Application of Galvanic Oxidation and Pyrite Dissolution for Sustainable In-Situ Mine Tailings Treatment

선광 및 제련과 같은 광산활동 과정에 발생하는 광미는 고농도의 중금속을 함유하고 있고, 그 중 황철석을 함유한 광미는광산주변 수계 및 토양 오염의 주요 원인이다. 이러한 황철석을 함유한 광미의 무해화를 위해 화학전지 (연료전지)의 개념을 활용할수 있다. 화학전지에서 황철석의 자발적인 산화, 즉, 갈바닉 산화를 통해 황철석이 용해되면서 Fe3+와 황산이 생성되어 pH가 감소하게된다. 이는 황철석 함유 광미 내 중금속의 용출 촉진 효과를 가져올 수 있다. 본 연구에서는 23°C 조건에서 4주 간 산성용액과갈바닉 반응기를 이용해 황철석을 처리하며 총 용존 철 농도와 용액의 pH를 확인하였다. 또한 주사전자현미경을 이용해 처리 후황철석 표면을 관찰하였다. 갈바닉 반응기를 이용한 황철석의 용해가 산성용액을 이용한 황철석의 용해에 비해 약 2.9배 높은 총철을 용출시킨 것을 확인하였고, pH 저감 효과도 더 큰 것을 확인하였다. 또한 표면 분석 결과 갈바닉 반응기 내에서 반응한 황철석의표면에서 더 많은 홈을 발견되었다. 본 연구를 통해 갈바닉 산화에 의해 황철석의 용해가 촉진된 것을 확인하였으며, 갈바닉 산화가황철석 함유 광미의 무해화 기술로 사용될 수 있는 가능성을 확인하였다. Mine tailings generated during mining activity often contain high concentrations of heavy metals, with pyrite-containing mine tailings in particular being a major cause of environmental problems in mining areas. Chemical cell technology, or fuel cell technology, can be applied to leach heavy metals in pyrite-containing mine tailings. As pyrite dissolves through spontaneous oxidation (i.e. galvanic oxidation) in the anode compartment of the cell, Fe3+, sulfuric acid are generated. A decrease in pH due to the generation of sulfuric acid allows heavy metals to be leached from pyrite-containing mine tailings. In this study, pyrite was dissolved for 4 weeks at 23°C in an acidic solution (pH 2) and in a galvanic reactor, which induces galvanic oxidation, and total Fe leached from pyrite and pH were compared in order to investigate if galvanic oxidation can facilitate pyrite oxidation. The change in the pyrite surface was analyzed using a scanning electron microscope (SEM). Comparing the total Fe leached from the pyrite, there were 2.9 times more dissolution of pyrite in the galvanic reactor than in the acidic solution, and thus pH was lower in the galvanic reactor than in the acidic solution. Through SEM analysis of the pyrite that reacted in the galvanic reactor, linear-shaped cracks were observed on the surface of the pyrite. The study results show that pyrite dissolution was facilitated through the galvanic oxidation in the galvanic reactor, and also implied that the galvanic oxidation can be one remediation option for pyrite-containing mine tailings.N

Soil Washing Technology for Sr and Cs-contaminated Soil Near Nuclear Power Plants using Calcium and Potassium Based Solutions

Calcium (Ca) and potassium (K) were introduced to remove Sr and Cs in soil, respectively. Four factor and three levelBox-Bhenken design was employed to determine the optimal washing condition of Ca- and K-based solutions, and theranges tested were 0.1 to 1M of Ca or K, L/S ratio of 5 to 20, washing time of 0.5 to 2 h, and pH of 2 to 7. The optimalwashing condition determined was 1 M of Ca or K, L/S ratio of 20, washing time of 1 h, and pH of 2, and Ca-based andK-based solutions showed 68 and 81% removal efficiency for Sr and Cs, respectively in soil. For comparison, widely usedconventional washing agents such as 0.075 M EDTA, 0.01M citric acid, 0.01M oxalic acid, and 0.05 M phosphoric acidwere tested, and they showed 25 to 30% of Sr and Cs removal efficiency. Tessier sequential extraction was employed toidentify the changes in chemical forms of Sr and Cs during the washing. In contrast to the conventional washing agents,Ca-based and K-based solutions were able to release relatively strongly bound forms of Sr and Cs such as Fe/Mn-oxideand organic matter bound forms, suggesting the involvement of direct substitution mechanism, probably due to thephysicochemical similarities between Sr-Ca and Cs-K.N

Aging and bioavailability, and their impact on risk-based remedial endpoint

유기오염물질은 토양에서 시간이 지날수록 점차 그 생물학적 및 화학적 이용성이 감소하게 되는데 이를 aging(또는 sequestration)이라고 명명하였다. 이러한 현상은 소수성 오염물질을 중심으로 여러가지 환경 매질에서 공통적으로 관찰되었으며 aging은 오염물질의 탈착저항성이나 비평형흡착 현상과 밀접한 연관이 있는 것으로 생각된다. Aging에 의한 생물학적 이용성의 감소는 오염물질에 의한 실질적인 위해성의 감소를 의미하며 이는 곧 위해성 평가의 결과에 영향을 미친다. 이러한 배경을 바탕으로 환경친화적인 정화수준이란 개념이 생겨나게 되었으며 이는 토양에 존재하는 오염물질의 절대농도보다는 잔류 오염물질의 생물학적 이용성 또는 생동성을 기준으로 정화수준을 결정하는 것을 기본으로 한다. 이 경우 주된 관심의 대상은 정화 후 토양에 잔류하는 오염물질의 절대량이 아니라 잔류물질의 탈착속도, 생물학적 이용성 또는 생독성이 된다. 이러한 요소들은 토양에서 오염물질의 이동 및 거동의 변화에 따라 그 정도에 영향을 받으며 나아가 오염물질의 수용체로의 노출 경로 및 정도에 영향을 미치게 된다. 이러한 점들을 고려하여 오염물질의 실질적인 위해성을 평가하여 정화 및 복원에 이용하는 것이 위해성에 근거한 복원전략의 행심이라 할 수 있다.본 연구는 두뇌한국 21 프로젝트(서울대/한양대 사회기반 및 건설기술인력양성사업단)와 서울대학교 공학연구소의 지원에 의해 수행되었으며 이에 감사를 드립니다

Determination of Target Clean-up Level and Risk-Based Remediation Strategy

위해성에 근거한 복원 전략(risk-based strategy, RBRS)은 위해성평가를 통하여 오염지역의 위해성 또는 오염원을 효율적으로 관리하기 위한 의사결정과정 중의 일부로서, 토양에 존재하는 독성물질이 인간이나 생태계와 같은 수용체로 전이되어 발현되는 독성을 감소시키는 것을 목적으로 한다. 토양오염에 대한 위해성평가는 토양에서 대기로 확산되어나가는 오염물질의 흡입, 토양에서 지하수로 용출된 오염물질의 섭취, 토양 자체의 섭취와 접촉 등에 의한 위해성평가를 포함하며, 오염물질의 특성뿐만 아니라 수리지질학적 자료, 토지이용용도, 수용체의 특성등 현장의 특이적인 요소들을 충분히 고려해야 한다. 위해성에 근거한 복원전략은 위해성산정을 위한 현장조사로부터 시작하여 구체화된 노출경로모델(conceptual site model, CSM)의 작성, 목표위해성 수준의경정, 오염물질의 물리화학적 특성 및 독성학적 자료의 수집을 거쳐, 일반적이고 보수적인 조건 하에 가장 안전한 목표정화수준을 산정하는 Tier 1 평가와 보다 정확한 오염현장의 조사를 통하여 현장특수성을 반영하는 Tier 2 평가를 단계적으로 적용한다. 현장의 오염농도가 Tier 1으로 결정된 허용오염수준(ridk-based sdreening level, RBSL)보다 높은 경우 Tier 2를 실시하여 현장의 특수성을 반영하는 목표정화수준(site0specific target level)을 산정하며, 이를 통하여 오염지역에 대한 과도한 정화처리나 비경제적인 복구사업 등을 피할 수 있다. 위해성에 근거한 복원전략은 이 밖에도 오염지역의 복원우선순위 결정, 토지이용용도에 따른 위해성 관리기준 수립 등 다양한 활용성을 가지지만, 여러가지 전제조건들과 현장조사 시에 발생하는 현실적 한계 등으로 인하여 불확실성을 가진다. 이를 극복하기 위하여 정확한 CSM의 작성, 복합오염에 대한 고려, 오염물질의 이동과 거동에 영향을 미치는 환경매질의 특성과 모델 입력변수 등을 신중하게 검토해야 하며, 신뢰할 만한 현장조사기법과 독성검사기법의 확립, 국내실정에 맞는 토양 및 지하수 특성자료와 인체 노출인자 등에 대한 여구가 지속적으로 이루어져야 할 것이다.본 연구는 과학기술부/한국과학재단 우수연구센터지원사업(R11-2003-006-05001-0)으로 수행되었으며 서울대학교 공학연구소의 기술적 지원에도 감사드립니다

Analysis on the Risk-Based Screening Levels Determined by Various Risk Assessment Tools (III): Proposed Methodology for Lead Risk Assessment in Korea

The most critical health effect of lead exposure is the neurodevelopmental effect to children caused by the increased blood lead level. Therefore, the endpoint of the risk assessment for lead-contaminated sites should be set at the blood lead level of children. In foreign countries, the risk assessment for lead-contaminated sites is conducted by estimating the increased blood lead level of children via oral intake and/or inhalation (United States Environmental Protection Agency, USEPA), or by comparing the estimated oral dose to the threshold oral dose of lead, which is derived from the permissible blood lead level of children (Dutch National Institute for Public Health and the Environment, RIVM). For the risk assessment, USEPA employs Integrated-Exposure-Uptake-Biokinetic (IEUBK) Model to check whether the estimated portion of children whose blood lead level exceeds 10 μg/dL, threshold blood lead level determined by USEPA, is higher than 5%, while Dutch RIVM compares the estimated oral dose of lead to the threshold oral dose (2.8 μg/kg-day), which is derived from the permissible blood lead level of children. In Korea, like The Netherlands, risk assessment for lead-contaminated sites is conducted by comparing the estimated oral dose to the threshold oral dose; however, because the threshold oral dose listed in Korean risk assessment guidance is an unidentified value, it is recommended to revise the existing threshold oral dose described in Korean risk assessment guidance. And, if significant lead exposure via inhalation is suspected, it is useful to employ IEUBK Model to derive the risk posed via multimedia exposure (i.e., both oral ingestion and inhalation).N

Risk Assessment of Volatile Organic Compounds for Vapor Intrusion Pathway Using Various Estimation Methodology of Indoor Air Concentration

Indoor inhalation of vapors intruded into buildings is an important exposure pathway in volatile organic compoundscontaminated sites. Site-specifically measured indoor air concentration is preferentially used for risk assessment. However, when indoor air concentration of VOC is not measured, the indoor air concentration needs to be estimated from soil concentration or measured soil gas concentration of the VOC. Some risk assessment guidance (e.g., Korea Ministry of Environment (KMOE) and American Society for Testing and Materials (ASTM) International guidance) estimate the indoor air concentration from soil concentration while other guidances (e.g., United States Environmental Protection Agency (USEPA) and Dutch National Institute for Public Health (RIVM)) estimate it from measured soil gas concentration. This study derived indoor inhalation risks of intruded benzene in two benzene-contaminated residential areas with four different risk assessment guidances (i.e., KMOE, USEPA, ASTM, and Dutch RIVM) and compared the derived risks. The risk assessment results revealed that indoor air estimation approach from soil concentration could either underestimate (when the contaminant is not detected in soil) or overestimate (when the contaminant is detected in soil even at negligible concentration) the indoor air inhalation risk. Hence, this paper recommends to estimate indoor air concentration from soil gas concentration, rather than soil concentration. Discussions about the various indoor air concentration estimation approaches are provided.N

Applicability of Stabilization with Iron Oxides for Arsenic-Contaminated Soil at the Forest Area near the Former Janghang Smelter Site

This study evaluated the applicability of stabilization of arsenic (As)-contaminated soil with iron (Fe) oxides at the former Janghang smelter site. Three Fe oxides (magnetite, goethite, and hematite) were tested as stabilizing agents to one soil sample collected from the study site. Amendment of 5% of magnetite, goethite, or hematite for one week showed the 64, 58, and 36% of reduction of the SBRC (Solubility/Bioavailability Research Consortium)-extractable (bioaccessible) As, respectively. Duration of stabilization more than one week did not show an additional reduction in SBRC-extractable As. Amendment of 5% of magnetite, which showed the highest As stabilization efficiency, was applied to 24 soil samples collected from the same site for one week, and 72% of reduction in the bioaccessible As was observed. The potential carcinogenic human health risk at the study site caused by As was 1.7×10?5, which could be reduced to 8.1×10?6 by the amendment of 5% magnetite for one week.N

The Toxicity Assessment of Explosives Contaminated Soil using Soil Microbial Activity Tests

This study was conducted to determine the toxic effect of TNT and RDX on indigenous soil microbes by measuring enzymatic activity. Denitrification activity, dehydrogenase activity, phosphatase activity, and fluorescein diacetate hydrolytic activity were determined for military firing range, field, and paddy soils exposed to TNT, and RDX from 0 to 1,000 mg/kg and 0 to 4,000 mg/kg, respectively, for 2, 4, and 8 weeks. Soil microbial enzymatic activities decreased with higher TNT and RDX concentration and longer exposure time. Microbial enzymatic activities of firing range soil were higher than field and paddy soils, indicating that indigenous microbes in firing range might have been adapted to TNT and RDX due to pre-exposure of the explosives. In addition, the toxicity of TNT and RDX decreased with higher organic matter because TNT and RDX tend to absorb to soil organic matter. No Observable Effect Concentration (NOEC) values of each microbial enzymatic activity were derived by the geometric mean of NOECs from exposure times (2, 4, and 8 weeks) and soil types (firing range, field, paddy soil). The derived NOECs ranged from 45.3 to 55.2 mg/kg for TNT and 286 to 309 mg/kg for RDX.N

Changes in Soil Properties Related to Soil Function due to Chemical Spills with Strong Acid and Base

본 연구에서는 강산 및 강염기 유출사고가 발생하였을 때 육상생물의 생육에 영향을 미칠 수 있는 토양특성의 변화를살펴보았다. 강산과 강염기 화학물질로 HCl과 NaOH을 선정하였으며 이들 물질을 토양과 반응시킨 후 토양의 토성, 비표면적, 유기물함량, pH, 양이온교환능력 및 치환성양이온 함량 변화를 측정하였다. 토양과 반응한 HCl 및 NaOH 농도가 각각 10 M과 1 M인경우 (즉, 토양 1 g 당 50 mmol의 HCl이나 5 mmol의 NaOH가 유입된 경우) 유의한 수준의 토양 특성 변화가 관찰되었다. 10 M HCl 및 1 M NaOH 용액과 반응한 토양의 토성은 sandy loam에서 loamy sand로 변하였으며, 비표면적은 5.84 m2/g에서 각각4.85 및 1.92 m2/g으로 감소하였다. 토양 유기물 함량은 3.23%에서 0.96 및 0.44%로 크게 감소하였으며, 반응 전 pH 5.05로 약산성인토양의 pH는 각각 2.35 및 10.65로 변하였다. 토양 내 양이온교환능력은 10.27 cmol/kg에서 4.52 및 5.60 cmol/kg으로 크게 감소하였으며Na+을 제외한 알칼리성 양이온 (K+, Mg2+, Ca2+)의 함량이 감소하였다. HCl과 반응한 경우 Na+ 함량은 감소, Al3+ 함량은 증가하였으나반대로 NaOH와 반응한 경우 Na+ 함량은 증가, Al3+ 함량은 감소하였다. 높은 농도의 Al3+과 Na+은 각각 토양생물에게 직접적인독성을 발현하거나 토양의 투수성을 감소시키고 중탄산염의 농도를 증가시켜 독성을 발현할 수 있다. 본 연구는 강산 및 강염기유출사고로 인하여 변화한 토양특성이 토양의 생태기능에 영향을 줄 수 있음을 보여준다. In this study, changes of soil properties including soil texture, specific surface area, organic matter content, pH, cation exchange capacity and exchangeable cations content were investigated in response to strong acid or base accident. The properties changed significantly when the soil reacted with 10 M HCl or 1 M NaOH (i.e., when one gram of soil received 50 and 5 mmol of HCl or NaOH), respectively. When the soil reacted with 10 M HCl or 1 M NaOH solution, soil texture changed from sandy loam to loamy sand and specific surface areas decreased from to 4.85 and , respectively. The soil organic matter content was reduced from 3.23% to 0.96 and 0.44%, and the soil pH changed from 5.05 to 2.35 and 10.65, respectively. The cation exchange capacity decreased from 10.27 cmol/kg to 4.52 and 5.60 cmol/kg, respectively. Especially, high concentrations of or were observed in acidic or basic spills, respectively, which is likely to cause toxicity to terrestrial organisms. The results suggest that restoration of soil properties, as well as soil remediation, needs to be carried out to maintain the soil function in chemical spill sites.N

Analysis on the Risk-Based Screening Levels Determined by Various Risk Assessment Tools (I): Variability from Different Analyses of Cross-Media Transfer Rates

Risk-based screening levels (RBSLs) of some pollutants for residential adults were derived with risk assessment tools developed by United States Environmental Protection Agency (USEPA), American Society for Testing and Materials (ASTM), and Korea Ministry of Environment (KMOE) and compared each other. To make the comparison simple, ingestion of soil, dermal contact with soil, outdoor inhalation of vapors, indoor inhalation of vapors, and inhalation of soil particulates were chosen as exposure pathways. The results showed that the derived RBSLs varied for every exposure pathway. For direct exposure pathways (i.e., ingestion of soil and dermal contact with soil), the derived RBSLs varied mainly due to the different default values for exposure factors and toxicity data. When identical default values for the parameters were used, the same RBSLs could be derived regardless of the assessment tools used. For inhalation of vapors and inhalation of soil particulates, however, different analysis methods for crossmedia transfer rates were used and different assumptions were established for each tool, identical RBSLs could not be obtained even if the same default values for exposure factors were used. Especially for inhalation of soil particulates pathway, screening level derived using KMOE approach (most conservative) was approximately 5000~10000 times lower than the screening level derived using ASTM approach (least conservative). Our results suggest that, when deriving RBSL using a specific tool, it is a prerequisite to technically review the analysis methods for cross-media transfer rates as well as to understand how the assessment tool derives the default values for exposure factors.N