Effects of Oxygen-Containing Functional Groups on the Electrochemical Performance of Activated Carbon for EDLCs.

Activated carbon (AC) is used in commercial electric double-layer capacitors (EDLC) as electrode active material owing to its favorable properties. However, oxygen functional groups (OFGs) present in AC reduce the lifespan of EDLCs. Thus, we investigated the correlation between the OFGs in AC and their electrochemical characteristics. Samples were prepared by heat-treating commercial AC at 300 °C-900 °C for 1 h under two gas atmospheres (N2 and 4% H2/N2 mixed gas). The textural properties were studied, and the reduction characteristics of AC under Ar and H2/Ar mixed gas atmospheres were investigated. Additionally, changes in the OFGs with respect to the heat-treatment conditions were examined via X-ray photoelectron spectroscopy. The specific surface areas of AC-N and AC-H were 2220-2040 and 2220-2090 m2/g, respectively. Importantly, the samples treated in hydrogen gas exhibited a higher yield than those treated in nitrogen while maintaining their pore characteristics. Additionally, the electrochemical performance of the AC was significantly enhanced after the reduction process; the specific capacitance increased from 62.1 F/g to 81.6 F/g (at 0.1 A/g). Thus, heat treatment in hydrogen gas improves the electrochemical performance of EDLCs without destroying the pore characteristics of AC.

Multifocal hot spots demonstrated by whole-body 131I scintigraphy and SPECT/CT after transaxillary endoscopic thyroidectomy.

A 35-year-old woman received open thyroidectomy for a thyroid nodule that was confirmed as papillary carcinoma. Whole-body 131I scintigraphy during thyroid ablation demonstrated high uptake in the thyroid bed and multiple focal hot spots in the thorax. SPECT/CT localized the hot spots to the right chest wall and axilla, as well as to the left chest wall. The surgeon recognized these sites to concur with the transaxillary tract used during endoscopic thyroidectomy for nodular hyperplasia 8 years previously. Thus, this case illustrates how thyroidal tissue fragments seeded during endoscopic thyroidectomy can be mistaken for thyroid cancer metastasis on 131I scintigraphy.

Primary Benign Intraosseous Meningioma on (18)F-FDG PET/CT Mimicking Malignancy.

We present a case of primary benign intraosseous meningioma in the sphenoid bone mimicking malignancy. A 44-year-old female patient who had a protruding right eye and headache came to our hospital. MRI showed a large, destructive, heterogeneously well-enhancing soft tissue mass in the right sphenoid bone suggesting malignancy. (18)F-FDG PET/CT showed a hypermetabolic mass in the same site with an SUVmax of 9.1 The pathological diagnosis by surgery revealed that this tumor was a WHO grade I transitional meningioma. This case suggests that primary benign intraosseous meningioma may show high (18)F-FDG uptake mimicking a malignancy.

Co-contamination of arsenic and fluoride in the groundwater of unconsolidated aquifers under reducing environments.

The co-contamination of arsenic (As) and fluoride (F(-)) in shallow aquifers is frequently observed worldwide, and the correlations between those contaminants are different according to the redox conditions. This study geochemically explores the reasons for the co-contamination and for the redox-dependent correlations by investigating the groundwater of an alluvial aquifer in Korea. Geochemical signatures of the groundwater in the study area show that the As concentrations are enriched by the reductive dissolution of Fe-(hydr)oxides, and the correlations between As and F(-) concentrations are poor comparatively to those observed in the oxidizing aquifers. However, F(-) concentrations are strongly dependent on pH. Desorption/adsorption experiments using raw soils and citrate-bicarbonate-dithionite treated soils indicated that Fe-(hydr)oxides are the important As and F(-) hosts causing the co-contamination phenomenon. The weaker correlation between F(-) and As in reducing aquifers is likely to be associated with sulfate reduction, which removes As from groundwater without changing the F(-) concentration.

Relations of As concentrations among groundwater, soil, and bedrock in Chungnam, Korea: implications for As mobilization in groundwater according to the As-hosting mineral change.

Arsenic (As) concentrations and As-bearing minerals in bedrock and soil, and their relations with groundwater concentrations were investigated in a small agricultural area of Korea. The As concentration of the bedrock shows a wide variation (<0.5-3990 mg/kg) and is well correlated with that in the contacting groundwaters (23-178 µg/L). Soils, the weathering product of bedrock, show the lower and more dispersed As concentrations (8.8-387 mg/kg) than the bedrock. But the soil As concentrations are very high relative to those reported from other areas. The As concentrations in the shallow groundwaters are comparatively low (<20 µg/L) and are independent of the soil concentration. Arsenopyrite is the major As-bearing mineral in the bedrock and its oxidation controls the As levels in deep groundwater. In contrast, As mostly resides in soil as Fe-(hydr)oxide-bound forms. Due to low pH and oxidizing redox condition, the release of As from Fe-(hydr)oxides is largely suppressed, and the shallow groundwater shows low As concentrations generally satisfying the drinking water limit. However, it is suggested that the disturbance of soil geochemical conditions by land use changes would cause a serious As contamination of the shallow groundwaters.

Processes controlling the variations of pH, alkalinity, and CO2 partial pressure in the porewater of coal ash disposal site.

Alkalinity, pH, and pCO2 are generally regarded as the most important parameters affecting trace element leaching from coal ashes. However, little is known about how those parameters are actually regulated in the field condition. This study investigated the processes controlling those parameters by observing undisturbed porewater chemistry in a closed ash disposal site. The site is now covered with 30-50 cm thick soils according to the management scheme suggested by the Waste Management Law of Korea and our results show the important role of soil cover regulating those parameters in the shallow porewater. Without the soil cover, the shallow porewater shows low pCO2 and alkalinity, and highly alkaline pH. In contrast, the porewater shows much higher alkalinity and near neutral pH range when the site was covered with the low permeability soils. This difference was caused by the CO2 supply condition changes associated with the changes in infiltration rate. The geochemical modeling shows that the calcite precipitations induced by porewater aging, dolomitization, and weathering of solid phases are the main processes controlling alkalinity, pH, and pCO2 in the deep saline porewaters. The weathering of coal ash plays the most important role decreasing the alkalinity in the deep porewater.

Arsenic concentration in porewater of an alkaline coal ash disposal site: Roles of siderite precipitation/dissolution and soil cover.

The geochemical behavior of As in porewaters of an alkaline coal ash disposal site was investigated using multilevel samplers. The disposal site was in operation from 1983 until 1994 and was covered with 0.3-0.5m thick soils in 2001 when this study was initiated. Sequential extraction analyses and batch leaching experiments were also performed using the coal ash samples collected from the disposal site. The results suggest the important roles of siderite (FeCO(3)) precipitation/dissolution and soil cover, which have been ignored previously. Arsenic levels in the porewater were very low (average of 10microgL(-1)) when the site was covered with soil due to coprecipitation with siderite. The soil cover enabled the creation of anoxic conditions, which raised the Fe concentration by the reductive dissolution of Fe-(hydr)oxides. Because of the high alkalinity generated from the alkaline coal ash, even a small increase in the Fe concentration (0.66mgL(-1) on average) could cause siderite precipitation. When the soil cover was removed, however, an oxidizing condition was created and triggered the precipitation of dissolved Fe as (hydr)oxides. As a result, the dissolution of previously precipitated As-rich siderite caused higher As concentration in the porewater (average of 345microgL(-1)).

Importance of surface geologic condition in regulating As concentration of groundwater in the alluvial plain.

The arsenic (As) concentrations in the groundwater of alluvial plains generally show high spatial variability. We geochemically explore the factors causing the spatial variability in an alluvial plain that is mainly used for rice cultivation, the commonest land-use pattern in alluvial plains of Asia. We investigate the chemical processes, sources of chemicals that affect the behavior of As, and their relationships with the geologic conditions at seven multilevel sampler sites. All sites showed As concentrations that increased with depth at shallow levels and decreased at greater depths, which is the typical vertical pattern in alluvial aquifers where Fe-(hydr)oxide reduction is the major As release mechanism. Data show that NO(3) and SO(4) originating from the land surface play important roles in suppressing the increase in As concentration by buffering the redox potential at shallow depths and by precipitating As with sulfide minerals at deep depths, respectively. The As concentration in the intermediate depth range was also low in the presence of SO(4), because its reduction can occur together with Fe-(hydr)oxide reduction in a wide range of redox potentials. As a result, the maximum As concentrations at the sites where the land was covered with a thick silt layer (approximately 5m) were 3- to 5-times higher than those at other sites due to the supply of NO(3) and SO(4) from land surface being largely limited by the silt layer. This indicates that the surface geology could be an important indicator for the As concentration in alluvial groundwater.

Arsenic fractions and enzyme activities in arsenic-contaminated soils by groundwater irrigation in West Bengal.

A study for the effect of arsenic (As) contamination on beta-glucosidase, urease, acid-/alkaline-phosphatase, and arylsulphatase activities was conducted in As contaminated soils of West Bengal, India. The studied soils show low total As contents relative to those in other As-contaminated sites. A sequential extraction technique was used to quantify water soluble, exchangeable, carbonate bound, Fe/Mn oxide bound, organic bound, and residual As fractions. Arsenic concentrations in the two most labile fractions (i.e., water soluble and exchangeable fractions) were generally low. The studied enzymes were significantly and negatively correlated with water soluble and exchangeable As forms but did not show any significant correlations with other forms, indicating that water soluble and exchangeable forms exert a strong inhibitory effect on the soil enzyme activities. It is thus suggested that the enzyme activity can be helpful in assessing the effects of As on biochemical quality of soils.