| Project/Area Number |
14550491
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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 |
Geotechnical engineering
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| Research Institution | Hokkaido University |
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Principal Investigator |
IGARASHI Toshifumi Hokkaido Univ., Grad.School of Eng., Assoc.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., Grad.School of Eng., Prof., 大学院・工学研究科, 教授 (20002305)
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| Project Period (FY) |
2002 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 2003: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2002: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Keywords | Pyrite / Calcite / Dissolution / precipitation / Leaching experiment / pH buffer function / Oxidation / reduction / Discharge investigation / Gypsum / 溶解速度 / 溶出量調査 |
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| Research Abstract |
Sulfuric acid is produced by pyrite oxidation when pyrite-bearing rocks are exposed to the air. On the other hand, calcite plays a role to neutralize acid when the solution pH including calcite is weakly alkaline. Thus, mixing the calcite-bearing rocks with the pyrite-bearing rocks is thought to be useful to buffer the leachate pH. Batch and column leaching experiments were conducted for the mixing samples of crushed calcite-bearing and pyrite-bearing rocks. The results showed that the solution pH was controlled by the mixing ratio of pyrite content to calcite content. However, the formation of gypsum removed a pH buffer capacity of calcite because of interrupting calcite dissolution.
Kinetic consideration of pyrite oxidation is also important to evaluate the production of acidity and to construct the measures for acid neutralization. The batch experiments showed that the mechanism of pyrite oxidation was divided into two. The one was the dissolution of a surface oxidation layer, which was modeled using a first-order reaction with respect to the solid-phase pyrite content. The other was diffusion through the surface layer.
A field-scale monitoring of sulfate ion discharge of an acid river in a catchment in Hokkaido, Japan was carried out. The results presented that the sulfate discharge in the river resulting from pyrite oxidation was estimated at 24 tons/km^2/y. The value corresponds to a weathering rate of 0.25mm/y.
Based on the above results, the mechanism and rate of pyrite oxidation are clarified, and the use of natural calcite is effective for neutralizing the sulfuric acid from pyrite oxidation.
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