The radiolytic decomposition of oxalic acid was investigated using gamma irradiation for decontamination of nuclear power systems. The study used high-purity analytical grade chemicals, with initial concentrations of oxalic acid prepared at 1, 2, 5, and 10 mM, and the initial pH was adjusted to 2-3 at each test condition. Gamma irradiation was performed using a high-level Co-60 source, and absorbed doses were 5, 10, 20, 30, and 50 kGy. The results showed that the efficiency of gamma irradiation decreased with longer gamma exposure time, and the G-value increased with the initial concentration of oxalic acid. Interestingly, the G-value decreased with accumulated radiation dose, but the removal increased. The dose constant ranged from 0.1695 to 0.0536 kGy-1 at different initial concentrations, and the G-value was inversely proportional to the dose constant. The study concluded that oxalic acid was successfully degraded by gamma irradiation, and 92% removal was obtained at the initial concentration of 10 mM. The mineralization of oxalic acid at higher concentrations was more difficult due to the great number of generated intermediates.

Cobalt (Co) is mainly used to prepare cathode materials for lithium-ion batteries (LIBs) and binder metals for WC-Co hard metals. Developing an effective method for recovering Co from WC-Co waste sludge is of immense significance. In this study, Co is extracted from waste cemented carbide soft scrap via mechanochemical milling. The leaching ratio of Co reaches approximately 93%, and the leached solution, from which impurities except nickel are removed by pH titration, exhibits a purity of approximately 97%. The titrated aqueous Co salts are precipitated using oxalic acid and hydroxide precipitation, and the effects of the precipitating agent (oxalic acid and hydroxide) on the cobalt microstructure are investigated. It is confirmed that the type of Co compound and the crystal growth direction change according to the precipitation method, both of which affect the microstructure of the cobalt powders. This novel mechanochemical process is of significant importance for the recovery of Co from waste WC-Co hard metal. The recycled Co can be applied as a cemented carbide binder or a cathode material for lithium secondary batteries.

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°C to 125°C. 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.

고리 1호기는 원전해체 계획에 따라 영구정지 이후 가능한 한 빠른 시일 내에 원자로냉각재계통의 화학제염을 수행할 계획으로, 계통제염 기술 확보를 위해 한수원에서는 2014년부터‘원전 해체설계를 위한 냉각재계통 및 기기제염 상용기술 개발’연구과제를 통해 화학제염기술을 개발하고 있다. 본 연구를 위해 Lab. 규모 계통제염 공정장치를 제작하였으며, 계통제염 대상의 주요재료인 STS304, 316, 410, Alloy600, SA508을 사용하여 화학제염 공정실험을 수행하였다. 화학제염 공정실험의 목적은 산화-환원공정의 최적시간, 최적제염제 및 공정횟수를 도출하기 위함이다. 화학제염 공정실험은 과망간산-옥살산 기반의 단위공정 및 연속공정 실험, 과망간산+질산-옥살산 기반의 연속공정 실험으로 나누어 수행하였다. 그 결과 단위공정실험을 통해 최적공정 시간인 산화공정 5시간, 환원공정 4시간을 도출하였으며, 연속공정실험을 통해 최적제 염제와 공정횟수를 도출하였다. 최적제염제는 산화제의 경우 200 mg·L-1 과망간산 + 200 mg·L-1 질산이고, 환원제는 2000 mg·L-1 옥살산이며, 공정횟수는 STS304와 SA508의 경우 2 cycle, Alloy600의 경우 3 cycle 이상 수행하는 것이 적절할 것 으로 평가되었다.

The culture filtrate of Lentinula edodes showed potent antimicrobial activity against the plant pathogenic bacteria and fungi. To purify antibacterial compound, the culture filtrate was subjected to Octadecyl-silica (ODS) column chromatography and was eluted with different concentrations from 5 to 100% methanol and each 50 μL aliquot of the methanol elutes did not show antimicrobial effect on the bacteria, but the water fraction that passed through the column maintained antibacterial activity on the bacteria. The pH of the passed fraction was 3.9, speculating the low pH can be caused by an organic acid. Qualitative analyses of organic acids from culture filtrate of L. edodes were carried out by high-performance liquid chromatography(HPLC). Nine organic acids including oxalic acid, phytic acid, malonic acid, and fumaric acid were identified and oxalic acid was a dominant component in culture filtrate of L. edodes and it made up 50% from HPLC analysis data. Oxalic acid concentrations over 300mg/L exhibited antimicrobial activities on eight phytopathogenic bacteria and different fungi. The quantitative analysis by HPLC revealed that the content of oxalic acid was more highly detected in water extract from spent mushroom substrate than that of liquid culture.

Oxalic acid has a nematicidal activity against the root-knot nematode Meloidogyne incognita. High producer of oxalic acid was isolated, and then named as Aspergillus niger F22. Oxalic acid production was investigated under various temperatures from 20 – 33oC and rotational speeds in 5 L jar fermenters. Yield of oxalic acid increased with decreasing temperature. The highest yield was obtained at 23oC, showing the yield of oxalic acid of 8.7 g/L, whereas oxalic acid production was least at 33oC. At 20oC, the yield was lower than that of 23oC. At a rotational speed of 300 rpm, serious oxygen depletion was present from 48 - 72 h, resulting in low productivity of 26.2 mg /L·h. When a rotational speed was set at 600 rpm, dissolved oxygen tension was over 40% and oxalic acid production increased up to approximately 55%. Viscosity during the culture differed with temperatures. Viscosity increased with the increment of temperatures. When A. niger F22 was cultured at 23oC, viscosity was 810 cP, which was favorable for oxalic acid production.