The increase in energy valorization of paper sludge and biomass waste through incineration results in a rise in waste paper fly ash (WPFA), often perceived as hazardous and requiring specific ...treatment. In this study, natural carbonation technology at a pilot scale was employed to mitigate the hazardous nature of WPFA by enhancing the stabilization of metal and metalloid trace elements (MMTE), particularly barium (Ba) and lead (Pb) leaching. Natural carbonation of WPFA was found to be optimal at a water/solid ratio of 0.3 L/kg under natural temperature and humidity conditions. Batch leaching tests based on thermodynamic equilibrium were used to assess MMTE solubility concerning pH in both non-carbonated and carbonated WPFA at natural pH. After 7 days of natural carbonation, the leaching concentration of Ba and Pb was below the legal limit in France. The concentration of Ba and Pb in carbonated samples decreased by 98.5% and 98%, respectively. Analyses using thermogravimetry, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy demonstrated the increased formation and quantity of calcite (CaCO3) with longer carbonation times, along with the formation of new minerals as BaCO3 and PbCO3, confirming the immobilization of these elements post-carbonation. The leaching behavior and release potential of carbonated WPFA were further evaluated using the four-stage sequential extraction procedure proposed by the European Commission’s Bureau of Reference (BCR). The speciation of Ba and Pb shifted significantly from the soluble substance (F1) at 17.6% and 14.8%, respectively, to the carbonate fraction (F2) at 0.49% and 0.02% after 90 days of carbonation. The percolation water collected during the carbonation process adheres to discharge standards into the sea.
•Pilot scale natural carbonation of WPFA has been performed.•Ba, Pb and Cl leaching concentration decreased effectively after natural carbonation.•After 7 days of natural carbonation, the WPFA becomes inert.•Percolation water can be eliminated without treatment.•Ba and Pb was precipitated as carbonate BaCO3 and PbCO3.
The concentration of CO2 in the atmosphere is constantly increasing, leading to an increase in the average global temperature and, thus, affecting climate change. Hence, various initiatives have been ...proposed to mitigate this process, among which CO2 sequestration is a technically simple and efficient approach. The spontaneous carbonation of ashes with atmospheric CO2 is very slow, and this is why accelerated carbonation is encouraged. However, not all ashes are equally suitable for this process, so a methodology to evaluate their potential should be developed. Such a methodology involves a combination of techniques, from theoretical calculations to XRF, XRD, DTA-TG, and the calcimetric determination of the CaCO3 content. The present study followed the approach of exposing ashes to accelerated carbonation conditions (4% v/v CO2, 50–55% and 80–85% RH, 20 °C) in a closed carbonation chamber for different periods of time until the maximum CO2 uptake is reached. The amount of sequestered CO2 was quantified by thermogravimetry. The results show that the highest CO2 sequestration capacity (33.8%) and carbonation efficiency (67.9%) were obtained for wood biomass bottom ash. This method was applied to eight combustion ashes and could serve to evaluate other ashes or comparable carbon storage materials.
Coal combustion by-products such as fly ash (FA), brine and CO2 from coal fired power plants have the potential to impact negatively on the environment. FA and brine can contaminate the soil, surface ...and ground water through leaching of toxic elements present in their matrices while CO2 has been identified as a green house gas that contributes significantly towards the global warming effect. Reaction of CO2 with FA/brine slurry can potentially provide a viable route for CO2 sequestration via formation of mineral carbonates. Fractionated FA has varying amounts of CaO which not only increases the brine pH but can also be converted into an environmentally benign calcite. Carbonation efficiency of fractionated and brine impacted FA was investigated in this study. Controlled carbonation reactions were carried out in a reactor set-up to evaluate the effect of fractionation on the carbonation efficiency of FA. Chemical and mineralogical characteristics of fresh and carbonated ash were evaluated using XRF, SEM, and XRD. Brine effluents were characterized using ICP-MS and IC. A factorial experimental approach was employed in testing the variables. The 20–150μm size fraction was observed to have the highest CO2 sequestration potential of 71.84kg of CO2 per ton of FA while the >150μm particles had the lowest potential of 36.47kg of CO2 per ton of FA. Carbonation using brine resulted in higher degree of calcite formation compared to the ultra-pure water carbonated residues.
Mining waste is globally available in abundance and can be seen as a useful mineral resource for long-term carbon capture which can be turned into revenue-generating products. This review highlights ...a new concept for mining waste utilization through an integrated carbon capture, utilization and storage (CCUS) technology in response to the long-term target for net-zero emissions. A framework for mining waste utilization by means of CCUS is introduced through integration of accelerated mineral carbonation and carbonation curing technologies. Potential CO2 sequestration of mining waste is mainly attributable to the availability of Ca-, Mg- and Fe-based silicate and oxide minerals and manipulation of process variables. It was estimated that the current rate of carbonation efficiency of mining waste through direct and indirect mineral carbonation is about 11 % and 55 %, respectively, while CO2 capture capacity through carbonation curing is about 20.6 %. It can be projected that with the current rate of CO2 sequestration, this accounts for about 21.1–100 % of the net-zero target by 2035 via CCUS. The combined mineral carbonation and carbonation curing might offset 33.4–100 % of CO2 emissions from the mining industry and 15.4–60.9 % of the net-zero target by 2050. Despite technical, economic and environmental challenges, the framework provides pathways for a sustainable mining waste recovery to meet the 2050 net-zero emissions target.
Chromium leaching from stainless steel tailings is an urgent problem risking of the environments, calcite integument of tailings by accelerated direct gas-solid carbonation process can be formed and ...the inhibition factor of carbonation degree on chromium leaching rate is discussed in detail. Stainless steel tailings accelerated direct gas-solid carbonation process is investigated at 300 °C–700 °C and 0.2–0.4 MPa, and the effect of temperature, reaction time, particle size and CO2 pressure on carbonation degree are analyzed by TGA-DSC, FTIR, SEM-EDS analysis. The results show that the maximum CO2 uptake obtained (8.2%), corresponding to 16% carbonation degree can be obtained when 48–75 μm stainless steel tailings are carbonated for 90 min at 300 °C and 0.4 MPa. Tailings particle size, carbonation time, and carbon dioxide pressure display a positive relationship with carbonation degree, but carbonation temperature has a negative relationship. 48–75 μm carbonated tailings with varied carbonation degree and original tailings are investigated for the inhibitory factor between carbonation degree and Cr leaching rate, when leaching process is at 60 °C for 90min on the condition that L/S ratio equals 20 ml/g. The results show the inhibitory factor is fitted by random function better, and the value decreases from 31.5% to 9.7%, when carbonation degree is from 2% to 8%, and then keeps stable, when carbonation degree is still increases from 8% to 14%, which illustrates that carbonation process as a better strategy of tailings innocuous treatment at high temperature is valid for restricting Cr leaching behavior.
•Calcite integument in matrix is achieved by stainless steel tailings gas-solid carbonation process.•The balance between CO2 sequestration efficiency and chromium leaching of carbonated tailings is discussed.•The inhibitory factor is originally proposed for chromium leaching process of carbonated tailings.
The carbonation efficiency in raceway ponds was improved by modeling CO2 desorption and absorption between the pond and the atmosphere. The Euler–Euler two-fluid method was used to model gas–liquid ...flow mixing with mass transfer in the raceway pond. The average gas hold-up, mass transfer coefficient, dissolved CO2 concentration, CO2 desorption rate to the atmosphere, and CO2 absorption rate from the atmosphere were investigated using the effects of sump configuration, pond geometry, and gas–liquid hydrodynamic properties. The carbonation efficiency of the entire raceway pond was investigated by considering the effects of sump geometrical design, aspect ratio, water depth, paddle wheel rotational speed, gas bubble size, and gas mass flux. The CO2 desorption and absorption rates were estimated using novel equations from the literature. Results showed that the CO2 desorption rate was low in wide and shallow raceway ponds. The gas–liquid mass transfer increased in ponds with a low aspect ratio and small water depths. The high rotational speeds of the paddle wheel enhanced gas dissolution, and large amounts of CO2 were desorbed to the atmosphere. Moreover, sump configuration as well as geometrical and gas–liquid hydrodynamic properties significantly affected the carbonation efficiency and algal productivity.
•Sump with slanting vertical baffle enhanced the gas–liquid transfer rates.•CO2 desorption to the atmosphere was reduced in the wide raceway ponds.•Less CO2 was desorbed to the atmosphere in the pond with higher water depths.•High paddle wheel rotational speeds increased flow mixing and CO2 desorption.•Large gas bubbles decreased the mass transfer and CO2 desorption rates.
One of the challenges of promoting accelerated carbonation curing (ACC) of concrete as a carbon sequestration strategy is ensuring that carbonation will not deteriorate mechanical strength. This ...study examined the mechanical strength, water sorptivity and carbonation efficiency of ten types of mortar containing dry or pre-soaked biochar subjected to internal and/or external carbonation. The results obtained enabled a typology of ACC to be proposed, in which the carbon dioxide absorption of mortar containing various types of CO
2
-dosed biochar ranged between 0.022% and 0.068% per unit dosage hour. In particular, the mortar containing dry biochar dosed with carbon dioxide was the top candidate for concurrently increasing both compressive strength (54.9 MPa) and carbon dioxide absorption (0.055% per unit dosage hour). Mortar containing pre-soaked biochar dosed with carbon dioxide was identified as a strategy that achieved the highest carbonation efficiency (0.068% per unit dosage hour), but it also reduced compressive strength (45.1 MPa). Collectively, the proposed typology offers a useful overview of the different ways by which biochar can be used to tune ACC in mortar, according to any technical constraints and/or intended functions of the carbonated concrete components.
Graphical Abstract
Highlights
A typology of accelerated carbonation curing for mortar was proposed
Dry and pre-soaked biochar was subjected to internal and/or external carbonation
Compressive and flexural strength, water sorptivity, and carbonation efficiency were measured
Dry biochar subjected to internal carbonation increased strength and carbonation of mortar
The promotion of carbon dioxide (CO2) reduction methods is due to the fact that the CO2 concentration has been increasing rapidly in 21st century. In order to prevent further damage of the ...environment caused by greenhouse gases, CO2 concentration should be stabilized by increasing CO2 fixation, which can reduce CO2 emission into the atmosphere. Mineral carbon sequestration or mineral carbonation is the process of utilizing minerals, mostly rich in calcium and magnesium (Ca/Mg) as the feedstock in reaction with CO2 to produce stable solid carbonates. Mineral carbonation through indirect pH swing process is a very effective method for producing calcium and magnesium carbonates. The Ca/Mg ions are extracted out of feedstock using suitable solvents at low pH condition and then in the second step the leached Ca/Mg ions are carbonated at elevated pH condition. In this paper the state-of-the-art of the carbonation involving pH swing method is updated.
The carbonate reaction of some alkaline-earth chlorides was investigated by a carbonate agent injection method in LiCl-KCl eutectic salts containing both SrCl
2
and BaCl
2
and LiCl molten salts ...containing SrCl
2
. The effects of the injected molar ratio of a carbonate agent (Li
2
CO
3
or K
2
CO
3
) and the temperature (450-750°C) on the conversion efficiencies of the strontium and barium chloride to their carbonates were determined. The forms of strontium and barium carbonate resulting from the carbonate reaction with carbonate agents were identified by XRD and SEM-EDS analyses. In these experiments, the carbonate agent injection method can carbonate strontium and barium chlorides effectively at over 99% under LiCl-KCl eutectic and LiCl molten salt conditions. For LiCl-KCl eutectic molten salts, carbonation efficiency was more favorable in the case of K
2
CO
3
injection than in the case of Li
2
CO injection, where strontium and barium were carbonated in the form of Ba
0.5
Sr
0.5
CO
3
. For LiCl molten salts, strontium was carbonated in the form of SrCO
3
by Li
2
CO
3
injection.
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