• Resources Recycling
• /
• v.32 no.1
• /
• pp.50-59
• /
• 2023

The amount of dust generated during the dissolution of scrap in an electric arc furnace is approximately 1.5% of the scrap metal input, and it is primarily collected in a bag filter. Electric arc furnace dust primarily consists of zinc and ion. The processing of zinc starts with its conversion into pellet form by the addition of a carbon-based reducing agent(coke, anthracite) and limestone (C/S control). These pellets then undergo reduction, volatilization, and re-oxidation in rotary kiln or RHF reactor to recover crude zinc oxide (60%w/w). Next, iron is discharged from the electric arc furnace dust as a solid called Fe clinker (secondary by-product of the Fe-base). Several methods are then used to treat the Fe clinker, which vary depending on the country, including landfilling and recycling (e.g., subbase course material, aggregate for concrete, Fe-source for cement manufacturing). However, landfilling has several drawbacks, including environmental pollution due to leaching, high landfill costs, and wastage of iron resources. To improve Fe recovery in the clinker, we pulverized it into optimal -sized particles and employed specific gravity and magnetic force selection methods to isolate this metal. A carbon-based reducing agent and a binding material were added to the separated coarse powder (>10㎛) to prepare briquette clinker. A small amount (1-3%w/w) of the briquette clinker was charged with the scrap in an electric arc furnace to evaluate its feasibility as an additives (carbonaceous material, heat-generating material, and Fe source).

• Journal of Soil and Groundwater Environment
• /
• v.13 no.5
• /
• pp.81-87
• /
• 2008

In accompany with the transfer of US army bases, recent surveys reported serious contamination of soils by the release of petroleum from storage facilities and heavy metals accumulated in rifle-ranges. These problems have made an increased concerns of cleanup technology for contaminated soils. In this study, a full-scale soil washing process improved by multistage continuous desorption and agitational desorption techniques was examined for petroleum-contaminated soils obtained from three different remedial sites that contained 29.3, 16.6, and 7.8% of silt and clay, respectively. The initial concentrations of total petroleum hydrocarbon (TPH) were 5,183, 2,560, and 4,860 mg/kg for each soil. Pure water was applied to operate washing process, in which water used for washing process was recycled 100% for over 6 months. The results of full-scale washing tests showed that the TPH concentrations for soils (> 3.0 mm) were 50${\sim}$356 mg/kg (85.2${\sim}$98.2% removal rates), regardless of the contents of silt and clay from in A, B and C soil, when the soils were washed at 3.0 kg/$cm^2$ of injection pressure with the method of wet particle separation. Based on the initial TPH concentration, the TPH removal rates for each site were 85.2, 98.2 and 89.9%. For soils in the range of 3.0${\sim}$0.075 mm, the application of first-stage desorption technique as a physical method resulted 834, 1,110, and 1,460 mg/kg of TPH concentrations for each soil, also additional multi-stage continuous desorption reduced the TPH concentration to 330, 385, and 245 mg/kg that were equivalent to 92.4, 90.6, and 90.1% removal rates, respectively. The result of multi-stage continuous desorption for fine soil (0.075${\sim}$0.053 mm) were 791, 885, and 1,560 mg/kg, and additional agitation desorption showed 428, 440, and, 358 mg/kg of TPH concentrations. Compared with initial concentration, the removal rates were 92.0, 93.9 and 92.9%, respectively. These results implied we could apply strategic process of soil washing for varies types of contaminated soils to meet the regulatory limit of TPH.

• Korean Chemical Engineering Research
• /
• v.50 no.6
• /
• pp.1034-1042
• /
• 2012

This study was performed by using an LFR (laminar flow reactor), which can be used to carry out different types of research on coal. In this study, an LFR was used to analyze coal flames, tar and soot yields, and structures of chars for two coals depending on their volatile content. The results show that the volatile content and oxygen concentration have a significant effect on the length and width of the soot cloud and that the length and width of the cloud under combustion conditions are less than those under a pyrolysis atmosphere. At sampling heights until 50 mm, the tar and soot yields of Berau (sub-bituminous) coal, which contains a large amount of volatile matter, are less than those of Glencore A.P. (bituminous) coal because tar is oxidized by the intrinsic oxygen component of coal and by radicals such as OH-. On the other hand, at sampling heights above 50 mm, the tar and soot yields of Berau coal are higher than those of Glencore A.P. coal by reacted residual volatile matter, tar and light gas in char and flame. With above results, it is confirmed that the volatile matter content and the intrinsic oxygen component in a coal are significant parameters for length and width of the soot cloud and yields of the soot. In addition, the B.E.T. results and the images of samples (SEM) obtained from the particle separation system of the sampling probe support the above results pertaining to the yields; the results also confirm the pore development on the char surface caused by devolatilization.

• Korean Journal of Optics and Photonics
• /
• v.21 no.2
• /
• pp.82-88
• /
• 2010

Photopolymer is a material for recording three dimensional holograms containing photo information. Photopolymer has been found to be a proper material due to many advantages such as high DE value, easy processing, and low price. Compositions of PVA, monomer, initiater and photosensitizer were determined by previous experiments and the compositions of $SeO_2$ and $TiO_2$ were considered as variable to find out the effects of $TiO_2$ on DE. The DE values were constant for the varying compositions of $TiO_2$ (0.1 mg~1.0 mg). In other words, $TiO_2$ is not directly effective on the DE values. Composition change experiments from $SeO_2$ 0.1 mg, $TiO_2$ 0.9 mg to $SeO_2$ 0.9 mg, $TiO_2$ 0.1 showed a maximum DE value of 73.75% at a component of $SeO_2$ 0.8 mg, $TiO_2$ 0.2 mg. It seemed that regardless of the amount of $TiO_2$, increasing the amount of $SeO_2$ gently increases DE`s. If nano particles are heavily added, transparent films could not be made due to the separation of particles by the solubility decrease. Photopolymer films could be made with high DE values for an extensive angle range if $TiO_2$ additions were kept minimum and $SeO_2$ additions were kept maximum.

• Korean Journal of Dental Materials
• /
• v.44 no.3
• /
• pp.207-216
• /
• 2017

The effect of cooling rate on precipitation hardening of a Pd-Cu-Ga-Zn metal-ceramic alloy during porcelain firing simulation was investigated and the following results were obtained. When the cooling rate was fast (Stage 0), the hardness of the alloy increased at each firing step and the high hardness value was maintained. When the cooling rate was slow (Stage 3), the hardness was the highest at the first stage of the firing, but the final hardness of the alloy after complete firing was lower. The increase in hardness of the specimens cooled at the cooling rate of Stage 0 after each firing step was caused by precipitation hardening. The decrease in hardness of the specimens cooled at the cooling rate of Stage 3 after each firing step was attributed to the coarsening of the spot-like precipitates formed in the matrix and plate-like precipitates. The matrix and the plate-like precipitates were composed of the $Pd_2(Cu,Ga,Zn)$ phase of CsCl-type, and the particle-like structure was composed of the Pd-rich ${\alpha}$-phase of face-centered cubic structure. Through the porcelain firing process, Cu, Ga, and Zn, which were dissolved in Pd-rich ${\alpha}$ particles, precipitated with Pd, resulting in the phase separation of the Pd-rich ${\alpha}$ particles into the Pd-rich ${\alpha}^{\prime}$ particles and ${\beta}^{\prime}$ precipitates composed of $Pd_2(Cu,Ga,Zn)$. These results suggested that the durability of the final prosthesis made of the Pd-Cu-Ga-Zn alloy can be improved when the cooling rate is fast during porcelain firing simulation.