• Economic and Environmental Geology
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• 제53권6호
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• pp.793-807
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• 2020

The policy for Green New Deal will promote the shift of the application to coal as feedstock from coal as fuel. Coal can be used as fuel for production of hydrogen and as feedstock materials such as synthetic graphite or activated carbon. Hydrogen is obtained from syngas produced through Steam carbon(SC), Water-Gas Shift(WGS), and Carbonation reactions, and these processes should be used in conjunction with CO2 sequestration technology. Anthracite has a potential in terms of cost advantage as a feedstock compared to a petroleum pitch, because Synthetic graphite is prepared by heat treating an anthracite with high rank to a graphitization temperature which is in the range of 2400~2800℃, in the presence of inorganic catalyst such as silicon or iron. From several studies, it has been confirmed that coal-based activated carbon(AC) is manufactured with quality similar to the large specific surface area and much micropore volume of lignin-based AC, can be prepared. Therefore it is expected that lignin-based AC is replaced to coal-based AC.

• Journal of Korean Society on Water Environment
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• 제27권1호
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• pp.110-114
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• 2011

In this paper, in order to eliminate Limnoperna fortunei inhabiting the water conduction pipeline, prechlorination at the intake station was employed to improve the degradation of water quality due to the high pH of raw water taken at the downstream of Paldang Dam, algal growth, etc.. With the prechlorination concentration of 1.0mg/L at the intake station, the pH in the water well at the treatment plant decreased by 0.4, and with 1.5mg/L, by 0.6. Also, it eliminated Chlorophyll-a by about 95%, and the population of algae by about 49%. Such disinfection by-products (DBPs) as Trihalomathanes (THMs), Haloacetic Acids (HAAs), and Chloral Hydrate (CH) were under the quality standard for potable water, showing no change by the prechlorination, while raising the prechlorination rate from 1.0 up to 1.5mg/L, the DBPs in the water well increased by 1.5 to 3.1 times. As a consequence of testing Kyungan Stream, a branch stream flowing into Lake Paldang, the prechlorination (0.57mg/L, 1.14mg/L, 1.71mg/L) had no effect of eliminating the taste and odor compounds and total organic carbon (TOC) which is the DBPs precursor. As for the efficiency of Geosmin elimination by the rates of prechlorination and powder activated carbonation (PAC), it was found that the higher the concentration of PAC was (30ppm>20ppm>10ppm), the higher the efficiency was; the higher the rate of prechlorination was, the lower the efficiency by PAC was. Therefore, when taste and odor occur from raw water, suspending prechlorination at the intake or lowering the rate was proved to be more effective in eliminating the taste and odor compounds by PAC.

• Membrane Journal
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• 제33권3호
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• pp.87-93
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• 2023

Electrodialysis (ED) is essential in separating ions through an ion exchange membrane. The disposal of brine generated from seawater desalination is a primary environmental concern, and its recycling through membrane separation technology is highly efficient. Alkali is produced by several chemical industries such as leather, electroplating, dyeing, and smelting, etc. A high concentration of alkali in the waste needs treatment before releasing into the environment as it is highly corrosive and has a chemical oxygen demand (COD) value. The concentration of calcium and magnesium is almost double in brine and is the perfect candidate for carbon dioxide adsorption, a major environmental pollutant. Sodium hydroxide is essential for the metal carbonation process which, is easily produced by the bipolar membrane electrodialysis process. Various strategies are available for its recovery, like reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and ED. This review discusses the ED process by ion exchange membrane for alkali recovery are discussed.

• Clean Technology
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• 제20권1호
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• pp.42-50
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• 2014

In this study, the $Mg(OH)_2$ slurry was made form ferro-nickel slag and then used for $CO_2$ sequestration. The experiments were in the order as leaching step, precipitation, carbonation experiments. According to the leaching results, the optimal leaching conditions were $H_2SO_4$ concentration of 1 M and the temperature of 333 K. In the $Mg(OH)_2$ manufacturing step, NaOH was added to increase the pH upto 8, the first precipitation was confirmed as $Fe_2O_3$. After removal the first precipitation, the pH was upto 11, the $Mg(OH)_2$ was generated by XRD analysis. The $Mg(OH)_2$ slurry was used for $CO_2$ sequestration. The pseudo-second-order carbonation model was used to apply for $CO_2$ sequestration. The $CO_2$ sequestration rate was increased by the $CO_2$ partial pressure and temperature. However, $CO_2$ sequestration rate was decreased when temperature upto 323 K. After $CO_2$ sequestrated by $Mg(OH)_2$, the $CO_2$ can be sequestrated stable as $MgCO_3$. This study also presented optimal sequestration condition was the pH upto 8.38, the maximum $MgCO_3$ can be generated. This study can be used as the basic material for $CO_2$ sequestration by ferro-nickel slag at pilot scale in the future.

• Journal of the Korea Concrete Institute
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• 제18권2호
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• pp.205-211
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• 2006

The objective of this study was to evaluate the durability of low shrinkage high performance concrete(LSHPC), which was combined with expansive additives and shrinkage reducing admixtures. We tested for not only LSHPC but also high performance concrete(HPC) and normal concrete(NC) to be compared with the durability of LSHPC. HPC was made in the same water-binder ratio of LSHPC without expansive additives and shrinkage reducing admixture. As a result, it was found that LSHPC had higher compressive and tensile strength than that of HPC. LSHPC showed more excellent performance than HPC and NC in the case of resistance to chloride ion penetration and resistance to carbonation and also showed nearly 100 durability factor in the freeze-thawing test with 500 cycles. From the examination about the watertightness and the pore distribution, it was found that the durability of LSHPC was improved because its hardened cement paste is organized closer. So we can conclude that when LSHPC is applied to structures in field, it is possible to reduce the shrinkage and crack in concrete and improve the durability.

• The Journal of Korean Academy of Prosthodontics
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• 제57권1호
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• pp.1-7
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• 2019

Purpose: The laser processability of dental prosthesis is investigated using two ceramic composites, including 3M, Lava Ultimate and Ivoclar vivadent, IPS e.max. Materials and methods: The $CO_2$ laser, picosecond laser and femtosecond laser are used to assess the processing power of dental prosthetic materials Lava Ultimate and IPS e.max and the line processing shape was measured using a confocal microscope. Results: The brittleness, carbonization and micro crack of the ceramic composite were influenced by heat accumulation of the material and could be controlled by the laser power and pulse time. Conclusion: In the case of $CO_2$ lasers, micro crack and carbonation occurred immediately, and in the picosecond laser processing, the micro cracks are partially improved, but the carbonization occurs continuously. Finally, we confirmed the high efficiency of laser processing with femtosecond laser. In particular, Lava Ultimate, a ceramic resin composite material, showed the best processability when processed using a femtosecond laser.

• Clean Technology
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• 제23권4호
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• pp.345-356
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• 2017

The composting is a biological process that converts organic matter into useful resources such as fertilizers. It is a continuous transition of microbial communities to adapt changes in organic matter and environmental conditions (carbonation rate, temperature, humidity, oxygen supply, pH, etc.). Most of the composting plants are located in the proximity of the residential areas. It is a general scenario where government authorities receive complaints from the local residents due to release of odor from the composting, and has become a social problem in Korea. Identification of dominant microorganisms, understanding change in microbial communities and augmentation of specific microorganism for composting is vital to enhance the efficiency of composting, quality of the compost produced, and reduction of odor. In this paper, we suggest the optimum operation conditions and methods for compost depot to reduce odor generation. The selection of the appropriate microorganisms and their rapid increase in population are effective to promote composting. The optimal growth conditions of bacteria such as aeration (oxygen), temperature, and humidity were standardized to maximize composting through microbial degradation. The use of porous minerals and moisture control has significantly improved odor removal. Recent technologies to reduce odor from the composting environment and improved composting processes are also presented.

• Resources Recycling
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• 제31권3호
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• pp.40-52
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• 2022

This study analyzed the amount of carbon dioxide reduction and economic benefits of detailed processes of CO₂ 6,000 tons plant facilities with mineral carbonation technology using carbon dioxide and coal materials emitted from domestic circulating fluidized bed combustion power plants. Coal ash reacted with carbon dioxide through carbon mineralization facilities is produced as a complex carbonate and used as a construction material, accompanied by a greenhouse gas reduction. In addition, it is possible to generate profits from the sales of complex carbonates and carbon credits produced in the process. The actual carbon dioxide reduction per ton of complex carbonate production was calculated as 45.8 kgCO₂eq, and the annual carbon dioxide reduction was calculated as 805.3 tonCO₂, and the benefit-cost ratio (B/C Ratio) is 1.04, the internal rate return (IRR) is 10.65 % and the net present value (NPV) is KRW 24,713,465 won, which is considered economical. Carbon mineralization technology is one of the best solutions to reduce carbon dioxide considering future carbon dioxide reduction and economic potential.

• Clean Technology
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• 제29권2호
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• pp.95-101
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• 2023

An experiment was conducted to produce vaterite-type precipitated calcium carbonate from waste oyster shells in order to use them as recyclable resources. Calcined oyster shells containing calcium oxide as their main component were prepared at a temperature of 800℃ for 24 h. The oyster shells were dissolved in nitric acid or hydrochloric acid solution to make 0.1 M calcium nitrate or calcium chloride aqueous solution, and a carbonation reaction was performed using a 0.1 M sodium carbonate aqueous solution under various experimental conditions, which included varying the amount of aspatic acid additive, the amount of NH₄OH added, the reaction time, the reaction temperature, the stirring speed, and the type of dissolved acid. The XRD, SEM, and size distributions were analyzed and the vaterite content was calculated. Spherical precipitated calcium carbonate with a vaterite content of 95.9% was synthesized by adding 0.1 mol aspatic acid/1 mol CaO and 2 cm³ of NH₄OH, and reacting for 1 h at 25℃ while stirring at 600 rpm. The average particle diameter was found to be 12.11 ㎛. Calcium carbonate contatining high vaterite is used as high value added calcium carbonate for medical, food, inke additiver, etc.

• Journal of the Korea Concrete Institute
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• 제17권3호
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• pp.411-418
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• 2005

Polymer-modified mortar and concrete are prepared by mixing either a polymer or monomer in a dispersed, or liquid form with fresh cement mortar and concrete mixtures, and subsequently curing, and if necessary, the monomer contained in the mortar or concrete is polymerized in situ. Although polymers and monomers in any form such as latexes, water-soluble polymers, liquid resins, and monomers are used in cement composites such as mortar and concrete, it is very important that both cement hydration and polymer phase formation proceed well the yield a monolithic matrix phase with a network structure in which the hydrated cement phase and polymer phase interpenetrate. In the polymer-modified mortar and concrete structures, aggregates are bound by such a co-matrix phase, resulting in the superior properties of polymer-modified mortar and concrete compared to conventional mortar and concrete. The purpose of this study is to obtain the necessary basic data to develope appropriate latexes as cement modifiers, and to clarify the effects of the monomer ratios and amount of emulsifier on the properties of the polymer-modified mortars using methyl methacrylate-butyl acrylate(MMA/BA) and methyl methacrylate-ethyl acrylate(MMA/EA) latexes. The results of this study are as follows, the water absorption, chloride ion penetration depth and carbonation depth of MMA/BA-modified mortar are lowest. However, they are greatly affected by the polymer-cement ratio rather than the bound MMA content and type of polymer.