본 연구는 전국에 산재된 폐금속광산 중에서 개황조사 결과 광해의 개연성이 확인되어 2007년부터 2009년까지 정밀조사를 실시한 310개 광산 중에서 강원도와 경기도에 소재하는 금과 은을 생산해온 폐금속광산 12개를 대상으로 폐금속광산에서 흔히 관찰되는 광산의 유형별 오염특성을 조사하고 폐금속광산의 유형별 주요시설에 대한 오염현황을 고찰하고자 하였으며, 중금속의 연속추출법과 전함량분석법에 따른 결과를 비교분석하여 폐금속광산 오염물질의 이동가능성을 평가하고 합리적인 정화방안을 마련하고자 하였다.
조사대상 12개 광산을 갱구만 존재하는 폐광산(Type I), 갱구와 폐석장이 존재하는 폐광산(Type II), 갱구와 광미 선별장이 존재하는 폐광산(Type III) 및 선광장이 존재하는 폐광산(Type IV)의 4가지 유형으로 구분하여 오염현황을 평가한 결과, Type I 광산의 토양오염은 임야, 밭토양, 논토양 등에서 As, Cd이 전 지역에서 비슷한 경향을 나타냈으며, Cu, Pb, Zn은 NW 광산에서만 갱구가 위치하고 있는 지역에서 다소 높은 농도를 보였으나, 하부지역 에서는 오염도가 관찰되지 않았다. 이러한 결과는 갱구만 존재하는 광산의 경우 폐광석 또는 광미, 갱내수 등의 오염원이 존재하지 않아 하류지역 토양환경에 영향을 크게 미치지 않은 결과로 사료된다.
갱구와 폐석장이 존재하는 광산(Type II) 중 SYG 및 DC광산의 경우 As, Cd, Pb 항목이 갱구 지역과 폐석장 지역에서 토양오염우려기준을 초과하는 것으로 조사되었다. 이러한 결과는 폐석장에 적치된 폐석 또한 폐광산지역에서 주요 오염원이며, 폐석장에 적치된 폐석에서의 중금속 용출 또는 폐석을 분쇄하는 공정에서의 분체의 확산 등이 원인인 것으로 사료된다.
갱구와 광미 선별장이 존재하는 광산(Type III)은 광미선별장에서 물리적 선광인 밀링 또는 타격을 통한 입자 크기를 분쇄하는 공정을 진행하였기 때문에 갱구와 폐석장이 존재하는 유형(Type II)의 폐광산과 비슷한 경향을 보였다.
그러나 갱구 및 폐석장, 선광장이 존재하는 광산 유형(Type IV)의 경우 Type I, Ⅱ, Ⅲ 광산에 나타나는 오염특성이 모두 관찰되는 것으로 조사되었으며, 갱구로부터 약 2,500m 까지도 오염이 확인되는 것으로 조사되었다. 한편, 이들 광산에서 오염이 관찰되는 지역은 주로 폐석장, 광미장, 선광장이 위치하고 있던 지역으로 이들 시설물이 모두 오염원으로 작용하는 것으로 나타났다. 광미의 경우 제조공정에서 다량의 물을 이용하게 됨에 따라 오염물질이 확산되기 쉬운 계곡 등에 위치하게 되며, 처리과정에서 세립의 입자 크기를 가지게 됨에 따라 수계를 따라 하류지역으로 물리적 확산이 쉽게 이루어진 것으로 판단된다.

폐갱구만 존재하는 광산지역, 폐갱구와 폐석단지가 혼재되어 존재하는 지역, 폐갱구, 폐석단지 및 광미장과 선광장이 혼재된 지역을 대상으로 주요시설에 대한 오염평가 결과, 광미장과 선광장이 혼재된 지역의 경우 분체를 조제하였던 곳 대부분이 고상의 대상광물을 기계적 분쇄법을 통하여 입자가 균일한 원료분말을 얻었던 곳으로 입자의 크기가 폐갱구(Clay함량 10.8% ~ 23.0%)만 있었던 지역보다는 세립한 형태(Clay함량 21.2% ~ 24.3%)의 입자 구조를 가지고 있는 것으로 나타났다.
폐갱구와 폐석이 혼재된 주변 지역의 경우 분체를 조제 하였던 곳으로 중금속 중 비소를 제외한 전 중금속이 높게 나타났다. 분체를 조제 하였던 곳의 경우 입자의 크기가 폐갱구만 있었던 지역보다는 세립한 형태의 입자구조를 가지고 있었고, 이러한 세립질 입자구조와 분쇄공정을 하였던 곳에서 발생된 폐석더미가 대부분 계곡에 위치하고 있어 호우 시 하천수에 의해 하류까지 중금속 분산이 발생해 1,000m∼2,000m까지 오염현상이 나타난 것으로 사료된다. 분쇄장 지역의 경우 입자가 작은 광석분들이 주변에 산재되어 자연생태계에 영향을 주었을 것으로 판단되며, 작은 입자의 분쇄장 주변 토양의 경우 입자 크기에 의한 영향으로 다른 폐석단지나 광석장보다도 원석에 함유된 대상 중금속 함량이 높게 나타나고 있다. 이러한 경우 오염원이 갱구주변과 광산활동을 대상으로 했던 지역 중류 및 하류까지 중금속 함량이 높게 나타나는 경향을 보였다.
폐갱구, 건식분쇄방법을 통한 분쇄장 및 선광장이 존재하였던 지역의 경우 갱구로부터 2,500m 지점까지 As, Cu 및 Pb가 높은 값을 나타내고 있다. 이 광산에서 토양오염에 영향을 주는 주요 요소로는 상류지역의 폐석더미와 중하류 지역 선광장과 광미장의 광미로 판단되며, 특히 선광장에서 중금속 함량이 높게 나타나는 이유는 선광과정에서 부유선광 시 부유선광에서 광석의 선별효과를 높이기 위하여 쓰는 약제에 의한 영향인 것으로 판단된다.

연구지역 토양에 함유되어 있는 As, Cd, Cu, Pb의 존재형태는 특성상 residual fraction을 제외한 존재형태 중 organic fraction 이 가장 높은 농도로 나타나 유기물의 분해 시 용출이 일어날 가능성이 크므로 토양 내 유기물 분해의 정도를 평가할 수 있는 토양 내 유기물의 부식화도를 분석하여 이동가능성에 대한 결과를 알아보는 것이 중요할 것으로 판단되었다.
2009년까지 사용되었던 토양오염공정시험기준인 0.1 N HCl 용출법, 1.0 N HCl 용출법의 경우 organic form(유기물 및 황화물 형태)과 residual form(잔류형태)은 추출이 되지 않는 경향을 보였다. 한편, 현행 사용되는 토양오염공정 시험기준의 전함량 분석법의 경우 왕수를 이용함에 따라 residual form(잔류형태)까지 추출하게 된다. 따라서 전함량 분석법으로 추출된 중금속 함량은 주변의 하천 및 토양 생태계로 전량 이동되지 않기 때문에 이러한 기준치로 현재의 토양 내 중금속의 오염 정도를 파악하여 정화를 실시할 경우 오염 량이 과대하게 계산되어 경제성을 고려한 토양 정화의 접근이 어려울 것으로 판단된다. 또한 Type I 또는 Ⅱ 광산의 경우 이동 가능한 부분(labile)에 중금속이 상대적으로 많이 분포하고 있으며, Type Ⅲ 또는 Ⅳ 광산의 경우 organic form 및 residual fraction이 상대적으로 많이 분포하고 있어 Type I 또는 Ⅱ 광산의 경우 산을 통한 용출, Type Ⅲ 또는 Ⅳ 광산의 경우 산용출 및 75㎛이하(silt 및 clay) 토양을 분리하기 위한 고도선별, 원광석을 처리하기 위한 자력선별을 적용하는 등의 정화기술의 접근 방법을 달리하는 것이 필요할 것으로 판단된다.

This study is to survey the contamination characteristics of mine by type mainly observed and to consider the extent of contamination for facilities in abandoned metal mine areas. Also the study of comparing the results between the continuous extraction method and the total analysis method was conducted to assess the possibility of movement and to address reasonable remediation alternatives for the contaminants in abandoned metal mine. The study sites of 12 abandoned mines are located in Gyeonggi-do and Gangwon-do and those were chosen among 310 sites that the Phase II survey was conducted from 2007 to 2009 after considering the results of Phase I for abandoned mines scattered all over the country.
12 study sites were classified into four types; Type I sites have pit mouth only. Type II sites have pit mouth and mine-waste field. Type III sites have pit mouth and tailing sorting field. Type IV sites have pit mouth, tailing sorting field and concentrator(s).
In forest land, paddy soil and farm land, etc, a tendency of Type I soil contamination of mine for Arsenic(As) and Cadmium(Cd) was similar with entire area. The concentrations of Copper(Cu), Lead(Pb) and Zinc(Zn) were high on the pit mouth area in NW mine but any contamination was not found in downstream area. It is considered that downstream area was not affected largely because there are no contamination sources such as waste rock, tailing and mine water in Type I area where the mines have pit mouth only.
In mine SYG and DC which are classified into Type II, the concentrations of As, Cd and Pb were exceeded worrisome level of soil contamination at the pit mouth area and mine-waste field area. It is considered that contamination sources were the extraction from waste rock in mine-waste field or the spread of particles from the process of grinding waste rock. The mines of Type III which had grinding particle process through physical separation of milling or hitting showed similar tendency with Type II. However, mines of Type IV, which have pit mouth, tailing sorting field and concentrator, showed all of the contamination characteristics from Type I, II, III and the contamination was found in the area which is about 2,500m away from pit mouth. On the other hand, mine-waste field, tailing field and concentrator usually have been located in the contaminated area, and those facilities have been an effect as a contamination source. The tailing usually exists in a valley, etc. where the contaminant spreads easily by using a great quantity of water during the manufacturing process. It is considered that the tailing has fine grained particle size in the process and spreads easily to the downstream area along the water system with physical mechanism.
As the results of contamination assessment for the main facilities in the mine areas having abandoned pit mouth only, the mine areas having abandoned pit mouth and mine-waste field, the mine areas having abandoned pit mouth, mine-waste field, tailing sorting field and concentrator(s), the particle size of the areas having tailing sorting field and concentrators, where the powder had been made and gained equal particle size powder, was finer(the clay content is 21.2% ~ 24.3%) than the areas having abandoned mouth pit only(the clay content is 10.8% ~ 23.0%). In the surrounding areas of abandoned pit mouth and mine-waste field, powder was made and the concentration of heavy metals except Arsenic(As) was high. In the place of the powder had been made, the size of particles was finer than the area had only pit mouth. The mine tailing piles with fine particle size originated from grinding process mostly located in a valley and the contamination of heavy metals spreaded up to 1,000m ~ 2,000m downstream areas through the stream water in heavy rain. In the grinding field area, it is considered that the fine particle sized powder of waste rock were affected to natural ecosystem and in the soils which have small particle size around grinding field area, the heavy metal content of quarry stone is higher than other waste rock complex and field. In such cases, the content of heavy metals, which is the contamination source, was high to the midstream and downstream area of pit mouth and mine activity area. The abandoned pit mouth, dry-grinding field and sorting field area were shown high level of Arsenic, Lead and Cupper up to the place 2,500 meters from pit mouth. The main sources of soil contamination were considered mine tailings piles in upriver region and tailings from concentrator(s) and tailing fields in As the results of contamination assessment for the main facilities in the mine areas having abandoned pit mouth only, the mine areas having abandoned pit mouth and mine-waste field, the mine areas having abandoned pit mouth, mine-waste field, tailing sorting field and concentrator(s), the particle size of the areas having tailing sorting field and concentrators, where the powder had been made and gained equal particle size powder, was finer(the clay content is 21.2% ~ 24.3%) than the areas having abandoned mouth pit only(the clay content is 10.8% ~ 23.0%). In the surrounding areas of abandoned pit mouth and mine-waste field, powder was made and the concentration of heavy metals except Arsenic(As) was high. In the place of the powder had been made, the size of particles was finer than the area had only pit mouth. The mine tailing piles with fine particle size originated from grinding process mostly located in a valley and the contamination of heavy metals spreaded up to 1,000m ~ 2,000m downstream areas through the stream water in heavy rain. In the grinding field area, it is considered that the fine particle sized powder of waste rock were affected to natural ecosystem and in the soils which have small particle size around grinding field area, the heavy metal content of quarry stone is higher than other waste rock complex and field. In such cases, the content of heavy metals, which is the contamination source, was high to the midstream and downstream area of pit mouth and mine activity area. The abandoned pit mouth, dry-grinding field and sorting field area were shown high level of Arsenic, Lead and Cupper up to the place 2,500 meters from pit mouth. The main sources of soil contamination were considered mine tailings piles in upriver region and tailings from concentrator(s) and tailing fields in As the results of contamination assessment for the main facilities in the mine areas having abandoned pit mouth only, the mine areas having abandoned pit mouth and mine-waste field, the mine areas having abandoned pit mouth, mine-waste field, tailing sorting field and concentrator(s), the particle size of the areas having tailing sorting field and concentrators, where the powder had been made and gained equal particle size powder, was finer(the clay content is 21.2% ~ 24.3%) than the areas having abandoned mouth pit only(the clay content is 10.8% ~ 23.0%). In the surrounding areas of abandoned pit mouth and mine-waste field, powder was made and the concentration of heavy metals except Arsenic(As) was high. In the place of the powder had been made, the size of particles was finer than the area had only pit mouth. The mine tailing piles with fine particle size originated from grinding process mostly located in a valley and the contamination of heavy metals spreaded up to 1,000m ~ 2,000m downstream areas through the stream water in heavy rain. In the grinding field area, it is considered that the fine particle sized powder of waste rock were affected to natural ecosystem and in the soils which have small particle size around grinding field area, the heavy metal content of quarry stone is higher than other waste rock complex and field. In such cases, the content of heavy metals, which is the contamination source, was high to the midstream and downstream area of pit mouth and mine activity area. The abandoned pit mouth, dry-grinding field and sorting field area were shown high level of Arsenic, Lead and Cupper up to the place 2,500 meters from pit mouth. The main sources of soil contamination were considered mine tailings piles in upriver region and tailings from concentrator(s) and tailing fields in midstream and downstream areas. Especially, it is considered that the reason of high concentration in the concentrator areas was the flotation agents which used during sorting process.

It is important to check the possibility of movement by analysis of humification grade of organic matter because in the existence forms of As, Cd, Cu, Pb, excluding residual fraction, the concentration of organic fraction is the highest level and the possibility of extraction is high while organic matters are decomposed. 0.1 N HCl extraction method and 1.0 N HCl method were used as the official test method on soil contamination until 2009, and in those methods, organic form and residual form were not extracted. The current official test method using aqua regia for total content analysis, however, extracts residual form. The content of heavy metals with total content analysis method was not spread to around streams and ecosystem wholly. Thus, if the heavy metal contamination in soil is calculated with current test method, it is hard to assess cost efficiency soil remediation because the extent of contamination to be remediated might be overestimated. In case of Type I and II mines, labile parts contain much of heavy metals relatively and in Type III and IV mines, organic form and residual fraction contained relatively high. Therefore, reasonable remediation approach methods are necessary, for example, acid extraction method is recommended for Type I and II mines, and application of advanced separation and magnetic separation techniques are recommended for Type III and IV mines.