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The successful disposition of radioactive nuclear waste has been considered to be a non-negligible task in the strategy for developing advanced nuclear fuel cycles. The physical behavior of sandstone has garnered widespread interest for use in highly radioactive nuclear waste repositories due to its potential impacts on stability at high temperatures. Here, we experimentally demonstrate the physical characteristics of sandstones by combining tensile strength and porosity at 500°C. Our results show that the quartz content has a significant impact on the physical characteristics of sandstones. Further, an experimental contour graph modelling via mass loss ratio and specific gravity of sandstones at 500°C was also observed. In all cases, the physical change of sandstones was less than 5%. We anticipate that sandstones can potentially serve as a natural barrier for secondary nuclear waste repositories which are in need to endure high temperatures.

This study examined the effect of alkalis on lyocell-based activated carbon fibres (ACFs) with high Brunauer-Emmett-Teller (BET) surface areas, using X-ray diffraction (XRD). Here, alkali treatments were conducted using 10 ~ 25 % NaOH and KOH on lyocell samples for 3 h at ambient room temperature. A secondary treatment with 4 % each of KOH and H3PO4 for an additional 3 h followed. An activated form of the samples was prepared by oxidation (stabilisation), carbonisation, and activation. The final ACF form of the samples showed a porous structure with high BET surface areas (> 1,000 m2 g-1). A 25 % dosage of NaOH produced the highest BET surface area compared to other samples. In terms of crystallinity, a 15 % dosage of KOH was found to be the optimum dosage to secure the highest degree of crystallinity among all samples. Meanwhile, the NaOH was successfully shifted the samples into the most distinct form of cellulose II. 15 % NaOH was found to secure the most stable thermal characteristics, as determined via thermo-gravimetric analysis. The present work demonstrates the various physio-chemistries of ACFs prepared with different proportions and types of alkalis, leading to intriguing potential applications.

Recent numerical approaches to extracting metal species using carbonaceous materials have de facto stimulated an interest in the field of microextraction, but theoretical observations inspired by randomness changes have been elusive. In this contribution, we present the degree of randomness using Cu (II) and Pb (II). Here, activated carbon fibres were employed as the skeleton adsorbent, providing scientific insights via the aqueous phase. Coupled isotherms of Langmuir and Freundlich were represented to unravel the aforementioned thermodynamics. Findings revealed that the Langmuir isotherm best described the equilibrium state and the trend was in accordance with the energy computation. The maximum microextraction performance was 84.75 mg/g and 102.04 mg/g for Cu (II) and Pb (II), respectively. Under all circumstances, there was a high randomness change as the microextraction performance increased.

Prussian blue (PB) has attracted substantial attention as a potential adsorbent for radionuclides due to its high water-insoluble characteristics. Here, PB-encapsulating activated carbon fibers (ACFs) obtained via a physicochemical in-situ synthesis were introduced for an effective cesium removal. ACFs were used as an anchor platform to hold PB within the pores. The physicochemical synthesis of PB (PB-ACF-B) was done by stirring ACFs in an iron chloride solution. Potassium ferrocyanate was injected during the stirring process. As the counterpart, powdered PB (PB-ACF-A) was prepared with a physical synthesis. Throughout the test, PB-ACF-B revealed a decrease in the specific surface characteristics compared to PB-ACF-A; however, it also experienced an increase in the 133Cs adsorption. In all the cases, the dosage of the absorbent and radionuclide was in positive correlation with the adsorption performance. Further, the amount of PB was found to be the key factor for the adsorption of 133Cs compared to the specific surface characteristics.

Radon (222Rn) is a member of the decay chain of 238U. It has been well documented that 222Rn is known to present a risk of lung cancer once inhaled. For practical implementation, this study makes use of activated carbon fibers (ACFs) to uptake 222Rn through environmental variations in the temperature, dosage of the adsorbent and circulate conditions. Here, three ACF samples were prepared via different carbonization and activation temperatures from 850 °C to 900 °C. The observed adsorption characteristics show that low temperature and high surface contact of an adsorbent with rich micropores allow the maximum adsorption of 222Rn. No such correlation was observed in the case of increasing the circulate conditions. However, there was a direct influence on the maximum adsorption capacity once the circulate conditions decreased. In summary, these findings expand the understanding of the adsorption, dependency on the factors and a proper carbonaceous-material design for reducing 222Rn.

Fibrous adsorbents, such as activated carbon fibers (ACF) have acknowledged advantages of rapid adsorption rate and ease of modification compared with granular and powdered adsorbents. Based on the surface modification of lyocell-based ACF, we observed different surface characteristics of ACF samples with variation in the mixing ratio and impregnation time of H3PO4, NaCl, and KMnO4 solution. For an engineering application, we also explored the adsorption characteristics of thus-produced ACF samples onto volatile organic compounds (VOCs). Isothermal adsorption experiments were performed using toluene and benzene as adsorbates. Results indicate that both physical and chemical surface properties have an effect on the adsorption of volatile organic compounds (VOCs).

We designed porous carbon fibers with the aid of CO2 during activation for effective malachite green (MG) adsorption. The physiochemical mechanisms have been characterized both experimentally and numerically to decipher the underlying relevance of CO2-activation on the MG adsorption capacity. The obtained samples are dominated by micropores, resulting in a high specific surface up to 1012 m2 g−1 via 60 min of CO2-activation. The adsorption isotherm was fitted to Langmuir with the maximum adsorption capacity of 555.56 mg L-1. The regeneration was secured over 80% during 3 trials. Thermodynamics revealed endothermic in nature and the spontaneous adsorption process.

In this study, pitch-based activated carbon fibers (ACFs) were modified with pyrolysis fuel oil (PFO). Carbonized ACF samples were activated at 850℃, 880℃ and 900℃. A scanning electron microscope (SEM) and a BET surface area apparatus were employed to evaluate the indoor radon removal of each sample. Among three samples, the BET surface area and micropore area of ACF880 recorded the highest value with 1,420 m2∙g-1 and 1,270 m2∙g-1. Moreover, ACF880 had the lowest external surface area and BJH adsorption cumulative surface area of pores with 151 m2∙g-1 and 35.5 m2∙g-1. This indicates that satisfactory surface area depends on the appropriate temperature. With the above scope, ACF880 also achieved the highest radon absorption rate and speed in comparison to other samples. Therefore, we suggest that the optimum activation temperature for PFO containing ACFs is 880℃ for effective indoor radon adsorption.

This paper aims to propose testing methods and standards for evaluating refrigerant recovery and recycling equipment so that the methodology can be used for alternative material-related technological research in South Korea. To achieve this, the paper establishes test methods based on international and domestic standards. Major test items can be classified into following categories; equipment performance and the quality of recycled refrigerant. Selected refrigerants are HCFC-22, HCFC-123 and HFC-134a. The resulted equipment performance revealed that the movable type, which is the majority model in South Korea, has recovery and capacity advantages to be suited into international standard. On the other hand, the quality of recycled refrigerant lagged in purity and high-boiling residue. The purity of HCFC-22 was 99.3% which was obviously contaminated than the pure refrigerant and the international standard. High-boiling residue of HCFC-22 and HCFC-123 also showed lower numerical value compared to the international standard. Aforementioned results imply the gap between international and domestic standard. Based on result values of test equipment and precedent studies, approximate standard performance criteria and values were set as proposed by South Korean standard.