Accelerated Carbonation Technology Research Articles

CO2 activation of magnesium slag for the preparation of unburned aggregate: Performance evaluation, CO2 absorption, and ecological benefits

For the development of unburned aggregate, accelerated carbonation technology is deemed to be a significant curing method. In this paper, accelerated carbonation was applied in preparing magnesium slag unburned aggregate (MSUA). The effects of curing time on physical property, phase evolution, CO2 absorption, microstructure and stability of MSUA were explored by employing XRD, TGA, MIP and SEM-BSE characterization techniques. According to the results, with the increase of carbonation time, the mechanical strength and apparent density of MSUA prepared by accelerated carbonation technology enhance, while the water absorption rate declines. The predominant form of the carbonation product is calcite (CaCO3), accompanied with amorphous silica gel. The amount of CO2 absorption has positive correlation with time, exhibiting an absorption rate of 18.5 % at 168 h of carbonation. On the other hand, with 3 h CO2 curing of MSUA, the alkali-silica reaction (ASR) expansion can be completely suppressed. As observed from MIP analysis, the increase of carbonation time reduces the porosity of aggregates. SEM analysis also reveals that gel pores are filled with carbonation products, leading to a denser structure of the aggregate matrix, which is possibly a crucial factor for the suppression to ASR expansion. Based on these findings, MSUA is demonstrated to have enormous potential in substituting natural aggregates and reducing carbon emissions.

Accelerated carbonation of waste paper fly ash by liquid process (NaHCO3) for stabilization of Ba and Pb

The increase of energy valorization of paper sludge waste and biomass due to their high calorific value by incineration leads to an increase of waste paper fly ash (WPFA) quantities, which are in most cases considered as hazardous, and must be dealt with accordingly. The Alternative options for the management of WPFA, such as stabilization/solidification, vitrification or sintering, are not fully developed or either costly. In the present study, accelerated carbonation technology was used to reduce the hazardous nature of WPFA by improving the stabilization of metallic and metalloids trace elements (MMTE), especially Barium (Ba) and Lead (Pb) leaching. The accelerated carbonation of WPFA was found to be optimal at a water/solid ratio of 0.3 L/kg under controlled temperature and humidity conditions. The use of water saturated with 25% sodium bicarbonate (NaHCO3) improved the carbonation of WPFA and the stabilization of Ba and Pb. Batch leaching tests based on thermodynamic equilibrium was used to evaluate the solubility of the MMTE as a function of pH and at the natural pH of non‑carbonated and carbonated WPFA. Thermogravimetry, X-ray diffraction, scanning electron microscopes and energy dispersive spectroscopy analyses were performed to investigate the evolution of carbonation over time and its effect on the chemical and mineralogical properties of WPFA. After 30 days of accelerated carbonation, the leaching concentration of Ba and Pb was below the French legal limit. The leaching concentration of Ba and Pb from carbonated samples decreased 99% and 99.5% respectively. The leaching and release potential behavior of carbonated WPFA were further evaluated using the four-step sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR). The speciation of MMTE underwent significant transformation, shifting predominantly from the soluble fraction to the carbonated fraction as a result of the carbonation reaction.

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.

Novel carbonation solidification process for recovery of Zn-contaminated slurry: Strength and leachability aspects

In this study, a continuous process of foam drying pre-treatment with steel slag powder and carbonation solidification (SSFD-C) was used to recycle zinc- (Zn-) contaminated slurry, which achieved the first implementation of accelerated carbonation technology in contaminated slurry recovery. Unlike conventional carbonation solidification methods, the steel slag component of the slurry also underwent a drying process as part of the SSFD-C process. During the drying process, the mechanism whereby the contaminating Zn ions interacted with steel slag, and the effects of these interactions on the carbonation efficiency and mechanical properties of the carbonated soil (CS) were investigated by testing CO2 uptake and unconfined compressive strength (UCS). In addition, the stabilizing effects of the drying and carbonation processes on Zn contamination were evaluated by establishing pH values and Zn leaching concentrations of the dried soil (DS) and CS under water/acid leaching. This study makes several important contributions to the existing literature on Zn contamination and its effect on the UCS of CS. We found that Zn contamination negatively impacted the UCS of CS by impairing its carbonation efficiency. Additionally, it was found that both drying and carbonation processes can efficiently reduce acid-leached Zn concentration by 45–85% compared to untreated contaminated samples. It was established that Zn contamination is stabilized as Zn(OH)2 in DS and CS specimens through an X-ray diffractometry and derivative thermogravimetric analysis. Furthermore, our study highlights the benefit of carbonation in stabilizing Zn leaching, as it lowers the pH value of water-leached samples.

Accelerated carbonation of ball-milling modified MSWI fly ash: Migration and stabilization of heavy metals

Mechanical ball-milling is an effective technique to reduce particle size, increase lattice defects, and enhance the activity of materials. After mechanical ball-milling modification, an accelerated carbonation technology of municipal solid waste incineration fly ash (FA) was proposed. The effects of ball-milling on carbonation efficiency, heavy metals stabilization, and heavy metals leaching characteristics were investigated. The results showed that the initial carbonation efficiency of ball-milled FA (MFA) was higher than that of the original FA (OFA) because of the in-situ carbonation reaction and the stability of Pb, Cu, and Cd in MFA was improved. The carbonation reaction of MFA was conducted thoroughly by the elevated ionic strength and mass transfer efficiency. The surface of carbonated OFA (COFA) and carbonated MFA (CMFA) stacked calcium carbonation in loose strips and compact spherical respectively, relating to the initial morphology. The dechlorination of CMFA was superior to COFA because the more in-depth carbonation eluted the chlorine from Friedel’s salt. The leaching concentrations of heavy metals in CMFA were lower than those in COFA, especially the immobilization efficiency of Pb and Zn reached 99.8 % and 98.5 %, respectively, contributed by the conversion of the Pb and Zn from ionic hydroxides to stable carbonates. Due to the low acid neutralization capacity of CMFA, when the pH dropped from 7 to 5, the heavy metals carbonate chemical precipitation dissolved, and the effect of calcium carbonation on heavy metals wrapping and adsorption disappeared, therefore the subsequent disposal of CMFA should avoid an acidic environment.

Effect of Extended Carbonation Curing on the Properties of γ-C2S Compacts and Its Implications on the Multi-Step Reaction Mechanism

Accelerated carbonation of the cement-based materials has attracted worldwide attention due to the advantages of rapid strength gain and CO₂ sequestration. This work was designed to investigate the mechanism of γ-C₂S compacts under extended carbonation curing to further develop the accelerated carbonation technology. Based on the variation of the mechanical properties, microstructure, and the phase assemblages through the extended carbonation, a multi-step reaction mechanism is proposed in this work. The process can be divided into three stages: phase-boundary-controlled stage; product layer CO₂ diffusion-controlled stage; and CO₂ diffusion and calcium ion dissolution-controlled stage. Correlation between the calcium carbonate polymorph and the controlling factors is also investigated, in which the high calcium ion concentration is beneficial to the formation of calcite. Meanwhile, the stepwise pressurization curing regime based on the multi-steps is proposed to increase the strength obviously, which further verifies the mechanism of multi-step reactions.

Accelerated carbonation technology for enhanced treatment of recycled concrete aggregates: A state-of-the-art review

• Reaction processes and factors of accelerated carbonation are summarized. • The quality of carbonated recycled concrete aggregates (RCAs) is evaluated. • The performance of concrete incorporating carbonated RCAs are discussed. • Environmental impacts and economic feasibility are analyzed. The accelerated carbonation technology has been utilized in order to enhance the properties of the recycled concrete aggregates (RCAs) and efficient sequestration of carbon dioxide. Numerous studies have been conducted on this developing technology, while there are few systematic reviews on this method. In the present paper, the reaction processes, influencing factors and mechanisms of the accelerated carbonation to treat RCAs are summarized. The quality of carbonated RCAs and the properties of concrete incorporating carbonated RCAs are evaluated. Moreover, the environmental impacts and economic feasibility of this technique are analyzed. Results showed that carbon dioxide could react with calcium hydroxide, calcium silicate hydrates and other calcium substances in RCAs leading to the precipitation of calcium carbonate. The carbonation processes were mainly determined by carbonation conditions and RCAs characteristics. Carbonated RCAs exhibited lower water absorption, lower crush value and higher apparent density than the non-carbonated ones. The mechanical properties and durability of the concrete containing carbonated RCAs were also improved significantly. This technology has been also confirmed an environmentally friendly and economically feasible method. Finally, some research perspectives on this technology are presented.

Accelerated carbonation treatment of recycled concrete aggregates using flue gas: A comparative study towards performance improvement

CO2 source is one of the limiting factors for popularizing the accelerated carbonation technology in recycled concrete aggregates (RCAs) improvement. In this paper, the feasibility of using flue gas (CO2 content of 20 %) from cement plant as alternative CO2 source to improve RCAs was systematically studied and evaluated. Results showed that the carbonation extent and physical properties of the RCAs treated by flue gas were obviously improved and were comparable to those treated by commercial mixed gas with CO2 content between 20 % and 100 %. Based on the results of thermal gravimetric (TG), fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis, calcium hydroxide and calcium silicate hydrates in RCAs were significantly transformed into calcium carbonate at the optimal gas flow rate (5 L/min) after 168 h of treatment. The workability, compressive strength and flexural strength of concrete incorporating carbonated RCAs treated by flue gas were comparable with those treated by mixed CO2 gas, but were much better than those of concrete containing non-carbonated RCAs at all the replacement rate. Finally, the environmental impact and economic feasibility using flue gas to improve RCAs were evaluated based on a combined waste recycling system. All indicated that flue gas could be effectively utilized as CO2 source to improve RCAs.

Accelerated carbonation technology granulation of industrial waste: Effects of mixture composition on product properties.

The use of accelerated carbonation technology in combination with a granulation process was employed to produce aggregates from a variety of industrial wastes, which included municipal solid waste incineration fly ash and air pollution control residue, oil shale ash, cement kiln dust, and quarry fines that have been produced in Estonia. Focusing mainly on the effects produced by the content of municipal solid waste incineration ash in the admixtures, the granule compositions were varied in order to tailor granule properties on the basis of CO2 uptake, strength development, leaching behaviour, microstructure, and morphology. All the steps involved in the accelerated carbonation technology granulation process, from mixing with additives to granulation and carbonation treatment, were carried out in the same apparatus - an Eirich EL1 intensive mixer/granulator. The amount of CO2 that was bound ranged from 23 to 108 kg per tonne of waste. The granules that included the optimised mixture of municipal solid waste incineration air pollution control residue, oil shale ash, cement kiln dust, and ordinary Portland cement were characterised by the highest compressive strength (4.03 MPa) and water durability for the size range of 4-10 mm. In addition, the process was found to be effective in reducing alkalinity (pH < 11.5) and immobilising heavy metals (especially zinc) and chloride. The composition and properties of the respective waste materials and mechanisms associated with the characteristics of the resulting granules were also addressed.

Particle Size Effects on Breakage of ACT Aggregates under Physical and Environmental Loadings

Aggregates manufactured from fine-grained thermal waste residues using accelerated carbonation technology (ACT) represent a potential sustainable alternative to natural aggregates. However, for these manufactured products to compete with virgin stone in geotechnical applications, their durability under mechanical and environmental loadings must be assessed. This paper describes the particle breakage that occurs for different grain sizes (entire sample, 5–2.5 mm and 2.5–1.25 mm) of a cement kiln dust accelerated carbonated manufactured aggregate after undergoing triaxial compression, triaxial shear, and freeze/thaw (f/t) testing. The particle breakage of the aggregate was dominated by the larger (5–2.5 mm) size fraction of the sample under all loading conditions. Particle breakage results from f/t testing indicated that the 5–2.5 mm size corresponded to similar or slightly less particle breakage than that under triaxial shear, whereas the particle breakage of the 2.5–1.25 mm aggregate after 20 cycles of freeze–thaw was relatively small. The performance of the carbonated aggregate in terms of relative breakage was similar or slightly better than the results for natural calcareous sand found in the literature.

Manufactured aggregate from cement kiln dust

This paper presents the results of a laboratory study that evaluated the geotechnical and geoenvironmental properties of a manufactured aggregate derived from cement kiln dust (CKD). The aggregate manufacturing process involves accelerated carbonation technology (ACT), has been used to treat contaminated soils at trial scale. The process operates at commercial scale in the UK, producing aggregates from thermal residues. The ACT process relies on the accelerated reaction of carbon dioxide with the calcium oxide in the CKD material in the presence of water. No additional binder was used in this study, relying solely instead on the formation of carbonate to form the aggregate. In this paper, the aggregate manufacturing process is briefly described. To explore future potential construction applications of the aggregate, several geotechnical test results are used to assess strength and durability (i.e. individual particle strength, internal shear strength of the particle assemblage, wet–dry testing, freeze–thaw testing). Screening tests on the aggregate’s geoenvironmental characteristics are discussed (metal leaching, dissolved heavy metal adsorption and hydraulic conductivity) to assess potential uses further. It is shown that the aggregate studied has adequate properties for a variety of construction applications, but is unsuitable for use in freezing and thawing environments.

Foaming characteristics and microstructure of aerated steel slag block prepared by accelerated carbonation

Abstract The present paper discusses investigated the foaming behaviors and microstructure of three aerated steel slag block (ASSB) samples prepared with three different foaming agents (namely animal protein, hydrogen peroxide, aluminum powder) and by accelerated carbonation. The composition and microstructure of the ASSB samples before and after accelerated carbonation were characterized using X-ray diffraction (XRD), Rietveld method, thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy (FE-SEM). It is an advisable method for foamed steel slag products to use the aluminum powder and accelerated carbonation technology. The aluminum powder favored a good foaming behavior for steel slag owing to (i) a high porosity and low dry density, (ii) a high hydration degree of minerals in steel slag, including brownmillerite, larnite, and lime, which was confirmed by the analysis of mineral compositions using Rietveld method, and (iii) the interlaced lamellas of monocarboaluminate and calcium silicate hydrate (C-S-H) gel strengthen the bubbles wall, which was confirmed by morphology analysis using FE-SEM. After accelerated carbonation, the monocarboaluminate shifted to aragonite, vaterite, calcite and amorphous aluminum hydroxide (Al(OH)3), which was confirmed by XRD, TGA and FT-IR. The network skeleton formed by aragonite crystals improved the compressive strength of ASSB prepared by aluminum powder. In addition, the reactions of the formation and carbonation of monocarboaluminate phase were proved to be thermodynamically possible in this work.

Effect of carbon-negative aggregates on the strength properties of concrete for permeable pavements

ABSTRACT Permeable pavements are engineered to temporarily store water to reduce flooding during rainfall events. Permeable pavements are distinguished primarily based on their surface materials which can vary from concrete, asphalt, clay brick, concrete pavers or plastic grids. This paper examined the effect of lightweight carbon-negative aggregates (CNA) on the behaviour of concrete intended for use as solid concrete block pavers in permeable pavements. Performance indicators targeted compressive strength, splitting tensile strength, density and water absorption. CNA were produced and sourced from manufacturing firm Carbon8 Systems in Kent U.K which applies patented accelerated carbonation technology to solidify incinerated ash into useful eco-friendly aggregates. The methodology involved substituting natural aggregates (NA) by mass, with CNA at percentages varying from 0 to 100. A scanning electron microscope was used to examine the aggregate–mortar interface. Both the compressive and tensile strengths decreased exponentially with the addition of CNA. Average 28-day compressive and splitting tensile strengths ranged from 69 MPa (10,000 PSI) to 18 MPa (2600 PSI) and 3.84 MPa (560 PSI) to 1.23 MPa (178 PSI) respectively. Density values decreased linearly with the addtion of CNA with average values ranging from 2200–2600 kg/m3. ⁠Conversely, water absorption increased with increases in CNA with average values ranging from 1.66% to 9.17%. Depending on the loading requirements, CNA can replace NA in solid permeable pavement blocks by up to 100%.

A Study on Strength and Xrd Analysis of Carbonated Concrete

There are number of factors which control the rate of process of natural carbonation and make it very slow in cement based material. Studies show that the effect of carbonation is mostly limited to corrosion of steel reinforcement in R.C.C. structures (including cover depth design and service life prediction). Research at global level is focused on developing a cost effective and safe technology for the possibility of carbon dioxide sequestration as per IPCC guide lines, and attempts are being made to apply the accelerated carbonation technology for CO2 sequestration in concrete. This paper discusses about the detailed study on the uptake quantity of carbon dioxide in concrete, increase of strength and changes in mineral content by adopting. The concrete grades of M15, M20, M25 and M30 were taken for investigating the strength with respect to time of exposure and pressure by adopting Accelerated Carbonation Technology by using commercially available pure CO2 for carbonation curing. After the testing of concrete for strength, XRD analysis was carried out to study the conversion of calcium hydroxide into calcium carbonate due to carbonation. This green technology would help cement, concrete, precast product and other similar manufacturing industries to obtain carbon credit and they can adopt this green technology to reduce their industrial carbon dioxide emissions into the atmosphere to reduce global warming.

Hygrothermal properties of blocks based on eco-aggregates: Experimental and numerical study

This paper presents a study of eco-aggregates produced by a new Accelerated Carbonation Technology (ACT) in a sustainable approach. These eco-aggregates, obtained by mixing industrial by-products or wastes such as ashes with carbon dioxide (CO2), have some characteristics which make them useful in the field of construction materials such as natural aggregates replacement in concrete or mortar. Hygric and thermal characterizations were performed on carbonated aggregates with adapted methods. The results have been compared to that obtained with two reference aggregates: natural gravel and expanded clay. Then thermal and hygric behaviors of concretes-based on carbonated aggregates were analyzed and discussed in the field of construction. These results proved that carbonated aggregates can be valorized through the manufacturing of concrete building blocks with several advantages: mechanical strength, thermal and hygric inertias. Experimental properties allowed a numerical/digital simulation in dynamic conditions for a simple and multilayered wall using the SPARK object-oriented simulation environment that is adapted to complex problems. Their performances were compared to those of concretes based on two reference aggregates in order to highlight the feasibility of manufacturing building blocks.

Changes in mineralogical and leaching properties of converter steel slag resulting from accelerated carbonation at low CO 2 pressure

Steel slag can be applied as substitute for natural aggregates in construction applications. The material imposes a high pH (typically 12.5) and low redox potential (Eh), which may lead to environmental problems in specific application scenarios. The aim of this study is to investigate the potential of accelerated steel slag carbonation, at relatively low pCO 2 pressure (0.2 bar), to improve the environmental pH and the leaching properties of steel slag, with specific focus on the leaching of vanadium. Carbonation experiments are performed in laboratory columns with steel slag under water-saturated and -unsaturated conditions and temperatures between 5 and 90 °C. Two types of steel slag are tested; free lime containing (K3) slag and K1 slag with a very low free lime content. The fresh and carbonated slag samples are investigated using a combination of leaching experiments, geochemical modelling of leaching mechanisms and microscopic/mineralogical analysis, in order to identify the major processes that control the slag pH and resulting V leaching. The major changes in the amount of sequestered CO 2 and the resulting pH reduction occurred within 24 h, the free lime containing slag (K3-slag) being more prone to carbonation than the slag with lower free lime content (K1-slag). While carbonation at these conditions was found to occur predominantly at the surface of the slag grains, the formation of cracks was observed in carbonated K3 slag, suggesting that free lime in the interior of slag grains had also reacted. The pH of the K3 slag (originally pH ± 12.5) was reduced by about 1.5 units, while the K1 slag showed a smaller decrease in pH from about 11.7 to 11.1. However, the pH reduction after carbonation of the K3 slag was observed to lead to an increased V-leaching. Vanadium leaching from the K1 slag resulted in levels above the limit values of the Dutch Soil Quality Decree, for both the untreated and carbonated slag. V-leaching from the carbonated K3 slag remained below these limit values at the relatively high pH that remained after carbonation. The V-bearing di-Ca silicate (C2S) phase has been identified as the major source of the V-leaching. It is shown that the dissolution of this mineral is limited in fresh steel slag, but strongly enhanced by carbonation, which causes the observed enhanced release of V from the K3 slag. The obtained insights in the mineral transformation reactions and their effect on pH and V-leaching provide guidance for further improvement of an accelerated carbonation technology.

Environmental Remediation and Conversion of Carbon Dioxide (CO2) into Useful Green Products by Accelerated Carbonation Technology

This paper reviews the application of carbonation technology to the environmental industry as a way of reducing carbon dioxide (CO2), a green house gas, including the presentation of related projects of our research group. An alternative technology to very slow natural carbonation is the co-called ‘accelerated carbonation’, which completes its fast reaction within few hours by using pure CO2. Carbonation technology is widely applied to solidify or stabilize solid combustion residues from municipal solid wastes, paper mill wastes, etc. and contaminated soils, and to manufacture precipitated calcium carbonate (PCC). Carbonated products can be utilized as aggregates in the concrete industry and as alkaline fillers in the paper (or recycled paper) making industry. The quantity of captured CO2 in carbonated products can be evaluated by measuring mass loss of heated samples by thermo-gravimetric (TG) analysis. The industrial carbonation technology could contribute to both reduction of CO2 emissions and environmental remediation.

Application of accelerated carbonation with a combination of Na 2CO 3 and CO 2 in cement-based solidification/stabilization of heavy metal-bearing sediment

The efficient remediation of heavy metal-bearing sediment has been one of top priorities of ecosystem protection. Cement-based solidification/stabilization (s/s) is an option for reducing the mobility of heavy metals in the sediment and the subsequent hazard for human beings and animals. This work uses sodium carbonate as an internal carbon source of accelerated carbonation and gaseous CO 2 as an external carbon source to overcome deleterious effects of heavy metals on strength development and improve the effectiveness of s/s of heavy metal-bearing sediment. In addition to the compressive strength and porosity measurements, leaching tests followed the Chinese solid waste extraction procedure for leaching toxicity – sulfuric acid and nitric acid method (HJ/T299-2007), German leaching procedure (DIN38414-S4) and US toxicity characteristic leaching procedures (TCLP) have been conducted. The experimental results indicated that the solidified sediment by accelerated carbonation was capable of reaching all performance criteria for the disposal at a Portland cement dosage of 10 wt.% and a solid/water ratio of 1:1. The concentrations of mercury and other heavy metals in the leachates were below 0.10 mg/L and 5 mg/L, respectively, complying with Chinese regulatory level (GB5085-2007). Compared to the hydration, accelerated carbonation improved the compressive strength of the solidified sediment by more than 100% and reduced leaching concentrations of heavy metals significantly. It is considered that accelerated carbonation technology with a combination of Na 2CO 3 and CO 2 may practically apply to cement-based s/s of heavy metal-bearing sediment.

Pb stabilization in fresh fly ash from municipal solid waste incinerator using accelerated carbonation technology

Carbonation technology with CO 2 absorption was used to enhance the stabilization of heavy metals in fresh fly ash from a municipal solid waste incinerator (MSWI). The influence of fundamental parameters affecting the stabilization of heavy metals, especially Pb and diffusivity and reactivity of CO 2, was evaluated. The results indicated that the addition of 10% or more of water could remarkably accelerate the absorption of CO 2 and could also accelerate the stabilization of MSWI fly ash. The stabilization of MSWI fly ash is not distinct within 1 d in the air atmosphere for low content of CO 2 (0.03%). The result of the XRD analysis indicated that CO 2 could combine with Ca(OH) 2 to form CaCO 3 and CO 2 could also combine with heavy metal oxide to form heavy metal carbonate in the adsorption of CO 2. The TGA analysis showed that MSWI fly ash has the sequestration capability of 3% (w/w) CO 2. The sequestration of CO 2 has a large impact on Pb, and the exchangeable Pb can be converted into carbonated form in rich CO 2 condition to be stabilized.

Comparison of properties of traditional and accelerated carbonated solidified/stabilized contaminated soils

The investigation of the long-term performance of solidified/stabilized (S/S) contaminated soils was carried out in a trial site in southeast UK. The soils were exposed to the maximum natural weathering for four years and sampled at various depths in a controlled manner. The chemical properties (e.g., degree of carbonation (DOC), pH, electrical conductivity (EC)) and physical properties (e.g., moisture content (MC), liquid limit (LL), plastic limit (PL), plasticity index (PI)) of the samples untreated and treated with the traditional and accelerated carbonated S/S processes were analyzed. Their variations on the depths of the soils were also studied. The result showed that the broad geotechnical properties of the soils, manifested in their PIs, were related to the concentration of the water soluble ions and in particular the free calcium ions. The samples treated with the accelerated carbonation technology (ACT), and the untreated samples contained limited number of free calcium ions in solutions and consequently interacted with waters in a similar way. Compared with the traditional cement-based S/S technology, e.g., treatment with ordinary portland cement (OPC) or EnvirOceM, ACT caused the increase of the PI of the treated soil and made it more stable during long-term weathering. The PI values for the four soils ascended according to the order: the EnvirOceM soil, the OPC soil, the ACT soil, and the untreated soil while their pH and EC values descended according to the same order.