Seong Taek Yun

Removal of divalent heavy metals (Cd, Cu, Pb, and Zn) and arsenic(III) from aqueous solutions using scoria: Kinetics and equilibria of sorption

Kinetic and equilibrium sorption experiments were conducted on removal of divalent heavy metals (Pb(II), Cu(II), Zn(II), Cd(II)) and trivalent arsenic (As(III)) from aqueous solutions by scoria (a vesicular pyroclastic rock with basaltic composition) from Jeju Island, Korea, in order to examine its potential use as an efficient sorbent. The removal efficiencies of Pb, Cu, Zn, Cd, and As by the scoria (size=0.1-0.2mm, dose=60gL(-1)) were 94, 70, 63, 59, and 14%, respectively, after a reaction time of 24h under a sorbate concentration of 1mM and the solution pH of 5.0. A careful examination on ionic concentrations in sorption batches suggested that sorption behaviors of heavy metals onto scoria are mainly controlled by cation exchange. On the other hand, arsenic appeared to be sensitive to specific sorption onto hematite (a minor constituent of scoria). Equilibrium sorption tests indicated that the removal efficiency for heavy metals increases with increasing pH of aqueous solutions, which is resulted from precipitation as hydroxides. Similarly, multi-component systems containing heavy metals and arsenic showed that the arsenic removal increases with increasing pH of aqueous solutions, which can be attributed to coprecipitation with metal hydroxides. The empirically determined sorption kinetics were well fitted to a pseudo-second order model, while equilibrium sorption data for heavy metals and arsenic onto scoria were consistent with the Langmuir and Freundlich isotherms, respectively. Natural scoria studied in this work is an efficient sorbent for concurrent removal of divalent heavy metals and arsenic.

Pilot scale study on the ex situ electrokinetic removal of heavy metals from municipal wastewater sludges.

In order to remove toxic heavy metals from municipal wastewater sludges, the ex situ electrokinetic technique was studied at pilot scale. This study focused on the feasibility of the electrokinetic removal of heavy metals from sludge and the effectiveness of this technique on the variations of abiotic (physicochemical) and biotic (intracellular and extracellular) speciations of heavy metals using several analytical methods. Even though the sludge used was taken from a municipal wastewater treatment plant, the sludge contained relatively high concentrations of target metal contaminants (Cd = 6.8 mg/kg, Cr = 115.6 mg/kg, Cu = 338.7 mg/kg, and Pb = 62.8 mg/kg). The removal efficiencies of heavy metals were significantly dependent on their speciations in the sludge matrices. The electrokinetic removal efficiencies of abiotic heavy metals exceeded 70% for the mobile and weakly bound fractions, such as, the exchangeable and carbonate fractions and were lower than 35% for the strongly bound fractions, such as, the organic/sulfide and residual fractions. In the case of the biotic heavy metals, the removal efficiencies of the extracellular fractions were slightly higher than those of the intracellular fractions.

Hydrochemical and multivariate statistical interpretations of spatial controls of nitrate concentrations in a shallow alluvial aquifer around oxbow lakes (Osong area, central Korea)

Hydrochemical and multivariate statistical interpretations of 16 physicochemical parameters of 45 groundwater samples from a riverside alluvial aquifer underneath an agricultural area in Osong, central Korea, were performed in this study to understand the spatial controls of nitrate concentrations in terms of biogeochemical processes occurring near oxbow lakes within a fluvial plain. Nitrate concentrations in groundwater showed a large variability from 0.1 to 190.6 mg/L (mean=35.0 mg/L) with significantly lower values near oxbow lakes. The evaluation of hydrochemical data indicated that the groundwater chemistry (especially, degree of nitrate contamination) is mainly controlled by two competing processes: 1) agricultural contamination and 2) redox processes. In addition, results of factorial kriging, consisting of two steps (i.e., co-regionalization and factor analysis), reliably showed a spatial control of the concentrations of nitrate and other redox-sensitive species; in particular, significant denitrification was observed restrictedly near oxbow lakes. The results of this study indicate that sub-oxic conditions in an alluvial groundwater system are developed geologically and geochemically in and near oxbow lakes, which can effectively enhance the natural attenuation of nitrate before the groundwater discharges to nearby streams. This study also demonstrates the usefulness of multivariate statistical analysis in groundwater study as a supplementary tool for interpretation of complex hydrochemical data sets.

Current Status of Trace Metal Pollution in Soils Affected by Industrial Activities

There is a growing public concern over the potential accumulation of heavy metals in soil, owing to rapid industrial development. In an effort to describe the status of the pollutions of soil by industrial activities, relevant data sets reported by many studies were surveyed and reviewed. The results of our analysis indicate that soils were polluted most significantly by metals such as lead, zinc, copper, and cadmium. If the dominant species are evaluated by the highest mean concentration observed for different industry types, the results were grouped into Pb, Zn, Ni, Cu, Fe, and As in smelting and metal production industries, Mn and Cd in the textile industry, and Cr in the leather industry. In most cases, metal levels in the studied areas were found to exceed the common regulation guideline levels enforced by many countries. The geoaccumulation index (I geo), calculated to estimate the enrichment of metal concentrations in soil, showed that the level of metal pollution in most surveyed areas is significant, especially for Pb and Cd. It is thus important to keep systematic and continuous monitoring of heavy metals and their derivatives to manage and suppress such pollution.

Distribution of Heavy Metals (Cr, Cu, Zn, Pb, Cd, As) in Roadside Sediments, Seoul Metropolitan City, Korea

Urban roadside sediments were collected for five months from eleven sites in Seoul Metropolitan City and were examined for spatial and temporal variation of heavy metal composition (Cr, Cu, Zn, Pb, Cd and As). Samples for analysis were treated with 0.1 N HCl for partial extraction and with mixed strong acid (HF + HNO3 + HClO4) for total extraction. Using the normalization of the acid extractable metal concentrations with aluminum (element/Al), two statistical approaches, i.e., two-way ANOVA test and R-mode factor analysis (FA), were performed to examine the major sources of variability in the heavy metal composition. The FA results show that Pb and Cr are strongly dependent on site-specific traffic density, whereas Cu, Cd and Zn vary with site characterization (especially the percentage of metal industry) as well as the temporal amount of precipitation. Arsenic, however, does not show any distinct change. As the roadside sediments are heavily polluted with heavy metals (especially Zn and Cu), the management and disposal of the sediments have to be guided by appropriate environmental measures.

Hydrochemistry of urban groundwater, Seoul, Korea: The impact of subway tunnels on groundwater quality

Hydrogeologic and hydrochemical data for subway tunnel seepage waters in Seoul (Republic of Korea) were examined to understand the effect of underground tunnels on the degradation of urban groundwater. A very large quantity of groundwater (up to 63 million m3 year(-1)) is discharged into subway tunnels with a total length of 287 km, resulting in a significant drop of the local groundwater table and the abandonment of groundwater wells. For the tunnel seepage water samples (n = 72) collected from 43 subway stations, at least one parameter among pathogenic microbes (total coliform, heterotrophic bacteria), dissolved Mn and Fe, NH4+, NO3(-), turbidity, and color exceeded the Korean Drinking Water Standards. Locally, tunnel seepage water was enriched in dissolved Mn (avg. 0.70 mg L(-1), max. 5.58 mg L(-1)), in addition to dissolved Fe, NH4+, and pathogenic microbes, likely due to significant inflow of sewage water from broken or leaking sewer pipes. Geochemical modeling of redox reactions was conducted to simulate the characteristic hydrochemistry of subway tunnel seepage. The results show that variations in the reducing conditions occur in urban groundwater, dependent upon the amount of organic matter-rich municipal sewage contaminating the aquifer. The organic matter facilitates the reduction and dissolution of Mn- and Fe-bearing solids in aquifers and/or tunnel construction materials, resulting in the successive increase of dissolved Mn and Fe. The present study clearly demonstrates that locally significant deterioration of urban groundwater is caused by a series of interlinked hydrogeologic and hydrochemical changes induced by underground tunnels.

NUMERICAL AND EXPERIMENTAL STUDIES ON CADMIUM (II) TRANSPORT IN KAOLINITE CLAY UNDER ELECTRICAL FIELDS

A numerical model was formulated to simulate cadmium (Cd) transport under an electric field using one-dimensional diffusion-advection equations describing the contaminant transport driven by chemical and electrical gradients in kaolinite clay. The numerical model includedcomplex physicochemical factors affecting the transport phenomena, such as soil pH value, zeta potential, aqueous phase reaction, adsorption, and precipitation. One-dimensional finite-difference computer models successfully predicted meaningful values for soil pH profiles and Cd concentration profiles. To verify the results of the proposed model by comparing them with experimental results, two different types of laboratory electrokinetic tests, unenhanced and enhanced tests, were conducted. The numerical and the experimental results showed good agreement. In addition, those results indicate that soil pH is the most important factor in governing the dissolution and/or desorption of Cd in the soil system under electrical fields. The removal efficiency of Cd in the unenhanced test was low (15.6%) due to a high accumulation in the region near the cathode. On the contrary, the cadmium concentration profile of the enhanced test showed a different pattern, and most of the residual concentrations appeared below the initial level at each local point within the soil cell after processing. The removal efficiency of the enhanced test was much higher (42.7%) than that of the unenhanced test, resulting from the prevention of hydroxide precipitation near the cathode using the acidic catholyte. Consequently, the result implies that the enhancement schemes such as conditioning of catholyte should be required to increase the effectiveness of the electrokinetic technology in removing metal contaminants from soils.

Atmospheric versus lithogenic contribution to the composition of first- and second-order stream waters in Seoul and its vicinity

The spatial variations in the chemistry of first- and second-order stream waters (N = 65) were investigated in the easterly bound of Seoul in order to assess the effects of urban air pollution on surface water chemistry. The sulfate (SO4(2-)) was high (range 3.9-17.8 mg l(-1), mean 11.8 mg l(-1)) within 30 km away from the center of Seoul, compared to the levels (range 1.1-7.7 mg l(-1), mean 4.3 mg l(-1)) observed in remote areas (30-70 km away). Both graphical examination and statistical evaluation (variogram) of sulfate concentration data consistently showed the decrease of sulfate concentration with increasing distance. The results of mass balance modeling also indicate that the concentrations of SO4(2-), Cl- and Na+ may be affected mainly by dry/wet deposition. However, the spatial variations of major cations such as Ca2+ and Na+ are well explained by the reaction of rainwater with diverse rocks in the watercourse. The water type was found to change from Ca(-Na)-SO4) type to Ca(-a)-HCO3 type with the increasing distance. It is thus inferred that the pollutants like SO2 emitted from strong man-made source areas of Seoul are transported to the considerable distance (at least 30 km away) by westerlies and that such mechanism may lead to the changes of the anion composition in surface water. In the remote area (> 30 km away from Seoul), the stream water chemistry appears to be influenced more effectively by the weathering of rock-forming minerals.

Coal fly ash and synthetic coal fly ash aggregates as reactive media to remove zinc from aqueous solutions.

Coal fly ash (CF) and synthetic coal fly ash aggregates (SCFAs) were evaluated as low-cost reactive media for the remediation of groundwater contaminated with Zn. The SCFAs were prepared by mixing CF, sodium silicate, and deionized (DI) water. Serial batch kinetic and static tests were conducted on both CF and SCFAs, under various conditions (i.e., pH, initial Zn concentration, reaction time, and solid dosage), using Zn(NO(3))(2).6H(2)O solutions. Serial column tests were also conducted on both CF and SCFAs. The final rather than the initial pH of the solution had a greater effect on the removal of Zn. At pH>7.0, the removal of Zn was due to precipitation, whereas at <7.0, the removal of Zn was due to adsorption onto the reactive media. The removal of Zn increased with increasing dosage of the reactive medium and decreasing initial Zn concentration. The results of the column and batch tests were comparable. Preferential flow paths were observed with CF, but not SCFA. The hydraulic conductivity of CF was more significantly decreased than that of SCFA with increasing dry density of the specimen.

Regional geologic setting and metallogenesis of central Inner Mongolia, China: guides for exploration of mesothermal gold deposits

Abstract The central Inner Mongolia district forms one of the most important metallogenic provinces in China, because the district has been influenced by repeated distinct tectonomagmatic activity. The genetic relationships and spatial–temporal evolution of ancient tectonism and associated geologic structures and metallogeny are discussed in this paper. An integrated genetic model for gold metallogeny is proposed. During the late Archean to Paleozoic, repeated north-southward accretional tectonics between the Paleo-Mongolia Oceanic Plate and the North China Paleoplate led to the formation of not only the E–W-trending deep crustal faults but also a series of sedimentary, volcanic and metamorphic events. Numerous stratiform, Fe, Cu (Au), Pb–Zn and REE ores formed in association with sedimentation and volcanism within the platform environments at this time. During the late Paleozoic to early Mesozoic, the central Inner Mongolia district was largely influenced by northwestward subduction of the Circum-Pacific Plate beneath the Eurasia Plate. A series of NE–SW-trending faults, together with S-type granitoid intrusions, formed as a result of this subduction. Mesothermal-type gold deposits (e.g., the Saiyingwusu, Laoyanghao, Shibaqin, Wulashan and Donghuofang deposits) formed during the Permian to Jurassic (158.5 to 275.4 Ma), preferentially at or near the intersections between NE–SW-trending and E–W-trending fault systems. At these intersections, the areas of not only late Paleozoic to early Mesozoic granitoids but also late Archean to early Proterozoic metamorphic rocks (especially the gold-rich, Seertengshan, Wulashan and Bayan Obo group rocks) may be promising exploration targets for mesothermal gold deposits.