•pH swing mineral carbonation studies have been critically reviewed.•pH swing mineral carbonation costs is too high compared to other mineral carbonation methods.•Relatively high carbonation ...efficiency is achieved through pH swing mineral carbonation.•High purity carbonates are produced by pH swing mineral carbonation.
Carbon dioxide (CO2) mineral sequestration technologies are potentially capable of sequestering billion tonnes of CO2 annually. In recent years, pH swing mineral carbonation has received significant attention due to its high potentiality toward CO2 fixation. This review compiles the work conducted by various researchers over the last few years on pH swing mineral carbonation process. In this review, feedstocks used for pH swing process are introduced. The extraction and carbonation steps, as the main steps of pH swing process are critically reviewed. The role of reaction condition on extraction efficiency of calcium and magnesium from feedstocks and the kinetics involved in extraction step are also critically reviewed. The experimental procedures of pH swing and in situ pH swing mineral carbonation using different minerals and industrial wastes are critically discussed. Moreover, the drawbacks of each pH swing process in terms of cost and energy analysis are also discussed in this review.
CO2 mineralisation by industrial wastes is a promising option for mitigating carbon emissions safely and permanently with low material cost. But there is still absence of a detailed understanding on ...how fly ash properties affect the carbonation reactions. To fill this knowledge gap, five coal combustion fly ashes, Beijing (BJ), Wuhai (WH), Hazelwood (HW), Yallourn (YA) and Loy Yang (LY) ashes, from China and Australia were selected for carbonation studies. Experiments were performed in a batch reactor at 40 and 140 °C with 20 bar initial CO2 pressure, 200 g/L solid to liquid ratio, 450 rpm stirring rate to compare the carbonation performance of the five fly ashes and the effect of fly ash properties on carbonation reactions. Then BJ, YA and HW ashes were then selected for further study in a wide temperature range (40–220 °C) because of their higher CO2 sequestration capacity than the other two ashes. Quantitative X-ray diffractometry (XRD) with Rietveld refinement was used to characterize the crystalline and amorphous phases in fresh and carbonated fly ashes. Scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) were used to characterize morphological and elemental properties of fresh and carbonated fly ash samples. Compared to LY and WH ashes, BJ, YA and HW ashes displayed much higher CO2 sequestration capacity due to the higher fraction of reactive Ca/Mg-bearing crystalline phases, including lime (CaO) and portlandite (Ca(OH)2) in BJ ash, periclase (MgO) and srebrodolskite (Ca2Fe2O5) in YA ash, and periclase and brucite (Mg(OH)2) in HW ash. Compared to YA and WH ashes, BJ ash displayed faster kinetics of carbonation reactions because the reactant phases of BJ ash were mainly Ca-bearing phases which have higher reactivity with CO2 than Mg-bearing phases. Also, particle size and morphological analyses indicated that the reacted particles displayed a lower porosity and pore area than the fresh sample due to the new precipitates not only depositing on the active surface, but also filling the pores of the fly ash particles, which was responsible for the reduced kinetics with time.
•The influence of fly ash properties on carbonation efficiency was determined.•Promoted carbonation efficiency was achieved at elevated temperature.•Ca-bearing phases displayed higher reactivity with CO2 than Mg-bearing phases
Mining waste is globally available in abundance and can be seen as a useful mineral resource for long-term carbon capture which can be turned into revenue-generating products. This review highlights ...a new concept for mining waste utilization through an integrated carbon capture, utilization and storage (CCUS) technology in response to the long-term target for net-zero emissions. A framework for mining waste utilization by means of CCUS is introduced through integration of accelerated mineral carbonation and carbonation curing technologies. Potential CO2 sequestration of mining waste is mainly attributable to the availability of Ca-, Mg- and Fe-based silicate and oxide minerals and manipulation of process variables. It was estimated that the current rate of carbonation efficiency of mining waste through direct and indirect mineral carbonation is about 11 % and 55 %, respectively, while CO2 capture capacity through carbonation curing is about 20.6 %. It can be projected that with the current rate of CO2 sequestration, this accounts for about 21.1–100 % of the net-zero target by 2035 via CCUS. The combined mineral carbonation and carbonation curing might offset 33.4–100 % of CO2 emissions from the mining industry and 15.4–60.9 % of the net-zero target by 2050. Despite technical, economic and environmental challenges, the framework provides pathways for a sustainable mining waste recovery to meet the 2050 net-zero emissions target.
•Unaltered basalt is more advantageous for mineral carbonation than serpentinized basalt.•Rapid aqueous phase CO2 injection may limit mineral carbonation and porosity enhancement near the wellbores ...in basalt.•Formation conductivity interferes the most with mineral carbonation in basalt.
Basalt formation is a new promising CO2 sink for providing secure long-term carbon storage via trapped CO2 in mineral phases. When water enters into the crystal structures of the divalent cation-bearing unaltered basalt, the rock is altered and serpentinized. The serpentinization of the unaltered basalt occurs widely around the world. To evaluate the mineral carbonation efficiency of unaltered and altered basalt over a longer time frame, a predictive modeling frame is established in TOUGHREACT based on data from core-scale static batch experiments and the field-scale Carbfix project. Results indicate that unaltered basalt has higher carbonation efficiency than altered basalt both in the carbonation rate and extent due to serpentine kinetic limitations for aqueous phase CO2 injection, and the carbonates mineralization extent and rate increase with the content of olivine minerals in basalt. Furthermore, under these conditions, the longer CO2 migration distance from the injection site enhances the chance for mineral carbonation in the serpentinized basalt. In addition, rapid aqueous phase CO2 injection may limit mineral carbonation and cause porosity reduction near wellbores in the basaltic reservoir, and this effect is more pronounced in case of unaltered basalt than in the altered basalt. Compared to the injection rate, the impact of reservoir conductivity is found to be significant on mineral carbonation in both the unaltered basalt and altered basalt; higher conductivity is more advantageous for CO2 mineralization under certain circumstances. In combination, the injectivity rate should be carefully assessed at sites based on the reservoir conductivity and whether the basalt is altered or unaltered and the extent of alteration.
This study focused on AOD stainless steel slag (AOD slag), utilizing a direct wet carbonation process at ambient temperature and pressure to effectively capture CO2. We first evaluated the impact of ...four distinct additives such as NaCl (Simulated seawater concentration, 2.43 mol/L), NaOH (Simulated cold rolling wastewater, 0.01 mol/L), NH4Cl (0.5 mol/L) and CH3COONH4 (0.5 mol/L) on the carbonation of AOD slag, ultimately selecting CH3COONH4 for its superior performance. Within the “AOD slag + CH3COONH4” system, we conducted a comprehensive examination of carbonation parameters, including additive concentration, particle size, solid-liquid ratio, temperature and time, with a focus on optimizing carbonation efficiency (ηc) and carbonation capacity (Cc). Additionally, we provided an in-depth exploration of the simultaneous efficient carbonation and detoxification mechanisms pertaining to the stainless steel slag. Under standard conditions (293 K, 1 atm), the system achieved an impressive ηc of 80.02%, and Cc of 386.62 kg CO2/ton slag, higher than those previously reported. Furthermore, after five experimental cycles, the system maintained a 70% original efficiency, with Cr leaching concentrations significantly below the national standard requirement of 1.5 mg/L.
The in-situ treatment of slag and CO2 in the “AOD slag + CH3COONH4″ system is achieved through direct wet carbonation under environmental conditions. Its ultra-high carbonation efficiency and ability, as well as good cycling and non-toxic properties, demonstrate its potential for industrial application. Display omitted
•An efficient direct carbonating AOD stainless steel slag method was proposed.•Improved CO2 fixation and detoxification of slag at ambient condition were realized.•The additive CH3COONH4 has great influence on carbonation performance of the slag.•Direct carbonation mechanism of “CH3COONH4+AOD slag” system was elucidated.•The detoxified slag powder meet the requirements of resource utilization.
•Side reactions produced serpentine and magnesium silicate hydroxide phases.•Extent of side reactions were elevated when experiments performed under nitrogen.•Side reactions reduced the magnesite ...yield by up to 40%.•Side reactions reduced the efficiency of direct aqueous carbonation process.
This work discloses a possible explanation for the relatively low efficiency and yield observed in direct aqueous carbonation of heat activated serpentine which remained a critical unanswered question during three decades of ex-situ mineral carbonation research and development. The discovery of undesirable side reactions, occurring during direct aqueous carbonation of heat activated serpentine has been reported and investigated in detail. These reactions result in the reformation of crystalline serpentine and precipitation of amorphous magnesium silicate hydroxide phase/s on the surface of reacting feed particles. Reformation of serpentine occurs under relatively mild conditions (in terms of pressure and temperature) and after only a few minutes of reaction which is in stark contrast to the conditions and rates which occur during geological serpentinisation and other laboratory studies. Scanning Electron Microscopy and Energy Dispersive X-ray spectroscopy analyses showed precipitation of amorphous magnesium silicate hydroxide phase/s during carbonation process. Fourier Transform Infrared Spectroscopy and Thermogravimetric analyses identified and quantified free and hydrogen bonded hydroxyls of silanol groups in the structure of the reaction products when heat activated lizardite and antigorite were carbonated. The growth of a crystalline serpentine phase was confirmed and quantified by X-ray Diffraction and Thermogravimetric analyses in the reaction products when heat activated antigorite was used a feed.
Estimating mineral reactive surface areas in geologic media remains one of the key challenges limiting the accuracy of reactive transport modeling (RTM) predictions of subsurface processes, ...particularly those controlling the fate of carbon dioxide (CO2) during geologic storage. Although there have been numerous attempts to combine imaging and experimental techniques to estimate mineral reactive surface area for use in RTM predictions of geologic CO2 storage, these techniques have yet to be adapted to basaltic reservoirs, which have pore structure, mineralogy, and chemical composition that is unique compared to their more often-studied sedimentary counterparts. Here, we address this issue by quantifying fluid-accessible mineral surface areas through image analysis of scanning electron microscope (SEM) backscatter electron images (high-resolution 500 nm/pixel) and Raman spectroscopic mapping of a basaltic rock sample from the Eastern Snake River Plain, Idaho. To evaluate whether the determined pore fluid-accessible mineral surface area accurately reflects reactive surface area, a micro-continuum scale RTM was developed and compared with a high-temperature, high-pressure flow-through CO2 mineralization experiment conducted on the characterized basalt. Importantly, simulations employing the image-derived pore fluid-accessible mineral surface areas match the experimental effluent chemistry well within uncertainties. These mineral surface areas were then used to parametrize a field-scale model representative of the Cascadia basin, Northeastern Pacific, to evaluate impacts of surface area variations on mineral carbonation. Simulations were carried out using variations in image-derived surface areas that cover one to two orders of magnitude increase and decrease in surface area, analogous to previously reported magnitudes of difference between total and reactive surface areas. Carbonation efficiency in terms of CO2 volume mineralized over the simulated period was tracked and compared. Simulations with surface area increased and decreased by two orders of magnitude show basalt carbonation efficiency that is three times faster and six times slower, respectively, than predictions with image-derived mineral surface area. These sensitivity analyses demonstrate that accurate quantification of mineral surface area is crucial for efforts to predict CO2 mineralization, and that efforts such as those employed here can dramatically reduce the uncertainty of field-scale predictions of basalt carbonation.
Carbon neutral or negative mining can potentially be achieved by integrating carbon mineralization processes into the mine design, operations, and closure plans. Brucite Mg(OH)2 is a highly reactive ...mineral present in some ultramafic mine tailings with the potential to be rapidly carbonated and can contain significant amounts of ferrous iron Fe(II) substituted for Mg; however, the influence of this substitution on carbon mineralization reaction products and efficiency has not been thoroughly constrained. To better assess the efficiency of carbon storage in brucite-bearing tailings, we performed carbonation experiments using synthetic Fe(II)-substituted brucite (0, 6, 23, and 44 mol % Fe) slurries in oxic and anoxic conditions with 10% CO2. Additionally, the carbonation process was evaluated using different background electrolytes (NaCl, Na2SO4, and Na4SiO4). Our results indicate that carbonation efficiency decreases with increasing Fe(II) substitution. In oxic conditions, precipitation of ferrihydrite Fe10 IIIO14(OH)2 and layered double hydroxides {e.g., pyroaurite Mg6Fe2 III(OH)16CO3·4H2O} limited carbonation efficiency. Carbonation in anoxic environments led to the formation of Fe(II)-substituted nesquehonite (MgCO3·3H2O) and dypingite Mg5(CO3)4(OH)2·∼5H2O, as well as chukanovite Fe2 IICO3(OH)2 in the case of 23 and 44 mol % Fe(II)-brucite carbonation. Carbonation efficiencies were consistent between chloride- and sulfate-rich solutions but declined in the presence of dissolved Si due to the formation of amorphous SiO2·nH2O and Fe–Mg silicates. Overall, our results indicate that carbonation efficiency and the long-term fate of stored CO2 may depend on the amount of substituted Fe(II) in both feedstock minerals and carbonate products.
Carbonation curing in cement-based composites presents a promising and environmentally friendly solution to lower carbon emissions in the cement industry. This paper aims to provide a comprehensive ...review of the current research landscape encompassing this emerging technology, focusing specifically on carbonation behavior, kinetics, influential factors, and strategies to enhance carbonation degree in calcium-bearing minerals. Detailed insights into the carbonation mechanism, reactivity, and product formation of calcium silicate and calcium aluminate minerals are provided. Non-hydraulic calcium silicate minerals exhibit excellent carbonation activity while calcium aluminate minerals have minimal reactivity with CO2. Additionally, a thorough analysis of factors affecting carbonation in calcium-bearing minerals, including particle size, water-to-solid ratio, relative humidity, temperature, and CO2 concentration, is conducted. The influencing factors mentioned not only impact the carbonation rate but also influence the carbonation products as well as the carbonation degree. Special attention is paid to exploring the carbonation kinetic models based on solid-state kinetic models, and the application of the shrinking core model and surface coverage model are discussed. When applied appropriately, classical solid-state kinetic models facilitate rapid assessment of reaction kinetics and allow for optimization of carbonation conditions. Furthermore, various effective methods to improve the carbonation degree of calcium-bearing minerals are summarized, with both enhancement mechanisms and limitations of each method given. Specifically, methods that promote the dissolution of calcium ions, provide additional pathways for CO2 diffusion, or generate more nucleation sites have proven efficient for facilitating a higher carbonation degree. Finally, the paper concludes by highlighting the current challenges and limitations and providing prospects for overcoming these obstacles.
•Non-hydraulic calcium silicate minerals exhibit excellent carbonation activity.•Classical solid-state kinetic models facilitate rapid assessment of reaction kinetics and allow for optimization of carbonation conditions.•Promoting the dissolution of calcium ions, facilicating the diffusion of CO2, and generating more nucleation sites are benefical for a higher carbonation degree.
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