Carbonation Of Slag Research Articles

Detailed measurements of in-furnace gas temperature and species concentration distribution regarding the primary-air distribution mode in a spreader and reversal chain-grate furnace

In order to uncover the coal combustion and NOx formation characteristics of chain-grate furnaces and evaluate the effect of the primary-air distribution mode, industrial-size tests with measurements taken of the overall gas temperature distribution in the furnace height direction and gas components (O2, CO, and NO) in the grate zone in a 35 t/h reversal chain-grate furnace were performed at four primary-air distribution modes of the uniform air mode, front-lean air mode, middle-concentrated air mode, and rear-enhanced air mode. Gas temperature decreased continuously in the furnace height direction while showed an increase-to-decrease trend as the grate proceeded. The high-temperature zones with levels below 1350 °C and a small suspension combustion share in the furnace height direction not only confirmed that the primary NOx formation relied on fuel-NO but also ruled against the availability of air staging along the furnace height for NOx reduction. The uniform air mode achieved the highest levels in both burnout and NOx emissions. The other three setups with a sharp air flux reduction in the former air box, decreased apparently NOx emissions while affected burnout to some extent. The rear-enhanced air mode delayed coal combustion with the largest extent and achieved the lowest NOx emissions but highest carbon in slag. In contrast, the middle-concentrated air mode relying on the highest air flux at the central air boxes for strengthening the primary combustion stage, resulted in both NOx emissions and carbon in slag showing acceptable levels of 493 mg/m3 (at 6% O2) and 9.27%, respectively. NOx emissions were reduced by about 18% and meanwhile carbon in slag raised only a limited extent in comparison to the conventional uniform air mode. Therefore, the middle-concentrated air mode was recommended as the optimal primary-air distribution pattern among the four setups.

Real-time investigation of the CO2 mineral carbonation reaction rate through direct aqueous route using semi-dry desulfurization slag

Mineral carbonation via alkaline solid wastes is considered an effective approach to capture and store flue gas CO2 from industries and power plants. In this study, direct mineral carbonation of semi-dry desulfurization slag (SDe-S) through an aqueous route was investigated with an online carbonation setup to measure the amount of CO2 consumed by Ca(OH)2 at atmospheric pressure in a slurry reactor. The carbonated solid and liquid products were characterized by X-ray fluorescence, X-ray diffraction and field emission scanning electron microscopy with energy dispersive X-ray spectrometry. The results show that carbonation caused the sample particle size to become more uniform. A large amount of Ca2+ was dissolved in the waste solution which could be recycled, thus increasing the utilization rate of Ca2+. The CO2 carbonation efficiency and absorption rate of SDe-S could be improved by controlling the reaction operation parameters. The optimal reaction conditions of this reactor were 100 g/L, 60 °C, 400 rpm and 300 mL/min, and the optimal reaction termination time was limited to 249 min to ensure a CO2 absorption efficiency of higher than 90 %. The carbonation process was controlled first by the film diffusion of liquid CO2, then by the chemical reaction, then by the film diffusion of liquid Ca(OH)2, and finally by the diffusion of the product layer. Experimental simulation suggests that the semi-dry desulfurization ash could achieve high CO2 absorption efficiency at atmospheric pressure and low temperature without producing any waste liquid. That is, it pretty economical and environmentally friendly.

Mechanical performance and resistance to carbonation of steel slag reinforced concrete

The use of residues as alternative materials in the production of cement-based composites is significantly growing since it embraces the circular economy concepts. This alternative reduces the demand for natural resources by the construction sector and provides a proper destination for a range of industrial residues. However, the alternative materials must perform properly for safe applications. In this way, the steel slag, a residue of the steel industry, stands out. The steel slag is already applied in some cement-based composites showing enhancement in the mechanical performance, although its durability is barely evaluated. So, this research produced eco-friendly structural concretes of three compressive strength classes and for similar application parameters. The evaluations were performed in concretes with total replacement of conventional aggregates by steel slag aggregates, containing no chemical admixtures and in the presence of a PCE-based superplasticizer. The mechanical performance and resistance to carbonation of these products were evaluated. An accelerated carbonation test was proposed and adopted to better understand the carbonation phenomenon within the research timeframe. The steel slag concretes presented higher compressive strengths and reductions in carbonation depths up to 60% compared to conventional ones. These results corroborate the technical feasibility of applying steel slag as aggregates in cement-based composites.

Effects of four woody plant species revegetation on habitat improvement and the spatial distribution of arsenic and antimony in zinc smelting slag

Broussonetia papyrifera, Cryptomeria fortunei, Arundo donax, and Robinia pseudoacacia were planted on a zinc smelting slag site. The habitat conditions and spatial distribution of arsenic (As) and antimony (Sb) in slag were analyzed after seven years of restoration. The results showed that the pH, conductivity (EC), and moisture content of phytoremediated slag were lower than those of the control slag. The redox potential (Eh) and EC decreased with increasing slag depth. Phytostabilization significantly increased the contents of total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), available phosphorus (AP), and dissolved organic carbon (DOC) in slag. TN, AN, AP, and DOC in slag showed obvious surface polymerization. Phytostabilization increased the content of calcite and gypsum in the slag. As and Sb concentrations were significantly lower than control slag, with an average decrease of 651–844 and 422–693 mg·kg −1, respectively. Residual As and Sb in phytoremediated slag was the most present form, the proportion of which was higher than that in the control slag. The proportions of calcium-bound and aluminum-bound As and Sb were lower. The contents of arsenic and antimony in plants had lower levels and followed the order of roots > leaves > stems. As and Sb showed a strong positive correlation with pH, EC, moisture content, and a negative correlation with TN, TP, AN, AP, and DOC. In summary, phytostabilization significantly improved slag site conditions and reduce As and Sb available concentrations. Novelty statement Co-contamination of As and Sb is common in mining areas because of similar chemical properties. There are only few reports on the effects of matrix modification and phytoremediation (without additional soil cover) on the soil physicochemical properties, the spatial distribution, and the bioavailability of As and Sb in zinc slag with an alkaline pH. The research determined that phytostabilization significantly improved slag site conditions and reduce As and Sb available concentrations. The results obtained can be used as necessary information for the large-scale ecological restoration or vegetation reconstruction of zinc smelting slag yards.

Effect of temperature on the initial properties of calcium sulfoaluminate binders synthesised at 1100°C

ABSTRACT In this investigation, it was studied the effect of curing temperature on the mechanical properties of pastes made with calcium sulfoaluminate cements synthesised from industrial wastes at a relatively low temperature of 1100°C. Fluorgypsum, fly ash, aluminium slag and calcium carbonate were used as raw materials. The main phases of synthesis were calcium sulfoaluminate and gehlenite. Pastes were prepared with different water/cement ratios, 15–25 wt-% hemihydrate and cured at 20 and 40°C. It was found that with higher total amounts of sulphates and increase in temperature, compressive strength is enhanced in the first days of curing and setting times decreased. Ettringite was found to be the main reaction product forming dense structures over time. Calcium sulphates hydration changed the ettringite formation causing fluctuations in the strength development, nevertheless, in some cases the strength surpassed 40 MPa at 28 days. Microstructures and hydration products were studied by SEM and XRD.

A parametric study of accelerated carbonation in alkali-activated slag

Resistance to carbonation is one important attribute that low-CO2 cement alternatives must possess, and is particularly crucial for cement alternatives subjected to aggressive CO2 concentrations such as those used in construction of oil wells and wells for below ground carbon sequestration. Here, a parametric study of alkali-activated slag (AAS) carbonation in aggressive environments has been conducted to examine (i) calcium carbonate polymorphism using X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy, and (ii) the extent of calcium carbonate formation and CO2 adsorption using thermogravimetric analysis (TGA). A range of AASs have been studied by varying the magnesium content of the slag, the activator type (sodium hydroxide and sodium silicate), the activator concentration, and the curing time prior to carbonation. It was uncovered that both (i) magnesium from the slag and (ii) silica from the activating solution are needed to reduce the propensity for the sodium-containing calcium-alumino-silicate-hydrate gel to undergo decalcification.

Performance of Hg0 removal from coal-fired flue gas over coal gasification slag

Mercury (Hg), a kind of heavy metal pollutant, has a great impact on the environment and human health. The highly efficient technology for Hg removal has attracted widespread attention from researchers. In this study, the coal gasification slag (CGS) and the slag after sorting were used as sorbents, and the Hg0 removal performance of the sorbents were investigated through the fixed-bed reactor and entrained flow reactor. The characterization methods such as N2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) were performed to analyze the physical and chemical characteristics of the sorbents. According to the results of fixed-bed Hg0 removal experiment, the Hg0 removal efficiency of the origin slag (OS) and high carbon slag (HCS) could maintain more than 91% at 60–120°C. The high ash slag (HAS) showed the highest Hg0removal efficiency of 97% at 60°C, which was greatly affected by the Hg0 removal temperature. The Hg-TPD (Hg-temperature program desorption) and XPS results indicated that the chemisorbed oxygen on the sorbent participated in the Hg0 oxidation process with HgO formed on the surface of the sorbent. According to the results of entrained flow Hg0 removal experiments, the Hg0 removal efficiencies of OS and HCS were 56% and 57% at C/Hg ratio of 40000 and the Hg0 removal temperature of 60°C, respectively. When the C/Hg ratio was 80000 and the Hg0 removal temperature was 60°C, the Hg0 removal efficiencies of OS and HCS were 100% and 82%, respectively.

CO2 sequestration exploration utilizing converter slag and cold-rolling waste water: The effect of carbonation parameters

The exploration of carbonation routine utilizing BOFs, CRW and CO2 has a significant effect on terminated treatment of metallurgical wastes resourceful disposal at a low cost. This paper investigated the collaborative effect of CRW composition on slag carbonation degree and CRW decalcification rate in CO2 sequestration system, furthermore, the effect of reaction time etc. on both were also discussed under optimal composition. Moreover, the carbonation process was simulated by Aspen software for comparing with the experimental results. The results showed that slag carbonation degree and CRW decalcification rate increased as CRW hardness increased, and kept stable. The optimal calcium conversion was 50.4 %, corresponding to 15.9g CO2/100g slag, and the decalcification rate was 87.1 %, respectively, at 80 °C and 10 L/kg for 60 min. The Aspen simulation results showed the correlation degrees were 0.94 for calcium conversion and 0.98 for decalcification rate.

Pressurized in situ X-ray diffraction insights into super/subcritical carbonation reaction pathways of steelmaking slags and constituent silicate minerals

This study explores mineral carbonation of industrial stainless steelmaking slags and relevant synthetic constituent minerals via in situ pressurized X-ray diffraction, to clarify carbonation reaction pathways and efficiency for carbon storage and waste valorization. The primary mineral phases of Argon Oxygen Decarburization (AOD) and Continuous Casting (CC) slags, namely, åkermanite, bredigite, cuspidine, merwinite, and β- and γ-C2S, were reacted in a custom-built beryllium-capped XRD reactor filled with either water-saturated (wet) subcritical CO2(g), or wet supercritical CO2(SC), in a series of carbonation experiments. Formation of calcite and aragonite was observed for most Ca-bearing minerals, transient precipitation of metastable vaterite was observed, while carbonation of AOD and CC slags in CO2(SC) resulted in hydrated crystalline calcium carbonates and indirect evidence of amorphous carbonate. Results obtained suggest that low-pressure subcritical carbonation routes are attractive for standalone slag carbonation processes, while high-pressure supercritical carbonation routes are amiable to symbiotic integration with CO2(SC)-generating green technologies.

Structural features and combustion reactivity of residual carbon in fine slag from entrained-flow gasification

The carbon content in fine slag during entrained-flow gasification is very high, at present, most of the fine slag was disposed by landfill. It is expected to provide a favorable technology by adding the fine slag to the circulating fluidized bed boilers to participate in combustion reaction. In this study, the gasification fine slags generated from GE, OMB and GSP gasifier, which are typical gasification processes in Ningdong energy and chemical base, was selected for investigation. The structural features and combustion reactivity of the residual carbon in the gasification fine slag were systematically studied by physical adsorption apparatus, laser Raman spectrum and thermogravimetric analyzer. The results showed that the materials in the original gasification fine slag could be divided into cohesive spherical particles, porous irregular particles and isolated large spherical particles, while the acid-washed gasification fine slag was mostly composed of loose fine particles and porous irregular massive particles. Additionally, the particle size of the residual carbon was clustered to 4–8 nm, and the specific surface area and active sites of that decreased orderly as follows: GE>OMB>GSP. The order degree of the residual carbon structure in GE slag was the lowest, and the amorphous carbon structure in it was the highest, while the case in GSP was the opposite. The combustion rate of the residual carbon in GE slag was the fastest, mainly due to its large specific surface area, more amorphous carbon structure and active site, and the comprehensive combustion index of residual carbon in GE slag was 5.26×10−7 %2/(min2·°C3).

Effects of ethylenediamine tetra-acetic acid (EDTA) on the accelerated carbonation and properties of artificial steel slag aggregates

Artificial steel slag aggregates were prepared via accelerated carbonation with the assistance of EDTA. The influences of EDTA on the CO2 uptake, microstructure, and properties of the carbonated steel slag aggregates as well as the performance of concrete were investigated. With the addition of EDTA, the carbonation of steel slag aggregates was enhanced, yielding increases in CO2 uptake, quantity of formed CaCO3 and bulk density whereas reduction in the crushing value. Moreover, EDTA improved the volume stability of the steel slag aggregate. The EDTA played a role as a catalyst in the process of steel slag carbonation, which chelated the calcium leached from steel slag and hence accelerated the calcium leaching. This hence increased the carbonation efficiency and carbonation degree of steel slag. Concretes cast with the steel slag aggregates modified by EDTA gained higher compressive strengths and more stable volumes than that of concretes cast with the steel slag aggregates without EDTA.

Accelerated carbonation of ladle furnace slag and characterization of its mineral phase

Ladle furnace slag is a high-calcium-based alkaline industrial solid waste inefficiently stacked at the site, which consumes large amount of land and pollutes water resources. Carbonation of refining slag not only solves the problem of poor compactness and poor stability of the refined slag as a product, but also eliminates waste and reduces greenhouse gases. Experiments were conducted to explore factors that affect the carbonation of refining slag. The optimal reaction conditions were found to be temperature of 20 °C, liquid-solid ratio of 5, aeration rate of 600 ml/min, and stirring speed of 700 rpm. The slag with less than 88 μm particle size showed the best carbonation effect with 39.6% degree of carbonation. XRD, SEM, FT-IR, and DG-DTA methods were used to investigate the changes in mineralogical characteristics with time in the carbonation process of refining slag. Variations in mineral phase with time were analyzed by semi-quantitative relative intensity ratio (RIR) method. TGA-DTG analysis quantified the Ca conversion, CO2 absorption, and also estimated the CaCO3 mass at different time periods.

Vezivanje ugljen-dioksida sa mineralima i šljakom pri visokom pritisku u autoklavu

Introduction/purpose: Carbonation of minerals (olivine and wollastonite) and secondary materials such as slag under high pressure in autoclaves has high importance due to environmetal problems. Methods: The most important for this process is to have a good knowledge of the behavior of carbon dioxide in water solution under high pressure, the precipitation of silica, dissolution of metals such as nickel and magnesium as well as subsequent filtration. Results: The carbonation process of olivine und slag under high pressure (from 40 to 80 bar) in an autoclave was successfully performed at 175°C, with and without additivies. Conclusion: A comparative analysis has confirmed better carbonation of slag (max. 300 kg/ton) in comparison to that of olivine (max. 70 kg/ton) under the same conditions.

Investigation of carbon-capture property of foam concrete using stainless steel AOD slag

Abstract This study investigated the effect of CO2 curing on the physical properties of foam concrete with porous structures using stainless steel-argon oxygen decarburization (ST-AOD) slag and fly ash. Foam concrete with higher porosity and more open pores allows more carbon dioxide to penetrate the matrix to improve carbon capture properties. Foam concrete was cured according to two methods: CO2 curing and normal curing. In the results of measuring the compressive strength, the specimens that used ST-AOD slag and fly ash all showed increase of strength by CO2 curing. Particularly, the specimens, in which 30% of OPC was replaced with the ST-AOD slag, demonstrated that the strength increase by CO2 curing was higher than that of Plain. The SEM observation showed that the hydrates produced by carbonation of ST-AOD slag were mainly calcite. The Brunauer-Emmett-Teller (BET) analysis results showed that the calcite produced by CO2 curing usually filled the micro-pores of less than 10 nm diameter. TG-DTG revealed that the CO2 uptake and calcite content were increased by mixing ST-AOD slag and fly ash. From the experimental results, it can be concluded that CO2 uptake of foam concrete is higher than that of normal concrete.

Froth flotation separation of carbon from barium slag: Recycling of carbon and minimize the slag

Barium slag is a kind of solid waste derived from the carbon reduction process of producing barium salt. Carbon is one of the main components in barium slag with a content of more than 10%. In this study, a barium slag was characterized using XRF, XRD and SEM-EDS, and froth flotation test was introduced to recover the carbon in the barium slag. In the process of froth flotation test, diesel was selected as a collector and terpenic oil was selected as a frother for carbon separation. The flotation influences of pulp pH, collector dosage, frother dosage and flotation time were investigated. The results showed that the obtained carbon concentrate had a carbon grade of 63.25% and its recovery was 82.70% under the conditions of pH 8.50, diesel 600 g/t, terpenic oil 500 g/t, and flotation time 5 min. SEM-EDS analysis results revealed that the flotation concentrate was coarse and its particle sizes had a homogeneous distribution. The findings of this research provide a new pathway for barium slag utilization. The carbon obtained from the flotation test in this study can be recycled as raw materials, while the reduction of the remaining tailings can be utilized as building material additives.

Analysis of carbonation and hydration of BOF steel slag for application as railway ballast

The reutilization of waste is a valuable alternative for the preservation of natural resources and the environment. In this sense, Basic Oxygen Furnace (BOF) steel slag is one of the most residues generated in steel the industry. It is estimated that for each ton of steel produced, about 150 kg of steel slag is generated in the BOF process. Generally, the newly produced BOF steel slag is volumetrically unstable, presenting expansive characteristics, and for this reason, its application should be based on stabilization studies. The main objective of this research was to analyze the chemical stabilization process of BOF steel slag by means of carbonation of the material. For this purpose, an experimental method based on hydration and carbonation in 2-meter high slag piles, moistened with sprinklers and instrumented with leaf wetting, temperature, precipitation and carbon dioxide content sensors was used. A control stack was also set up to accompany the stabilization process through the conventional procedure, in which the material is disposed of in large stacks and subjected to the weather conditions for long periods. The laboratory campaigns were developed in the laboratories of the Federal University of Ouro Preto. Thus, through the results obtained, it was possible to conclude that the stabilization method based on hydration and carbonation for the BOF steel slag was efficient, reducing the free lime content to values well below those prescribed internationally.

Carbon-Dioxide and Hydrogen-Sulfide Removal from Simulated Landfill Gas Using Steel Slag

Municipal solid waste landfills are a source of major greenhouse gases such as methane (CH4) and carbon dioxide (CO2) and emit a trace amount of hydrogen sulfide (H2S). Recently, steel slag has extensively been used for mineral CO2 sequestration to minimize the CO2 releases to the atmosphere. This study explores the potential of basic oxygen furnace (BOF) steel slag to simultaneously remove CO2 and H2S from landfill gas (LFG). Various batch and column tests were conducted to evaluate the CO2 and H2S removal potential of the BOF slag under various conditions such as moisture content and particle size of the BOF slag. The three different particle sizes of BOF slag (coarse, as-is, and fine) were exposed to continuous flow of a synthetic LFG [50% CO2, 48.25% CH4, and 1.75% H2S by volume (v/v)] in a column reactor to evaluate the effect of particle size on CO2 and H2S removal capacity of the slag. Similarly, the BOF slag was exposed to synthetic LFG as well as 20% (v/v) of H2S alone in batch reactors at varying moisture contents (10%–30% by weight) to evaluate the effect of moisture content on the CO2 and H2S removal capacity of the slag. A significant H2S removal of 27 g H2S kg−1 BOF slag and CO2 removal of 76 g CO2 kg−1 BOF slag were obtained in the batch reactor. The fine BOF slag (<0.106 mm) showed the maximum CO2 removal (300 g CO2 kg−1 BOF slag) and H2S removal (38 g H2S kg−1 BOF slag) upon exposure to continuous synthetic LFG flow in the column reactor. The quantitative X-ray diffraction (QXRD) analysis showed the highest increase in carbon (77.5 g C kg−1 BOF slag) and sulfur (28 g S kg−1 BOF slag) contents in the fine BOF slag, which was consistent with the mass balance of carbon and sulfur from CO2 and H2S uptake in column tests. The major reaction product with H2S was elemental sulfur depicted by the significant increase in the sulfur content in the X-ray fluorescence analysis. The key minerals involved in carbonation reactions were lime, portlandite, and larnite, as these minerals showed significant reduction in weight percentage (100%, 82%, and 80%, respectively) in the QXRD analysis. Overall, BOF slag showed promising results in mitigating CO2 and H2S from LFG.

Influence of various additives on the early age compressive strength of sodium carbonate activated slag composites: An overview

Abstract The use of sodium carbonate as an alkali activator for slag to produce alkali-activated slag is promising due to its sustainable, economic and user-friendly properties. However, the lower early age performance of composites made with such binder has limited its use especially in applications where higher early age is required. Hence, in order to propel the application of this sustainable binder, it is imperative to find ways in which the early age performance can be enhanced without having a detrimental effect on later age performance. One of the effective and sustainable ways to enhance the early age strength of sodium carbonate activated slag is by incorporation of various additives as partial replacement of sodium carbonate on/and slag. In order to propel more application of sodium carbonate slag for various applications, this current study was undertaken. In this paper, an overview of the types of various additives that can be used to enhance the early age compressive strength of sodium carbonate activated slag composites was discussed. The mechanism and dosage of each of the additives were briefly discussed alongside the limitation and advantages of the additives. Findings from this overview showed that the early age compressive strength of sodium carbonate activated slag can be enhanced with the use of additives such as calcium oxide, calcium hydroxide, Portland cement, sodium hydroxide and sodium silicate.

Structure Evolution and Crystallization Behavior of CaO–SiO2-Based Slags with Varying Carbon

The effect of carbon on the structure and crystallization behavior of CaO–SiO2-based slags was investigated through Raman and single hot thermocouple technique. Raman analysis showed that with increasing carbon, Q3, Q2 increased, Q1, Q0 decreased (Qn, n is the number of bridge oxygen in a [SiO4]-tetrahedral unit), and then the degree of polymerization (i.e., the complexity of silicate slag network structure) increased. The time–temperature-transformation result showed that the incubation time first prolonged and then shortened with adding carbon, which was related to the form of carbon in slags. When carbon dissolved in slags, it reacted with O2−, increased viscosity, and then inhibited the crystallization property. When carbons existed in the particles form, it enhanced the heterogeneous nucleation and then the crystallization behavior. The crystallization kinetics research indicated that with the addition of carbon, the limiting factor of crystallization could be converted from interface reaction controlled to diffusion controlled and then to interface reaction controlled again. Concurrently, the activation energy of crystallization first increased from 370.36 to 446.61 kJ/mol and then reduced to 313.37 kJ/mol.

Effect of hydrophobicity on autogenous shrinkage and carbonation of alkali activated slag

The aim of this study is to investigate the feasibility of applying super-hydrophobic slag (s-slag) to reduce the autogenous shrinkage and enhance resistance to carbonation of alkali-activated slag (AAS). The s-slag is produced by milling slag with stearic acid. The influence of the s-slag on the wetting behaviour is characterized by the water contact angle. It was found that the addition of s-slag has a significant influence on the hygroscopic and water absorption properties of the AAS. The hydration kinetics, reaction products, internal humidity, surface tension of pore solution and carbonation depth are investigated in order to explain the mitigation mechanism of the autogenous shrinkage and carbonation test. After applying 20% s-slag, the autogenous shrinkage and carbonation depth of AAS can be reduced by 68% and 70%, respectively compared to the reference. The surface coating by stearic acid reduces the contact between the slag and the activated solution, which decreases the heat release of AAS. The hydrophobic modification alters the wetting property of the AAS which is helpful to decrease the capillary pressure and obstruct contact with CO2. As a result, the autogenous shrinkage and carbonation depth are dramatically decreased. In addition, the introduction of the s-slag increases the compressive strength and flexural strength of AAS.