• Journal of the Mineralogical Society of Korea
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• v.26 no.3
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• pp.161-174
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• 2013

The geology of the weondong deposit area consists mainly of Cambro-Ordovician and Carboniferous-Triassic formations, and intruded quartz porphyry and dyke. The skarn mineralized zone in the weondong deposit is the most prospective region for the useful W-mineral deposits. To determine the skarn-mineralization age, U-Pb SHRIMP and K-Ar age dating methods were employed. The U-Pb zircon ages of quartz porphyry intrusion (WD-A) and feldspar porphyry dyke (WD-B) are 79.37 Ma and 50.64 Ma. The K-Ar ages of coarse-grained crystalline phlogopite (WD-1), massive phlogopite (WDR-1), phlogopite coexisted with skarn minerals (WD-M), and vein type illite (WD-2) were determined as $49.1{\pm}1.1$ Ma, $49.2{\pm}1.2$ Ma, $49.9{\pm}3.6$ Ma, and $48.3{\pm}1.1$ Ma, respectively. And the ages of the high uranium zircon of hydrothermally altered quartz porphyry (WD-C) range from 59.7 to 38.7 Ma, which dependson zircon's textures affected by hydrothermal fluids. It is regarded as the effect of some hydrothermal events, which may precipitate and overgrow the high-U zircons, and happen the zircon's metamictization and dissolution-reprecipitation reactions. Based on the K-Ar age datings for the skarn minerals and field evidences, we suggest that the timing of W-skarn mineralization in weondong deposit may be about 50 Ma. However, for the accurate timing of skarn mineralization in this area, the additional researches about the sequence of superposition at the skarn minerals and geological relationship between skarn deposits and dyke should be needed in the future.

• Journal of Conservation Science
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• v.5 no.1 s.5
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• pp.20-40
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• 1996

For obtaining the basic data for establishing plan on the conservation of the Gameunsa 3-story and Naweonri 5-story Pagodas located at the Kyeongju city, the characteristics of the rock and weathering phenomena have been investigated. The former consists of quartz-rlch granite containing small amount of biotite, and the latter of alkali granite with abundant perthite, These rock phases are nearly identical to the marginal phase of medium-grained hornblende-biotite granodiorite and alkali granite respectively, which are distributed around the Kyeongju city. The rock weathering may be governed mainly by chemical weathering of feldspar following physical segregation of quartz grains and pervasive moss. The feldspar easily dissolve In the solution with pH<7 to precipitate clay mineral such as a kaolinite as a secondary phase on the feldspar surface. However, the chemical weathering of feldspar may continue when the surface is washed by the rain according to removal of the reprecipitated phase. On forwarding, the weathering may be greatly Influenced by the acid rain. Exfoliation and weathering along igneous lineation resulting in exfoliating along the structural line are the characteristic weathering phenomena. Also the secondary small cracks are irregularly developed on the rocks due to different strain on places by the overall structural unbalance of the pagodas. Along these cracks, the rain water intrudes deeply into the rocks and weathering occurs intensively compared to other parts. Weathering may be artificially promoted by the grinding or sculpturing when the pagodas were made. Because it may influence on the physical properties of the rocks as well as destruct the surface of the feldspar crystals, the major constituents of the rocks, it results in providing the environment of easy chemical weathering along time. For conservation, the pagodas must be structurally balanced by compacting the soil basement and supplementing rocks on the destroyed part. On the exfoliated part it is better not to be artifically treated as using cementing material. But the cracks may be filled up by cementing material to avoid the intrusion of acidic water. To supplement the rocks on the destroyed part, it may be better to use similar rock phases from identical biotite granite and alkali granite masses around the Kyeongju city.

• Economic and Environmental Geology
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• v.42 no.5
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• pp.495-500
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• 2009

Actinide sorption to the geological materials can reduce the mobility and bioavailability of radionuclides released to the environment through the development of nuclear weapons and nuclear energy. Under circumneutral pH conditions, actinide sorption can be enhanced by phosphate anions sorbed on oxide mineral surfaces as indicated by the sorption of trivalent lanthanide ions ($Ln^{3+}$), the chemical analog for trivalent actinide ions ($Ac^{3+}$). In this paper, we examined a ternary sorption system of trivalent europium ions ($Eu^{3+}$) sorbed onto boehmite (${\gamma}$-AlOOH) surfaces pre-sorbed with phosphate anions (${PO_4}^{3-}$), using extended X-ray absorption fine structure (EXAFS) spectroscopy. In the Eu-$PO_4$-boehmite ternary sorption system, $EuPO_4$ surface precipitates were formed as implicated by Eu $L_{III}$-edge EXAFS spectroscopy. Phosphorus K-edge EXAFS fingerprinting indicated a bidentate mononuclear surface complex formation of phosphate sorbed on boehmite surfaces as well as $EuPO_4$ surface precipitate formation.

• Economic and Environmental Geology
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• v.55 no.4
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• pp.377-388
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• 2022

Laboratory-scale experiments were performed to identify the As removal mechanism of the residual slag generated after the mineral carbonation process. The residual slags were manufactured from the steelmaking slag (blast oxygen furnace slag: BOF) through direct and indirect carbonation process. RDBOF (residual BOF after the direct carbonation) and RIBOF (residual BOF after the indirect carbonation) showed different physicochemical-structural characteristics compared with raw BOF such as chemical-mineralogical properties, the pH level of leachate and forming micropores on the surface of the slag. In batch experiment, 0.1 g of residual slag was added to 10 mL of As-solution (initial concentration: 203.6 mg/L) titrated at various pH levels. The RDBOF showed 99.3% of As removal efficiency at initial pH 1, while it sharply decreased with the increase of initial pH. As the initial pH of solution decreased, the dissolution of carbonate minerals covering the surface was accelerated, increasing the exposed area of Fe-oxide and promoting the adsorption of As-oxyanions on the RDBOF surface. Whereas, the As removal efficiency of RIBOF increased with the increase of initial pH levels, and it reached up to 70% at initial pH 10. Considering the PZC (point of zero charge) of the RIBOF (pH 4.5), it was hardly expected that the electrical adsorption of As-oxyanion on surface of the RIBOF at initial pH of 4-10. Nevertheless it was observed that As-oxyanion was linked to the Fe-oxide on the RIBOF surface by the cation bridge effect of divalent cations such as Ca²⁺, Mn²⁺, and Fe²⁺. The surface of RIBOF became stronger negatively charged, the cation bridge effect was more strictly enforced, and more As can be fixed on the RIBOF surface. However, the Ca-products start to precipitate on the surface at pH 10-11 or higher and they even prevent the surface adsorption of As-oxyanion by Fe-oxide. The TCLP test was performed to evaluate the stability of As fixed on the surface of the residual slag after the batch experiment. Results supported that RDBOF and RIBOF firmly fixed As over the wide pH levels, by considering their As desorption rate of less than 2%. From the results of this study, it was proved that both residual slags can be used as an eco-friendly and low-cost As remover with high As removal efficiency and high stability and they also overcome the pH increase in solution, which is the disadvantage of existing steelmaking slag as an As remover.

• Journal of Soil and Groundwater Environment
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• v.12 no.2
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• pp.27-36
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• 2007

A recent study showed that MTBE can be degraded by Fenton's Reagent (FR). The treatment of MTBE with FR, however, has a definite limitation of extremely low pH requirement (optimum pH $3{\sim}4$) that makes the process impracticable under neutral pH condition on which the ferrous ion precipitate forming salt with hydroxyl anion, which result in the diminishment of the Fenton reaction and incompatible with biological treatment. Consequently, this process using only FR is not suitable for in-situ remediation of MTBE. In order to overcome this limitation, modified Fenton process using NTA, oxalate, and acetate as chelating reagents was introduced into this study. Modified Fenton reaction, available at near neutral pH, has been researched for the purpose of obtaining high performance of oxidation efficiency with stabilized ferrous or ferric ion by chelating agent. In the MTBE degradation experiment with modified Fenton reaction, it was observed that this reaction was influenced by some factors such as concentrations of ferric ion, hydrogen peroxide, and each chelating agent and pH. Six potential chelators including oxalate, succinate, acetate, citrate, NTA, and EDTA were tested to identify an appropriate chelator. Among them, oxalate, acetate, and NTA were selected based on their remediation efficiency and biodegradability of each chelator. Using NTA, the best result was obtained, showing more than 99.9% of MTBE degradation after 30 min at pH 7; the initial concentration of hydrogen peroxide, NTA, and ferric ion were 1470 mM, 6 mM, and 2 mM, respectively. Under the same experimental condition, the removal of MTBE using oxalate and acetate were 91.3% and 75.8%, respectively. Optimum concentration of iron ion were 3 mM using oxalate which showed the greatest removal efficiency. In case of acetate, $[MTBE]_0$ decreased gradually when concentration of iron ion increased above 5 mM. In this research, it was showed that modified Fenton reaction is proper for in-situ remediation of MTBE with great efficiency and the application of chelatimg agents, such as NTA, was able to make the ferric ion stable even at near neutral pH. In consequence, the outcomes of this study clearly showed that the modified Fenton process successfully coped with the limitation of the low pH requirement. Furthermore, the introduction of low molecular weight organic acids makes the process more available since these compounds have distinguishable biodegradability and it may be able to use natural iron mineral as catalyst for in situ remediation, so as to produce hydroxyl radical without the additional injection of ferric ion.