2015 Fiscal Year Research-status Report
Micro-seeds-enhanced and smart-carrier assisted pyrite encapsulation to prevent the generation of acid mine drainage
| Project/Area Number |
26820390
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| Research Institution | Hokkaido University |
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Principal Investigator |
タベリン カーリット 北海道大学, 工学(系)研究科(研究院), 助教 (60626125)
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| Project Period (FY) |
2014-04-01 – 2017-03-31
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| Keywords | acid mine drainage / smart encapsulation / micro seed encapsulation / pyrite oxidation |
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| Outline of Annual Research Achievements |
Significant achievements of this study are as follows:
1. We found that hematite interferes with the cathodic half-cell reaction that minimized the overall dynamics of pyrite oxidation. Although it could not uniformly coat pyrite, these data have important implications in the understanding of pyrite oxidation dynamics in actual field conditions where pyrite coexist with other metal oxides.
2. We found that alumina interferes with the cathodic half-cell reaction of pyrite oxidation, but in comparison to hematite, its pH buffering effect was very strong that it raised the pH by several units and enhanced the overall pyrite oxidation dynamics.
3. Even under acidic conditions, a mechanically strong and stable coating could be formed to passivate pyrite using precursor mineral phases like schwertmannite and ferric arsenate. Because these precursor minerals could be transformed into more stable Fe-oxyhydroxides, we are looking into ways to optimize this process.
4. Ferric-catechol complexes could be used as a smart-oxidant that would specifically target sulfide minerals like pyrite in a complex system such as tailings and pyritic waste rocks.
5. Formation of a passivating coating on pyrite could also be induced using galvanic interactions between a more anodic metal/sulfide and pyrite.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
1. Although micro-seed enhanced encapsulation of pyrite did not work very effectively in the pH range of 6-10 because of the rapid oxidation of the pyrite surface that interfered with the electrostatic interaction of this mineral with the micro-seeds, we found that we could form a stable coating on pyrite using this method under acidic conditions. Moreover, rather than use metal oxides directly as micro-seeds, we found that precursor minerals like schwertmannite or ferric arsenate maybe much better candidates, and we are currently investigating this alternative route.
2. We found that Ferric-catechol complexes could act as smart oxidants of pyrite at pH 7-10. Using this selective and enhanced oxidation of pyrite, a coating made of Fe-phosphate or Fe-silicate could be formed on pyrite if ions like phosphate and silicate are present in the solution.
3. We found a new approach to form a coating on pyrite using galvanic interaction between metallic aluminum/iron and pyrite. Our preliminary experiments showed that this is a promising approach but ways to electrically link pyrite and these metals should be evaluated.
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| Strategy for Future Research Activity |
1. We will focus our future efforts in the understanding of the coating formation mechanism under acidic conditions. Because the coating formed was composed primarily of precursor minerals like ferric arsenate and schwertmannite, they could be transformed later on to more stable iron oxides like goethite or hematite by raising the pH to more alkaline conditions. The advantage of these approach is that most AMD problem areas are already acidic with high concentrations of Fe, SO42- and As, which could be utilized to form the coating eliminating the need to introduce additional expensive reagents.
2. Optimization of the coating process using batch and column experiments to evaluate the coating stability under various conditions and look for ways to apply this concept in real world situations.
3. We are also looking for ways to use Fe3+-catechol complexes as catalysts that will only target pyrite in a complex system. Our next experiments would investigate the effects of coexisting minerals and ions on the formation of the iron-phosphate coating. We will also expand this technique and try to form iron-silicate coatings on pyrite.
4.We have also started our studies on the use of metal-catechol complexes to passivate other sulfide minerals like arsenopyrite and the use of other common ions like aluminum.
5. We are evaluating ways to more effectively combine pyrite and electrochemically anodic metals like aluminum and iron. Chief among them is the use of a normal reaction vessel with rapid stirring and mechanochemical treatment using a ball mill or planetary mill.
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| Causes of Carryover |
アジアでの国際会議を、大学の経費から支出したため
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| Expenditure Plan for Carryover Budget |
当初計画では、アジアでの国際会議に参加予定であったが、カナダでの国際会議参加に変更する
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Research Products
(3 results)
