Browsing by Author "Georgakopoulos, Evangelos"
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Item Open Access Granulation–carbonation treatment of alkali activated steel slag for secondary aggregates production(Springer Verlag (Germany), 2016-11-26) Morone, M.; Costa, G.; Georgakopoulos, Evangelos; Manovic, Vasilije; Stenardo, S.; Baciocchi, R.In view of the EU’s circular economy strategy, there is a need to develop treatments that may allow to improve the management of industrial residues such as steel manufacturing slag, for example by producing secondary products that may be used for different applications. This work evaluates the performance of a combined carbonation and granulation treatment applied to basic oxygen furnace (BOF) steel slag with the aim of producing secondary aggregates and of storing CO2 in a solid and stable form. In order to improve the mechanical properties of the product, a solution of sodium silicate and sodium hydroxide was tested as binder instead of water in both the granulation and combined granulation–carbonation tests. The results showed that the granules produced using the alkali activator with or without CO2 addition, presented a mean size ranging from 1 to 5 mm and adequate mechanical properties for use in civil engineering applications. The maximum CO2 uptake attained was of 4% wt. for the alkali activated and carbonated granules after 60 min of treatment and 7 days curing. As for the leaching behaviour of the produced granules, an increase in the release of Cr and V was found for the product of the granulation–carbonation treatment with alkali activation. Instead, granulation with alkali activation or granulation with carbonation showed to decrease the release of Ba and Cr with regard to the untreated residues.Item Open Access Improving the yield of sonochemical precipitated aragonite synthesis by scaling up intensified conditions(Taylor and Francis, 2016-09-08) Santos, Rafael M.; Thijs, Jolien; Georgakopoulos, Evangelos; Chiang, Yi Wai; Creemers, Ann; van Gerven, TomPrecipitated aragonite can be synthesized at relatively low temperatures by combining the application of low-frequency sonication with the use of magnesium chloride additive, as demonstrated by our prior study. In the present study, new process conditions were found that promote aragonite formation while accelerating and increasing the reaction yield. It was found that Mg-to-Ca molar ratio of 3:1, together with higher slurry concentration (74 g/L Ca(OH)2) and higher power-to-volume ratio (800 W/L gross, achieved by reducing slurry volume), promoted the aragonite formation while working at a higher CO2 flow rate (2.0 NL/min), and consequently higher precipitated calcium carbonate production rate (1 g/(L · min) CaCO3). The yield was thus improved while conserving the desired product properties as follows: high polymorph purity (95.7 wt%), small and narrow particle size distribution (D[3,2] = 0.74 µm), and unique shape (hubbard squash-like).Item Open Access Influence of process parameters on carbonation rate and conversion of steelmaking slags – Introduction of the ‘carbonation weathering rate’(Wiley, 2016-07-05) Georgakopoulos, Evangelos; Santos, Rafael M.; Chiang, Yi Wai; Manovic, VasilijeAlkaline industrial wastes are considered potential resources for the mitigation of CO2 emissions by simultaneously capturing and sequestering CO2 through mineralization. Mineralization safely and permanently stores CO2 through its reaction with alkaline earth metals. These elements are found in a variety of abundantly available industrial wastes that have high reactivity with CO2, and that are generated close to the emission point-sources. Among all suitable industrial wastes, steelmaking slag has been deemed the most promising given its high CO2 uptake potential. In this paper, we review recent publications related to the influence of process parameters on the carbonation rate and conversion extent of steelmaking slags, comparing and analyzing them in order to define the present state of the art. Furthermore, the maximum conversions resulting from different studies are directly compared using a new index, the Carbonation Weathering Rate (CWR), which normalizes the results based on particle size and reaction duration. To date, the carbonation of Basic Oxygen Furnace steelmaking slag, under mild conditions, presents both the highest carbonation conversion and CWR, with values equal to 93.5% and 0.62 μm/min, respectively.Item Open Access Two-way valorization of blast furnace slag: synthesis of precipitated calcium carbonate and zeolitic heavy metal adsorbent(Journal of Visualized Experiments (JoVE), 2017-02-21) Georgakopoulos, Evangelos; Manovic, VasilijeThe aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with sufficient heavy metal adsorption capacity. To this end, blast furnace slag, a residue from iron-making, is utilized as the starting material. Calcium is selectively extracted from the slag by leaching with acetic acid (2 M CH3COOH) as the extraction agent. The filtered leachate is subsequently physico-chemically purified and then carbonated to form precipitated calcium carbonate (PCC) of high purity (<2 wt% non-calcium impurities, according to ICP-MS analysis). Sodium hydroxide is added to neutralize the regenerated acetate. The morphological properties of the resulting calcitic PCC are tuned for its potential application as a filler in papermaking. In parallel, the residual solids from the extraction stage are subjected to hydrothermal conversion in a caustic solution(external) (2 M NaOH) that leads to the predominant formation of a particular zeolitic mineral phase (detected by XRD), namely analcime (NaAlSi2O6∙H2O). Based on its ability to adsorb Ni2+, as reported from batch adsorption experiments and ICP-OES analysis, this product can potentially be used in wastewater treatment or for environmental remediation applications.