Engineering of activated carbons (ACs) through chemical activation of organic precursors has been extensively studied for a wide variety of biopolymers, biomasses, wastes and other fossil-based precursors. Despite huge efforts to engineer evermore performant and sustainable ACs, “searching-for-the-best-recipe” type of studies are more the rule than the exception in the published literature. Emerging AC applications related to energy and gas storage require strict control of the AC properties and a better understanding of the fundamentals underlying their engineering. In this study, we provide new insights into the K2CO3 chemical activation of plant-based polyphenols—lignins and tannins—through careful thermoanalytical and structural analyses. We showed for the the first time that the reactivity of polyphenols during K2CO3 chemical activation depends remarkably on their purity and structural properties, such as their content of inorganics, OH functionalities and average molecular weight. We also found that the burn-off level is proportional to the K2CO3/ lignin impregnation ratio (IR), but only within a certain range—high impregnation ratios are not needed, unlike often reported in the literature. Furthermore, we showed for the first time that the K2CO3 chemical activation of different carbon surfaces from lignins and tannins can be modelled using simple global solid-state decomposition kinetics. The identified activation energies lay in the range of values reported for heterogenous gas-carbon surface gasification reactions ( O2-C, H2O- C, or CO2- C) in which the decomposition of C(O) surface complexes is the common rate-limiting step.

Various disposal methods for spent nuclear fuels (SNFs) are being researched, and one of these methods involves separating high heat-generating nuclear isotopes such as Strontium-90 (90Sr) and Cesium-137 (137Cs) for deep disposal. These isotopes has relatively short half-lives and substantial decay energies. Especially, 90Sr undergoes decay through Yttrium-90 to Zirconium-90, emitting intense heat with beta radiation. Therefore, the removal of these high heat-generating isotopes will significantly contribute to reducing disposal site area. To remove 90Sr from SNFs, molten salt was utilized in KAERI. During this process, it was discovered that 90Sr dissolves in the molten salt in the form of SrCl2 and/or Sr4OCl6. Afterwards, it is crucial to recover 90Sr in the form of oxide from the salt to create immobilized forms for disposal. This can be achieved by reactive distillation with K2CO3. However, the amount of 90Sr within the SNFs is only 0.121wt%, and even if all the 90Sr in the SNFs were to leach into the molten salt, the quantity of 90Sr in the molten slat would still be very small. Therefore, adding K2CO3 to the molten salt for reactive distillation could result in significant possibilities of side reactions occurring. In this study, a two-step process was employed to mitigate the side reactions: the 1st step involves evaporating the all molten salts and the 2nd step includes adding K2CO3 to make oxides through solid-solid reaction. Eutectic LiCl-KCl, which is the most commonly used salt, was employed. The eutectic LiCl-KCl with SrCl2 was heated at 850°C for 2 h to evaporate the salts under a vacuum (> 0.02 torr). However, after examining the distillation product before the solid-solid reaction, it was observed that SrCl2 reacted with KCl in the salt, resulting in the formation of KSr2Cl5. It means that salts containing KCl are not suitable candidates for reactive distillation aimed at producing immobilized forms. As an alternative, MgCl2 could be a highly promising candidate because it is inert to SrCl2 and according to a recent study in KAERI, MgCl2 exhibited the most efficient separation of Sr among various salts. Therefore, we plan to proceed with the two-step reactive distillation using MgCl2 for the future work.

Salacca peel-based porous carbon (SPPC) with high surface area (1945 m2 g−1) and large specific pore volume (1.68 cm3 g−1) was prepared by pre-carbonization and K2CO3 activation method. Based on the TGA results, it can be estimated that up to 70 wt% of sulfur-active materials could be infiltrated into the pores of SPPC to form SPPC/S composite cathode for LiS battery. The porous structure of SPPC could act as a buffer layer against volume expansion and minimize the shuttle effect due to the penetration of intermediate polysulfides during cycle tests. Optimization on sulfur loading (50, 60 and 70 wt%) in SPPCC/S composite was also investigated. It was found that the SPPC/S composites with 60 wt% of sulfur loading had the best electrochemical performances. With 60 wt% of sulfur loading, SPPC/S composite electrodes showed excellent electrochemical performances in terms of high initial specific discharge capacity of 1006 mAh g− 1 at 0.5 C and capacity retention of 71% until the 100th cycle. For both cases of low and high sulfur loading, they caused much worse electrochemical performances. Based on the experimental results, it can be concluded that porous carbons derived from the salacca peel were promising materials for sulfur loading in LiS battery.

Activated carbons (ACs) have been used as EDLC (electric double-layer capacitor) electrode materials due to their high specific area, stability, and ecological advantages. In order to prepare ACs with high density and crystallinity, coal tar pitch (CTP) was activated by K2CO3 and the textural and electrochemical properties of the obtained ACs were investigated. Although the CTP ACs formed by K2CO3 activation had much smaller specific surface area and pore volume than did the CTP ACs formed by KOH activation, their volumetric specific capacitance (F/cc) levels as electrode materials for EDLC were comparable due to their higher density and micro-crystallinity. Structural characterization and EDLC-electrode performance were studied with different activation conditions of CTP/K2CO3 ratio, activation temperature, and activation period.

사용후핵연료 파이로프로세싱에서 발생하는 방사성폐기물의 양을 최소화하기 위해서는 방사성 핵종 함유 염폐기물을 효과 적으로 처리할 수 있는 기술개발이 필요하다. 이를 위해 탄산화물(Li2CO3, K2CO3)을 이용한 반응증류공정에서 LiCl-KCl 공융 염 내 NdCl3의 분리특성을 관찰하였다. HSC-Chemistry 프로그램을 이용한 탄산화물과 NdCl3의 반응모델결과에서 NdCl3는 탄산화물의 주입조건 및 온도변화에 따라 산염화물(NdOCl) 또는 산화물(Nd2O3) 형태로 전환됨이 확인되었으며, 탄산화물 의 주입조건에 따른 LiCl-KCl-NdCl3계의 반응증류시험에서 반응모델결과와 유사한 경향을 확인하였다. 이 결과들을 이용하 여 LiCl-KCl 공융염 내 NdCl3를 고화가 용이한 산화물 형태로 분리하기 위한 공정조건을 도출하였다.

Most heavy metals are well-known toxic and carcinogenic agents and when discharged into wastewater represent a serious threat to the human population and the fauna and flora of the receiving water bodies. The present study aims to develop a procedure for Pb(II) removal. The study was based on using powdered activated carbon, which was prepared from walnut shells generated as plant wastes and modified with potassium carbonate or phosphoric acid as chemical agents. The main parameters, such as effect of pH, effect of sorbent dosage, Pb(II) concentrations, and various contact times influence the sorption process. The experimental results were analyzed by using Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich adsorption models. The kinetic study of Pb(II) on activated carbon from walnut shells was performed based on pseudo-first order and pseudo-second order equations. The data indicate that the adsorption kinetics follow the pseudo-second order rate. The procedure was successfully applied for Pb(II) removal from aqueous solutions.