• Economic and Environmental Geology
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• v.38 no.5 s.174
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• pp.499-512
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• 2005

EPMA determined that Fe(Mn)-(oxy)hydroxides and well-crystallized Fe-(oxy)hydroxides and could contain a small amount of As $(0.3-11.0\;wt.\%\;and\;2.1-7.4\;wt.\%\;respectively)$. Amorphous crystalline Fe-(oxy) hydroxide assemblages were identified as the richest in As with $28-36\;wt.\%$. On the ternary $As_2O_5-SO_3-Fe_2O_3$ diagram, these materials were interpreted here as 'scorodite-like'. Dissolved As was attenuated by the adsorption on Fe-(oxy) hydroxides and Fe(Mn)-(oxy) hydroxides and/or the formation of an amorphous Fe-As phase (maybe scorodite: $FeAsO_4\cdot2H_2O$). Leaching tests were performed in order to find out leaching characteristics of As and Fe under acidic conditions. At the initial pHs 3 and 5, As contents dissolved from tailings of the cheongyang mine significantly increased after 7 days due to the oxidation of As-bearing secondary minerals (up to ca. $2.4\%$ of total), while As of Seobo mine-tailing samples was rarely released (ca. $0.0-0.1\%$ of total). Dissolution experiments at an initial pH 1 liberated a higher amount of As (ca. $1.1-4.2\%$ of total for Seobo tailings, $1.5-14.4\%$ of total for Cheongyang tailings). In addition, good correlation between As and Fe in leached solutions with tailings was observed. The kinetic problems could be the important factor which leads to increasing concentrations of As in the runoff water. Release of As from Cheongyang tailings can potentially pose adverse impact to surface and groundwater qualities in the surrounding environment, while precipitation of secondary minerals and the adsorption of As are efficient mechanisms for decreasing the mobilities of As in the surface environment of Seobo mine area.

• Journal of the Mineralogical Society of Korea
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• v.25 no.4
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• pp.185-195
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• 2012

Due to the high reduction and sorption capacity as well as the large specific surface area, nanosized mackinawite (FeS) is useful in reductively transforming chlorinated organic pollutants and sequestering toxic metals and metalloids. Due to the dynamic nature in its colloid stability, however, nanosized FeS may be washed out with the groundwater flow or result in aquifer clogging via particle aggregation. Thus, these nanoparticles should be modified such as to be built into permeable reactive barriers. This study employed coating methods in efforts to facilitate the installation of permeable reactive barriers of nanosized mackinawite. In applying the methods, nanosized mackinawite was coated on non-treated silica sand (NTS) and chemically treated silica sand (CTS). For both silica sands, the maximum coating of mackinawite occurred around pH 5.4, the condition of which was governed by (1) the solubility of mackinawite and (2) the surface charge of both silica and mackinawite. Under this pH condition, the maximum coating by NTS and CTS were found to be 0.101 mmol FeS/g and 0.043 mmol FeS/g respectively, with such elevated coatings by NTS likely linked with impurities (e.g., iron oxides) on its surface. Arsenite sorption experiments were performed under anoxic conditions using uncoated silica sands and those coated with mackinawite at the optimal pH to compare their reactivity. At pH 7, the relative sorption efficiency between uncoated NTS and coated NTS changed with the initial concentration of arsenite. At the lower initial concentration, uncoated NTS showed the higher sorption efficiency, whereas at the higher concentration, coated NTS exhibited the higher sorption efficiency. This could be attributed to different sorption mechanisms as a function of arsenite concentration: the surface complexation of arsenite with the iron oxide impurity on silica sand at the low concentration and the precipitation as arsenic sulfides by reaction with mackinawite coating at the high concentration. Compared to coated NTS, coated CTS showed the lower arsenite removal at pH 7 due to its relatively lower mackinawite coating. Taken together, our results indicate that NTS is a more effective material than CTS for the coating of nanosized mackinawite.

• Economic and Environmental Geology
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• v.50 no.3
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• pp.215-224
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• 2017

Arsenic (As) is known to be the most toxic element and frequently detected in groundwater environment. Inorganic As exists as arsenite [As(III)] and arsenate [As(V)] in reduced and oxidized environments, respectively. It has been reported that the toxicity of arsenite is much higher than that of arsenate and furthermore arsenite shows relatively higher mobility in aqueous environments. For this reason, there have been numerous researches on the process for oxidation of arsenite to arsenate to reduce the toxicity of arsenic. In particular, photooxidation has been considered to be simple, economical, and efficient to attain such goal. This study was conducted to evaluate the applicability of naturally-occurring goethite as a photocatalyst to substitute for $TiO_2$ which has been mostly used in the photooxidation processes so far. In addition, the effects of several factors on the overall performance of arsenite photocatalytic oxidation process were evaluated. The results show that the efficiency of the process was affected by total concentration of dissolved cations rather than by the kind of those cations and also the relatively higher pH conditions seemed to be more favorable to the process. In the case of coexistence of arsenite and arsenate, the removal tendency by adsorption onto goethite appeared to be different between arsenite and arsenate due to their different affinities with goethite, but any effect on the photocatalytic oxidation of arsenite was not observed. In terms of effect of humic acid on the process, it is likely that the higher concentration of humic acid reduced the overall performance of the arsenite photocatalytic oxidation as a result of competing interaction of activated oxygen species, such as hydroxyl and superoxide radicals, with arsenite and humic acid. In addition, it is revealed that the injection of oxygen gas improved the process because oxygen contributes to arsenite oxidation as an electron acceptor. Based on the results of the study, consequently, the photocatalytic oxidation of aqueous arsenite using goethite seems to be greatly feasible with the optimization of process.

• Journal of Korea Soil Environment Society
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• v.1 no.1
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• pp.55-65
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• 1996

Soil quality of most of Soil Network area was estimated healthy by employing Soil Pollution Indices (Soil Pollution Score and Soil Pollution Class). However, 1.5∼3.7% of the total Soil Network area was determined Soil Pollution Class (SPC) 4 which may need cleanup process due to slight or heavy pollution with arsenics and heavy metals. Numbers of the SPC 4 sites were 9, 47, 19, 17, and 17 in 1987, 1989, 1991, 1993, and 1994, respectively During 1987 and 1994, all of SPC 4 sites were identified agricultural land except one in 1994. Soil Pollution Scores (SPSs) was determined high around smelters, metalliferous mines, and industrial sites among the 16 major soil pollution sources of the Soil Network. Also, most area of SPC 4 sites were densely populated in these area of the Soil Network. SPSs of Inchon and Taegu were high among the other major cities and provinces in Korea. Numbers of SPC 4 were high in the province of Kangwon, Kyongbuk, Kyongnam amongst. Cumulative numbers of SPC 4 multiplied by a weighting value 0.3 during 1987 and 1994 of the Soil Network were regressed to develop a model equation for prospecting the soil quality. The model equation was Y= 1.16+0.23x, where as Y is the number of Class 4 and x is the year. Resulting the area of SPC 4 were 4.8%, 6.0%, 6.6% of the Soil Network in the year of 2001, 2006, 2011, respectively Based on this results, the area of SPC 4 would increase 5, 7, and 10 times comparing the area polluted with heavy metals in 1987.

• Economic and Environmental Geology
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• v.42 no.5
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• pp.487-494
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• 2009

The purpose of this study was to investigate the feasibility of As(V) reduction by aqueous Fe(II), and subsequent As(III) immobilization by the precipitation of As(III) incorporated magnetite-like material [i.e., co-precipitation of As(III) with Fe(II) and Fe(III)]. Experimental results showed that homogeneous As(V) reduction did not occur by dissolved Fe(II) at various pH values although the thermodynamic calculation was in favor of the redox reaction between As(V) and Fe(II) under the given chemical conditions. Similarly, no heterogeneous reduction of sorbed As(V) by sorbed Fe(II) was observed using synthetic iron (oxy)hydroxide (Goethite, ${\alpha}$-FeOOH) at pH 7. Experimental results for the effect of As(V) on the oxidation of Fe(II) by dissolved oxygen showed that As(V) inhibited the oxidation of Fe(II). These results indicate that As(V) could be stable in the presence of Fe(II) under the anoxic or subsurface environments.

• Economic and Environmental Geology
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• v.56 no.4
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• pp.409-419
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• 2023

Acid mine drainage(AMD) treatment is classified as both passive and active treatment. During the treatment, about 5,000 tons of neutralization sludge is generated as a by-product per year in Korea. This study was conducted to evaluate the characteristics of sludge generated from physico·chemical treatment processes as an active treatment from 5 different sources (D, H, S, T, Y) and the possibility of the sludges being recycled. The sludges have a pH range of 5.86 ~ pH 7.89, and a water content range of 51% ~ 82%. Most of particle sizes were less than 25 ㎛. In analysis of inorganic elements, the concentration of Al, Fe, and Mn were between 1,189 mg/kg ~ 129,344 mg/kg, 106,132 mg/kg ~ 338,011 mg/kg, and 3,472 mg/kg ~ 11,743 mg/kg, respectively. The concentration of As and Zn in sludge-T, Cd in sludge-D, Ni in sludge-H, Zn in sludge-S, and Cd in sludge-Y exceeded the soil contamination standards of Korea. The results from 2 separate kinds of leaching test, the Korea Standard Leaching Test(KSLT) and Toxicity Characteristic Leaching Procedure(TCLP), showed that all the sludges met the Korea groundwater standards. From the XRD and SEM-EDS analysis, the peaks of calcite and quartz were found in the sludges. The sludge also had a high proportion of Fe and O, and the majority of the composition was amorphous iron hydroxide.