Applied Geochemistry 16 (2001) 1369–1375 www.elsevier.com/locate/apgeochem
Heavy metal contamination of soils and waters in and around the Imcheon Au–Ag mine, Korea Myung Chae Jung * Department of Earth Resources and Environmental Geotechnics Engineering, Semyung University, Jecheon, Choongbuk, 390-711, South Korea
Abstract The heavy metal contamination of soils and waters by metalliferous mining activities in an area of Korea was studied. In the study area of the Imcheon Au–Ag mine, soils and waters were sampled and analyzed using AAS for Cd, Cu, Pb and Zn. Analysis of HCO3 , F , NO3 and SO24 in water samples was also undertaken by ion chromatography. Elevated concentrations of the metals were found in tailings. The maximum contents in the tailings were 9.4, 229, 6160 and 1640 mg/kg extracted by aqua regia and 1.35, 26.4, 70.3 and 410 mg/kg extracted by 0.1 N HCl solution for Cd, Cu, Pb and Zn, respectively. These metals are continuously dispersed downstream and downslope from the tailings by clastic movement through wind and water. Because of the existence of sulfides in the tailings, a water sample taken on the tailings site was very acidic with a pH of 2.2, with high total dissolved solids (TDS) of 1845 mg/l and electric conductivity (EC) of 3820 mS/cm. This sample also contained up to 0.27, 1.90, 2.80, 53.4, 4,700 mg/l of Cd, Cu, Pb, Zn and SO24 , respectively. TDS, EC and concentrations of metals in waters decreased with distance from the tailings. The total amount of pulverized limestone needed for neutralizing the acid tailings was estimated to be 46 metric tons, assuming its volume of 45,000 m3 and its bulk density of 1855 kg/m3. # 2001 Elsevier Science Ltd.
1. Introduction Mining and milling operations, together with grinding, concentrating ores and disposal of tailings, provide obvious sources of contamination in the surface environment, along with mine and mill waste water (Adriano, 1986). As a result, elevated levels of heavy metals can be found in and around disused metalliferous mines due to discharge and dispersion of mine wastes into nearby agricultural soils, food crops and stream systems. Eventually, they may pose a potential health risk to residents in the vicinity of mining areas. Many studies have been conducted on heavy metal contamination in soils, plants, waters and sediments from metalliferous mines throughout the world (e.g. Thornton, 1980; Fuge et al., 1989; Merrington and Alloway, 1994; Jung, 1995; Jung and Thornton, 1997). Metals associated with Au–Ag mines, including Cd, Cu,
* Tel.: +82-43-649-1317; fax: +82-43-648-7853. E-mail address:
[email protected] (M.C. Jung). 0883-2927/01/$ - see front matter # 2001 Elsevier Science Ltd. PII: S0883-2927(01)00040-3
Pb and Zn can be dispersed downstream due to the weathering process of tailings. Thus, the extent and degree of heavy metal contamination around the mines vary depending upon geochemical characteristics and mineralization of tailings. For example, tailings containing large quantities of sulfide minerals could influence nearby agricultural lands and stream. In contrast, Au mineralization in a quartz vein with no sulfide produced relatively little heavy metal contamination (Chon et al., 1997). In Korea, Au–Ag mines were distributed over almost all of the country and were actively operated until the early 1980s. Since then, however, most of the mines were closed, mainly due to economic reasons. Upon closure of the mines, mine waste materials, including tailings, were left without full environmental treatment. Thus, soils, plants, waters and sediments in the vicinity of the mines have been contaminated by potentially toxic elements from tailings by clastic movement through wind and water. The objective of this study was to investigate soil and water contamination in the vicinity of the Imcheon Au–
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Ag mine, and examine the possibility of lime treatment for increasing the pH of acid mine tailings to decrease the solubility of heavy metals, especially Cd, Cu, Pb and Zn.
2. Materials and methods The study area around the Imcheon Au–Ag mine is located in the western part of South-Choongchung Province in Korea. During its operation in the 1970s, the mine produced up to 86 kg of Au per year. The geology of the mining area is mainly composed of severely weathered biotite gneiss and biotite granite. The mineralization of the mine is Au–Ag bearing quartz vein type with sulfides including pyrite (FeS2) and galena (PbS). The mine ceased production in 1978 and large quantities of waste materials, including tailings, have been left untreated. Thus, these materials have been dispersed downslope both by surface erosion and wind action and by effluent draining the wastes into lower lying land used for growth of paddy rice and household garden crops. Surface soils (0–15 cm in depth) were sampled by hand auger (3.0 cm in diameter) in and around the mine, from tailings, paddy fields, uncultivated land, household garden and a nearby control area (Fig. 1). Each soil sample comprised a composite of 9 subsamples taken from an area of 11 m. Soils were air-dried at room temperature for 5 days. After grinding, the samples were passed through a 180 mm sieve. As a Korean Standard Method, the soils were also decomposed by 0.1 N HCl solution and analyzed by atomic absorption spectrometry (AAS) for Cd, Cu, Pb and Zn. In addition, estimates of total concentrations were determined by digesting with aqua regia and analyzing by AAS for the same metals (Ure, 1990). The soil pH was determined by
a 2:1 ratio of soil to de-ionized water and a Woodruff buffer method was used for measurement of lime requirement (Sobek et al., 1978). Water samples were taken in and around the mine both in spring (dry season) and summer (wet season). The samples were filtered through 0.45 mm Millipore membrane filter using a hand-pump at the sampling site. The pH, total dissolved solid (TDS), electric conductivity (EC) and temperature of the samples were measured in the field using a portable pH-TDS-EC meter. After acidification with concentrated nitric acid, the samples were stored in a cool box before chemical analysis. For anion determination, the filtered waters were directly stored in a cool box without acidification. Cadmium, Cu, Pb and Zn concentrations in acidified waters were determined by AAS and the concentrations of HCO3 , F , NO3 and SO24 in non-acidified waters were measured by ion chromatography (IC). Data were assessed for accuracy and precision using a quality control system integral to the analytical procedure (Ramsey et al., 1987). The precision and bias of the chemical analysis was less than 10%.
3. Results and discussion 3.1. Soil pH The mean and range of soil pH values are shown in Table 1. The pH of tailings ranged widely from 1.9 to 7.4 due to a mixture of various mine waste materials. The low pH of the tailings may be due to the weathering of sulfide minerals and high values may be due to the reaction with carbonates and cyanides (by-products of mineral processing for Au and Ag). Wide ranges of the pH values were also found in soils sampled at other sites due to the differences in their mineralogy and origin. However, there is no statistical difference between soil pH in each soil type (P>0.05) due to the wide variation of soil pH. 3.2. Heavy metal concentrations in soils extracted by 0.1 NHCl solution
Fig. 1. Sampling locations of soils and waters in the vicinity of the Imcheon Au–Ag mine.
The range and mean concentrations of heavy metals in soils extracted by the solution are shown in Table 1. The maximum concentrations of the metals were found in the center of the tailings sites (Fig. 1), with up to 1.35, 26.4, 70.3 and 410 mg/kg of Cd, Cu, Pb and Zn, respectively. According to a Soil Conservation Act of Korea, the maximum allowed levels of heavy metals are 30 mg/kg of Cd, 500 mg/kg of Cu and 1000 mg/kg of Pb in soils developed in factory and industrial area. Although heavy metal concentrations in the tailings are lower than the maximum allowed metal levels of the act, they become an important source of the metals in the
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M.C. Jung / Applied Geochemistry 16 (2001) 1369–1375 Table 1 The mean and range of pH, lime requirement and Cd, Cu, Pb and Zn concentrations in surface soils Type
pH
Lime req. (ton)a
Extracted by 0.1 N HCl (mg/kg) Cd
c
Cu
Pb
Extracted by aqua regia (mg/kg) Zn
4.60 2.67 0.540.56 0.53 0.42 19.0 6.18 46.8 22.3 155 165 1.93–7.41 0.00–1.29 0.15–1.35 12.0–26.4 14.8–70.3 33.3–410
Cd
Cu
Pb
Zn
3.8 3.2 102 71.7 4252 3339 879 554 0.6–9.4 27.0–229 142–8500 283–1640
Tailings (n=6)b
AM S.D. Range
Paddy soil (n=9)
AM S.D. Range
6.12 1.11 0.200.16 0.38 0.20 6.57 3.91 32.3 18.9 39.9 38.0 1.4 0.7 23.8 14.1 4.91–7.78 0.00–0.50 0.05–0.85 1.95–16.0 11.4–65.6 5.10–132 0.4–2.6 9.20–57.2
124 60.0 51–225
227 120 68–465
Uncultivated AM S.D. soil (n=9) Range
48.9 0.69 0.510.22 0.06 0.02 3.34 1.71 10.5 7.62 5.28 4.04 0.6 0.2 19.1 7.90 4.05–6.00 0.21–0.84 0.05–0.01 1.40–6.10 2.70–29.6 1.40–13.1 0.2–1.0 5.40–29.0
75 119 22–392
66 45 24–167
Garden soil (n=3)
AM S.D. Range
6.19 1.32 0.250.27 0.07 0.03 2.30 1.13 13.6 8.85 6.23 7.73 0.5 0.3 18.1 7.2 4.67–6.99 0.08–0.56 0.05–0.10 1.10–3.35 8.40–23.9 1.40–15.2 0.2–0.8 9.8–3.0
58 41 20–100
73 46 20–104
Control soil (n=7)
AM S.D. Range
4.92 0.50 0.470.22 0.08 0.04 2.69 1.30 10.2 6.39 5.15 2.50 0.5 0.2 14.7 9.3 4.49–5.89 0.10–0.78 0.05–0.15 1.45–5.10 2.40–20.4 1.65–7.95 0.2–0.8 7.0–33.4
38 10 26–51
68 29 39–108
a b c
Lime req. (ton), lime requirement (the number of tons of pulverized limestone per 1000 tons of materials). n, number of samples. AM S.D., arithmatic mean standard deviation.
vicinity of the sites. The concentrations of the metals, however, were relatively low in a nearby control area with the same geology as the mine. The results of a t-test indicate that there is a statistical difference between average metal concentrations in the contaminated and control soils (P
