Villafane,O.R.S., Igarashi,T., Kurosawa,M. and Takase,T.(2012): Comparison of potentially toxic metals leaching from weathered rocks at a closed mine site between laboratory columns and field observation. Applied Geochemistry, 27, 2271-2279.

『実験室のカラムと野外観察の間での閉山サイトの風化岩から浸出している毒性の可能性が高い金属の比較』


Abstract
 Potentially toxic metals, such as Cu, Pb and Zn, are leached from weathered rocks at many closed mine sites due to the acidic environments and mineralogical modifications. The mobilized toxic metals may cause contamination of surrounding water bodies. In this study, both laboratory column experiments and field observations at a former mine located in the north of Japan were carried out to compare the leaching behavior of Cu, Pb and Zn. The thickness of the surface weathered rock was varied (10, 20 and 30 cm) for the columns experiments while porous cups for porewater sampling were set up at different depths (GL-15, -45, -70, and -95 cm) for the field observations. Deionized water was added once a week over 75 weeks to the columns to simulate rainfall while porewater was extracted by a vacuum pump in several sampling campaigns (over 18 months). Similar low pH and leaching behavior of potentially toxic metals were observed for column experiments and field observations. A moderate increase in concentration with depth was observed for Cu and Zn. However, no increase in concentration was observed for Pb. This suggests that the leaching of Cu and Zn is enhanced by the length of the flow pathway through the weathered rock layer while Pb concentration is restricted by the precipitation of insoluble Pb sulfate. Thus, the thickness of the weathered rock layer is an important parameter that should be taken into consideration to estimate the loads of some potentially toxic metals, which is important when designing remediation schemes.』

1. Introduction
2. Materials and methods
 2.1. Site description and characterization of rock samples
 2.2. Laboratory column experiments
 2.3. Field observations
 2.4. Chemical analysis
 2.5. Partition coefficient calculations
 2.6. Geochemical evaluation
3. Results
 3.1. Characterization of weathered rock samples
 3.2. Laboratory column experiments
 3.3. Porewater sampling
4. Discussion
 4.1. Acidity of weathered rocks and load of potentially toxic metals
 4.2. Potentially toxic metal leaching and mineral equilibria
 4.3. Bedrock height effect
5. Conclusions
Acknowledgement
References


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