2005 Fiscal Year Final Research Report Summary
Study on the disposal of high-background heavy metal rich soils and rocks by maintaining an anoxic condition
| Project/Area Number |
16560708
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Earth system and resources enginnering
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| Research Institution | HOKKAIDO UNIVERSITY |
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Principal Investigator |
IGARASHI Toshifumi Hokkaido Univ., Graduate School of Eng., Asso.Prof., 大学院・工学研究科, 助教授 (90301944)
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| Co-Investigator(Kenkyū-buntansha) |
ASAKURA Kuniomi Hokkaido Univ., Graduate School of Eng., Prof., 大学院・工学研究科, 教授 (20002305)
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| Project Period (FY) |
2004 – 2005
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| Keywords | Rock / Oxidation / reduction / Leaching / Arsenic / Oxygen concentration / pH / in situ experiments / Impoundment |
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| Research Abstract |
Leaching of acid water or heavy metal from excavated soils and rocks with high heavy metal contents is highly concerned in relation to soil and groundwater pollution after the execution of Soil Contamination Countermeasures Act in Japan. This is because the act only covers artificial pollutions, and not covers natural pollutions from high-background soils and rock of heavy metals. Therefore, the rationalization of impoundment of heavy-metal rich soils and rocks is required.
Batch leaching and column leaching experiments for pyrite-bearing rocks were carried out to clarify the mechanism of acid effluent. The results showed that the acid water occurred due to the oxidation of pyrite in the rocks, and that calcite-bearing rocks played an important role in buffering the pH of the effluent. This indicates that the use of calcite-bearing rocks is effective for mitigating the acidity of the effluent. The duplicate-impoundment method consisting of a upper pyrite-bearing layer and a bottom calcite-bearing layer is proposed.
Batch leaching experiments and in-situ impoundment experiments were conducted to clarify the mechanism of arsenic leaching. Arsenic is one of the critical elements that easily leach from excavated soils and rocks. The results showed that arsenic leaching and pyrite oxidation occurred at the same time, indicating that the arsenic is leached from pyrite during its oxidation. This suggests that the geochemical conditions, such as an oxidation/reduction potential of the impoundment control the leaching behavior. A reasonable impoundment method of arsenic-rich rocks for keeping the condition anoxic is proposed based on the experiments.
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