• Membrane Journal
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• v.32 no.3
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• pp.181-190
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• 2022

Membrane separation provides various advantages including cost effectiveness and high efficiency over traditional wastewater treatment methods such as flocculation and adsorption. However, the effectiveness of membrane separation greatly declines due to membrane fouling, where pollutants are accumulated on the membrane surface. Among different groups of membranes, ceramic membranes can provide good antifouling properties due to its hydrophilicity and chemical stability. In addition, composite membranes such as graphene oxide modified membranes can help prevent membrane fouling. Recently, hybrid photocatalytic membranes have been proposed as a solution to prevent membrane fouling and provide synergetic effects. Membrane separation can solve the disadvantages of photocatalytic oxidation such as low reutilization rate, while photocatalytic oxidation can help reduce membrane fouling.

• Clean Technology
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• v.28 no.2
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• pp.147-154
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• 2022

Titanate nanotubes (TNTs) were synthesized via alkaline hydrothermal treatment using commercial TiO₂ nanoparticles (P25). The TNTs were prepared at various TiO₂/NaOH ratios, hydrothermal temperatures, and hydrothermal times. The synthesized catalysts were characterized by X-ray diffraction, field-emission scanning electron microscopy, N₂ adsorption-desorption isotherms, field-emission transmission electron microscopy, and ultraviolet-visible spectroscopy. TNTs were generated upon a decrease in the TiO₂/NaOH ratio due to the dissolution of TiO₂ in the alkaline solution and the generation of new Ti-O-Ti bonds to form titanate nanoplates and nanotubes. The hydrothermal treatment temperature and time were important factors for promoting the nucleation and growth of TNTs. The TNT catalyst with the largest surface area (389.32 m² g^-1) was obtained with a TiO₂/NaOH ratio of 0.25, a hydrothermal treatment temperature of 130 ℃, and a hydrothermal treatment time of 36 h. Additionally, we investigated the photocatalytic activity of methyl violet 2B (MV) over the TNT catalysts under UV irradiation and found that the degradation efficiencies of the TNTs were higher than that of P25. Among the TNT catalysts, the TNT catalyst that was hydrothermally synthesized for 36 h (TNT 36 h) exhibited a 96.9% degradation efficiency and a degradation rate constant that was 4.8 times higher than P25 due to its large surface area, which allowed for more contact between the MV molecules and TNT surfaces and facilitated rapid electron transfer. Finally, these results were correlated with the specific surface area.

• Nuclear Engineering and Technology
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• v.55 no.2
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• pp.516-522
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• 2023

The co-precipitation process plays a key role in the decontamination of radionuclides from low and intermediate levels of liquid waste. For that reason, the removal of Cs ions from waste solution by the co-precipitation method was carried out. A simulated liquid waste (¹³³Cs) was prepared from a 0.1 M CsCl solution, while wastewater generated by washing steel ash served as a representative of radioactive cesium solution (¹³⁷Cs). By co-precipitation, potassium ferrocyanide was applied for the adsorption of Cs ions, while nickel nitrate and iron sulfate were selected for supporting the precipitation. The amount of residual Cs ions in the CsCl solution after precipitation and filtration was determined by ICP-OES, while the radioactivity of ¹³⁷Cs was measured using a gamma-ray spectrometer. After cesium removal, the amount of cesium appearing in both XRD and SEM-EDS was analyzed. The removal efficiency of ¹³³Cs was 60.21% and 51.86% for nickel nitrate and iron sulfate, respectively. For the ash-washing solution, the removal efficiency of ¹³⁷Cs was revealed to be more than 99.91% by both chemical agents. This implied that the co-precipitation process is an excellent strategy for the effective removal of radioactive cesium in waste solution treatment.

• Korean Journal of Materials Research
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• v.33 no.10
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• pp.430-438
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• 2023

In this study, we synthesized pH-controlled resorcinol-formaldehyde (RF) gels through the polymerization of two starting materials: resorcinol and formaldehyde. The prepared RF gels were dried using an acetone substitution method, and they were subsequently carbonized under nitrogen atmosphere to obtain carbon xerogels (CX_Y) prepared at different pH (Y). The carbon xerogels were utilized as active materials for coin-type organic supercapacitor electrodes to investigate the influence of pH on the electrochemical properties of the carbon xerogels. The carbon xerogels prepared at lower pH (CX_9.5 and CX_10) exhibited sufficient particle growth, with a three-dimensional network of particles during the RF gel formation, resulting in the development of abundant mesopores. Conversely, the carbon xerogels prepared at higher pH (CX_11 and CX_12) retained densely packed structures of small particles, leading to pore collapse and low specific surface areas. Consequently, CX_9.5 and CX_10 showed high specific surface areas, and provided ample adsorption sites for the formation of electric double layers with electrolyte ions. Moreover, the three-dimensional particle network in CX_9.5 and CX_10 significantly enhanced electrical conductivity. The presence of well-developed mesopores in these materials further facilitated the effective transport of electrolyte ions, contributing to their superior performance as organic supercapacitor electrodes. This study confirmed that pH-controlled carbon xerogels are one of the promising active materials for organic supercapacitor electrodes. Furthermore, we concluded that pH during RF gel formation is a crucial factor determining the electrode performance of the carbon xerogels, highlighting the need for precise pH control to obtain high-performance carbon xerogel electrodes.

• Economic and Environmental Geology
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• v.55 no.4
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• pp.377-388
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• 2022

Laboratory-scale experiments were performed to identify the As removal mechanism of the residual slag generated after the mineral carbonation process. The residual slags were manufactured from the steelmaking slag (blast oxygen furnace slag: BOF) through direct and indirect carbonation process. RDBOF (residual BOF after the direct carbonation) and RIBOF (residual BOF after the indirect carbonation) showed different physicochemical-structural characteristics compared with raw BOF such as chemical-mineralogical properties, the pH level of leachate and forming micropores on the surface of the slag. In batch experiment, 0.1 g of residual slag was added to 10 mL of As-solution (initial concentration: 203.6 mg/L) titrated at various pH levels. The RDBOF showed 99.3% of As removal efficiency at initial pH 1, while it sharply decreased with the increase of initial pH. As the initial pH of solution decreased, the dissolution of carbonate minerals covering the surface was accelerated, increasing the exposed area of Fe-oxide and promoting the adsorption of As-oxyanions on the RDBOF surface. Whereas, the As removal efficiency of RIBOF increased with the increase of initial pH levels, and it reached up to 70% at initial pH 10. Considering the PZC (point of zero charge) of the RIBOF (pH 4.5), it was hardly expected that the electrical adsorption of As-oxyanion on surface of the RIBOF at initial pH of 4-10. Nevertheless it was observed that As-oxyanion was linked to the Fe-oxide on the RIBOF surface by the cation bridge effect of divalent cations such as Ca²⁺, Mn²⁺, and Fe²⁺. The surface of RIBOF became stronger negatively charged, the cation bridge effect was more strictly enforced, and more As can be fixed on the RIBOF surface. However, the Ca-products start to precipitate on the surface at pH 10-11 or higher and they even prevent the surface adsorption of As-oxyanion by Fe-oxide. The TCLP test was performed to evaluate the stability of As fixed on the surface of the residual slag after the batch experiment. Results supported that RDBOF and RIBOF firmly fixed As over the wide pH levels, by considering their As desorption rate of less than 2%. From the results of this study, it was proved that both residual slags can be used as an eco-friendly and low-cost As remover with high As removal efficiency and high stability and they also overcome the pH increase in solution, which is the disadvantage of existing steelmaking slag as an As remover.

• Economic and Environmental Geology
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• v.37 no.1
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• pp.61-72
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• 2004

The soil samples were collected from the paddy field near the mine tailing dumps in the abandoned Duckum mine in Korea. In the laboratory, the soil solution was extracted from the soil using centrifuge, and analysed for the chemical composition. Physical and chemical soil properties were also analysed. Kaolinite is the main clay minerals in the paddy soil and the CEC value is therefore relatively low. Nearly all soil samples show enrichment in their trace elemental concentrations(Cd, Cu, Pb and Zn) compared with natural background level. Some soil samples exceed the soil remediation intervention values for Cd, Pb and Zn and target value for Cu, when compared with Dutch standard, whereas As, Ni and Cr are in normal range. Lead concentrations in some samples near the mine tailing dumps also exceed the standard for remediation act for agricultural area set by Korean soil conservation law. The trace elemental concentrations are higher in the paddy soil nearer the mine tailing dumps and lower for the samples from distance. Similar trend with distance is found for the soil solution chemistry but the decrease with distance from the mine tailing dumps are sharper than the changes in soil chemistry. Cadmium, Cu and Pb concentrations in the soil solution are very low, ranging from a tenth and hundredths to a maximum of several mg/l, whereas their concentrations in soils are highly enriched for natural background. Most of the trace elements are thought to be either removed by reduced iron sulphides or iron oxides, depending on the redox changes. Geochemical equilibrium modelling indicate the presence of solubility controlling solid phases for Cd and Pb, whereas Zn and Cu might have been controlled by adsorption/desorption processes. Although pollutants migration through solution phase are thought to be limited by adsorption onto various Fe, Mn solid phases, the pollutants exist as easily releasable fractions such as exchangeable site. In this case, the paddy soil would act as pollutant pool, which will supply to plants in situ. whenever the geochemical conditions favour.

• Clean Technology
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• v.25 no.1
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• pp.91-97
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• 2019

Oxidative desulfurization (ODS) has received much attention in recent years because refractory sulfur compounds such as dibenzothiophenes can be oxidized selectively to their corresponding sulfoxides and sulfones, and these products can be removed by extraction and adsorption. In this work, The oxidative desulfurization of marine diesel fuel was performed in a batch reactor with hydrogen peroxide ($H_2O_2$) in the presence of various supported heteropoly acid catalysts. The catalysts were characterized by XRD, XRF, XPS and nitrogen adsorption isotherm techniques. Based on the sulfur removal efficiency of promising silica supported heteropoly acid catalysts, the ranking of catalytic activity was: $30\;H_3PW_{12}/SiO_2$ > $30\;H_3PMo_{12}/SiO_2$ > $30\;H_4SiW_{12}/SiO_2$, which appears to be related with their intrinsic acid strength. The $30\;H_3PW_{12}/SiO_2$ catalyst showed the highest initial sulfur removal efficiency of about 66% under reaction conditions of $30^{\circ}C$, $0.025g\;mL^{-1}$ (cat./oil), 1 h reaction time. However, through the recycle test of the $H_3PW_{12}/SiO_2$ catalyst, significant deactivation was observed, which was attributed to the elution of the active component $H_3PW_{12}$. By introducing cesium cation ($Cs^+$) into the $H_3PW_{12}/SiO_2$ catalyst, the stability of the catalyst was improved with changing the solubility, and the $Cs^+$ ion exchanged catalyst could be recycled for at least five times without severe elution.

• Korean Chemical Engineering Research
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• v.62 no.1
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• pp.36-43
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• 2024

Fishing net waste (FNW) constitutes over half of all marine plastic waste and is a major contributor to the degradation of marine ecosystems. While current treatment options for FNW include incineration, landfilling, and mechanical recycling, these methods often result in low-value products and pollutant emissions. Importantly, FNWs, comprised of plastic polymers, can be converted into valuable resources like syngas and pyrolysis oil through pyrolysis. Thus, this study presents a process for generating high-purity hydrogen (H₂) by catalytically pyrolyzing FNW in a CO₂ environment. The proposed process comprises of three stages: First, the pretreated FNW undergoes Ni/SiO₂ catalytic pyrolysis under CO₂ conditions to produce syngas and pyrolysis oil. Second, the produced pyrolysis oil is incinerated and repurposed as an energy source for the pyrolysis reaction. Lastly, the syngas is transformed into high-purity H₂ via the Water-Gas-Shift (WGS) reaction and Pressure Swing Adsorption (PSA). This study compares the results of the proposed process with those of traditional pyrolysis conducted under N₂ conditions. Simulation results show that pyrolyzing 500 kg/h of FNW produced 2.933 kmol/h of high-purity H₂ under N₂ conditions and 3.605 kmol/h of high-purity H₂ under CO₂ conditions. Furthermore, pyrolysis under CO₂ conditions improved CO production, increasing H₂ output. Additionally, the CO₂ emissions were reduced by 89.8% compared to N₂ conditions due to the capture and utilization of CO₂ released during the process. Therefore, the proposed process under CO₂ conditions can efficiently recycle FNW and generate eco-friendly hydrogen product.

• Journal of Soil and Groundwater Environment
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• v.13 no.1
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• pp.32-42
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• 2008

A surfactant recovery and reuse process by selective adsorption with activated carbon was proposed to reduce surfactant cost in a soil washing process. Mathematical model simulation was performed for the whole process, which consists of soil washing, soil recovery, and soil re-washing. The optimal range of surfactant dosage was $6{\sim}10$-fold critical micelle concentration in soil. The efficiency of surfactant reuse process was decreased with increasing the dosage of activated carbon. Effectiveness factor for activated carbon significantly altered the efficiency of the reuse process unlike effectiveness factor for soil. Total requirement of surfactant was reduced to 20-30% with the reuse process compared to the conventional soil washing process. The contamination of wastewater after soil washing was reduced with the reuse process. This mathematical model can be used to estimate performance of the whole process of soil washing including surfactant recovery and to obtain optimal ranges of operating conditions without extra labor-intensive experimental works.

• Journal of Soil and Groundwater Environment
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• v.13 no.2
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• pp.1-11
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• 2008

Phenanthrene uptake by surfactant sorbed on activated carbon was investigated to recycle of surfactant in washed solution for contaminated soil. The partitioning of phenanthrene to the activated carbon coating with Triton X-100 as a surfactant was also evaluated by a mathematical model. Phenanthrene-contaminated soil (200 mg/kg) was washed in 10 g/L of surfactant solution. Washed phenanthrene in solution was separated by various particle loadings of granular activated carbon through a mode of selective adsorption. Removal of phenanthrene was 99.3%, and surfactant recovery was 88.9% by 2.5 g/L of granular activated carbon, respectively. Phenanthrene uptake by activated carbon was greater than that of phenanthrene calculated by a standard model for a system with one partitioning component. This is accounted for enhanced surface solubilization by hemi-micelles adsorbed onto granular activated carbon. The effectiveness factor is greater than 1 and molar ratio of solubilization to sorbed surfactant is higher than that of liquid surfactant. Results suggest that separation of contaminants and surfactants by activated carbon through washing process in soil is much effective than that of calculated in a theoretical model.