Indirect Mineral Carbonation Research Articles

CO2 sequestration by indirect mineral carbonation of industrial waste red gypsum

Abstract In this research, the characterization of red gypsum (RG) and its reaction progress during the indirect mineral carbonation process were studied. X-ray diffraction results showed that the calcium sulfate and hematite are the dominant components in the RG samples. Three main phases of calcium in the RG were recognized: Ca (OH)2, Ca-S-O, and Ca-Fe-O. Element analysis by ICP-OES also revealed that the RG consists of three major constitutions: CaO (32.2%), SO3 (31.6%), and Fe2O3 (28.99%). To understand the reaction progress of RG in the carbonation process, the reaction model code PHREEQC-2.18 was found to be a very useful tool since it allows the exposure of all dissolved species of RG and presents its mineral phases at each time step. Furthermore, the mineral carbonation of RG delivered the reaction progress changes with Ca phases and, therefore, dissolved calcium (hydr)oxide starts to control the pH and the CO2 uptake. In short, the findings of this study could be useful in resolving problem of greenhouse gases with less environmental issues.

Phase diagrams of the MgSO4-Al2(SO4)3-(NH4)2SO4-H2O system at 25 and 55 °C and their application in mineral carbonation

A route for the indirect mineral carbonation of blast furnace slag using (NH4)2SO4 as a recyclable reagent has recently been proposed. The main challenges associated with this route are reducing its energy consumption and improving its cost-efficiency. In this process, the recycling of (NH4)2SO4 by evaporation of the carbonation liquor make up a large proportion of the total energy consumption. Thus, controlling the water dosage during leaching of the products of roasting the blast furnace slag with (NH4)2SO4, which are mainly various sulfates of Ca, Mg, Al, and NH4+, is of great importance. In this study, the solubilities of the quaternary MgSO4-Al2(SO4)3-(NH4)2SO4-H2O system were measured at 25 and 55 °C using the isothermal method. The resulting phase diagrams are instructive for determining the lowest liquid-to-solid ratio required for leaching and for recovery of the value-added byproduct, ammonium alum, from the leachate. The results show that the crystalline region of NH4Al(SO4)2·12H2O dominates in the phase diagrams, indicating that it is easily crystallized out and that the use of this route for the separation of aluminum as ammonium alum is feasible. The liquid-to-solid ratios for the leaching unit were calculated to be 4.55 and 1.97 mL/g at 25 and 55 °C, respectively. The liquid-to-solid ratio at 55 °C was reduced by 56.7% compared to the ratio at 25 °C.

Phase Equilibrium of the MgSO4–(NH4)2SO4–H2O Ternary System: Effects of Sulfuric Acid and Iron Sulfate and Its Application in Mineral Carbonation of Serpentine

The carbonation Mg-rich natural minerals or industrial wastes is an attractive route to store CO2. Recently, an approach involving the indirect mineral carbonation of serpentine with recyclable (NH4)2SO4 or NH4HSO4 is receiving widespread attention. In this study, the solubilities associated with the mineral process (ternary system of (NH4)2SO4–MgSO4–H2O) were measured and calculated using the isothermal method and Pitzer model, respectively. The effects of adding small amounts of H2SO4 and iron sulfate on the solubilities were evaluated. The results showed that the crystalline region of MgSO4·(NH4)2SO4·6H2O (boussingaultite) is larger than those of the other species, which indicates that boussingaultite is crystallized out easily. The presence of H2SO4 at a concentration of up to 10 wt % and iron sulfate of 2.5 wt % almost had no effect of the solubilities. The minimal ratios of liquid to solid during the leaching unit were calculated as 3.45, 2.19, and 1.36 mL/g at 25, 55, and 80 °C, respectively. Compa...

Preparation of Silica-Alumina Nanoparticles via Blast-Furnace Slag Dissolution in Low-Concentration Acetic Acid for Carbonation

Blast-furnace slag (BFS) has been used as a feedstock for CO2 sequestration by indirect mineral carbonation to produce calcium carbonate precipitates and solid residues. The most-abundant elements in these residues, Si and Al, are usually considered to be impurities that need to be removed in acid-dissolution processes involving BFS. The co-production of value-added materials from these residues is an attractive option for strengthening the economic competitiveness of mineral carbonation methods. In view of this, we separated the Si and Al, as their hydrated forms, during the dissolution of BFS in acetic acid prior to carbonation. During the sol-gel processing of Si-Al nanoparticles, a catalyst is usually required during the hydrolysis and subsequent condensation processes. In this study, only condensation occurs because the low-concentrations of acetic acid used facilitate in-situ hydrolysis during the dissolution process. Aging was carried out not only to structurally arrange the Si and Al but also to oxidize the marginal Fe(II) to reddish Fe(III). Silica-alumina nanoparticles (78% Si and 22% Al) were prepared by a simple sol-gel route at ambient pressure. These nanoparticles were amorphous and below 20 nm in size. Fourier-transform infrared (FT-IR) studies reveal that the nanoparticles consist of Si–O–Si and Si–O–Al bonds. 27Al nuclear magnetic resonance (NMR) spectroscopy reveals a significant resonance corresponding to tetra-coordinated Al inside the particle framework.

Indirect mineral carbonation of titanium-bearing blast furnace slag coupled with recovery of TiO 2 and Al 2 O 3

Abstract Large quantities of CO2 and blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial CO2 emission reduction and comprehensive utilization of the solid waste. This paper describes a novel route for indirect mineral carbonation of titanium-bearing blast furnace (TBBF) slag, in which the TBBF slag is roasted with recyclable (NH4)2SO4 (AS) at low temperatures and converted into the sulphates of various valuable metals, including calcium, magnesium, aluminium and titanium. High value added Ti- and Al-rich products can be obtained through stepwise precipitation of the leaching solution from the roasted slag. The NH3 produced during the roasting is used to capture CO2 from flue gases. The NH4HCO3 and (NH4)2CO3 thus obtained are used to carbonate the CaSO4-containing leaching residue and MgSO4-rich leaching solution, respectively. In this study, the process parameters and efficiency for the roasting, carbonation and Ti and Al recovery were investigated in detail. The results showed that the sulfation ratios of calcium, magnesium, titanium and aluminium reached 92.6%, 87% and 84.4%, respectively, after roasting at an AS-to-TBBF slag mass ratio of 2:1 and 350 °C for 2 h. The leaching solution was subjected to hydrolysis at 102 °C for 4 h with a Ti hydrolysis ratio of 95.7%and the purity of TiO2 in the calcined hydrolysate reached 98 wt%. 99.7% of aluminium in the Ti-depleted leaching solution was precipitated by using NH3. The carbonation products of Ca and Mg were CaCO3 and (NH4)2Mg(CO3)2·4H2O, respectively. The latter can be decomposed into MgCO3 at 100–200 °C with simultaneous recovery of the NH3 for reuse. In this process, approximately 82.1% of Ca and 84.2% of Mg in the TBBF slag were transformed into stable carbonates and the total CO2 sequestration capacity per ton of TBBF slag reached up to 239.7 kg. The TiO2 obtained can be used directly as an end product, while the Al-rich precipitate and the two carbonation products can act, respectively, as raw materials for electrolytic aluminium, cement and light magnesium carbonate production for the replacement of natural resources.

Indirect mineral carbonation of blast furnace slag with (NH4)2SO4 as a recyclable extractant

Large quantities of CO2 and blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial CO2 emission reduction and comprehensive utilisation of the solid waste. In this study, a recyclable extractant, (NH4)2SO4, was used to extract calcium and magnesium from blast furnace slag (main phases of gehlenite and akermanite) by using low-temperature roasting to fix CO2 through aqueous carbonation. The process parameters and efficiency of the roasting extraction, mineralisation, and Al recovery were investigated in detail. The results showed that the extractions of Ca, Mg, and Al can reach almost 100% at an (NH4)2SO4-to-slag mass ratio of 3:1 and at 370 °C in 1 h. Adjusting the pH value of the leaching solution of the roasted slag to 5.5 with the NH3 released during the roasting resulted in 99% Al precipitation, while co-precipitation of Mg was lower than 2%. The Mg-rich leachate after the depletion of Al and the leaching residue (main phases of CaSO4 and SiO2) were carbonated using (NH4)2CO3 and NH4HCO3 solutions, respectively, under mild conditions. Approximately 99% of Ca and 89% of Mg in the blast furnace slag were converted into CaCO3 and (NH4)2Mg(CO3)2•4H2O, respectively. The latter can be selectively decomposed to magnesium carbonate at 100–200 °C to recover the NH3 for reuse. In the present route, the total CO2 sequestration capacity per tonne of blast furnace slag reached up to 316 kg, and 313 kg of Al-rich precipitate, 1000 kg of carbonated product containing CaCO3 and SiO2, and 304 kg of carbonated product containing calcium carbonate and magnesium carbonate were recovered simultaneously. These products can be used, respectively, as raw materials for the production of electrolytic aluminium, cement, and light magnesium carbonate to replace natural resources.

Leaching optimization of mining wastes with lizardite and brucite contents for use in indirect mineral carbonation through the pH swing method

This study investigated the leaching process in order to maximize Mg and Fe extraction and to produce amorphous silica (SiO2) with high purity. For this, a mining waste identified as S-GO was employed; which is a serpentinite rock with high lizardite 1T and native brucite contents. A Taguchi Experiment Design was used in order to assess the parameters that influence the leaching process such as: granulometry, hydrochloric acid concentration (HCl), leaching temperature, and mass/volume ratio. Furthermore, thermogravimetric analysis (TGA) was done to understand the interrelation between the mineral structure and leaching performance. Results show that lizardite 1T-bearing serpentinite presents a low content of tetrahedral Al3+ and high octahedral Fe3+ contents on S-GO. Native brucite delayed the formation of a hydrated silica layer and improved dissolution of serpentines. For this, Mg and Fe extractions are efficient, reaching 88 ± 2% of Mg and Fe extracted during the first 30 min of reaction, under mild process conditions: stoichiometric mass/volume ratio, 1M HCl concentration, pressure of 1 bar, temperature of 100 °C, and 300 μm particle size. On the other hand, an excess of acid improves Mg and Fe extraction by only 10 ± 5% for S-GO. Such characteristics reduce energetic penalties and costs involved on indirect mineral carbonation processes by the pH swing method.

Optimum conditions for extracting Ca from CKD to store CO2 through indirect mineral carbonation

Cement Kiln Dust (CKD), a by-product of the cement industry, was used as the raw material to determine the optimum conditions of Ca extraction, which could ultimately be used for indirect mineral carbonation. CKD was a suitable raw material for mineral carbonation due to its high CaO content (42.7%) and fine particle size (23.08 μm), not requiring a pretreatment such as grinding and pH adjustment. Extractions were conducted by varying the factors such as the solvent type, reaction time, temperature, solid-liquid ratio, solvent concentration, and stirring speed, which could affect the Ca extraction. The solvents used (hydrochloric acid, acetic acid, ammonium chloride, ammonium acetate, and sodium citrate) resulted in high Ca extraction efficiencies, and the resultant Ca extract (except for hydrochloric acid) had sufficiently high pH for the carbonation reaction. The optimum conditions set for extracting Ca from the CKD were: 30 min reaction time, 25°C reaction temperature, 1:10 solid-liquid ratio, 1.74 M solvent concentration, and 250 rpm stirring speed. Under these conditions, Ca extraction efficiencies were very high and depended on the solvent used: hydrochloric acid (94.3%), acetic acid (93.7%), ammonium chloride (86.9%), ammonium acetate (85.3%), and sodium citrate (70%). Calcium carbonate was produced by reacting CO2 with Ca extracted with ammonium chloride and ammonium acetate.

Carbon dioxide capture and storage by pH swing mineralization using recyclable ammonium salts and flue gas mixtures

AbstractCO2 mineral sequestration through the employment of silicate rocks such as serpentine is an important technology for the mitigation of CO2 emissions. Most mineral carbonation works in this study use pure CO2. The indirect carbonation process employed different flue gases (5, 15, 25% CO2) and the presence of SOx and NOx. Also, the direct contact of CO2 with the Mg source was compared to the indirect reaction of Mg with CO2 as NH4CO3. The impact of variables such as temperature, solid‐liquid ration (S/L), and molar ratio of additives on carbonation rate and degree was studied. An average carbonation efficiency of about 90% was achieved at 80°C after 30 min for indirect mineral carbonation process. The carbonation efficiency decreased to 50‒60% when the process was directly employed. The carbonation efficiency obtained in the presence of 15‒25% CO2 was very similar to that with 100% CO2 at 140°C, while at 80°C, the carbonation efficiency in presence of flue gas (40‒55%) was much larger compared to that using pure C02 (10% after 3 h). SOx and NOx co‐removal efficiency was 54.4% and 18% at 140˚C and 20 bar, respectively.

Leaching and indirect mineral carbonation performance of coal fly ash-water solution system

The leaching and carbonation performances of indirect mineral carbonation are investigated using coal fly ash (FA) as the raw source and water as the solvent. The reactions were conducted at ambient temperature and pressure with a gas mixture comprised of 15 and 33mol% CO2. The overall CO2 storage and mineral carbonation capacities of FA suspended solution in which alkaline components had been previously leached for 2h (2S33) were 31.06 and 17.36mg CO2/g FA, respectively. The mineral carbonation capacity of FA in 2S33 was 18% of the theoretical value and its mineral carbonation storage capacity ratio was 55.9%. The performance of 2S33 was higher than that of its filtrate because the alkaline components were leached from the suspended FA simultaneously with the mineral carbonation. Submicrometer-sized particles were present in raw FA and their size was reduced by stirring during the leaching, as well as slightly increased, compared to the original raw FA, due to the carbonation. These submicro FA particles strongly affected the performance of the mineral carbonation of the FA-water solution.

Metal extraction and indirect mineral carbonation of waste cement material using ammonium salt solutions

Abstract The effects of different ammonium salts on the cation extraction and mineral carbonation of waste cement were evaluated using four different ammonium salt solutions: CH 3 COONH 4 , NH 4 Cl, NH 4 NO 3 , and (NH 4 ) 2 SO 4 . Extraction and carbonation tests were conducted using waste cement powder as the raw material under ambient temperature and pressure conditions at a solid to liquid ratio of 50 g/L with two different concentrations of ammonium salt solution (0.5 M and 1.0 M). At higher concentration (1 M), the Ca extraction efficiency (∼70%) was higher in the CH 3 COONH 4 and NH 4 NO 3 solutions, but lower in the NH 4 Cl (32%) and (NH 4 ) 2 SO 4 solutions (5%). The Ca selectivity (∼98%) was higher in the CH 3 COONH 4 , NH 4 NO 3 , and NH 4 Cl solutions, but lower in the (NH 4 ) 2 SO 4 solution (90%). The carbonation efficiency was comparable to the extraction efficiency. The carbonation efficiency with the CH 3 COONH 4 and NH 4 NO 3 solutions was higher. Regardless of the type of ammonium salt, high purity vaterite was precipitated after CO 2 injection.

Carbon dioxide capture and storage by pH swing aqueous mineralisation using a mixture of ammonium salts and antigorite source

Carbon Capture and Storage by mineralisation aims to reduce carbon dioxide emissions (CO2) by reacting CO2 with rocks rich in magnesium or calcium oxide and producing solid mineral carbonates, which can provide safe storage capacity. Recently, indirect mineral carbonation by pH swing mineralisation processes that use recyclable ammonium salts has shown promising results, but the process needs to be optimised. For example, the feasibility of this process in the presence of a mixture of NH3-salts has not been demonstrated. Accordingly, carbonation of rocks rich in magnesium and a mixture of NH4HCO3 and (NH4)2CO3 under different temperatures was investigated to reproduce a real scenario from an ammonia capture process. The highest ‘carbonation efficiency’ (expressed as the conversion of Mg ions to hydromagnesite) was 93.5% at 80°C and 1:4:3 as Mg:NH4 salts:NH3 molar ratio, while the ‘total CO2 captured’ was 62.6% under the same conditions, indicating that the process in presence of ammonium salts mixture is feasible.

Mg‐Silicate Carbonation Based on an HCl‐ and NH3‐Recyclable Process: Effect of Carbonation Temperature

AbstractA new indirect mineral carbonation process is studied which could mitigate anthropogenic CO2 emissions. In this process, magnesium silicate is dissolved in HCl and the resulting MgCl2 solution is subsequently reacted with CO2 in NH3. HCl and NH3 are recovered from NH4Cl in a two‐step thermal decomposition. Carbonation is investigated from 30 °C to 180 °C at 4 MPa CO2 pressure and Mg‐carbonate morphology transformations with increasing temperature are identified. Nesquehonite (MgCO3 · 3H2O) is obtained below 70 °C, hydromagnesite (Mg5(CO3)4(OH)2 · 4H2O) is formed at 100 °C, and further temperature increase to 180 °C leads to magnesite (MgCO3) precipitation. Nesquehonite and magnesite can fix more CO2 per mole Mg than hydromagnesite.