• Title/Summary/Keyword: MgO-Cr Refractory

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Fabrication of Cr$_2$O$_3$powder from waste MgO-Cr refractory

  • Lee, Hoon-Ha;Sohn, Jin-Gun;Lee, Jae-Young;Kim, Dae-Young
    • Proceedings of the IEEK Conference
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    • 2001.10a
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    • pp.357-361
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    • 2001
  • The possibility of producing Cr$_2$O$_3$powder from waste magnesia-chromium refractory was investigated by sulfuric acid reaction, alkali fusion, water leaching & purification and heat treatment. The effects of temperature, the amount of NaOH added and the flow rate of air on chromium extraction efficiency in an alkali fusion step were investigated. The fusion product was leached with methanol to solve free-NaOH, and then leached with water to produce a Na$_2$CrO$_4$solution. The purity of chrome(Ⅵ) oxides, prepared both from monochromate with an impurity content and monochromate purified with $CO_2$were also examined. The purified monochromate solution was reduced from Cr(Ⅵ) to Cr(III) with NaHSO$_3$solution. The reduced solution was neutralized with NaOH to produce Cr(OH)$_3$. Water washing was treated to eliminate Na$_2$SO$_4$from neutralized Cr(OH)$_3$slurry. The washed Cr(OH)$_3$was dried and thermally treated to produce Cr$_2$O$_3$powder. The properties like lightness and hue of Cr$_2$O$_3$fabricated in this study were L=47.47, a=-14.40 and b=17.21.

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Evaporation characteristics of materials from resistive heating sources(I) (저항가열원에 의한 물질의 증발특성(I))

  • 정재인;임병문;문종호;홍재화;강정수;이영백
    • Journal of the Korean institute of surface engineering
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    • v.24 no.1
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    • pp.25-30
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    • 1991
  • The evaporation characteristics of Ag, Al, Au, Cr. Cu, In, Mg, Mn, Pb, Pd, Si, SiO, Sn, Ti and Zn with the various resistive heating sources have been studied. The employed sources are refractory metal (Mo, Ta and W) boats, W-wire, ceramic (usually Al2O3)-coated and -barriered refractory metal boats, and special boats such as baffled boats and intermetallic boats (nitride compound and graphite). We investigated the melting mode, evaporation rate at a specific power, and lifetime of the sources. A special boat holder is also discussed which is needed to cool the sources at a large heat capacity.

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Optimal Condition for Decomposition of Ethylenediaminetetraacetic Acid (EDTA) in Supercritical Water Oxidation (초임계수 산화공정에서 Ethylenediaminetetraacetic Acid (EDTA) 분해 최적화 연구)

  • Lee, Hyeon-Cheol;In, Jung-Hyun;Kim, Jong-Hwa;Lee, Chang-Ha
    • Korean Chemical Engineering Research
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    • v.43 no.2
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    • pp.318-323
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    • 2005
  • Supercritical water oxidation (SCWO, P>221 bar, T>$374^{\circ}C$) is a promising method for the decomposition of refractory organic compounds. In this study, the SCWO of Ethylenediaminetetraacetic acid (EDTA) was carried out in a tubular-type continusous reactor system with an $H_2O_2$ oxidant at $387-500^{\circ}C$, 250 bar and residence time (RT) of 15.9-88.9 s. The decomposition efficiencies increased with increasing temperature and oxidant amount, while it was inversely proportional to feed flow rate. The decomposition efficiency of 99.6% was obtained at $500^{\circ}C$, 250 bar, oxidant amount of 400% and residence time of 40.1 s. The effect of temperature on the decomposition efficiency was more significant than that of oxidant amount. In the case of the decomposition efficiency of 5,000 mg/L of EDTA (3,063 mg/L as $COD_{Cr}$), the decompostion of 99% or higher was obtained at the condition of over 40.1 s (RT) and 200 stoichiometric % of $H_2O_2$ in the supercritical water of $500^{\circ}C$ and 250 bar.

Prediction of Tcv for Coal Slags under Reducing Condition (환원 조건에서 석탄 슬래그의 Tcv 예측)

  • Park, Yoonkyung;Oh, Myungsook
    • Korean Chemical Engineering Research
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    • v.44 no.6
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    • pp.623-630
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    • 2006
  • The slag viscosity is an important factor determining the operation temperature of entrained flow type of gasifiers. The temperature of critical viscosity, $T_{cv}$, for 5 crystalline slags was predicted by empirical models and FactSage equilibrium calculations, and the validity of each method was tested. Two empirical models were employed: one using $T_h$ from the ash fusion test, and the other using the concentrations of 5 major components. The first model using $T_h$ over-predicted $T_{cv}$ by $20{\sim}100^{\circ}C$, while the model based on the slag composition under-predicted $T_{cv}$ by $80{\sim}120^{\circ}C$. In the equlibrium calculations, $T_{cv}$ was obtained from the liquidus temperature. When the 4-major component concentrations were used in the calculation, the predicted temperatures were higher than the observed. The liquidus temperature was very sensitive to the concentrations of minor components, and the addition of MgO and $Na_2O$ lowered the liquidus temperature. The results with 4 major and 3 minor components most closely described experimentally observed $T_{cv}$. In the case that a chromia refractory was used, it was shown that $Cr_2O_3$ concentration in the slag also needs to be included for more accurate prediction of $T_{cv}$.

Treatment of reactive dyes wastewater by electrochemical method (전기화학적인 방법에 의한 반응성 염료폐수의 처리)

  • Yu, Jae-Jeong;Jeon, Seong-Hwan;Park, Jeong-Min;Jeong, Jae-Ho;Park, Sang-Jeong;Min, Kyung-Sok
    • Journal of Korean Society on Water Environment
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    • v.18 no.3
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    • pp.245-251
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    • 2002
  • Reactive dyes waste water, a toxic and refractory pollutant, was treated by an electrochemical method using $Ti/IrO_2$ as anode and Stainless Steel 316 as cathode. In this technique, sodium chloride as an electrolyte was added. A number of experiments were run in a batch system. Artificial samples (reactive blue 19, red 195, yellow 145) were used. Operation parameters, such as supporting electrolyte concentration, current density, pH and sample concentration have been investigated for their influences on COD and color removal efficiencies during electrolysis. After 5 and 90 minites of eletrolysis, color was reduced by 51.5% and 98.9% respectively. Under the condition of current density $10A/dm^2$, NaCl concentration 12mg/l and pH 3, 62.9% of $COD_{Cr}$ was removed after electrolysis for 90 minites. The optimum condition of color removal and COD reduction in this work was found to be the following : pH 3, sodium chloride concentration 20g/l, current density $10A/dm^2$. As a result, we confirmed to be effective to color removal and reduction of refractory organic material.