Rapid Carbonation for Calcite from a Solid-Liquid-Gas System with an Imidazolium-Based Ionic Liquid

Aqueous carbonation of Ca(OH)₂ is a complex process that produces calcite with scalenohedral calcite phases and characterized by inadequate carbonate species for effective carbonation due to the poor dissolution of CO₂ in water. Consequently, we report a solid-liquid-gas carbonation system with an ionic liquid (IL), 1-butyl-3-methylimidazolium bromide, in view of enhancing the reaction of CO₂ with Ca(OH)₂. The use of the IL increased the solubility of CO₂ in the aqueous environment and enhanced the transport of the reactive species (Ca²⁺ and CO₃²⁻) and products. The presence of the IL also avoided the formation of the CaCO₃ protective and passivation layer and ensured high carbonation yields, as well as the production of stoichiometric rhombohedral calcite phases in a short time.     

Mechanism and kinetics of wollastonite fibre dissolution in the aqueous solution of acetic acid

The dissolution of fibrous wollastonite (CaSiO₃) in the aqueous solution of acetic acid (3 mol dm^− 3) was investigated in the temperature interval from 25 to 50 °C using mixed batch-type reactor. An incongruent dissolution of wollastonite proceeds under applied acidic condition. The pH of solvent was increasing during leaching of calcium and its actual value depended on the concentration of Ca²⁺ ions in the solution according to the Henderson buffer equation. That enabled the monitoring of dissolution kinetics via concentration of Ca in the dispersion medium of suspension of wollastonite measurement. The kinetic parameter of the process was evaluated from measured dissolution rates of wollastonite at constant temperature using the empirical Arrhenius equation. The apparent activation energy and pre-exponential factor estimated from the Arrhenius plot are 47 ± 1 kJ mol^− 1 and (1.8 ± 0.9) × 10³ s^− 1. The kinetics analysis of the process indicates that the process is driven by the stationary two-dimensional diffusion (D₂).     

Mechanisms of aqueous wollastonite carbonation as a possible CO2 sequestration process

The mechanisms of aqueous wollastonite carbonation as a possible carbon dioxide sequestration process were investigated experimentally by systematic variation of the reaction temperature, CO₂ pressure, particle size, reaction time, liquid to solid ratio and agitation power. The carbonation reaction was observed to occur via the aqueous phase in two steps: (1) Ca leaching from the CaSiO₃ matrix and (2) CaCO₃ nucleation and growth. Leaching is hindered by a Ca-depleted silicate rim resulting from incongruent Ca-dissolution. Two temperature regimes were identified in the overall carbonation process. At temperatures below an optimum reaction temperature, the overall reaction rate is probably limited by the leaching rate of Ca. At higher temperatures, nucleation and growth of calcium carbonate are probably limiting the conversion, due to a reduced (bi)carbonate activity. The mechanisms for the aqueous carbonation of wollastonite were shown to be similar to those reported previously for an industrial residue and a Mg-silicate. The carbonation of wollastonite proceeds rapidly relative to Mg-silicates, with a maximum conversion in 15 min of 70% at , 20 bar CO₂ partial pressure and particle size of . The obtained insight in the reaction mechanisms enables the energetic and economic assessment of CO₂ sequestration by wollastonite carbonation, which forms an essential next step in its further development.     

Kinetic study on carbonation of crude Li<Subscript>2</Subscript>CO<Subscript>3</Subscript> with CO<Subscript>2</Subscript>-water solutions in a slurry bubble column reactor

Investigations were conducted to purify crude Li₂CO₃ via direct carbonation with CO₂-water solutions at atmospheric pressure. The experiments were carried out in a slurry bubble column reactor with 0.05 m inner diameter and 1.0 m height. Parameters that may affect the dissolution of Li₂CO₃ in the CO₂-water solutions such as CO₂-bubble perforation diameter, CO₂ partial pressure, CO₂ gas flow rate, Li₂CO₃ particle size, solid concentration in the slurry, reaction temperature, slurry height in the column and so on were investigated. It was found that the increases of CO₂ partial pressure, and CO₂ flow rate were favorable to the dissolution of Li₂CO₃, which had the opposite effects with Li₂CO₃ particle size, solid concentration, slurry height in the column and temperature. On the other hand, in order to get insight into the mechanism of the refining process, reaction kinetics was studied. The results showed that the kinetics of the carbonation process can be properly represented by 1−3(1−X)^2/3+2(1–X)=kt+b, and the rate-determining step of this process under the conditions studied was product layer diffusion. Finally, the apparent activation energy of the carbonation reaction was obtained by calculation. This study will provide theoretical basis for the reactor design and the optimization of the process operation.     

Effects on the removal of Pb2+ from aqueous solution by crab shell

The effects of temperature, pH, chitin and chitosan on Pb²⁺ removal by crab shell were investigated. Pb²⁺ removal by crab shell was greater than that of chitin and chitosan, indicating that chitin did not contribute to Pb²⁺ removal by crab shell. The quantity and rate of Pb²⁺ removal increased as the pH value increased. The rate of Pb²⁺ removal increased with increased temperature, but the maximum amount of Pb²⁺ removal was constant irrespective of temperature. Metal ions (K⁺, Na⁺, Mg²⁺, Ca²⁺) were released from crab shell concomitant with Pb²⁺ removal by ion exchange. The amount of Ca²⁺ released was greater than any for other metal ions in both Pb²⁺ and Pb²⁺‐free solutions. The amount of Ca²⁺ released in Pb²⁺ solution was greater than that in Pb²⁺‐free solution, whereas CO₃^2? release in Pb²⁺ solution was less than in Pb²⁺‐free solution. Pb²⁺ removal was mainly a consequence of dissolution of CaCO_3(s) with consequence precipitation of Pb₃(CO₃)₂(OH)_2(s) and PbCO_3(s). Pb²⁺ accelerated the dissolution of CaCO_3(s) by ion exchange and the precipitation occurred both at the surface and in the inner part of the crab shell. © 2001 Society of Chemical Industry     

Energy efficiency analysis of CO2 mineral sequestration in magnesium silicate rock using electrochemical steps

A thermodynamic efficiency analysis using the exergy concept is used to assess CO₂ mineral sequestration process routes where electrochemical steps (electrolysis and fuel cells) are used to produce aqueous hydrochloric acid and sodium hydroxide reactant solutions. Results from three recent publications on the subject that come to different conclusions are used for this case study. It is shown that including electrolysis as one of the steps of a magnesium silicate mineral carbonation process route results in input energy requirements that will exceed the output of a fossil fuel-fired power plant that produces the CO₂ that is bound to (hydro-) carbonates. At the same time, fuel cells are not efficient enough to change this.     

Acid dissolution of mineral matrix in Green River oil shale

The mineral matrix in Green River oil shale was partially removed by treatment with dilute HCl. The major ionic species in the solution from acid treatment (AT) were identified as Na⁺, Al³⁺, Fe²⁺, Mg²⁺, and Ca²⁺. The ion yields expected from reaction stochiometry, gravimetric analyses and comparison of calculated CO₂ yields with measured levels were consistent with the fact that Na⁺ and Al³⁺ originated primarily from analcite: Fe²⁺ and Mg²⁺ from dolomitic ankerite and Ca²⁺ from both dolomitic ankerite and calcite. Temperature and shale particle size were important parameters in the efficacy of AT. An increase in temperature and a decrease in particle size increased the rate of mineral dissolution. Fe²⁺ showed an anomalous trend in that the rate initially declined with increasing temperature after which it showed the usual increase with temperature. The kinetics of ion build-up in the solution from AT were analysed in detail for the case of Al³⁺. The Arrhenius expression was found to be valid only for finer particle sizes (e.g., ?35, +45 US mesh shale). A simple model is finally presented to account for the combined effect of temperature and shale particle size on mineral dissolution rates.     

Lithium recovery from pretreated α-spodumene residue through acid leaching at ambient temperature

A novel alkaline hydrothermal approach for low-temperature conversion of α-spodumene into Li₂SiO₃ residue was proposed, providing a promising method for extracting lithium from α-spodumene as a pretreatment process. This work proposed a systematic investigation for extracting lithium from the residue by acid leaching and preparing lithium carbonate. The reaction feasibility between Li₂SiO₃ and acids (HCl and H₂SO₄) was first evaluated through thermodynamic calculation. Compared with the leaching effects of hydrochloric acid and sulphuric acid, sulphuric acid is the preferred leaching agent due to its higher extraction efficiency for lithium and lower acid consumption. Lithium extraction efficiency from the residue achieved up to 87.48% under the following optimized conditions: 0.75 mol/L H₂SO₄, 0.4 times the theoretical amount of acid, 10 min, 30°C, and 100 rpm. Based on the optimized conditions, the lithium-containing solution was concentrated through three consecutive cycles of leaching, which obtained a concentration of 17.78 g/L for lithium. The leaching solution was purified by CaO-Na₂CO₃, resulting in the removal rates of SiO₃²⁻, Mg²⁺, and Ca²⁺ of 84.22%, 95.51%, and 90.55%, respectively. Finally, the solution was precipitated with sodium carbonate to prepare Li₂CO₃. This paper facilitates the development of an economical process for efficient lithium extraction from spodumene at low temperatures.     

Dissolution rates of alkaline rocks by carbonic acid: Influence of solid/liquid ratio,temperature, and CO2 pressure

Dissolution rates of alkaline rocks, including wollastonite (CaSiO₃), olivine (Mg₂SiO₄), and phlogopite (KMg₃AlSi₃O₁₀(OH)₂), with high pressure aqueous CO₂ solution were measured to examine the feasibility of CO₂ fixation via carbonation. Influence of solid/liquid ratio (1.0–10 g/250 mL), temperature (303–353 K), and CO₂ pressure (1.0–3.0 MPa) on the extraction rates of calcium or magnesium ions was investigated. Under the experimental conditions studied, the calcium ion extraction rate from wollastonite was the highest among the three rock samples studied. The calcium concentration reached about 120 mg/L, and about 12% of the calcium in wollastonite sample was extracted after 60 min at 353 K with 1.0 MPa CO₂. The calcium and magnesium extraction ratios from the alkaline rocks were much lower than those from waste concrete powder. Increasing the extraction time and temperature would be an effective way to promote calcium extraction from wollastonite.     

Effects of humidity on calcite block fabrication using calcium hydroxide compact

Calcite has attracted attention as an artificial bone replacement material and as a precursor for the fabrication of carbonate apatite, which is also an artificial bone replacement material. In this study, the effect of humidity on calcite block fabrication was investigated using calcium hydroxide (Ca(OH)₂) compact. Ca(OH)₂ compact and Ca(OH)₂ paste compact were exposed to CO₂ at room temperature under 0%, 50%, and 100% humidity for two weeks. No carbonation was observed when Ca(OH)₂ compact was exposed to CO₂ under 0% humidity. In contrast, Ca(OH)₂ compact transformed into pure calcite under 100% humidity. Forty percent of the Ca(OH)₂ compact transformed into calcite under 50% humidity, while 30% of the Ca(OH)₂ paste compact transformed into calcite. Interestingly, the diametral tensile strength of the Ca(OH)₂ paste compact was four times higher than that of the Ca(OH)₂ compact when both were exposed to CO₂ under 100% humidity, despite the paste compact׳s lower conversion into apatite. After exposure to CO₂, SEM observations revealed that in the case of the paste compact, the Ca(OH)₂ powder was bridged with a precipitate, whereas in the case of Ca(OH)₂ compact, no precipitate was found. Results obtained in this study demonstrated that carbonation of the Ca(OH)₂ compact at room temperature was the result of a dissolution–precipitation reaction. Ca(OH)₂ powder was dissolved into water to supply the Ca²⁺, and CO₃²⁻ was supplied for the calcite precipitation from the interaction of CO₂ and water. Excess humidity from the paste compact was the key to the precipitation of the calcite bridge. The presence of the calcite bridge resulted in a higher mechanical strength for the calcite block.     

Investigation into the Mechanism of Interaction of Calcium and Magnesium Silicates with Carbon Dioxide in the Course of Mechanical Activation

A prolonged grinding of diopside, akermanite, sphene, wollastonite, and enstatite is accompanied by absorption of CO₂ from the environment (carbonation) along with amorphization and hydration. The IR spectra of ground minerals contain bands of distorted carbonate groups due to absorption of carbon dioxide. If the mechanical activation is not attended by the distortion of the crystal lattice, the sorption of carbon dioxide results in the formation of undistorted [CO₃ ^2–] groups.     

Feasibility of Na-based thermochemical cycles for the capture of CO2 from air—Thermodynamic and thermogravimetric analyses

Three Na-based thermochemical cycles for capturing CO₂ from air are considered: (1) a NaOH/NaHCO₃/Na₂CO₃/Na₂O cycle with 4 reaction steps, (2) a NaOH/NaHCO₃/Na₂CO₃ cycle with 3 reactions steps, and (3) a Na₂CO₃/NaHCO₃ cycle with 2 reaction steps. Depending on the choice of CO₂ sorbent – NaOH or Na₂CO₃ – the cycles are closed by either NaHCO₃ or Na₂CO₃ decomposition, followed by hydrolysis of Na₂CO₃ or Na₂O, respectively. The temperature requirements, energy inputs, and expected products of the reaction steps were determined by thermodynamic equilibrium and energy balance computations. The total thermal energy requirement for Cycles 1, 2, and 3 are 481, 213, and 390 kJ/mol of CO₂ captured, respectively, when heat exchangers are employed to recover the sensible heat of hot streams. Isothermal and dynamic thermogravimetric runs were carried out on the pertinent carbonation, decomposition, and hydrolysis reactions. The extent of the NaOH carbonation with 500 ppm CO₂ in air at 25 °C – applied in Cycles 1 and 2 – reached 9% after 4 h, while that for the Na₂CO₃ carbonation with water-saturated air – applied in Cycle 3 – was 3.5% after 2 h. Thermal decomposition of NaHCO₃ – applied in all three cycles – reached completion after 3 min in the 90–200 °C range, while that of Na₂CO₃ – applied in Cycle 1 – reached completion after 15 min in the 1000–1400 °C range. The significantly slow reaction rates for the carbonation steps and, consequently, the relatively large mass flow rates required, introduce process complications in the scale-up of the reactor technology and impede the application of Na-based sorbents for capturing CO₂ from air.     

Development of a Scalable Method for Manufacturing High‐Temperature CO2 Capture Sorbents

An engineered process for scalable manufacture of a calcium aluminum carbonate CO₂ sorbent with production amounts of about 1000 g per hour has been developed. The process includes mixing and heating, solid‐liquid separation, drying and extrusion, crushing and conveying, and calcined molding steps. The sorbent preparation involves the coprecipitation of Ca²⁺, Al³⁺, and CO₃^2– under alkaline conditions. By adjusting the Ca:Al molar ratio, a series of Ca‐rich materials could be synthesized for use as CO₂ sorbents at 750 °C. A calcium acetate‐derived sorbent exhibited better cyclic stability than sorbents originating from CaCl₂ and Ca(NO₃)₂. The initial sorption capacity increased with CaO concentration. High stability of more than 90 % was maintained by the Ca:Al sorbents after 40 looping tests.     

三元复合钙基材料CaO-Ca3Al2O6-MgO的合成及其CO2吸附性能

采用Al₂O₃和MgO同时掺杂改性的方法制备了CaO-Ca₃Al₂O₆-MgO复合钙基高温吸附CO₂材料。复合钙基材料孔隙发达,活性物相为CaO,惰性骨架物相为Ca₃Al₂O₆和MgO。Ca₃Al₂O₆/MgO质量比偏小的材料,表面微粒粒径较小。在10%（体积分数,下同）CO₂和90% N₂的混合气气氛下,采用热重分析仪测量了复合钙基材料吸附CO₂容量、碳化反应速率以及循环碳化（670℃）/煅烧（900℃）过程的稳定性。结果发现,复合钙基材料CaO-Ca₃Al₂O₆-MgO具有较好的吸附CO₂性能,提高Ca₃Al₂O₆/MgO质量比,合成材料的循环稳定性较好;降低Ca₃Al₂O₆/MgO质量比,合成材料的碳化反应速率加快,CaO转化率提高。最后,通过对不同循环次数下复合钙材料的比表面积、孔径分布、微观形貌、表面元素分布,晶相、晶粒大小进行研究分析,对合成材料的失活以及掺杂物质对烧结的抑制机理进行了讨论。     

Identification of straight-chain fatty acids associated with metallic cations in coals

Straight-chain fatty acids and associated cations, such as Ca²⁺, Mg²⁺ and Fe³⁺, in the solvent extracts from the humic substances of Joban lignite and Taiheiyo coal were analysed after treatment with hydrochloric acid. Gas chromatographic analyses showed the most abundant presence of C₁₆ in the C₁₄ to C₃₂ straight-chain fatty acids. The amount of Ca²⁺ bonded to the fatty acids was calculated to be about 20 ppm of the humic substances.     

The β-nucleating effect of wollastonite-filled isotactic polypropylene composites

Wollastonite (W) with β-nucleating effect (β-W₁₀₀) for iPP crystallization was obtained through reaction between Ca²⁺ in wollastonite and pimelic acid (PA) and the β-iPP composites filled by different content of β-W₁₀₀ were prepared. The effect of PA and wollastonite contents on β-nucleation, crystallization and melting behavior, and crystalline morphology of W and β-W₁₀₀-filled iPP composites was investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction, and polarizing optical microscopy. The results indicated that incorporation of W and β-W₁₀₀ increase the crystallization peak temperature of iPP due to its heterogeneous nucleating ability. And iPP/W composites predominantly crystallize in the α-phase iPP and iPP/β-W₁₀₀ composites in the β-phase iPP. The results of DSC multi-scanning in same and different melting temperatures showed that β-W₁₀₀ not only has strong heterogeneous β-nucleating effect but also DSC multi-scanning in same and different melting temperatures has no influence on the heterogeneous β-nucleating effect of β-W₁₀₀. The β-iPP containing high wollastonite content with high β-phase content can be easily prepared.     

the effect of CO2 on the kinetics and extent of calcination of limestone and dolomite particles in fluidised beds

Measurements have been made of the rates of calcination of limestone particles (diam. 0.4–2.0 mm) in a fluidised bed, electrically heated to a well-defined temperature. Experiments were conducted at atmospheric pressure and also at pressures of 3, 6, 12 and 18 bar, for bed temperatures varying from 1073 to 1248 K. The fluidising gases were air, or occasionally nitrogen, containing up to 20 vol. % CO₂. The results indicate that under these conditions the rate of calcination of such limestone particles is controlled by chemical reaction at a sharp interface between CaCO₃ and CaO. The temperature of this reaction zone is only a few degrees (< 15 K) below that of the fluidised bed. The rate of calcination is found to be of the form: k̄(p^eCO₂ - pⁱCO₂ - Py_I) kmol/m² s, where p^eCO₂ and pⁱCO₂ are, respectively, the partial pressures of CO₂ for equilibrium at the temperature of the reaction interface and in the fluidising gas, k̄ is the rate constant associated with the reverse carbonation reaction (CO₂ + CaO → CaCO₃), P is the total pressure, and y_I is a constant, which depends on the temperature of the bed. Values of k̄ were measured. They appear to be independent of temperature, indicating that carbonation proceeds without an associated activation energy. It is hard to explain the appearance of y_I (an effective mole fraction for CO₂) in the above rate expression. The calcination of one dolomite has been briefly studied and calcination times etc. measured. In general, this appears to be a two-stage process, with the calcination of the MgCO₃ component being insensitive to pressure, unlike the CaCO₃. The value of k̄ for CO₂ + MgO → MgCO₃ is similar to that for the calcium case.     

Mineral carbonation accelerated by dicarboxylic acids as a disposal process of carbon dioxide

Mineral carbonation is based on the reaction of carbon dioxide with metal-oxide bearing minerals, usually containing magnesium or calcium silicate, to form hardly soluble carbonates and other solid byproducts. The concept is based on acceleration of the naturally occurring rock weathering process. In the present work the calcium silicate is present in the mineral, wollastonite. To accelerate the process and make it potentially useful for practical applications, mineral carbonation is conducted here using an indirect two-step route in which the reactive component (Ca²⁺ ions in considered case) is first extracted from the mineral matrix and afterwards carbonated. Two solid byproducts are formed in this process: silica in the extraction step and calcium carbonate in the carbonation step. In the experimental part of this work, both stages of mineral carbonation are investigated using three extraction media: acetic acid and two dicarboxylic acids, succinic and adipic. To interpret the extraction stage of the mineral carbonation process the shrinking core - shrinking shell model is proposed. In the model, the change of the unreacted core size is due to surface reaction that is affected by the porous layer diffusion, with the porous layer subject to abrasion. The model of abrasion is based on the theory of turbulence. Results of investigations show that succinic acid is most effective, followed by adipic acid and acetic acid when both stages of the process are considered in detail.     

New insights into the mechanisms of carbon dioxide mineralization by portlandite

Portlandite (Ca(OH)₂; also known as calcium hydroxide or hydrated lime), an archetypal alkaline solid, interacts with carbon dioxide (CO₂) via a classic acid–base “carbonation” reaction to produce a salt (calcium carbonate: CaCO₃) that functions as a low-carbon cementation agent, and water. Herein, we revisit the effects of reaction temperature, relative humidity (RH), and CO₂ concentration on the carbonation of portlandite in the form of finely divided particulates and compacted monoliths. Special focus is paid to uncover the influences of the moisture state (i.e., the presence of adsorbed and/or liquid water), moisture content and the surface area-to-volume ratio (s_a/v, mm⁻¹) of reactants on the extent of carbonation. In general, increasing RH more significantly impacts the rate and thermodynamics of carbonation reactions, leading to high(er) conversion regardless of prior exposure history. This mitigated the effects (if any) of allegedly denser, less porous carbonate surface layers formed at lower RH. In monolithic compacts, microstructural (i.e., mass-transfer) constraints particularly hindered the progress of carbonation due to pore blocking by liquid water in compacts with limited surface area to volume ratios. These mechanistic insights into portlandite's carbonation inform processing routes for the production of cementation agents that seek to utilize CO₂ borne in dilute (≤30 mol%) post-combustion flue gas streams.     

Production of Ceramic Pigments Based on Natural Wollastonite Using the Gel Method

The authors consider the possibility of producing ceramic pigments based on natural wollastonite using the gel method, which contributes to the formation of an amorphous structure in wollastonite under the effect of hydrochloric acid. The chromophores are soluble salts containing Fe³⁺, Ni²⁺, Cr³⁺, Cu²⁺, and Co²⁺ ions. The wollastonite structure is restored under firing; the color characteristics of pigments after the gel-formation stage improve. The use of the gel method does not require a cardinal modification of the technological scheme and equipment but facilitates a significant improvement of the color properties of pigments and paints.__________Translated from Steklo i Keramika, No. 1, pp. 25 – 27, January, 2005.