• 한국세라믹학회지
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• 제56권4호
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• pp.387-393
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• 2019

A N₂H₄-Cu(I)-HNO₃ solution was used to dissolve magnetite powders and a simulated oxide film on Inconel 600. The addition of Cu(I) ions to N₂H₄-HNO₃ increased the dissolution rate of magnetite, and the reaction rate was found to depend on the solution pH, temperature, and [N₂H₄]. The dissolution of magnetite in the N₂H₄-Cu(I)-HNO₃ solution followed the contracting core law. This suggests that the complexes of [Cu⁺(N₂H₄)] formed in the solution increased the dissolution rate. The dissolution reaction is explained by the complex formation, adsorption of the complexes onto the surface ferric ions of magnetite, and the effective electron transfer from the complexes to ferric ions. The oxide film formed on Inconel 600 is satisfactorily dissolved through the successive iteration of oxidation and reductive dissolution steps.

• 방사성폐기물학회지
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• 제16권4호
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• pp.421-429
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• 2018

본 연구에서는 하이드라진 기조의 환원성 제염제를 이용한 마그네타이트 산화물의 용해를 다루고 있다. 마그네타이트로부터의 Fe(II) 및 Fe(III)의 용해는 protonation, surface complexation 및 reduction에 의해 지배를 받는다. 하이드라진과 황산은 산소결합을 파괴하거나 Fe(III)이온을 Fe(II)이온으로 환원시키기 위한 수소 및 전자를 각각 제공하게 된다. 속도론적 관점에서 보다 효율적인 용해를 위하여 다수의 전이금속의 영향을 분석하여 Cu(II) 이온이 효과적임을 확인한 바 있다. Cu(I) 이온은 Cu(II) 이온으로 산화되는 동안 전자를 방출하여 Fe(III) 이온을 환원시키고 다시 하이드라진에 의해 Cu(I) 이온으로 환원되게 된다. 본 연구를 통해 제염용액에 매우 적은 양의 구리 이온 (약 0.5 mM)을 첨가함에 따라 평균 40% 용해속도가 향상됨을 확인하였고, 특히 특정 조건에서는 70% 이상 용해속도가 향상 됨을 확인하였다. 구리 이온이 하이드라진과 배위결합을 이루는 지에 대해서는 아직 명확하지 않으나, 분명한 것은 $Cu(II)/H^+/N_2H_4$으로 이루어진 제염제는 효과적인 용해성능을 가지고 있다는 것이다.

• 방사성폐기물학회지
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• 제19권2호
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• pp.187-196
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• 2021

Chemical equilibrium calculations for multicomponent aqueous systems involving the reductive dissolution of magnetite (Fe₃O₄) with oxalic acid (H₂C₂O₄) were performed using the HSC Chemistry® version 9. They were conducted with an aqueous solution model based on the Pitzer's approach of one molality aqueous solution. The change in the amounts and activity coefficients of species and ions involved in the reactions as well as the solution pH at equilibrium was calculated while changing the amounts of raw materials (Fe₃O₄ and H₂C₂O₄) and the system temperature from 25℃ to 125℃. In particular, the conditions under which Fe₃O₄ is completely dissolved at high temperatures were determined by varying the raw amount of H₂C₂O₄ and the temperature for a given raw amount of Fe₃O₄ fed into the aqueous solution. When the raw amount of H₂C₂O₄ added was small for a given raw amount of Fe₃O₄, no undissolved Fe₃O₄ was present in the solution and the pH of the solution increased significantly. The formation of ferrous oxalate complex (FeC₂O₄) was observed. The equilibrium amount of FeC₂O₄ decreased as the raw amount of H₂C₂O₄ increased.

• 대한화학회지
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• 제27권3호
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• pp.194-200
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• 1983

${\alpha}-Fe_2O_3$의 HCl 또는 $H_2SO_4$에 의한 용해반응에 있어서 금속염의 첨가효과를 분광광도법과 중량법으로 검토하였다. 환원성 금속염은 현저한 반응촉진 효과를 보이나 비환원성 금속염은 부의 효과를 나타내었다. $FeCl_2$와 같은 환원성 금속염을 첨가한 경우에 ${\alpha}-Fe_2O_3$의 용해속도가 크게 촉진되는 것은 $Fe^{3+}$ 와 $Fe^{2+}$ 사이에 chloro-brige가 형성되어 전하이동이 일어나면서 ${\alpha}-Fe_2O_3$ 표면의 격자에너지를 감소시키기 때문인 것으로 추측된다. 이 전하이동으로 인한 ${\alpha}-Fe_2O_3$ 표면의 격자 에너지 변화가 반응의 활성화에너지 변화와 대응된다고 보면 약 0.36e의 부분전하가 $Fe^{3+}$ 쪽으로 옮겨간 것으로 계산되었다.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1892-1900
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• 2023

A protective oxide layer forms on the material surfaces of a Nuclear Power Plant during operation due to high temperature. These oxides can host radionuclides, the activated corrosion products of fission products, resulting in decommissioning workers' exposure. These deposited oxides are iron oxides such as Fe₃O₄, Fe₂O₃ and mixed ferrites such as nickel ferrites, chromium ferrites, and cobalt ferrites. Developing a new chemical decontamination technology for domestic CANDU-type reactors is challenging due to variations in oxide compositions from different structural materials in a Pressurized Water Reactor (PWR) system. The Korea Atomic Energy Research Institute (KAERI) has already developed a chemical decontamination process for PWRs called 'HyBRID' (Hydrazine-Based Reductive metal Ion Decontamination) that does not use organic acids or organic chelating agents at all. As the first step to developing a new chemical decontamination technology for the Pressurized Heavy Water Reactor (PHWR) system, we investigated magnetite dissolution behaviors in various HyBRID inorganic acidic solutions to assess their applicability to the PHWR reactor system, which forms a thicker oxide film.

• 자원환경지질
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• 제55권2호
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• pp.127-135
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• 2022

Excessive presence of As level in groundwater is a major health problem worldwide. In the Red River Delta in Vietnam, several million residents possess a high risk of chronic As poisoning. The As releases into groundwater caused by natural process through microbially-driven reductive dissolution of Fe (III) oxides. It has been extracted by Red River residents using private tube wells for drinking and daily purposes because of their unawareness of the contamination. This long-term consumption of As-contaminated groundwater could lead to various health problems. Therefore, a predictive model would be useful to expose contamination risks of the wells in the Red River Delta Vietnam area. This study used four machine learning algorithms to predict the As probability of study sites in Red River Delta, Vietnam. The GBM was the best performing model with the accuracy, precision, sensitivity, and specificity of 98.7%, 100%, 95.2%, and 100%, respectively. In addition, it resulted the highest AUC of 92% and 96% for the PRC and ROC curves, with Eh and Fe as the most important variables. The partial dependence plot of As concentration on the model parameters showed that the probability of high level of As is related to the low number of wells' depth, Eh, and SO₄, along with high PO₄^3- and NH₄⁺. This condition triggers the reductive dissolution of iron phases, thus releasing As into groundwater.

• Applied Biological Chemistry
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• 제41권4호
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• pp.241-245
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• 1998

Two oxidation states of chromium commonly occur in natural soil/water systems, Cr(III) and Cr(VI). The oxidized form, Cr(VI), exists as the chromate ion and is more mobile and toxic than Cr(III). Therefore oxidation of Cr(III) by various Mn-oxides in natural systems is a very important environmental concern. Organic substances can inhibit the Cr(III) oxidation by binding, Cr(III) strongly and also by dissolving Mn-oxides. Most of Cr(III) oxidation studies were carried out using in vitro systems without organic substances which exist in natural soil/water systems. In this study effect of organic acids - oxalate and pyruvate - on Cr(III) oxidation by $birnessite({\delta}-MnO_2)$ was examined. The two organic acids significantly inhibited Cr(III) oxidation by birnessite. Oxalate showed more significant inhibition than pyruvate. As solution pH was lowered in the range of 3.0 to 5.0, the Cr(III) oxidation was more strongly depressed. Addition of more organic acids reduced the Cr(III) oxidation mare extensively. Different inhibition effects by the organic acids could be due to their ability of reductive dissolution of Mn-oxides and/or Cr(III) binding. Organic acids dissolved Mn-oxide during the Cr(III) oxidation by the oxide, Dissolution by oxalic acid was much greater than that by pyruvate, and the dissolution was more extensive at lower pH. Inhibition of Cr(III) oxidation was parallel to the dissolution of Mn-oxide by organic acids. Although the effect of Cr(III) binding by organic acids on Cr(III) oxidation is not known yet, Mn-oxide dissolution by organic acids could be a main reason for the inhibition of Cr(III) oxidation by Mn-oxide in presence of organic acids. Thus oxidation of Cr(III) to Cr(VI) by various Mn-oxides in natural systems could be much less than the oxidation estimated by in vitro studies with only Cr(III) and Mn-oxides.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.472-477
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• 2001

Spent catalysts containing platinum were generated in petroleum refinery and other chemical industries. The reclamation of precious metals from such wastes has long been attempted in view of their rare, expensive and indispensable nature. In this study, the recovery of platinum from petroleum catalysts was attempted by a method consisting mainly of dissolving alumina substrate with sulfuric acid thereby concentrating insoluble platinum. Also, platinum dissolved partially in sulfuric acid was recovered by a cementation method using aluminum metal as a reductive agent. The effect of temperature, time, concentration of sulfuric acid. and pulp density on the dissolution of substrate was investigated. When the substrate of platinum catalyst was ${\gamma}$-AI$_2$O$_3$ about 95% alumina was dissolved in 6.0M sulfuric acid at 10$0^{\circ}C$ for 2 hours. When the substrate was the mixture of ${\gamma}$-A1$_2$O$_3$and $\alpha$-A1$_2$O$_3$about 92% was dissolved after 4 hours. As a result, more than 99% of platinum could be recovered by this method and aluminum sulfate was obtained as byproduct.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2543-2551
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• 2020

Calculations of chemical equilibrium for multicomponent aqueous systems of the HyBRID dissolution of magnetite were performed by using the HSC Chemistry. They were done by using a Pitzer-based aqueous solution model with the recipe of raw materials in experiments conducted at KAERI. The change in the amounts of species and ions and the pH values of the solution at equilibrium was observed as functions of temperature and raw amount of CuSO₄. Precipitation of Cu₂O occurred at a large amount of CuSO₄ added to the solution, while no precipitation of Cu(OH)₂ was found at any amounts of CuSO₄. The E-pH diagrams for Cu were constructed at various Cu concentrations to provide the effect of the Cu concentration on the pH values at boundaries where the coexistence of Cu⁺ ion and Cu₂O solid occurred. To prevent Cu⁺ ions from being precipitated to Cu₂O, the raw amount of CuSO₄ should be adjusted so that the pH value of the solution from the equilibrium calculation is less than that from the E-pH diagram. We provided guidelines for the raw amount of CuSO₄ and the pH value of the solution, which prevent the formation of Cu₂O precipitates in the HyBRID dissolution experiments for magnetite.

• 광물과 암석
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• 제34권2호
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• pp.95-106
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• 2021

자로사이트 내의 SO₄는 다른 산화음이온으로 치환될 수 있는데 자로사이트가 침철석으로 전이되는 과정은 공침된 산화음이온의 거동에 중요한 역할을 하게 된다. 본 연구에서는 다양한 산화음이온과 함께 공침된 자로사이트가 환원성 용해에 의하여 상변화를 거칠 때 산화음이온 종에 따른 상변화의 양상과 이와 수반된 산화음이온의 거동을 광물학적 및 지구화학적으로 연구하였다. 다섯 가지의 산화음이온이 SO₄를 5 몰% 치환한 자로사이트가 본 연구에 사용되었다. 본 연구에서는 암모늄 옥살레이트를 이용한 환원성 용해 시 일어나는 자로사이트의 광물상의 변화를 측정하였으며 자로사이트의 침철석으로의 전이 속도는 MoO₄-자로사이트 ≥ SeO₄-자로사이트 ≥ CrO₄-자로사이트 > 순수한 자로사이트 > SeO₃-자로사이트 > AsO₄-자로사이트의 순서를 보여 치환된 산화음이온에 따라서 자로사이트의 상전이 속도가 다름을 보여주었다. 이에 따른 Fe의 용출은 시간과 산화음이온의 종류에 따라 큰 차이를 보이지 않았다. 광물의 변화에 따라 용출되어져서 나온 각 산화음이온의 농도는 전체적으로 Mo > Se(SeO₃) > As > Se(SeO₄) > Cr의 농도 순위를 보였으며 시간에 따라 약간의 증가를 보였다. 이러한 경향은 광물상의 변화보다는 산화음이온 종류의 특성에 의한 것으로 파악된다. 본 연구 결과는 산화음이온의 종류에 따라 자로사이트의 침철석으로의 변화는 영향이 있었으나 이러한 경향이 용출되는 산화음이온의 농도에 영향을 미치지 않음을 보여주었다.