2014 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
|
|---|
| Research Institution | Hokkaido University |
|---|
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)
|
|---|
| Project Period (FY) |
2014-04-01 – 2017-03-31
|
| Keywords | Pyrite passivation / Pyrite oxidation / Acid Mine Drainage |
|---|
| Outline of Annual Research Achievements |
Our first experiments were conducted to confirm that the two main steps in our new technique would work under real-world conditions: attachment of μ-seeds and formation of a more stable coating. Attachment was more likely to occur when μ-seeds are introduced in suspension. In addition, not all metal oxides could attach onto pyrite and their attachment is strongly related to their net surface charge relative to pyrite. For example, hematite and rutile could attach onto pyrite at around pH 5-7 because both of them have net positively charged surfaces, but not Al2O3 (negatively charged). Once attached, these μ-seeds were stable and did not detach even after repetitive washing with agitation. The quality of the coating was also altered when μ-seeds are attached onto pyrite. Rather than the iron sulfate/sulfur coating prevalent in the untreated pyrite, those with μ-seeds had coatings consisting mainly of goethite-like mineral. We also found catechol (1,2-dihydroxybenzene) as a potential “smart” carrier because it can form stable metal complexes that would dissociate only via redox reactions. We successfully extracted ferric ions from hematite (Fe2O3) using catechol but not from magnetite (Fe3O4). This result is important because during passivation, any excess catechol would not destabilize the coating. We also found that these ferric complexes were stable even at strongly alkaline conditions, indicating that it can be applied even onto “fresh” flotation tailings (pH 10).
|
| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
Our project is going smoothly despite necessitating a lot of preliminary experiments to investigate the fundamental processes involved in μ-seed attachment and coating formation. Although pyrite oxidation has been extensively studied, nobody evaluated how it would change in the presence of colloidal particles in suspension or when attached onto pyrite. With the help of Prof. Naoki Hiroyoshi, a collaborator in this study, who is an expert in the electrochemical studies of sulfide minerals, we will be able to evaluate the effects of μ-seeds on the anodic and cathodic reactions of pyrite oxidation independently. In addition, we will be able to use this approach to understand how pyrite oxidation changes in a complex system containing μ-seeds and redox sensitive species (e.g., Fe2+ and Fe3+).
|
| Strategy for Future Research Activity |
We will mostly follow our original plan for the second year with only a little bit of additional objectives and experiments. Based on our original plan, we will continue investigating the physico-chemical interactions of μ-seeds and metal-catechol complexes/metal-organic with pyrite using electrochemical techniques, batch experiments and flow-through studies under various conditions. We will also start evaluating the combined effects of μ-seed and ferric-catechol complexes in the passivation/oxidation of pyrite using batch and column experiments. In addition, we will continue evaluating potential μ-seed materials and other organic compounds as potential “smart” carriers to fine tune our new passivation technique. Specifically, we will conduct the following experiments:
1.Investigate the change in anodic and cathodic reactions of pyrite oxidation and how these processes change when μ-seeds, ferric-catechol and coexisting ions are present.
2.Evaluate the effects of parameters like pH, dissolved oxygen, μ-seed/ferric-catechol complexes concentrations, treatment time and mixing speeds on the formation and stability of the coating.
3.Characterize the kind of coating formed under various conditions using electrochemistry, microscopy (optical and SEM-EDX) and X-ray photoelectron spectroscopy (XPS).
4.Develop an appropriate column setup to evaluate the effects of μ-seed/ferric-catechol complexes, treatment time and dissolved oxygen on pyrite passivation under flow-through conditions.
|
| Causes of Carryover |
The left-over fund was originally intended to procure a complete column setup for our flow-through experiments. However, during the course of our batch experiments, it became apparent that the original column setup was not appropriate and a an overhaul was necessary, so we postponed buying the column setup. For example, we needed a smaller column with constant temperature control because pyrite oxidation is sensitive to temperature. Recently, sensors have been developed to accurately monitor changes in pH, dissolved oxygen and water content in porous media, so we will incorporate such technological advances to our setup if possible. We would also add in the new design a way to collect porewater samples at certain depths to understand the effects of dissolved oxygen/ion distributions.
|
| Expenditure Plan for Carryover Budget |
After finishing our re-evaluation of the column design, we are planning to use the left-over fund to procure a complete column setup. This will most likely include several glass columns (with and without sampling ports), fraction collector, sensors for pH/DO/water content (if possible/available), data logger, pump, connectors and tubes.
|
Research Products
(2 results)
