Jae-Young Yu

Apparent solubilities of schwertmannite and ferrihydrite in natural stream waters polluted by mine drainage

The apparent solubilities of schwertmannite and ferrihydrite were estimated from the H+, OH−, Fe3+, and SO42− activities of the natural stream waters in Korea and mine drainage in Ohio, USA. Both chemical composition of the stream waters and the mineralogy of the precipitates were determined for samples from two streams polluted by coal mine drainage. This study combines these new results with previous data from Ohio, USA to redetermine solubilities. The activities of the dissolved species necessary for the solubility determinations were calculated from the chemical compositions of the waters with the WATEQ4F computer code. Laboratory analyses of precipitates indicated that the main minerals present in Imgok and Osheep creek were schwertmannite and ferrihydrite, respectively. The schwertmannite from Imgok creek had a variable chemical formula of Fe8O8(OH)8−2x(SO4)x· nH2O, where 1.74 ≤ x ≤ 1.86 and 8.17 ≤ n ≤ 8.62. The chemical formula of ferrihydrite was Fe2O3· 1.6H2O. With known mineralogy of the precipitates from each stream, the activities of H+, OH−, Fe3+, and SO42− in the waters were plotted on logarithmic activity-activity diagrams to determine apparent solubilities of schwertmannite and ferrihydrite. The best estimate for the logarithm of the solubility product of schwertmannite, logKs, was 10.5 ± 2.5 around 15°C. This value of logKs constrains the logarithm of the solubility product of ferrihydrite, logKf, to be 4.3 ± 0.5 to maintain the stability boundary with schwertmannite observed in natural waters.

Dilution and removal of dissolved metals from acid mine drainage along Imgok Creek, Korea

Abstract The dilution factors ( D i ) and removal fractions ( R i ) of pollutants from acid mine drainage (AMD) were quantitatively estimated using two different methods, the conservative component and mass balance method, along Imgok Creek in Korea. The conservative component method assumes that SO 4 is a perfectly conservative component and calculates D i and R i from the concentration ratios of SO 4 . The mass balance method solves the simultaneous equations relating the concentrations of dissolved components to their precipitation stoichiometries to obtain D i and R i . The results from both methods are little different, indicating that SO 4 concentration is a good indicator of dilution for Imgok creek. The calculated D i s of pollutants quickly decrease from the site of AMD input to the site a few km downstream, but then remain more or less constant over the reaches farther downstream. This is because D i loses its sensitivity in the reaches where difference in SO 4 concentration between the main stream and combining tributaries significantly diminishes. The calculated R i s show that approximately 90, 95, and 75% of the original Fe input were removed from the streamwater in October 1996, April 1997, and October 1997, respectively. Aluminum was almost completely removed in April 1997, but only 50% of the original Al was removed in October 1997. The removal of Fe was due to the precipitation of schwertmannite or ferrihydrite and Al due to amorphous Al 4 (OH) 10 SO 4 . The maximum removal fraction of dissolved SO 4 was only 5%. The other metals from AMD were significantly removed from the stream water only in April 1997. These metals were removed not by precipitation but by adsorption on and/or coprecipitation with Fe/Al-compounds. The relatively abundant freshwater supply in April 1997 might raise stream pH higher than the adsorption edge and consequently, contribute to rapid metal attenuation by forcing not only more precipitation but also more adsorption of the dissolved metals.

Sulfur and oxygen isotopic compositions of the dissolved sulphate in the meteoric water in Chuncheon, Korea

The meteoric water deposited in the Chuncheon area was collected from July 2002 to May 2004 and its chemical and isotopic compositions were analyzed to examine if the isotopic data can help trace the sources of the sulfur pollutant and understand the details of acid formation processes in the air. The chemical compositions of the meteoric water indicate that the sulfate mostly comes from anthropogenic sources. The sulfur isotopic compositions of the dissolved sulfate in the meteoric water (δ34Sso4) vary from 2.6 to 7.5‰ with little seasonal differences, which are significantly different from those of the sulfur in the coal being locally consumed (−4.5 to −0.7‰). This difference indicates that the local coal consumption gives insignificant contribution to the pollutant sulfur in the acid deposition of the area. The relationship between (δ34Sso4) and the concentration of sulfate suggests that the sources of pollutant sulfur are variable and inhomogeneous. The oxygen isotopic compositions of the dissolved sulfate in the meteoric water (δ18O4) range from 9.0 to 17.2‰ which are generally lower in winter than in spring. Comparison between the measured and calculated values of (δ18Oso4) suggests that the oxygen isotopic exchange between sulfite and water occurs before its oxidation to sulfate. The extent of isotopic exchange seems to be not controlled by equilibrium but by kinetic fractionation. The poor correlation between δ34S4) and the oxygen isotopic composition of the meteoric water confinns the disequilibrium nature of the isotopic exchange.

Adsorption of phenol and chlorophenols on Ca-montmorillonite in aqueous solutions

Adsorption of phenol, 2-chlorophenol, and 2,4-dichlorophenol on Ca-montmorillonite was studied with batch experiments at 25°C. The results from the experiments show that the amount of the adsorption of the phenolic compounds increases with chlorination, i.e., phenol <2-chlorophenol <2,4-dichlorophenol. This adsorption trend is due to the differences in the affinity of the phenolic compounds between the adsorbent and water, that is more affinity to water leads to less adsorption. The adsorption of phenol is unrecognizable, while 2,4-dichlorophenol is showing the highest adsorption density despite the repulsion between dissociated dichlorophenol anions and montmorillonite surface. Freundlich model fits moderately well to the adsorption isotherm of 2-chlorophenol and 2,4-dichlorophenol. The calculated model parameters aren=1.50, 0.49 and logkF=0.51, 1.09 for 2-chlorophenol and 2,4-dichlorophenol, respectively.

Estimation of mercury speciation in soil standard reference materials with different extraction methods by ion chromatography coupled with ICP-MS

Analytical methods for the speciation of mercury, based on microwave extraction and sonication extraction, have been tested to determine the inorganic mercury and methyl mercury contents in two standard soil reference materials: SRM 2710 Montana Soil and BCR 580 estuarine sediment. Prior to applying the speciation extraction methods, the mineral compositions were analyzed via XRD analysis, with SRM 2710 shown to be composed mostly of aluminum silicate minerals, while carbonate minerals were the major constituent in BCR 580. Two extraction methods, microwave and sonication, were tested for the analysis and recovery efficiency of total mercury. The accuracy and efficiency of each extraction method was also compared. In the analysis of total mercury, the microwave extraction method, with using methanol and HCl as extractants, was better for SRM2710, while the application of the sonication extraction method was more efficient for the calcite-based BCR 580. The results showed good separation and recovery efficiencies, with values reaching 100% of those estimated. The sonication method was selected for the speciation of mercury, especially in BCR 580. An extraction solution comprising of a 1:1 mixture of methanol and HCl was used for the sonication extraction of BCR 580, with the resulting extractants analyzed by IC-HG-ICP-MS for methyl mercury and inorganic mercury. As a simple, rapid, sensitive, and accurate method, sonication extraction was found to be satisfactory.

Adsorption of phenol and chlorophenols on hexadecyltrimethylammonium-and tetramethylammonium-montmorillonite from aqueous solutions

Batch experiments were carried out at 25°C to obtain the adsorption isotherms of phenol, 2-cholorophenol, 4-chlorophenol and 2,4-dichlorophenol on hexadecyltrimethylammonium-exchanged-and tetramethylammonium-exchanged-montmorillonite (HDTMA-M and TMA-M) prepared from Wyoming bentonite SWy-2. The isotherms were interpreted principally using the Freundlich model. The reaction orders (n) and Freundlich constants (kF) for the adsorption of an adsorbate on HDTMA-M and TMA-M remain approximately constant against the variation of adsorbate to adsorbent ratios. Then value for most of the phenolic adsorbates on HDTMA-M is close to unity, indicating Langmuir-type adsorption but that on TMA-M is variable among different phenolic adsorbates. The degree of adsorption of phenolic compounds on HDTMA-M is primarily controlled by the hydrophobicity of the adsorbates but those on TMA governed by the complicated combinations of size, shape and hydrophobicities of the adsorbates. The estimated model parameters for the adsorption isotherms on HDTMA-M are in disagreement with those of earlier workers probably because of the differences in experimental conditions. This study also estimated the model parameters on TMA-M, which are not available in the literature.

Theoretical calculation of Gibbs free energy of mixing of biotite: phlogopite-annite-eastonite-siderophyllite system

The Gibbs free energy of mixing (ΔGmix) can be represented as the sum of the ideal mixing energy (ΔGid) and the excess energy (Gex). For biotite in phlogopite (Ph)-annite (An)-eastonite (Es)-siderophyllite (Sd) system, ΔGid is estimated based on MOS (mixing on site) model andGex is obtained from the theoretically calculated binding energies of biotite. Previous experimental works suggested that Ph-An and possibly Ph-Es pairs form ideal solutions. In this study, however,Gex shows that none of the binary solutions among Ph-An-Es-Sd end-members are ideal. The calculated ΔGmix indicates that Ph-An and Es-Sd pairs form complete solutions, but Ph-Es and An-Sd pairs both mixed by Tschermaks substitution show miscibility gaps. The limit of Tschermaks substitution in biotite is a function of the mole fraction of Fe in the trioctahedral site,X(Fe), and temperature. A comparison of the solvus and spinodal points obtained from the calculated ΔGmix with the chemical compositions of the synthesized and natural biotites implies that Es and Sd are metastable and the limits of Tschermaks substitution are determined not by solvus curves but by spinodal ones. Most chemical compositions of natural biotite fall fairly well within the range defined by the estimated spinodal curves at 800°C, although there are some out-lying biotites especially when theirX(Fe) is between 0.5 and 0.7. The general good agreement in limits of Tschermaks substitution between what natural biotite shows and what this study predicts suggests that the theoretical function of thermodynamic mixing of this study seems promising to be applied for understanding the behavior of not only biotite but also other similar solid solutions, particulary when experimental approach is difficult.