『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