Papers by Author: Yoo Taek Kim

Abstract: Geopolymers are prospective cement substitutes because their production generates smaller amounts of carbon dioxide and they have sufficient mechanical strength. Geopolymers have attracted increasing interest from construction industries because of their recyclability and eco-friendliness. The compressive strength of geopolymers is known to be associated with their Si/Al ratio. Fused slag from gasification processes using low-grade coal (FSLC) and spent catalyst slag (SCS) were used as raw materials for making geopolymers; the Si/Al ratio was controlled by mixing different ratios of FSLC and SCS. The compressive strength of a geopolymer with a Si/Al ratio of 1.04 had the highest strength (125.6 MPa). Scanning electron microscopy (SEM) analysis was also in good agreement with the compressive strength measurements of compressive strength. There were many small crystallites in the geopolymer matrix. Using transmission electron microscopy (TEM), these crystallites were found to be single crystals, which have a perfect crystal structure. It is speculated that the formation of small crystallites 10-30 nm in size, as well as large single crystals with diameters greater than 80 nm, in the matrix of a geopolymer during the geopolymerization process might increase its compressive strength.

Abstract: This research concerns the characteristics of ALA made of magnetically separated desulfurized fly ash (DFA) generated from the coal power plant having fluidized bed type boiler. Being believed that these alkali-rich components could be separated by magnetic separation, desulfurized fly ash was separated by using 10,000 Gauss magnets as magnetic desulfurized fly ash (MDFA) and non-magnetic desulfurized fly ash (DFA). The dependence of composition and sintering temperature on physical property of ALA was studied. It seems to be apparent that the glass phase which is one of the main problems in the ALA manufacturing process could not be controlled by the magnetic separation only, but the formation of pores could be considerably controlled by the magnetic separation. It is also clear that neither DFA nor MDFA can be used as raw materials for making ALA; however, magnetic separation of desulfurized fly ash from fluidized bed type boiler is effective to collect bloating components for self-bloating of ALA without addition of an extra bloating agent.

Abstract: This study was conducted to evaluate the feasibility of using bottom ash after magnetic separation and dredged soil from the coal power plants as raw materials for artificial lightweight aggregate (ALA). The dependence of composition and sintering temperature on physical properties of ALA was investigated. Fe compounds play an important role in the bloating reaction, thus specimens containing more ferrous materials such as Fe₃O₄ are more easily bloated. Both black core region and bloating phenomenon were increased with an increase in the contents of dredged soil. Specimens made use of MBA(Magnetic separated bottom ash which has magnetic components) showed lower bulk density than those of NMBA(non-magnetic separated bottom ash which has much less ferrous materials. It was confirmed that MBA could be used as an effective raw material for making ALA having low density because the ferrous components in it act as bloating agents.

Abstract: This research provides a comparison of ALAs which was made up of two different raw materials, that is, MDFA and MDBA which were produced from fluidized bed type boiler of power plant and then magnetically separated. ALAs made up of MDFA had too much liquid phase at high temperature; on the other hand, those made up of MDBA showed a black core region as well as good distribution of various sizes of pores inside ALA. Although a good quality of ALA can be made of MDBA only, the optimum composition was obtained under the conditions of MDBA:DS=5:5 and at 1200°C. Nonetheless for its high sintering temperature, MDBA is a prospective recycling material for making lightweight aggregate.

Abstract: The dependence of composition and sintering temperature on physical properties of ALA was investigated. Mechanism of black discoloration(sometimes called black core) usually found in the interior cores of artificial lightweight aggregate was also investigated by the optical observations. As a result, the primary cause of black discoloration in the interior of the lightweight aggregate body resulting from incomplete burn-out of carbonaceous impurities and iron-containing materials.In the cross-sectional morphology of ALA, bloating phenomena as well as formation of large pores were found in the samples containing ferrous materials. By increasing content of ferrous materials, both specific gravity and water absorption have been decreased.

Abstract: The corrosion behavior of glass and glass-ceramics fabricated with silicate glass frit mixed with 50~70 wt% EAF dust in the acidic solution was analyzed by both heavy metal leaching test and microstructural observation. The crystallization temperature, Tc of glassy specimens was around 850
measured by DTA and the heat treatment temperature to crystallize a glassy specimen was selected as 950
/ 1 hr. The spinel crystal peaks were found in XRD analysis for the glass containing dust > 60 wt%. For the glass-ceramics, however, the spinel peaks in a specimen containing dust > 50 wt% was found with weak willemite peaks. The glass and glass-ceramic specimens showed the first stage of corroding reaction according to Clark models in acidic solution. The glass-ceramic specimens showed much lower a heavy metal leaching concentration than that of glass specimens in the corrosion test in acidic solution of pH=2.95. Especially, the glass-ceramics containing dust 60 wt% showed a heavy metal leaching concentration of 66 % Pb, 60 % Zn and 98 % Fe lower than that of glass specimens due to crystal phases formed, thermodynamically more stable than a glass network structure. From the leaching test that more Zn ion leached out than Fe ion, the spinel crystal phase [ZnFe2O4] showed better corrosion resistant in the acidic solution than the willemite [Zn2SiO4].

Abstract: Plasticity indexes (PI) of clay bodies including bottom ashes (BA) and various wastes by using Atterberg limits were measured for the effective recycling of coal bottom ashes from the power plant. Coal bottom ash (BA)-red clay (RC or simply clay), dredged soil (DS)-BA, coal fly ash (FA)-red clay, DS-FA were used as samples for the PI measurement. From the comparison of clay bodies with BA and DS, PI of DS-BA body was higher than that of BA-red clay body because liquid limit (LL) was high and plastic limit (PL) of DS-red clay was low, respectively. Comparing clay bodies with FA and BA, PI of BA-clay body was higher than that of FA-clay body because both LL and PL of BA-clay body were low. When stone ashes and sewage sludge (SS) were added to BA-clay bodies, PI decreased with increasing both stone ash and sewage sludge contents. It is concluded that the measurement of plasticity index can be used as an indicator of forming performance of green bodies with various compositions.

Abstract: Stabilizing characteristics of heavy metals in the silicate glass (SD) and lead silicate glass(PD) containing Electric Arc Furnace(EAF) dust was studied by the toxic characterization leaching procedure(TCLP) test. Dependence of the amount of EAF dust upon structural changes of SD and PD glasses and TCLP results was also investigated by FT-IR spectroscopy. In the TCLP test, the concentration of heavy metals leached from a glass increased with the amount of EAF dust added. The SD series specimens showed heavy metal leaching lower than the PD series specimens, but the Pb leaching from the PD series specimens was the highest owing to the high Pb content in the PD glass composition. The value R(oxygen/network former ion ratio) was used to compare the leaching characteristics of glasses, and the SD had a higer R than PD series specimens to show a better chemical durability. Adding the EAF dust to the SD mother glass decreased the Si-O-Si symmetry and increased the non-bridging oxygen, which weakened the structure and decreased the chemical durability of glasses. It is concluded that SD is more effective in stabilizing the heavy metals of EAF dust than PD series glass.

Abstract: Thermal behaviors of EAF dust, water-washed EAF dust, and EAF dust/heavy clay mixtures with wet mixing process were characterized by TG/ DTA analysis. The ionic concentrations of some metal ions and anions in the supernatant from water-washing process were evaluated by ICP and IC analysis. Weight loss of water-washed EAF dust above the temperature range of 1000°C was significantly decreased because of the washing effect of chloride and sulfate compounds. The variation of volatile ZnO and PbO contents were not detected in 20wt% D dust-80wt% clay sample. The wet mixing process not only enhanced the homogeneous mixing of EAF dust and clay particles, but also reduced the volatilization of heavy metals(Zn, Pb, etc.) at the high temperature range.