary focus was on ex-situ carbon mineralization, which encompasses both direct and indirect carbonation routes, while elucidating the intricate mechanisms underlying both types of carbonation. Current challenges such as low leaching efficiency rates, slow kinetics, complex slag structures and silicate passivation phenomena are also addressed. For practical applications, it is essential to integrate valuable material production with the carbon mineralization process. Accordingly, various methods for producing precipitated calcium carbonates, construction materials with heavy-metal stabilization, valuable element recovery, and possible integration with hydrogen production processes, were introduced. Lastly, we provide an overview of the current state of the art of carbon mineralization technology and suggest future research directions.

Carbon Capture and Storage (CCS) aims to gather and store atmospheric CO2, often in geologic reservoirs, to mitigate the increasing atmospheric CO2 concentrations that lead to climate change. While the majority of CCS projects to date focus on structurally trapping CO2 in gaseous form in porous sedimentary rocks, carbon mineralization approaches storage from a much more secure perspective by storing CO2 as a solid carbonate mineral phase. During the carbon mineralization process, interactions between the host rock and the fluids flowing through the rock’s permeable pathways exert a primary control on the evolution of permeability of the system. Precipitation of mineral phases within the fracture network can significantly reduce the permeability of the overall system (clogging), whereas mineral dissolution and volume positive mineral reactions (leading to cracking) can enhance permeability. The coupling between these competing processes dictates reservoir permeability and thus the long-term storage capacity and lifetime of CO2 storage reservoirs. Experimental studies are therefore vital to understand the chemo-mechanical controls on dissolution, precipitation, and carbonation-induced cracking, as well as to quantify their effect on the permeability of the system. In this study, we perform experiments using a new AutoLab triaxial deformation apparatus equipped with independently servo-controlled axial load, confining, and fluid pressures. Samples are prepared via cold press from Twin Sisters peridotite powdered to a mean particle size of 94 µm. Experimental conditions are set to reproduce shallow crust conditions at viable injection depths and are controlled at a confining pressure of 20 MPa and fluid pressures of 10 MPa. Experimental temperatures range from 20 to 150 °C. Pore fluids are mixed in a joint mixing vessel using deionized water and sodium bicarbonate forming a solution of 0.6 M concentration. The solution is then pressurized using CO2 (99.9% purity) to a pressure of 3.5 MPa serving both as a vehicle for CO2 transport and as pH buffer. Permeability, ultrasonic wave velocities, axial strain, pH and fluid composition are monitored during these flow-through experiments. Preliminary results relate progress of the mineral carbonation reaction through the sample with a systematic decrease in permeability and an associated increase in P wave velocity. The results of this experimental study will be used to constrain the most favourable conditions for CO2 storage in a solid form, which is fundamental to the upscaling of carbon mineralization as an innovative, efficient and safe method for CO2 storage.

Nanoparticle organic hybrid materials (NOHMs) are self-suspended liquid-like nanoparticle-based functional materials consisting of a surface-functionalized inorganic nanocore and oligomeric or polymeric chains. They often exhibit complex intermolecular and intramolecular interactions among their constituents, resulting in versatile physicochemical characteristics that range from glassy solids to solvent-free nanoparticle fluids. A variety of applications involving NOHMs have been investigated thus far, including thermal management fluids, lubricants, magnetic fluids, nanocomposites, electrolytes, water treatment and biomass pretreatment chemicals, and CO2 capture solvents. In particular, NOHMs have recently been recognized as a promising CO2 capture and utilization medium. To capture CO2 more effectively, a variety of specific functional groups of strong chemical affinity to CO2 can be added to the polymeric canopy (enthalpic contribution), and various steric considerations induced by attractive/repulsive interactions among the nanocores and canopies can be introduced (entropic contribution). These occur while maintaining negligible vapor pressure and enhanced thermal stability. Here, we investigated the canopy dynamics of NOHMs with different-sized SiO2 nanocores, aiming to reveal the hidden nature of the entropic interaction occurring in NOHMs. Pulse-field gradient nuclear magnetic resonance spectroscopy (with 1H) was employed to investigate the canopy dynamics of the NOHMs synthesized using 7, 12, and 22 nm SiO2 particles, and these results were compared with those from a ternary mix of all three sizes of SiO2 nanocores. The self-diffusion coefficient and thermal diffusivity were also evaluated.

This study reports the thermochemical transformation of lignin model compounds using nanoparticle organic hybrid materials (NOHMs). NOHMs have recently been developed as an emerging class of self-suspended nanoparticle solvent systems created by ionically or covalently grafting organic oligomers or polymers (canopy) onto surface-modified inorganic nanoparticles (core). Because NOHMs exhibit negligible vapor pressure with the ability to tailor physicochemical properties, they could be a promising catalytic solvent for the lignin thermochemical conversion process. The thermochemical conversion of lignin model compounds was achieved with the synthesized NOHM at an elevated temperature of 473 K, and the results were compared with the case of the ionic liquid [EMIM][ESO4]. The fractured moieties of the lignin model compounds were qualitatively identified by ATR FT-IR and 2D COSY NMR spectroscopies. The results indicated that the NOHM decomposed the C-O and/or C-C bonds of lignin model chemicals more efficiently than [EMIM][ESO4].

The transformation of CO2 into a precipitated mineral carbonate through an ex situ mineral carbonation route is considered a promising option for carbon capture and storage (CCS) since (i) the captured CO2 can be stored permanently and (ii) industrial wastes (i.e., coal fly ash, steel and stainless-steel slags, and cement and lime kiln dusts) can be recycled and converted into value-added carbonate materials by controlling polymorphs and properties of the mineral carbonates. The final products produced by the ex situ mineral carbonation route can be divided into two categories-low-end high-volume and high-end low-volume mineral carbonates-in terms of their market needs as well as their properties (i.e., purity). Therefore, it is expected that this can partially offset the total cost of the CCS processes. Polymorphs and physicochemical properties of CaCO3 strongly rely on the synthesis variables such as temperature, pH of the solution, reaction time, ion concentration and ratio, stirring, and the concentration of additives. Various efforts to control and fabricate polymorphs of CaCO3 have been made to date. In this review, we present a summary of current knowledge and recent investigations entailing mechanistic studies on the formation of the precipitated CaCO3 and the influences of the synthesis factors on the polymorphs.