Direct Aqueous Mineral Carbonation Research Articles

Direct aqueous mineral carbonation of carbide slag in a bubble column reactor under ambient conditions

The accelerated carbonation technology utilizing the alkaline minerals or alkaline wastes incurs high operation and investment costs low conversion efficiency and high energy consumption. Due to the strong alkalinity of the carbide slag, good feedstock availability and great performance of the bubble column reactor, the direct aqueous mineral carbonation of the carbide slag in a bubble column at ambient conditions is evaluated. The impact mechanism of the liquid to solid ratio (5 mL/g−50 mL/g) and gas velocity (0.0041 m/s−0.205 m/s) on the reactions are investigated. The flow patterns are identified by empirical mode decomposition (EMD) energy entropy, and carbonation efficiencies at different flow regimes are compared and illustrated. It is found that this route has a high carbonation efficiency and short reaction time. The maximum carbonation efficiency is 100% and the capture capacity is 214.05 g CO2 / kg carbide slag. The discrete bubble regime (DBR) and bubble coalescence regime (BCR) are observed, and the increase of the L/S ratio can promote the bubble coalescence. The hydrodynamics can influence the processes of the CO2 mass transfer from gas to liquid phase, Ca(OH)2 dissolution, reactant diffusion, collision and ionic reactions. At small L/S ratio, the greater carbonation efficiency is achieved in discrete bubble regime attributing to the longer gas residence time, larger gas–liquid interfacial area and better CO2 mass transfer than that in BCR. At large L/S ratio, the greater carbonation efficiencies are achieved both in DBR and BCR. It has good CO2 mass transfer in DBR and has the strong liquid turbulence intensity in BCR which is good for the reactant diffusion and collision. The enhancement factor increases when enhancing the L/S ratio in DBR. The 30 mL/g and the gas velocity operated in the discrete bubble regime are recommended considering the better three-phase contact, good carbonation conversion and low energy consumption.

Kinetic analysis on CO2 sequestration from flue gas through direct aqueous mineral carbonation of circulating fluidized bed combustion fly ash

In this work, the suitability of fly ash from 600 MW circulating fluidized bed boiler for CO2 sequestration through direct aqueous route was evaluated. The circulating fluidized bed combustion fly ash exhibited favorable carbon capture characteristics with a maximum CO2 sequestration capacity of 0.128 g CO2/g CFA and a corresponding carbonation efficiency of 78.17 %. A modified shrinking core model incorporated gaseous CO2 dissolution and time-dependent effective coefficient of internal diffusion was proposed to determine the gas–liquid-solid carbonation kinetics. The key kinetic parameters were assessed as a function of various carbonation conditions including reaction temperature, solid–liquid (S/L) ratio, energy input and superficial gas velocity. The mass diffusion through the liquid film near the gas–liquid interface was the rate-controlling step during the initial period of time, while diffusion through the expanded passivation layer constituted the controlling mechanism at the final stage. The model provides a more accurate representation of the gas–liquid-solid carbonation process and can be generalized to describe the carbonation of other solid wastes of interest.

Evaluation of the kinetics of direct aqueous mineral carbonation of wood combustion ash using modified shrinking core models.

The direct aqueous mineral carbonation of wood combustion ash (WCA), which is a representative high-calcium waste from combustion process, was systematically investigated by varying complex operating conditions, including reaction time, liquid-to-solid ratio (L/S), CO2 concentration, and particle size. The WCA exhibited high CO2 sequestration characteristics with an optimal carbonation efficiency of 76.4%, corresponding to a CO2 sequestration capacity of 0.314g CO2/g WCA. In addition to solid carbonates, dry residues from liquid products with high potassium contents are potential feedstocks for quality potash fertilizer. Modified shrinking core models based on diffusion-controlled mechanism were proposed to evaluate the carbonation process. The theoretical framework assumes a contracting interface mechanism where active CaO reacts with CO2 to form a product layer. The effective diffusion coefficient of CO2 through the product layer decreases over time, giving deficient carbonation efficiency. The newly proposed models corresponding to different geometrical dimensions provided more perfect fit to the experimental data when compared with the most commonly used kinetic equations. The low apparent activation energy of the carbonation reaction demonstrated the diffusion-controlled mechanism. This work is useful for improving the economics and feasibility of bioenergy carbon capture and storage (CCS) technology chain.

Carbon mineralization with concurrent critical metal recovery from olivine

Carbon dioxide utilization for enhanced metal recovery (EMR) during mineralization has been recently developed as part of CCUS (carbon capture, utilization, and storage). This paper describes fundamental studies on integrating CO2 mineralization and concurrent selective metal extraction from natural olivine. Nearly 90% of nickel and cobalt extraction and mineral carbonation efficiency are achieved in a highly selective, single-step process. Direct aqueous mineral carbonation releases Ni2+ and Co2+ into aqueous solution for subsequent recovery, while Mg2+ and Fe2+ simultaneously convert to stable mineral carbonates for permanent CO2 storage. This integrated process can be completed in neutral aqueous solution. Introduction of a metal-complexing ligand during mineral carbonation aids the highly selective extraction of Ni and Co over Fe and Mg. The ligand must have higher stability for Ni-/Co- complex ions compared with the Fe(II)-/Mg- complex ions and divalent metal carbonates. This single-step process with a suitable metal-complexing ligand is robust and utilizes carbonation processes under various kinetic regimes. This fundamental study provides a framework for further development and successful application of direct aqueous mineral carbonation with concurrent EMR. The enhanced metal extraction and CO2 mineralization process may have implications for the clean energy transition, CO2 storage and utilization, and development of new critical metal resources.

Glycine-induced synthesis of vaterite by direct aqueous mineral carbonation of desulfurization gypsum

Glycine-induced synthesis of vaterite by direct aqueous mineral carbonation of desulfurization gypsum

Characteristics of carbide slag slurry flow in a bubble column carbonation reactor

Abstract The direct aqueous mineral carbonation of carbide slag was investigated. The flow characteristics of carbide slag-CO2-water reaction system in a bubble column were studied, which included the bubble Sauter mean diameter, gas holdup, bubble residence time, and the gas-liquid interfacial area. Bubble flow behaviors in the reactor were characterized by analyzing the bed pressure signals. The effects of the gas velocity (U g ) and liquid to solid ratio (L/S ratio) were discussed and analyzed. The results showed that the larger bubbles were easy to form at the larger L/S ratio, which indicated that the bubble coalescence was promoted. The gas holdup was larger when increasing U g or reducing the L/S ratio. The better gas-liquid interfacial areas were found in a wide range of L/S ratio at U g = 0.082 m/s. The optimum conditions were found at U g = 0.082 m/s and L/S ratio = 15–30 mL/g for the better gas-liquid interfacial area and the higher carbide slag conversion. The work provided the theoretical basis for the direct aqueous carbonation of the carbide slag and the operation condition optimization.

Kinetic modeling of direct aqueous mineral carbonation using carbide slag in a stirred tank reactor

Direct aqueous mineral carbonation by carbide slag at various temperatures, power inputs, superficial gas velocities, and CO2 partial pressures in a stirred tank reactor were systematically studied. Based on the Two-Film Theory, a novel kinetic model that exhibited extraordinary agreement with the experimental data was proposed to express the relationship between carbonation efficiency and reaction time. Carbonation efficiencies of more than 90% were achieved in all the experiments. The rate-controlling step of the reaction was gas-liquid mass transfer initially, although solid-liquid mass transfer was the rate-controlling step at the final stage. Changes in the mineralogy and morphology of the carbide slag before and after carbonation confirmed the reaction mechanism. The effect of various operating parameters on gas-liquid mass transfer was quantitatively investigated using an empirical equation. The present study contributes to the large-scale, rational utilization of energy, operation optimization of CO2 mineral carbonation in gas-liquid-solid reaction systems.

Application of concurrent grinding in direct aqueous carbonation of magnesium silicates

Formation of silica-rich passivation layers formed on the periphery of reacting feed particles is one of the primary obstacles in obtaining high magnesite yields during direct aqueous mineral carbonation of peridotites and serpentinites. The disruption of the silica-rich layer around partially reacted grains as a result of concurrent grinding on the degree of carbonation (magnesite yield) was investigated in this work. Three types of naturally-occurring magnesium silicate feedstocks, dunite, olivine and lizardite, as well as three types of grinding media, were examined.Discrete size fractions of feed samples, with and without grinding media, were carbonated. SEM readily disclosed the formation of a silica-rich shell around a magnesium rich core during carbonation. EDS analysis was employed to study the elemental composition of reacted particles’ shell and core. The method confirmed that during concurrent grinding these silica-rich layers were removed and continuously produced a fresh surface available for further reaction. The removal of the silica-rich layer was shown to significantly improve magnesite yields up to a 600 % increase in yield. Among the three different grinding media used in this work, zirconia and stainless steel media resulted in similar and highest magnesite yields, which is believed to be due to a combination of their high densities and hardness. The findings of this research showed that enhanced magnesite yields could be achieved for all feedstock without the need for energy intensive pre-treatment steps (e.g. ultrafine grinding and heat-activation). Moreover, concurrent grinding resulted in a magnesite yield when raw lizardite was carbonated.

Kinetic evaluation of mineral carbonation of natural silicate samples

Carbon sequestration by mineral carbonation of basic silicate minerals is an important technique for climate change mitigation, because of the formation of stable mineral carbonate products and the abundant resources of amenable minerals in nature. In practice, direct aqueous mineral carbonation may need to treat natural multiple-mineral mixtures including partially serpentinized ultramafic silicates, as potentially combined with mineral processing operations and enhanced metal recovery. This work investigated the kinetics of direct mineral carbonation of multiple-minerals natural silicate samples under conditions of 34.5 bar CO2 partial pressure, 175 ℃ and concentration of 1.5 m NaHCO3, with corresponding carbonation efficiency more than 85% in 3 h. It was found that the carbonation of a natural mixture of minerals was kinetically controlled by chemical reaction of the olivine dissolution under moderate CO2 partial pressure and aqueous ionic strength, regardless of olivine content and associated mineral compositions. It was important for kinetics analysis to calculate the effective mineral carbonation capacity based on the magnesium and iron contents in olivine. If the carbonation capacity was calculated based on the total content of magnesium, calcium and iron as is conventional, the mineral carbonation efficiency was proportional to the olivine content in natural silicate samples. The carbonation process of the natural mixtures could be completely attributed to the reaction of olivine while the other silicate minerals including serpentine and diopside, as well as iron sulfides and magnetite, did not significantly participate.

Utilization of Malaysia EAF slags for effective application in direct aqueous sequestration of carbon dioxide under ambient temperature

Iron and steel industries are among the contributors of CO2 emission in large volume into the atmosphere, causing detrimental effects to the environment and the ecosystem at large scale. These industries also generate solid wastes in the form of electric arc furnace (EAF) slag during operations which result in about 10–15% slag wastes per ton of steel produced. In this study, the EAF slags from an iron and steel-making factory in Klang, Malaysia was utilized for CO2 sequestration through direct aqueous mineral carbonation. According to the surface area analysis, the fresh EAF slag has a mesoporous structure, its elemental composition shows the presence of 20.91 wt.% of CaO that was used for the sequestration of CO2 through carbonation. The sequestration capacity was found to be 58.36 g CO2/kg of slag at ambient temperature in 3 h, with the liquid/solid (L/S) ratio of 5:1 and using <63μm particle size. Moreover, the shrinking core model (SCM) was used to analyze the solid-fluid reaction in a heterogeneous phase and the CO2 sequestration shows to be controlled by the product layer phase. The EAF slag is demonstrated to have the potential of CO2 sequestration at ambient temperature.

CO2 sequestration through direct aqueous mineral carbonation of red gypsum

Abstract In this study, the physical and chemical characteristics and direct aqueous mineral carbonation of red gypsum have been investigated. The characterization studies showed that red gypsum is a very potential feedstock for mineral carbonation. It is mainly consisted of CaO, Fe2O3 and SO3 along with some impurities. On the other hand, the carbonation results showed that direct aqueous carbonation of red gypsum resulted in CaCO3 and FeCO3 production, however, the carbonates purity and carbonation efficiency are still very low.

Ultra-fine grinding and mechanical activation of mine waste rock using a planetary mill for mineral carbonation

In order to mitigate the effects of climate change, a worldwide effort is being launched to use ultramafic mine waste as feedstock for CO2 sequestration by mineral carbonation. To enhance the rate of mineral carbonation at any specific mine site, it is important to develop individualized methods for use at that specific mine site, and with respect to its particular waste mineralogy. This study examines mechanical activation as the pre-treatment method for ultramafic mine waste containing forsterite and serpentine. Particle size distribution, specific surface area, microstructure and direct aqueous mineral carbonation were measured to test the effects of mechanical activation. The Rietveld method was used to analyze the microstructure of untreated and mechanically-activated material. It was found that, as a result of the grinding energy input on olivine, particle size was decreased, surface area was increased, crystallite size was reduced and micro-strain was accumulated. During the dry mechanical activation of mine waste, serpentine content was partially dehydrated and converted to olivine. The concurrent grinding of serpentine with olivine promoted the formation of new surface area, but it hindered the disordering of the crystal structure of forsterite. Forsterite makes up the majority of the content and contributes to CO2 sequestration under selected carbonation conditions. The CO2 sequestration conversion of mechanically-activated olivine and mine waste are 22.5% and 31.5%, respectively, with 3600kWh/t specific milling energy input after one hour direct aqueous carbonation. For the purposes of mineral carbonation, the mechanical activation of mine waste is preferable to simply grinding pure olivine.

Direct Aqueous Mineral Carbonation of Waste Slate Using Ammonium Salt Solutions

The carbonation of asbestos-containing waste slate using a direct aqueous mineral carbonation method was evaluated. Leaching and carbonation tests were conducted on asbestos-containing waste slate using ammonium salt (CH3COONH4, NH4NO3, and NH4HSO4) solutions at various concentrations. The CH3COONH4 solution had the highest Ca-leaching efficiency (17%–35%) and the NH4HSO4 solution had the highest Mg-leaching efficiency (7%–24%) at various solid dosages and solvent concentrations. The CaCO3 content of the reacted materials based on thermogravimetric analysis (TGA) was approximately 10%–17% higher than that of the as-received material for the 1 M CH3COONH4 and the 1 M NH4HSO4 solutions. The carbonates were precipitated on the surface of chrysotile, which was contained in the waste slate reacted with CO2. These results imply that CO2 can be sequestered by a direct aqueous mineral carbonation using waste slate.

CO&lt;sub&gt;2&lt;/sub&gt; Sequestration by Direct Aqueous Mineral Carbonation under Low-Medium Pressure Conditions

As CO2 is the largest contributor to the greenhouse effect, reducing the total CO2 emissions into the atmosphere has been considered as the breakthrough point of mitigating the greenhouse effect. Mineral carbonation is a potential route for CO2 sequestration. In this paper, the mineral carbonation reaction characteristics of wollastonite, serpentine and olivine under low-medium pressure conditions were investigated. Many tests including XRD, XRF, BET and thermal decomposition were applied. Parameters, such as reaction temperature, reaction pressure, particle size, solution composition and heat-treatment, were discussed in details. The results show that besides increase of reaction temperature and pressure, addition of NaHCO3 and decrease of particle size can also effectively accelerate the carbonation reaction for all the three minerals. Heat-treatment of minerals is only useful for serpentine. Highest carbonation conversion efficiency of 83.5%, 47.7% and 16.9% was respectively achieved for wollastonite, serpentine and olivine under the condition of T=150°C, P=40 bar and particle sizes <30 µm. Compared the conversion efficiencies, it is indicated that wollastonite was the most reactive mineral and olivine was suggested to be not suitable for CO2 sequestration by direct aqueous mineral carbonation under low-medium pressure conditions.

Development of an attrition-leaching hybrid process for direct aqueous mineral carbonation

Mineral carbonation is the single most eligible companion solution to geosequestration for mitigation of anthropic CO2 emissions on a large scale. Amongst its possible pathways, direct aqueous mineral carbonation stands out as one of the most promising ones. The originality of the present work lies in the transposition of the concomitant exfoliation/mineralisation concept, which was first proposed by the mineral carbonation research group from the Arizona State University in early 2000s, inside a dedicated attrition environment, more specifically inside a stirred bead mill. Experimental results and analyses bring definite proofs about the possibility and synergy of concomitant exfoliation and mineralisation. Given high carbonation yield for olivine and serpentinised ores (up to 35% in 5h and 80% in 24h in water, and 70% in 5h with inorganic additives) and the capacity of stirred mills to process mining size throughputs, this work leads to real perspectives for developing large scale robust solutions for direct aqueous mineral carbonation.

CO2 Sequestration from flue gas by direct aqueous mineral carbonation of wollastonite

Emission of carbon dioxide is considered to be the main cause of the greenhouse effect. Mineral carbonation, an important part of the CCS technology, is an attractive option for long-term CO2 sequestration. In this study, wollastonite was chosen as the feedstock and the feasibility of direct aqueous mineral carbonation in the simulated flue gas was investigated via a series of experimental studies carried in a stirred reactor. X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), ion chromatography (IC) and thermal decomposition were used to determine the carbonation conversion. The influences of various factors, including reaction temperature, reaction pressure, solution composition, heat-treatment and particle size, were discussed. Concurrently, the effects of SO2 and NO presented in simulated flue gas were also investigated and a possible mechanism was used to explain the results. Experimental results show that reaction temperature, reaction pressure and particle size can effectively improve the carbonation reaction. Addition of 0.6 M NaHCO3 was also proved to be beneficial to the reaction and heat-treatment is not needed for wollastonite to get a higher carbonation conversion. Compared with carbonation in purified CO2 gas, CO2 sequestration directly from simulated flue gas by mineral carbonation is suggested to have a certain degree of economic feasibility in the conditions of medium and low-pressure. A highest carbonation conversion of 35.9% is gained on the condition of T=150°C, P=40 bar and PS <30 μm in distilled water for 1 h.

Comprehensive analysis of direct aqueous mineral carbonation using dissolution enhancing organic additives

Direct aqueous mineral carbonation using organic anions has been presented by many as a promising strategy for mineral carbonation, on the basis that additives such as oxalate increase the rate and extent of dissolution of magnesium silicates several folds. Through geochemical modelling and detailed solid characterisation, this paper discusses and extends our current understanding of this process. The role of disodium oxalate as a dissolution enhancing agent for olivine is thoroughly examined through experiments in which all phases are carefully analysed. We show that under 20bar of CO2 pressure formation of strong oxalate–magnesium complexes in solution and precipitation of MgC2O4·2H2O (glushinskite) impede any chance of obtaining significant amounts of magnesium carbonate. Other promising ligands from a dissolution perspective, namely citrate and EDTA salts, are also investigated. Contrary to oxalate, these ligands do not form any solid by-products with magnesium, and yet they do not produce better carbonation results, thereby casting strong doubts on the possibility of developing a direct aqueous mineral carbonation process using organic salts. Geochemical modelling permits successful simulation of the dissolution kinetics of magnesium silicate using a shrinking particle model that accounts for the precipitation of glushinskite, amorphous silica and a magnesium phyllosilicate at advanced stages of the dissolution process.

Understanding the chemistry of direct aqueous carbonation with additives through geochemical modelling

Amongst possible mineral carbonation strategies, direct aqueous mineral carbonation using organic salts is perhaps the most promising one. By going to and from between geochemical modelling and experimental results, this paper reviews key findings and conclusions to date about this process. With the magnesium silicate – oxalate system, the paper makes a strong case for the necessity to characterize both solid and liquid phases in order to analyze any aqueous mineral carbonation test results. It is shown that partial information about reaction products, such as liquid phase analysis without characterization of the associated solid phase, can easily lead to flawed conclusions. Proper analysis of solid products is recognized however to complicate experimental work considerably, with many analytical techniques being required to reveal the true nature of the solid phases present in aqueous mineral carbonation chemical systems. Given the complexity of such systems, geochemical equilibrium modelling is found to be an invaluable companion tool for planning and interpretation of experimental results. However, in contrast with the performance of geochemical simulation tools available today, such as the CHESS package used in this work, the lack of thermodynamic data necessary to simulate the behaviour of relevant chemical systems is a real issue that must be addressed.

The CO2 -binding by Ca-Mg-silicates in direct aqueous carbonation of oil shale ash and steel slag

Abstract This study was focused on carbonation of waste materials having low water-solubility in which Ca and Mg are generally bound as silicates. Here, pulverized firing oil shale ash (PFA from Narva Power Plants, Estonia), electric arc furnace slag (EAFS, types 1 and 2 from Uddeholm Tooling, Sweden) and ladle slag (LS from Uddeholm Tooling, Sweden) were studied as sorbents for binding CO 2 from flue gases in direct aqueous mineral carbonation process. The experiments were carried out at room temperature and atmospheric pressure. Results showed that Ca-Mg-silicate phases bound up to 9 g of CO 2 per 100 g of initial ash, which formed 30% of the total CO 2 bound in direct aqueous carbonation of PFA. The CO 2 uptakes for steel slags (EAFS1, EAFS2 and LS) were 8.7 g CO 2 /100 g EAFS1, 1.9 g CO 2 /100 gEAFS2 and 4.6 g/100 g LS. Quantitative XRD analysis indicated that Ca 2 SiO 4 and Ca 3 Mg(SiO 4 ) 2 were the main CO 2 binding low solubility components of oil shale ash as well as steel slags. The main carbonation product was calcite (CaCO 3 ), indicating that Mg-compounds were not reactive towards CO 2 at these mild conditions. Based on multifaceted studies on carbonation of oil shale ash, a new method for eliminating CO 2 from flue gases by Ca-containing waste material was proposed. The process includes contacting the aqueous suspensions of Ca-containing waste material with CO 2 containing flue gas in two steps: in the first step the suspension is bubbled with flue gas keeping the pH levels in the range of 10–12 and in the second step keeping the pH levels in the range of 7–8. The water-soluble components such as free lime are carbonated in the first step and the components of low solubility, in which Ca is generally contained in the form of silicates, are carbonated in the second step.