• Clean Technology
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• v.16 no.2
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• pp.124-131
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• 2010

Effects of $Ca(OH)_2$ concentration (0.16~0.64 wt%), surfactant concentration (2~16 wt%), total volumetric flow rate (3~6 L/min) and $CO_2$ volume fraction $(0.3{\sim}0.6)$ on morphology, crystal structure, mean particle diameter, aggregation and specific surface area of the precipitated $CaCO_3$ were investigated in the slurry bubble column reactor. Experiments were carried out in acrylic reactor ($0.11\;m-ID{\times}1.0\;m-high$) with a internal tube ($0.04\;m-ID{\times}1.0\;m-high$h). The reaction time of $CaCO_3$ synthesis decreased with adding Dispex N40 of the anionic surfactant. The reaction rate of $Ca(OH)_2$ increased with increasing the volumetric flow rate of $CO_2$. From SEM images, the single crystal of $CaCO_3$ increased with increasing the reaction rate in the saturated concentration of $Ca(OH)_2$ (0.16 wt %) and the concentration of Dispex N40 (2 wt%). The mean particle size of $CaCO_3$ varied with adding Dispex N40. In addition, the specific surface area of $CaCO_3$ increased with adding of surfactant (2 wt%) from $35m^2/g$ to $44m^2/g$ at the volumetric flow rate of $CO_2$ (0.9 L/min) and the concentration of $Ca(OH)_2$(0.64 wt %).

• Korean Chemical Engineering Research
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• v.54 no.5
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• pp.612-620
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• 2016

Aqueous mineral carbonation process, in which $CO_2$ is captured through the reaction with aqueous calcium oxide (CaO) solution, is one of CCU technology enabling the stable sequestration of $CO_2$ as well as economic value creation from its products. In order to enhance the carbon capture efficiency, it is required to maximize the dissolution rate of solid reactants, CaO. For this purpose, the proper design of a reactor, which can achieve the uniform distribution of solid reactants throughout the whole reactor, is essential. In this paper, the effect of internal reactor designs on the solid dispersion quality is studied by using CFD (computational fluid dynamics) techniques for the pilot-scale reactor which can handle 40 ton of $CO_2$ per day. Various combination cases consisting of different internal design variables, such as types, numbers, diameters, clearances and speed of impellers and length and width of baffles are analyzed for the stirred tank reactor with a fixed tank geometry. By conducting sensitivity analysis, we could distinguish critical variables and their impacts on solid distribution. At the same time, the reactor design which can produce solid distribution profile with a standard deviation value of 0.001 is proposed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.45-55
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• 2015

Currently, extreme weather events such as super typhoon, extreme snowfall, and heat wave are frequently occurring all over the world by natural and human caused factors. After industrial growth in the 1970s, earth's temperature has risen sharply. due to greenhouse effect. Global warming can be attributed to gases emitted from using fossil fuel such as average carbon dioxide, perfluorocarbons, nitrous oxide, and methane. Especially, carbon dioxide has the highest composition of about 90%. in the fossile fuel usage emitted gas. Concrete has excellent durability as a building material climate change. However, due to various of physical and chemical environmental effect such as conditions during its curing process, the performance degradation may occur. Carbon dioxide in the atmosphere causes steel corrosion and durability decreases by lowering the alkalinity of concrete. Therefore, in this study, concrete durability performance with respect to carbonation from curing conditions change due to wind speed and sunshine exposure time. Concrete carbonation experiment are performed. using wind speed (0, 2, 4, 6) m/s and sunlight exposure time (2, 4, 6, 8) hrs. Also, performance based evaluation through the satisfaction curve based on the carbonation depth and carbonation rate test results are performed.

• Resources Recycling
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• v.16 no.2 s.76
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• pp.23-31
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• 2007

In this study, the crystallization of neodymium carbonate from neodymium chloride solution by addition of ammonium bicarbonate was investigated. The concentration of reactants such as neodymium chloride and ammonium bicarbonate, and reaction temperature play an important part in order to obtain the crystal of neodymium carbonate. It seemed that amorphous neodymium carbonate was prepared by aggregation of primary particles formed through nucleation. If reaction rate was increased by increasing the concentration of reactants and reaction temperature, then neodymium carbonate crystal could be obtained. Lanthanite-type neodymium carbonate[$Nd_2(CO_3)_3{\cdot}8H_2O$] and tengerite-type neodymium carbonate[$Nd_2(CO_3)_3{\cdot}2.5H_2O$] could be obtained with reaction renditions. Lanthanite-type neodymium carbonate was sensitive to temperature. The thermal decomposition of neodymium carbonate contained the processes or dehydration, decarbonation and crystalization of $Nd_2O_3$. The shape of lanthanite-type neodymium carbonate was irregular lump type, and tengerite-type neodymium carbonate had the shape of needle type. The shape of $Nd_2O_3$ was affected by the shape of neodymium carbonate.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.909-916
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• 2013

Concrete containing lightly burnt MgO has long term expansibility. It also could compensate for the thermal shrinkage of mass concrete, because the hydration of MgO proceeds at a slow pace to long-term age. Thus, lightly burnt MgO has been applied to the construction of mass concrete such as dams. Recently, the expansion characteristics of MgO concrete with fly ash that could be applied to mass concrete for the reduction of hydration heat have been studied and however, limited studies on its durability. This study investigates the long-term durability characteristics of fly ash concrete with lightly burnt MgO. The durability tests on carbonation, freezing-thawing, diffusion of chloride, and resistance to sulfate attack were carried out for MgO concrete with curing for 360 days in submerged condition with different temperature of 20 and $50^{\circ}C$. The results reveal that MgO concrete shows a greater resistance of carbonation, diffusion of chloride, and resistance to sulfate attack. On the other hand the resistance of freezing-thawing was little influenced by MgO powder.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.537-540
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• 2008

Up to now, the RC structures have been recognized as being socially semi-permanent. But in recent years there were reports about the cases of early deterioration of RC structures. Most of all pore structure effects on the durability of concrete as well as mechanical properties of concrete. Therefore, in this study, mixing design was proportioned with the water-binder ratio 0.55 binder compositions corresponding to cement without any supplementary materials(OPC), cement with 50% blast-furnace slag replacement (BFS50), cement with 15% fly ash replacement (FA15), and ternary cement with cement, 15% fly ash, and 35% slag replacement (BFS35+FA15). And this study is to compare pore structure property of concrete by carbonation to investigate the effect of the permeation of deterioration factors such as $CO_2$ and chloride ion under the combined deterioration environments. The results showed that pore volume effects on the diffusibility of chloride ion.

• Journal of the Korean Institute of Gas
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• v.18 no.2
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• pp.73-80
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• 2014

The objective of this paper is to assess the service life and retrain methods of specimens, which were subjected to carbonation attack, obtained from mix proportion of Sam-cheok LNG storage tank under construction. As the results, accelerated-carbonation penetration depths of 7, 28, 56 ages indicated 4.45, 9.19, 13.37mm, and even considering for cover depths of steel of LNG storage tank under real operation, it was enough. In addition, with carbonation velocity coefficient calculated by carbonation penetration depths, the service life to design cover depth(70, 80, 90, 100mm) of PC outer tank of LNG storage tank was 779, 1017, 1287, 1589 years and 466, 609, 771, 951 years, respectively, considering the $CO_2$ concentration in air which account for the 0.03% and 0.05%. Also, the restrain methods to carbonation attack were feasible through controlling the factors affecting the changes of hydration products such as $Ca(OH)_2$, ion composition in pore solution and matter mobility of organization structures within hardened concrete.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.2
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• pp.78-81
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• 2004

The nacre of imaged abalone pearls was obtained as a calcium carbonate of aragonite type. This result was same the nacre of natural abalone pearl. From the observation of SEM for the nacre adhered on the pearl nucleus, it was known that the layers of calcium carbonate and conchiolin were stratified. The growth rate of nacre was found to be 0.0056∼0.0074 mm/day, which is twice faster than that of traditional method used shells. The pendant and brooch were manufactured using the imaged abalone pearls.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.520-527
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• 2020

Hwangtoh is the rich resource that accounts for about 15.0% of the domestic soil, and can be used as the admixture of concrete with Pozzolan characteristics if activated by rapidly freezing after burning with high temperature. In this study, the mortar curbs containing active hwangtoh were produced, based on the mixture for the mortar curbs sold on the market. The substitution rate of active hwangtoh were considered 10.0% and 25.0%, and the test items were selected to compressive and flexural strength tests, freezing/thawing resistance tests, accelerated carbonation tests, and accelerated chloride diffusion tests. In the results of the mechanical performance, it was showed that the highest strength was evaluated in OPC mixture, and the increase in strength was small by the increase of age, which was believed to be due to the fact that most of the strength in each mixture was created in three days of steam curing. The results of the freezing/thawing tests for 28 aged days showed the reduction rate of compressive strength was 85.0% or higher for all specimen, meeting the criteria presented. The accelerated carbonation tests were carried out on the specimen at 28 days of age, and the results showed that the mortar with active hwangtoh had lower carbonation resistance performance than mortar with OPC. The passed charge of each mixture was assessed in accordance with ASTM C 1202 on 28 and 91 aged days. The OPC mixture had "Low" rate and the mortar with active hwangtoh had "Moderate" rate. So it was thought that the mortar with active hwangtoh had appropriate resistance performance for chloride attack.

• Korean Chemical Engineering Research
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• v.47 no.6
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• pp.727-733
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• 2009

Effects of $Ca(OH)_2$ concentration(0.16~0.64 wt%), total volumetric flow rate(3~6 L/min) and $CO_2$ volume fraction(0.3~0.6) on morphology of the precipitated $CaCO_3$ and the mean particle size of the precipitated $CaCO_3$ were investigated in the slurry bubble column reactor. Experiments were carried out in acrylic reactor($0.11m-ID{\times}1.0m-high$) with a internal tube($0.04m-ID{\times}1.0m-high$). The calibration curve on the mass ratio of $CaCO_3$ to $Ca(OH)_2$ was obtained by FT-IR for the conversion of $Ca(OH)_2$ with the reaction time. The reaction rate of $Ca(OH)_2$ increased with increasing the volumetric flow rate of $CO_2$. From SEM images, the crystal size of $CaCO_3$ increased with increasing the reaction rate in the saturated concentration of $Ca(OH)_2$ (0.16 wt%). In addition, the crystal size of precipitated $CaCO_3$ decreased with increasing the concentration of $Ca(OH)_2$, but the mean particle size of precipitated $CaCO_3$ increased with increasing the concentration of $Ca(OH)_2$.