Jung Hwan Kim

Preparation of ZrO2 coated graphite powders

Graphite powders were coated with ZrO2 by the controlled hydrolysis of a zirconium oxychloride aqueous solution. Thehydrolysis process was carried out with temperature control because of the low wettability of ZrO2 to the surface of thegraphite. PVA was added to the solution for the enhancement of Zr ion adsorption. The surface of the graphite particles coatedwith ZrO2 was observed by TEM. There are two types of ZrO2 particles; (a) primary particles a few nm in size and (b) secondary particles with ∼0.1 μm size were obtained. The data of oxidation weight loss and surface potentialshow that the graphite surface was successfully modified by the forced hydrolysis of the zirconium chloride aqueous solution.

Efflorescence and Leaching Behavior of Metal Ions for EAF Dust-Clay Based Bricks

Brick samples were prepared through vitrification process with two different kinds of EAF dust. Leaching concentrations of various metal ions and anions for the bricks(20wt% EAF dust-80wt% clay) were evaluated by ICP and IC analysis. The results of leaching test showed that the concentration of ions leached from bricks were proportional to the square root of time and saturated with leaching time. The saturated concentrations of alkali and alkali-earth metal ions were 0.1-250ppm; on the other hand, the heavy metal ions were 0-0.084ppm. The efflorescence mechanism of EAF dust-clay bricks was studied by quantitative analysis for the effects of various metal ions and anions. Efflorescence formed on the brick surfaces which were immersed in DI water and dried slowly in the air were characterized by SEM, EDS and XRD. The results of EDS and XRD showed that the main component of the efflorescence was water soluble Na2SO4 .

Properties of Artificial Aggregate for Orchid Culture Fabricated from Solid Wastes

The artificial aggregates were fabricated from several industrial wastes such as waste white clay at 1100 ∼ 1150°C/10min in a rotary kiln and its physical properties were evaluated. The water absorption, porosity and emission rate of aggregates were controlled by changing processing methods or compositions which change the microstructure of specimens. The natural aggregates showed many macro pores(120∼180 μm), high porosity, high water absorption and low unit weight compared to artificial aggregates, while a porosity of artificial aggregates whose apparent shape is more regular was higher than that of a natural aggregates. Increasing waste white clay content in aggregates enhanced bloating during sintering, so increased the absorptivity of specimens. The void contents influenced a initial water emission and the natural aggregates showed a higher void content compared to artificial one due to their irregular shape. The artificial aggregates having shell structure showed a excellent water release control ability. Especially, for after 6 days, its water emission amount was lower than that of natural aggregates. However, artificial aggregates whose shell is removed through crushing process showed deteriorated water release ability.

Corrosion of Silicate Glasses and Glass-Ceramics Containing EAF Dust in Acidic Solution

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].

Investigation of Plasticity Index of Clay Bodies Including Bottom Ashes from the Power Plant

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.

Thermal and Leaching Behaviors of EAF Dust-Clay Systems

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.

Heavy Metal Leaching Behavior of Glasses Containing EAF Dust

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.