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Magnetite Dissolution by Copper Catalyzed Reductive Decontamination
Seonbyeong Kim,Sangyoon Park,Wangkyu Choi,Huijun Won,Jungsun Park,Bumkyoung Seo 한국방사성폐기물학회 2018 방사성폐기물학회지 Vol.16 No.4
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 하이드라 진과 배위결합을 이루는 지에 대해서는 아직 명확하지 않으나, 분명한 것은 Cu(Ⅱ)/H+/ N2H4으로 이루어진 제염제는 효과적인 용해성능을 가지고 있다는 것이다. Hydrazine based reductive dissolution applied on magnetite oxide was investigated. Dissolution of Fe(Ⅱ) and Fe(Ⅲ) from magnetite takes place either by protonation, surface complexation, or reduction. Solution containing hydrazine and sulfuric acid provides hydrogen to break bonds between Fe and oxygen by protonation and electrons for the reduction of insoluble Fe(Ⅲ) to soluble Fe(Ⅱ) in acidic solution of pH 3. In terms of dissolution rate, numerous transition metal ions were examined and Cu(Ⅱ) ion was found to be the most effective to speed up the dissolution. During the cycle of Cu(I) ions to Cu(Ⅱ) ions, the released electron promoted the reduction of Fe(Ⅲ) and Cu(Ⅱ) ions returned to Cu(I) ion due to the oxidation of hydrazine. In the experimental results, the addition of a very low amount of cupric ion (about 0.5 mM) to the solution increased the dissolution rate about 40% on average and up to 70% for certain specific conditions. It is confirmed that even though the coordination structure of copper ions with hydrazine is not clear, the Cu(Ⅱ)/H+/N2H4 system is acceptable regarding the dissolution performance as a decontamination reagent.
Laser Scabbling of a Concrete Block Using a High-Power Fiber Laser
Oh, Seong Y.,Lim, Gwon,Nam, Sungmo,Kim, TaekSoo,Kim, Ji-Hyun,Chung, Chul-Woo,Park, Hyunmin,Kim, Seonbyeong Korean Radioactive Waste Society 2021 방사성폐기물학회지 Vol.19 No.3
A laser scabbling experiment was performed using a high-power fiber laser to investigate the removal rate of the concrete block and the scabbled depth. Concrete specimens with a 28-day compressive strength of 30 MPa were used in this study. Initially, we conducted the scabbling experiment under a stationary laser beam condition to determine the optimum scan speed. The laser interaction time with the concrete surface varied between 3 s and 40 s. The degree of spalling and vitrification on the surface was primarily dependent on the laser interaction time and beam power. Furthermore, thermal images were captured to investigate the spatial and temporal distribution of temperature during the scabbling process. Based on the experimental results, the scan speed at which the optical head moved over the concrete was set to be 300 mm·min<sup>-1</sup> or 600 mm·min<sup>-1</sup> for the 4.8-kW or 6.8-kW laser beam, respectively. The spalling rates and average depth on the concrete blocks were measured to be 87 cm<sup>3</sup>·min<sup>-1</sup> or 227 cm<sup>3</sup>·min<sup>-1</sup> and 6.9 mm or 9.8 mm with the 4.8-kW or 6.8-kW laser beams, respectively.