• 자원환경지질
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• 제57권5호
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• pp.487-497
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• 2024

공극 규모 반응성 운송 모델링은 유체 유동과 지화학 반응의 결합이 일어나는 마이크로미터 수준의 프로세스 분석을 수행하는 연구 기법이다. 이는 지질매체 내에서 일어나는 복잡한 물질 거동을 정밀하게 고찰할 수 있게 하는 강력한 연구 기법이지만, 매우 높은 연산 자원이 필요하다는 한계가 존재한다. 이러한 한계를 극복하기 위하여, 본 연구에서는 반응성 운송 모델링에서 대부분의 연산 자원을 소모하는 지화학 반응을 대체하는 인공신경망 기반의 대리모형을 개발하였다. 공극 규모에서는 광물의 공간적 분포에 따라 독립적 지화학 반응 연산을 수행한다는 점에 착안하여 본 연구에서는 광물의 용해/침전과 용질의 흡착 반응을 동시에 고려하는 통합모형(CM)과 독립적으로 고려하는 독립모형(IM)의 두 가지 대리모형의 정확성과 효율을 비교하였다. 평균 제곱 오차(MSE), 결정 계수(R²), 질량 균형 오차(mass balance error) 등의 지표를 통해 모형들을 비교한 결과, 통합모형은 공극 규모에서 발생하는 순차적 반응에서 성능이 저하된 반면, 독립모형은 같은 조건에서도 높은 정확도를 유지하며 복잡한 지화학 반응을 효과적으로 처리하였다. 이 결과는 지화학 반응 대리모형 구축에 있어, 복잡한 지화학 반응 네트워크를 포괄하는 단일모형을 매번 새롭게 구축할 필요 없이, 개별 지화학 반응을 학습한 신경망 모형의 합성을 통하여 공극 규모의 지화학 반응을 대체할 수 있을 것으로 기대된다.

• 자원환경지질
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• 제50권6호
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• pp.545-554
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• 2017

버네사이트(birnessite)는 토양 및 심해저 환경에서 가장 흔히 발견되는 주요 망간수산화물 및 망간산화물(Mn(oxyhydr)oxides, 이하 망간산화물로 통칭) 중 하나로 일반적으로 나노 크기의 작은 입자로 구성되어 있으며 결정도가 매우 낮은 특징을 보인다. 특히 버네사이트는 구조 내 결함(structural defects)과 비어있는 양이온 자리(cation vacancies), 다양한 비율로 혼합된 구조 내 망간 산화수(mixed valences of structural Mn)의 특징에 따라 자연환경에서 다양한 생/지화학적 반응에 높은 반응성을 가지고 참여하는 것으로 알려져 있다. 이와 같이 다양한 생/지화학적 반응을 통해 버네사이트 주변에 존재하는 무기 및 유기물질의 자연 환경적 거동에 중요한 영향을 미칠 뿐 아니라 버네사이트의 상변화 반응이 수반되어 물리 화학적 특성이 전혀 다른 새로운 망간산화물이 형성된다. 본 리뷰 논문에서는 기존 선행 연구결과들을 바탕으로 버네사이트의 상변화 반응을 통해 형성되는 다양한 망간산화물들을 조사하고 반응에 영향을 미치는 다양한 지화학적 반응인자들을 검토하였다. 기존 선행연구 결과에 따르면 버네사이트의 상변화 반응은 용존 Mn(II) 및 용존 산소의 유무, 용액의 pH 조건, 그리고 함께 존재하는 양이온(i.e., $Mg^{2+}$)에 영향을 받는 것으로 사료되며, 다양한 반응인자들이 복합적으로 관여하는 버네사이트의 상변화 반응 경로에 대해서는 여전히 이해되지 않은 부분이 많은 것으로 확인되었다. 따라서, 앞으로 다양한 망간산화물들의 형성과 상변화 반응에 대한 보다 다양하고 심층적인 연구가 수행되어야 할 것이다.

• Nuclear Engineering and Technology
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• 제38권6호
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• pp.459-482
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• 2006

A geochemical approach to the long-term safety of waste disposal is discussed in connection with the significance of actinides, which shall deliver the major radioactivity inventory subsequent to the relatively short-term decay of fission products. Every power reactor generates transuranic (TRU) elements: plutonium and minor actinides (Np, Am, Cm), which consist chiefly of long-lived nuclides emitting alpha radiation. The amount of TRU actinides generated in a fuel life period is found to be relatively small (about 1 wt% or less in spent fuel) but their radioactivity persists many hundred thousands years. Geological confinement of waste containing TRU actinides demands, as a result, fundamental knowledge on the geochemical behavior of actinides in the repository environment for a long period of time. Appraisal of the scientific progress in this subject area is the main objective of the present paper. Following the introductory discussion on natural radioactivities, the nuclear fuel cycle is briefly brought up with reference to actinide generation and waste disposal. As the long-term disposal safety concerns inevitably with actinides, the significance of the aquatic actinide chemistry is summarized in two parts: the fundamental properties relevant to their aquatic behavior and the geochemical reactions in nanoscopic scale. The constrained space of writing allows discussion on some examples only, for which topics of the primary concern are selected, e.g. apparent solubility and colloid generation, colloid-facilitated migration, notable speciation of such processes, etc. Discussion is summed up to end with how to make a geochemical approach available for the long-term disposal safety of nuclear waste or for the performance assessment (PA) as known generally.

• 대한자원환경지질학회:학술대회논문집
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• 대한자원환경지질학회 2002년도 제18차 공동학술강연회 자연저감고 지질학 (대한 자원 환경지질학회)
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• pp.81-100
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• 2002

While most of regulatory communities in abroad recognize ' 'natural attenuation " to include degradation, dispersion, dilution, sorption (including precipitation and transformation), and volatilization as governing Processes, regulators prefer "degradation" because this mechanism destroys the contaminant of concern. Unfortunately, true degradation only applies to organic contaminants and short- lived radionuclides, and leaves most metals and long-lived radionuclides. The natural attenuation Processes may reduce the potential risk Posed by site contaminants in three ways: (i)contaminants could be converted to a less toxic form througy destructive processes such as biodegradation or abiotic transformations; (ii) potential exposure levels may be reduced by lowering concentrations (dilution and dispersion); and (iii) contaminant mobility and bioavailability may be reduced by sorption to geomedia. In this review, authors will focus will focul on "sorption" among the natural attenuation processes of hazardous inorganic contaminants including radionuclides. Note though that sorption and transformation processes of inorganic contaminants in the natural setting could be influenced by biotic activities but our discussion would limit only to geochemical reactions involved in the natural attenuation. All of the geochemical reactions have been studied in-depth by numerous researchers for many years to understand "retardation" process of contaminants in the geomedia. The most common approach for estimating retardation is the determination of distrubution coefficiendts ($K_{d}$) of contaminants using parametric or mechanistic models. As typocally used in fate and contaminant transport calculations such as predictive models of the natural attenuation, the $K_{d}$ is defined as the ratio of the contaminant concentration in the surrounding aqueous solution when the system is at equilibrium. Unfortunately, generic or default $K_{d}$ values can result in significant error when used to predict contaminant migration rate and to select a site remediation alternative. Thus, to input the best $K_{d}$ value in the contaminant transport model, it is essential that important geochemical processes affecting the transport should be identified and understood. Precipitation/dissolution and adsorption/desorption are considered the most important geochemical processes affecting the interaction of inorganic and radionuclide contaminants with geomedia at the near and far field, respectively. Most of contaminants to be discussed in this presentation are relatively immobile, i.e., have very high $K_{d}$ values under natural geochemical environments. Unfortunately, the obvious containment in a source area may not be good enough to qualify as monitored natural attenuation site unless owner demonstrate the efficacy if institutional controls that were put in place to protect potential receptors. In this view, natural attenuation as a remedial alternative for some of sites contaminated by hazardous-inorganic components is regulatory and public acceptance issues rather than scientific issue.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2004년도 총회 및 춘계학술발표회
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• pp.19-22
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• 2004

Two-dimensional modeling studies using TOUGHREACT were conducted to investigate the coupling between flow and transport developed as a consequence of differences in density, dissolution/ precipitation, and medium heterogeneity. The model includes equilibrium reactions for aqueous species, kinetic reactions between tile solid phases and aqueous constituents, and full coupling of porosity and permeability changes resulting from precipitation and dissolution reactions in porous media. Generally, the evolutions in the concentrations of the aqueous phase are intimately related to the reaction-front dynamics. Plugging of the medium contributed to significant transients in patterns of flow and mass transport.

• 한국지하수토양환경학회지:지하수토양환경
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• 제20권7호
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• pp.90-102
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• 2015

To understand the hyrogeochemical variation of bedrock aquifer during underground space construction, various graphical methods including multiple-component plots and chemical trends were used to estimate the mixing rate between seawater and freshwater and to investigate the evolution of water quality. The water chemistry and mixing rate between fresh and sea waters, which are generally localized in the construction area (MW-7, in land), shows typical characteristics of freshwater that doesn’t affect its validity as seawater intrusion. Especially, the water chemistry of a MW-4 (coastline) was classified as Na-Cl type, Na-HCO₃ type, and Ca-Cl type due to the influence of the seawater intrusion. And hydrogeochemical and isotopic data show that local freshwater is subjected to geochemical processes, such as reverse ion-exchange. Throughout the Chadha’s diagrams, four different case histories with the temporal and spatial variation of groundwaters in the study area were proposed, which is recommended to interpret the hydrogeochemical reactions effectively.

• 자원환경지질
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• 제32권1호
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• pp.101-111
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• 1999

Sedimentary organic matter, exposed to continental surficial environment, reacts with oxygen supplied from the atmosphee and forms carbon-containing oxidation products. Knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time. Under the abiological conditions, the oxidation rate of coal organic matter by molecular oxygen is enhanced by the increase of oxygen concentration and temperature. At ambient temperature and pressure, aqueous coal oxidation results in the formation of dissolved $CO_2$ dissolved organic carbon and solid oxidation products which are all quantitatively significant reaction products. The effects of pH, ultraviolet light, and microbial activity on the weathering of sedimentary organic matter are poorly contrained. Based on the results of geochmical and environmental studies, it is believed that the photochemical reaction should play an important role in the decomposition and oxidation of sedimentary organic matter removed from the weathering profile. At higher pH conditions, the production rate of DOC can be accelerated due to base catalysis. These high molecular weight oranic matter can react with man-made pollutants such as heavy metal ions via adsorption/desorption or ion exchange reactions. The effect of microbial activity on the oxidative weathering of sedimentary organic matter is poorly understood and remains to be studied.

• 자원환경지질
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• 제47권4호
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• pp.421-430
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• 2014

본 연구에서는 지중 유입된 이산화탄소가 심부 지질구조 내 지하 환경에 미치는 지화학적 및 광물학적 영향을 규명하기 위한 일련의 고압셀 실험이 수행되었다. 실험을 통하여 이산화탄소 지중저장 조건에 해당하는 $50^{\circ}C$와 100 bar의 고온 고압조건을 고압셀 내에서 구현하고, 초임계 $CO_2$-지하수-광물 시스템 내에서의 반응 실험을 실시하였다. 반응 실험은 최근 국내 이산화탄소 지중저장의 후보지로서 많은 연구가 진행되고 있는 포항분지에 널리 분포하는 광물 중 하나인 제올라이트와 지하 800 m에서 채취된 심지층의 지하수를 대상으로 수행되었다. 상온 상압 및 고온 고압 환경에서 30일간 진행된 $CO_2$-지하수-제올라이트 반응으로 야기된 광물과 지하수 시료의 지화학적 및 광물학적 변화는 XRD, XRF, ICP-OES 등의 분석을 통해 정량적으로 규명하였다. 실험의 결과는 초임계 이산화탄소의 용해로 조성된 산성 환경에서 제올라이트 시료의 용해 반응이 촉진되었음을 보여 주었다. 제올라이트 시료로부터 용출된 양이온 농도가 증가함에 따라 지하수 내 $H^+$가 소모되고, 반응 10일 이후에는 지하수의 pH가 10.35 까지 증가하였다. 또한 제올라이트 시료의 용해 반응으로 인해 지하수 내 용존 양이온의 농도는 전반적으로 증가하는 경향을 보였으나, Si는 산성조건에서 비정질 규산염으로 재침전되고, Ca는 양이온 교환과 방해석으로의 재침전으로 농도가 감소한 것으로 나타났다. 실험 과정을 통하여 초임계 이산화탄소의 유입이 대수층 내 구성 광물의 용해 특성, 지하수의 화학적 조성과 물성, 대수층의 광물학적 조성 등에 변화를 발생시킬 수 있음을 보여주었다. 또한 광물상의 용해/침전과 양이온 교환 등 지화학적 반응들이 지중저장 관련 지층의 암석과 지하수의 물리적 또는 화학적 변화에 중요한 역할을 담당하고 있음을 보여주었다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제25권1호
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• pp.25-36
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• 2020

In a redox transition zone, geochemical reactions are facilitated by active bacteria that mediate reactions involving electrons, and arsenic (As) and iron (Fe) cycles are the major electron transfer reactions occurring at such a site. In this study, the effect of repetitive redox changes on soil bacterial community in As-contaminated soil was investigated. The results revealed that bacterial community changed actively in response to redox changes, and bacterial diversity gradually decreased as the cycle repeated. Proportion of strict aerobes and anaerobes decreased, while microaerophilic species such as Azospirillum oryzae group became the predominant species, accounting for 72.7% of the total counts after four weeks of incubation. Bacterial species capable of reducing Fe or As (e.g., Clostridium, Desulfitobacterium) belonging to diverse phylogenetic groups were detected. Indices representing richness (i.e., Chao 1) and phylogenetic diversity decreased from 1,868 and 1,926 to 848 and 1,121, respectively. Principle component analysis suggests that repetitive redox fluctuation, rather than oxic or anoxic status itself, is an important factor in determining the change of soil bacterial community, which in turn affects the cycling of As and Fe in redox transition zones.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.477-480
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• 2007

Inlet fluid temperature of the BRE in the geothermal heat pump system depends on heat exchange rate between the refrigerant of the heat pump and the leaving fluid from the BRE. Because the outlet fluid temperature of the BHE varies with time, inlet fluid temperature has to vary with time. In this study, the module to calculate inlet fluid temperature is developed, which can consider the time-varying outlet fluid temperature and the heat exchange capacity of the heat pump. It is assumed that heat loss or gain of the leaving fluid from outlet to inlet of the BHE is negligible, except when the fluid contacts with the refrigerant of the heat pump. This module is combined with TOUGHREACT, a widely accepted three-dimensional numerical simulator for heat and water flow and geochemical reactions in geothermal systems and is applied to data analyses of the thermal response test.