Sorption studies for evaluating the effects of thermally altered carbonaceous matter on fate and transport of chlorinated volatile organic compounds

The sorption effects of thermally altered carbonaceous matter (TACM) in subsurface sediments were investigated for chlorofluorocarbons (CFC: CFC-11, CFC-12, and CFC-113) using laboratory batch techniques. The purpose of this research was to determine the CFC sorption properties and mechanisms to TACM (e.g., black carbon and kerogen) and to link these to sorption behavior in surficial sedimentary environments. For the surficial sediments, aquifer and aquitard sediments deposited in late Quaternary were obtained from two different sedimentary basins containing kerogen-rich shale formation as potential TACM source rock. The TACM in these young sediments were little affected by weathering processes compared to the TACM in old sediments. Wood char, kerogen-rich shales, and kerogen-containing surficial sediments exhibited nonlinear sorption behavior for the CFCs with ∼10–1000 times greater C-normalized partition coefficients ( Koc) than the reference Koc at low concentrations relative to compound solubilities (Cw/S ). Adsorption based on pore-filling mechanism characterized the observed CFC sorption to the wood char, while heterogeneous kerogen in the shales and surficial sediments showed both of partitioning and adsorption behavior. Predominant composition of the kerogen was unstructured carbonaceous matter (CM) with minor fraction of condensed CM. It is believed that the observed dual-mode sorption behavior reflects the kerogen composition. Adsorption component of the dual-mode sorption dominantly contributed to overall CFC sorption at low relative concentrations, Cw/S<∼10 −2. The estimated retardation factors for the kerogen-containing aquifer sediment increased 2–7 times more than the retardation determined by partitioning only. Solubility-normalized sorption isotherms are coincident for each of the kerogen-containing subsurface sediment with three CFCs. The CFC isotherms were quite consistent with sorption isotherms for other similar hydrophobic chlorinated contaminants at Cw /S∼10−5–10 −1

Dynamic Behavior of CO2 in a Wellbore and Storage Formation: Wellbore-Coupled and Salt-Precipitation Processes during Geologic CO2 Sequestration

For investigating the wellbore flow process in CO2 injection scenarios, coupled wellbore-reservoir (WR) and conventional equivalent porous media (EPM) models were compared with each other. In WR model, during the injection, conditions for the wellbore including pressure and temperature were dynamically changed from the initial pressure (7.45–8.33 MPa) and temperature (52.0–55.9°C) of the storage formation. After 3.35 days, the wellbore flow reached the steady state with adiabatic condition; temperature linearly increased from the well-head (35°C) to the well-bottom (52°C). In contrast, the EPM model neglecting the wellbore process revealed that CO2 temperature was consistently 35°C at the screen interval. Differences in temperature from WR and EPM models resulted in density contrast of CO2 that entered the storage formation (~200 and ~600 kg/m3, resp.). Subsequently, the WR model causing greater density difference between CO2 and brine revealed more vertical CO2 migration and counterflow of brine and also developed the localized salt-precipitation. Finally, a series of sensitivity analyses for the WR model was conducted to assess how the injection conditions influenced interplay between flow system and the localized salt-precipitation in the storage formation

A Batch Experiment of Cesium Uptake Using Illitic Clays with Different Degrees of Crystallinity

Radiocesium released by the severe nuclear accident and nuclear weapon test is a hazardous material. Illitic clays play a key role in the spatial distribution of radiocesium in groundwater environments due to selective uptake sites at the illite mineral, such as frayed edge sites. However, the cesium uptake capabilities of illitic clays are diverse, which could be associated with the illite crystallinity. This study was performed to determine the cesium uptake of illitic clays and evaluate the crystallinity effects on cesium uptake using statistical approaches. A total of 10 illitic clays showed various crystallinity, which was parameterized by the full width at half maximum (FWHM) at 10 Å XRD peak ranging from 0.15 to 0.64. The uptake behavior of illitic clays was well fitted with the Freundlich model (i.e., r2 > 0.946). The uptake efficiency of illitic clays increased with the decrease in dissolved cesium concentrations. The cesium uptake was significantly correlated with the FWHM and cation exchange capacity, suggesting that the uptake becomes higher with decreasing crystallinity through expansion of the edge site and/or formation of ion-exchangeable sites

A Batch Experiment of Cesium Uptake Using Illitic Clays with Different Degrees of Crystallinity

Radiocesium released by the severe nuclear accident and nuclear weapon test is a hazardous material. Illitic clays play a key role in the spatial distribution of radiocesium in groundwater environments due to selective uptake sites at the illite mineral, such as frayed edge sites. However, the cesium uptake capabilities of illitic clays are diverse, which could be associated with the illite crystallinity. This study was performed to determine the cesium uptake of illitic clays and evaluate the crystallinity effects on cesium uptake using statistical approaches. A total of 10 illitic clays showed various crystallinity, which was parameterized by the full width at half maximum (FWHM) at 10 Å XRD peak ranging from 0.15 to 0.64. The uptake behavior of illitic clays was well fitted with the Freundlich model (i.e., r2 &gt; 0.946). The uptake efficiency of illitic clays increased with the decrease in dissolved cesium concentrations. The cesium uptake was significantly correlated with the FWHM and cation exchange capacity, suggesting that the uptake becomes higher with decreasing crystallinity through expansion of the edge site and/or formation of ion-exchangeable sites

Uptake Mechanism for Iodine Species to Black Carbon

Natural organic matter (NOM) plays an important role in determining the fate and transport of iodine species such as iodide (I^–) and iodate (IO₃^–) in groundwater system. Although NOM exists as diverse forms in environments, prior iodine studies have mainly focused on uptake processes of iodide and iodate to humic materials. This study was conducted to determine the iodide and iodate uptake potential for a particulate NOM (i.e., black carbon [BC]). A laboratory-produced BC and commercial humic acid were used for batch experiments to compare their iodine uptake properties. The BC exhibited >100 times greater uptake capability for iodide than iodate at low pH of ∼3, while iodide uptake was negligible for the humic acid. The uptake properties of both solids strongly depend on the initial iodine aqueous concentrations. After uptake reaction of iodide to the BC, X-ray absorption fine structure spectroscopy results indicated that the iodide was converted to electrophilic species, and iodine was covalently bound to carbon atom in polycyclic aromatic hydrocarbons present in the BC. The computed distribution coefficients (i.e., <i>K</i>_d values) suggest that the BC materials retard significantly the transport of iodide at low pH in environmental systems containing even a small amount of BC

Efficient mercury sequestration from wastewaters using palm kernel and coconut shell derived biochars

Elevated mercury (Hg) concentrations in water bodies caused by illegal artisanal gold mining in Ghana is a serious health concern given the toxicity of Hg. As an ecofriendly cost-effective solution for removing Hg from these water bodies, we synthesized biochars using palm kernel (PB) and coconut shells (CB), which are dominant biomass wastes in Ghana. The biochars were sulfurized (SPB, SCB) and fabricated into polysulfone-based beads for Hg(II) sorption. The Hg(II) concentration, contact time, sorbent mass, and solution pH were investigated and were found to be influential on the sorption of Hg(II) from aqueous solution. The sulfurized biochars showed a faster Hg(II) removal (within 1h) compared to the pristine biochars. Sorption tests conducted using natural riverine water samples confirmed the potential use of the biochars, with SPB and SCB showing higher efficiencies than pristine PB and CB. The fabricated beads exhibited 70–90% efficiency in Hg(II) removal from 1.0 mg L−1 Hg solution and the sorption capacity was below 0.1 mg g−1, which we attribute to the mass of biochar used for the beads. The Hg(II) sorption mechanisms of PB and CB from spectroscopic analyses suggest that the biochars synthesized in this study can be used to treat Hg polluted waters and suitable for large-scale applications in natural water bodies.11Yscopu

Comparison of physicochemical properties between fine (PM2.5) and coarse airborne particles at cold season in Korea

Although it has been well-known that atmospheric aerosols affect negatively the local air quality, human health, and climate changes, the chemical and physical properties of atmospheric aerosols are not fully understood yet. This study experimentally measured the physiochemical characteristics of fine and coarse aerosol particles at the suburban area to evaluate relative contribution to environmental pollution in consecutive seasons of autumn and winter, 2014-2015, using XRD, SEM-EDX, XNI, ICP-MS, and TOF-SIMS. For these experimental works, the fine and coarse aerosols were collected by the high volume air sampler for 7 days each season. The fine particles contain approximately 10 μg m-3 of carbonaceous aerosols consisting of 90% organic and 10% elemental carbon. The spherical-shape carbonaceous particles were observed for the coarse samples as well. Interestingly, the coarse particles in winter showed the increased frequency of carbon-rich particles with high contents of heavy metals. These results suggest that, for the cold season, the coarse particles could contribute relatively more to the conveyance of toxic contaminants compared to the fine particles in the study area. However, the fine particles showed acidic properties so that their deposition to surface may cause facilitate the increase of mobility for toxic heavy metals in soil and groundwater environments. The fine and coarse particulate matters, therefore, should be monitored separately with temporal variation to evaluate the impact of atmospheric aerosols to environmental pollution and human health